"Deep in the sea are riches beyond compare.
But if you seek safety, it is on the shore."

BIOS GUIDE

BIOS settings are a frequent problem asked about in several hardware related newsgroups. Did you ever experienced a system lock up or poor performance and erratic behavior due to improper BIOS settings? Have you ever been left in the dark by a cryptic 5 pages, badly written motherboard manual? The answer is probably yes.

BIOS

Basic Input Output System. All computer hardware has to work with software through an interface. The BIOS gives the computer a little built-in starter kit to run the rest of softwares from floppy disks (FDD) and hard disks (HDD). The BIOS is responsible for booting the computer by providing a basic set of instructions. It performs all the tasks that need to be done at start-up time: POST (Power-On Self Test, booting an operating system from FDD or HDD). Furthermore, it provides an interface to the underlying hardware for the operating system in the form of a library of interrupt handlers. For instance, each time a key is pressed, the CPU (Central Processing Unit) perform an interrupt to read that key. This is similar for other input/output devices (Serial and parallel ports, video cards, sound cards, hard disk controllers, etc...). Some older PC's cannot co-operate with all the modern hardware because their BIOS doesn't support that hardware. The operating system cannot call a BIOS routine to use it; this problem can be solved by replacing your BIOS with an newer one, that does support your new hardware, or by installing a device driver for the hardware.

CMOS

Complementary Metal Oxide Semiconductor. To perform its tasks, the BIOS need to know various parameters (hardware configuration). These are permanently saved in a little piece (64 bytes) of CMOS RAM (short: CMOS). The CMOS power is supplied by a little battery, so its contents will not be lost after the PC is turned off. Therefore, there is a battery and a small RAM memory on board, which never (should...) loses its information. The memory was in earlier times a part of the clock chip, now it's part of such a highly Integrated Circuit (IC). CMOS is the name of a technology which needs very low power so the computer's battery is not too much in use.

Actually, there is not a battery on new boards, but an accumulator (Ni_Cad in most cases). It is recharged every time the computer is turned on. If your CMOS is powered by external batteries, be sure that they are in good operating condition. Also, be sure that they do not leak. That may damage the motherboard. Otherwise, your CMOS may suddenly "forget" its configuration and you may be looking for a problem elsewhere. In the monolithic PC and PC/XT, this information is supplied by setting the DIP (Dual-In-line Package) switches at the motherboard or peripheral cards. Some new motherboards have a technology named the Dallas Nov-Ram. It eliminates having an on-board battery: There is a 10 year lithium cell epoxyed into the chip.

Chipset

A PC consists of different functional parts installed on its motherboard: ISA (Industry Standard Architecture), EISA (Enhanced Industry Standard Architecture) VESA (Video Enhanced Standards Association) and PCI (Peripheral Component Interface) slots, memory, cache memory, keyboard plug etc... Not all of these are present on every motherboard. The chipset enables a set of instructions so the CPU can work (communicate) with other parts of the motherboard. Nowadays most of the discrete chips; PIC (Programmable Interrupt Controller), DMA (Direct Memory Access), MMU (Memory Management Unit), cache, etc... are packed together on one, two or three chips; the chipset. Since chipsets of a different brand are not the same, for every chipset there is a BIOS version. Now we have fewer and fewer chipsets which do the job. Some chipsets have more features, some less. OPTi is such a commonly used chipset. In some well integrated motherboards, the only components present are the CPU, the two BIOS chips (BIOS and Keyboard BIOS), one chipset IC, cache memory (DRAMs, Dynamic Random Access Memory), memory (SIMMs, Single Inline Memory Module, most of the time) and a clock chip.

Setup

Setup is the set of procedures enabling the configure a computer according to its hardware caracteristics. It allows you to change the parameters with which the BIOS configures your chipset. The original IBM PC was configured by means of DIP switches buried on the motherboard. Setting PC and XT DIP switches properly was something of an arcane art. DIP switches/jumpers are still used for memory configuration and clock speed selection. When the PC-AT was introduced, it included a battery powered CMOS memory which contained configuration information. CMOS was originally set by a program on the Diagnostic Disk, however later clones incorporated routines in the BIOS which allowed the CMOS to be (re)configured if certain magic keystrokes were used.

Unfortunately as the chipsets controlling modern CPUs have become more complex, the variety of parameters specifiable in SETUP has grown. Moreover, there has been little standardization of terminology between the half dozen BIOS vendors, three dozen chipset makers and large number of motherboard vendors. Complaints about poor motherboard documentation of SETUP parameters are very common.

To exacerbate matters, some parameters are defined by BIOS vendors, others bychipset designers, others by motherboard designers, and others by various combinations of the above. Parameters intended for use in Design and Development, are intermixed with parameters intended to be adjusted by technicians -- who are frequently just as baffled by this stuff as everyone else is. No one person or organization seems to understand all the parameters available for any given SETUP.

Hardware Performance

Although computers may have basic similarities (they all look the same on a shelf), performance will differ markedly between them, just the same as it does with cars. The PC contains several processes running at the same time, often at different speeds, so a fair amount of coordination is required to ensure that they don't work against each other.

Most performance problems arise from bottlenecks between components that are not necessarily the best for a particular job, but a result of compromise between price and performance. Usually, price wins out and you have to work around the problems this creates.

The trick to getting the most out of any machine is to make sure that each component is giving of its best, then eliminate potential bottlenecks between them. You can get a bottleneck simply by having an old piece of equipment that is not designed to work at modern high speed - a computer is only as fast as its slowest component, but bottlenecks can also be due to badly written software.

System Timing

The clock is responsible for the speed at which numbers are crunched and instructions executed. It results in an electrical signal that switches constantly between high and low voltage several millions times a second.

The System Clock, or CLKIN, is the frequency used by the processor; on "*?s and 386s, this will be half the speed of the main crystal on the motherboard (the CPU devides it by two), which is often called CLK2IN. 486 processors run at the same speed, because they use both edges of the timing signal. A clock generator chip (82284 or similar) is used to synchronize timing signals around the computer, and the data bus would be run at slower speed synchronously with the CPU, e.g. CLKIN/4 for an ISA bus with a 33 MHz CPU.

ATCLK is a separate clock for the bus, when it's run asynchronously, or not derived from CLK2IN. There is also a 14.138 MHz crystal which was used for all system timing on XTs. Now it's only used for the colour frequency of the video controller (6845).

Memory Access

The cycle time is the time it takes to read from and write to a memory cell, and it consists of two stages; precharge and access. Precharge is where the capacitor in the memory cell is able to recover from a previous access and stabilize. Access is where a data bit is actually moved between memory and the bus or the CPU. Total access time includes the finding of data, data flow and recharge, and parts of the access time can be eliminated or overlapped to improve performance. The combination of precharge and access equals cycle time, which is what you should use to calculate wait states from.

There are ways of making refreshes happen so that the CPU doesn't notice (i.e. Concurrent and Hidden), which is helped by the 486 being able to use its on-board cache and not needing to use memory so often anyway. In addition, you can affect the Row Access Strobe (RAS), or have Column Access Strobe (CAS) before RAS (see Advanced Chipset Setup).

The fastest DRAM commonly available is rated at 60ns. As these chips need alternate refresh cycles, under normal circumstances data will actually be obtained every 120ns, giving you and effective speed of around 8 MHz for the whole computer, regardless of the CPU speed, assuming no action is taken to compensate. Memory chips therefore need to be operating at something like 20ns to keep up, assuming that the CPU needs only one clock cycle for each one from the memory bus; one internal cycle for each external one. Intel processors mostly use two for one, so the 33 MHz CPU is actually ready to use memory every 60ns, but you need to allow a little more for overheads, such as data assembly and the like. One way of matching the capacities of components with different speeds includes the use of wait states.

Wait States

A wait state indicates how many ticks of the system clock the CPU has to wait for memory to catch up-it will generally be 0 or 1, but can be up to 3 if you're using slower memory chips. Ways of avoiding wait states include:

· Page-mode memory. This will cut-down address cycles to retrieve information form one general area, based on the fact that the second access to a memory location on the same page takes around half the time as the first; addresses are normally in two halves, with high bits (for row) and low bits (for column) being multiplexed onto one set of address pins. The page address of data is noted, and if the next data is in the same area, a second address cycle is eliminated as a whole row of memory cells can be read in one go; that is, once a row access has been made, you can get to subsequent column addresses in that row in the time available (you should therefore increase row access time for best performance). Otherwise data is retrieved normally, which will take twice as long. Fast Page Mode is a quicker version of the same thing; the DRAMs concerned have a faster CAS access speed. Memory capable of running in page mode is different from normal bit-by-bit type, and the two don't mix. It's unlikely that low capacity SIMMs are so capable.

· Interleaved memory, which divides memory into two or four portions that process data alternately; that is, the CPU sends information to one section while another goes through a refresh cycle; a typical installation will have odd addresses on one side and even on the other (you can have word or block interleave). If memory accesses are sequential, the precharge of one will overlap the access time of the other. To put interleaved memory to best use, fill every socket you've got (that is, eight 1 Mb SIMMs are better than two 4 Mb ones). The SIMM types must be the same. As an example, a machine in non-interleaved mode (say a 386SX/20) may need 60ns or faster DRAM for 0ws access, where 80ns chip could do if interleaving were enabled.

· A processor RAM cache, which is a bridge between the CPU and slower main memory; it consists of anywhere between 32-512K of (fast) Static RAM chips and is designed to retain the most frequently accessed code and data from main memory. It can make 1 wait state RAM look like that with 0 wait states, without physical adjustments, assuming that the data the CPU wants is in the cache when required (known as a cache hit). To minimize the penalty of a cache miss, cache and memory access are often in parallel, with one being terminated when not required. On a 486, how much cache you need really depends on the amount of memory; Dell say that jumping from 128K to 256K only increases the hit rate by around 5% and Viglen say you only need more than 256K if you have more than 32 Mb RAM. A cache should be fast and capable of holding the contents of several different parts of main memory. Software plays a part as well, since cache operation is based on the assumption that programs access memory where they have done so already, or are likely to next, maybe through looping (where code is reused) or code is organized to be next to other relevant parts. A basic cache design will look up an address for the CPU and return the data inside one clock cycle, or 20ns at 50 MHz. Asynchronous SRAM will be used for this. As the round trip from the CPU to cache and back again takes up a certain amount of time, only the remainder is available to retrieve data, which gets smaller as the motherboard speed is increased. Synchronous SRAM uses a buffer to keep the whole routine inside one clock cycle, even though it may use two (or more) clock cycles the first time round. The address from the CPU is stored, and while the next is coming in to the buffer, the data for the first is retrieved, and the cycle continues. Pipeline SRAM uses more clock cycles, typically three, the first time round, and Burst SRAM will deliver 4 words (blocks of data) over for consecutive cycles if the request from the CPU is for the first; there will be no waiting for the CPU to request each one individually. Note the level 2 cache can be unreliable, so be prepared to disable it in the interests of reliability. For maximum efficiency, or minimum access time, a cache may be subdivided into smaller blocks that can be separately loaded, so the chances of a different part of memory being requested and the time needed to replace a wrong section are minimized. There are three mapping schemes that assist with this:

· Fully Associative, where the whole address is kept with each block of data in the cache (in tag RAM), needed because it is assumed there is no relationships between the blocks. This can be inefficient, as an address comparison needs to be made with every entry each time the CPU presents the address for its next instruction.

· Direct Mapped, where every block can only be in one place in the cache, so only one address comparison is needed to see if the data required is there. Although simple, the cache controller must go to main memory more frequently if program code needs to jump between locations with the sane index, which defeats the object somewhat, as alternate references to the same cache cell mean cache misses for other processes. The "index" comes form the lower order addresses presented by the CPU.

· Set Associative, a compromise between the above two. Here, an index can select several entries, so in a 2 Way Set Associative cache, 2 entries can have the same index, so two comparisons are needed to see if the data required is in the cache. Also, the tag field is correspondingly wider and needs larger SRAMs to store address information. As there are two locations for each index, the cache controller has to decide which one to update or overwrite, as the case may be. The most common methods used to make these decisions are Random Replacement, First In First Out (FIFO) and Least Recently Used (LRU). The latter is the most efficient. It the cache is large enough (e.g. 64K), performance from this over direct-mapping may not be much. A Write Thru Cache means that every write access is immediately passed on to memory; although it means that cache contents are always identical to main memory, it is slow, as the CPU then has to wait for DRAMs. Buffers can be used to provide a variation on this, where data is written into a temporary buffer so the CPU is released quickly before main memory is updated. A Write Back Cache, on the other hand, exists where changed data is temporarily stored in the cache and written to memory when the system is quiet, or when absolutely necessary. This will give better performance when main memory is slower than the cache, or when several writes are made in a very short space of time, but is more expensive. A "dirty bit" is used as a mental note that the cache and main memory contents are different, and that the cache contains the most up to date data. This bit will be checked if the cache needs to be written to, and main memory updated first if this bit is set. Some motherboards don't have the required SRAM for the dirty bit, but it's still faster than Write Thru.

Shadow RAM

ROMs are used by components that need their own instructions to work properly, such as video card of cacheing disk controller. ROMs are 8-bit devices, so only one byte is accessed at a time; also, they typically run between 150-400ns, so using them will be slow relative to 32-bit memory at 60-80ns, which is capable of making four accesses at once.

Shadow RAM is the process of copying the contents of a ROM directly into extended memory which is given the same address as the ROM, from where it will run much faster. The original ROM is then disabled, and the new location write protected. If your applications execute ROM routines often enough, enabling Shadow RAM will make a difference in performance of around 8%, assuming a program spends about 10% of its time using instructions from ROM, but theoretically as high as 300%. The drawback is that the RAM set aside for shadowing cannot be used for anything else, and you will lose a corresponding amount of extended memory, The remainder of Upper Memory, however, can usually be remapped to the end of extended memory and used there.

With some VGA cards, if video shadow is disabled, you might get DMA errors, because of timing when code is fetched from the VGA BIOS, when the CPU cannot accept DMA requests. Some programs don't make use of the video ROM, preferring to directly address the card's registers, so you may want to use extended memory for something else. If you machine hangs during the startup sequence for no apparent reason, check that you haven't shadowed an area of upper memory containing a ROM that doesn't like it-particularly one on a hard disk controller, or that you haven't got two in the same 128K segment.

Bus Types

The expansion bus (where expansion cards go) is an extension of the Central Processor, so when adding cards to it, you are extending the capabilities of the CPU itself. The relevance of this regard to the BIOS is that older cards are less able to cope with modern buses running at higher speeds than the original design of 8 or so MHz. Also, when the bus is accessed, the whole computer slows down to the bus speed, so it's often worth altering the speed of the bus or the wait states between it and the CPU to speed things up. The PC actually has four buses; the processor bus connects the CPU to its support chips, the memory bus connects it to its memory, the address bus is part of both of them, and the I/O (or expansion) bus is what concerns us here.

ISA

Industry Standard Architecture. The 8-bit version cane on the original PC and the AT, but the latter uses an extension to make it 16-bit. It has a maximum data transfer rate of about 8 megabits per second on an AT, which is actually well above the capability of disk drives, or most network and video cards. The average data throughput is around a quarter of that. Its design makes it difficult to mix 8- and 16-bit RAM or ROM within the same 128K block of upper memory; an 8-bit VGA card could force all other cards in the same (C000-DFFF) range to use 8 bits as well, which was a common source of inexplicable crashes where 16-bit network card were involved.

EISA

Extended Industry Standard Architecture. An evolution of ISA and (theoretically) backward compatible with it, including the speed (8 MHz), so the increased data throughput is mainly due to the bus doubling in size-but you must use EISA expansion cards. It has its own DMA arrangements, which can use the complete address space. On advantage of EISA (and Micro Channel) is the ease of setting up expansion cards-plus them in and run the configuration software which will automatically detect their settings.

MCA

Micro Channel Architecture. A proprietary standard established by IBM to take over from ISA, and therefore incompatible with anything else. It comes in two versions, 16- and 32-bit and, in practical terms, is capable of transferring around 20 mbps.

Local Bus

The local bus is one more directly suited to the CPU; it's next door (hence local), has the same bandwidth and runs at the same speed, so the bottleneck is less (ISA was local in the early days). Data is therefore moved along the bus at processor speeds. There are two varieties:

· VL-BUS, a 32-bit bus which allows bus mastering, and uses two cycles to transfers a 32-bit word, peaking at 66 Mb/sec. It also supports burst mode, where a single address cycle precedes four data cycles, meaning that 4 32-bit words can move in only 5 cycles, as opposed to 8, giving 105 Mb/sec at 33 MHz. The speed is mainly obtained by allowing VL-Bus adapter cards first choice at intercepting CPU cycles. It's not designed to cope with more than a certain number of cards at particular speeds; e.g. 3 at 33, 2 at 40 and only 1 at 50 MHz, and even that often needs a wait state inserted. VL-Bus 2 is 64-bit, yielding 320 Mb/sec at 50 MHz. There are two types of slot; Master and Slave. Master boards (e.g. SCSI controllers) have their own CPUs which can do their own things; slaves (i.e. video cards) don't. A salve board will work on a master slot, but not vice versa.

· PCI, which is a mezzanine bus, divorced from the CPU, giving it some independence and the ability to cope with more devices, so it's more suited to cross-platform work. It is time multiplexed, meaning that address and data lines share connections. It has its own burst mode that allows 1 address cycle to be followed by as many data cycles as system overheads allow. At nearly 1 word per cycle, the potential is 264 Mb/sec. It can operate up to 33 MHz, or 66 MHz with PCI 2.1 and can transfer data at 32 bits per clock cycle so you can get up to 132 Mbytes/sec (264 with 2.1). Each PCI card can perform up to 8 functions, and you can have more than one busmastering card on the bus. It should be noted, though, that many functions are not available with PCI, such as sound. Not yet, anyway. It is part of the plug and play standard, assuming your operating system and BIOS agree, so it is auto configuring (although some cards use jumpers instead of storing information in a chip); it will also share interrupts under the same circumstances. The PCI chipset handles transactions between cards and the rest of the system, and allows other buses to be bridged to it (typically and ISA bus to allow older cards to be used). Not all of them are equal, though; certain features, such as byte merging, may be absent. The connector may vary according to the voltage the card uses (3.3 or 5v; some cards can cope with both).

Basic Optimization Tricks

This section is intended for users who have a limited knowledge of BIOS setup. It provides four fundamental procedures that may help improve the performance of your system.

· Make sure that all standard settings correspond to the installed components of your system. For instance, you should verify the date, the time, available memory, hard disks and floppy disks. For more information, go to the

Standard CMOS Setup

section.

· Make sure that your cache memory (internal and external) is enabled. Of course you must have internal (L1) and external (L2) cache memory present which is always the case for recent systems (less than five years old). For more information, go to the Advanced CMOS Setup section. Recently, some motherboards were found having fake cache memory. Some unscrupulous manufacturers are using solid plastics chips containing no memory to lure vendors and customers and then gain extra profits in an highly competitive semiconductors market. Beware!

Make sure that your Wait States values are at the minimum possible. You must however be careful because if values are too low, your system may freeze (hang up).

Make sure to shadow your Video and System ROM. On older systems, this may improve performance significantly.

Make sure to use a coherent power management strategy. Choosing the right timing may increase the life expectancy of your hard disk. See the Power Management section.

Hard disk speed is the major bottleneck for a system performance, notably for those with 16 MB of memory and more. You may have the fastest CPU, lots of memory and a confortable cache, but if you have a crummy hard disk, you may not see improvement in performances.

POST and Entering Setup

When the system is powered on, the BIOS will perform diagnostics and initialize system components, including the video system. (This is self-evident when the screen first flicks before the Video Card header is displayed). This is commonly referred as POST (Power-On Self Test). Afterwards, the computer will proceed its final boot-up stage by calling the operating system. Just before that, the user may interrupt to have access to SETUP.

To allow the user to alter the CMOS settings, the BIOS provides a little program, SETUP. Usually, setup can be entered by pressing a special key combination (DEL, ESC, CTRL-ESC, or CRTL-ALT-ESC) at boot time (Some BIOSes allow you to enter setup at any time by pressing CTRL-ALT-ESC). The AMI BIOS is mostly entered by pressing the DEL key after resetting (CTRL-ALT-DEL) or powering up the computer. You can bypass the extended CMOS settings by holding the <INS> key down during boot-up. This is really helpful, especially if you bend the CMOS settings right out of shape and the computer won't boot properly anymore. This is also a handy tip for people who play with the older AMI BIOSes with the XCMOS setup. It allows changes directly to the chip registers with very little technical explanation.

A Typical BIOS POST Sequence

Most BIOS POST sequences occur along four stages:

1. Display some basic information about the video card like its brand, video BIOS version and video memory available.

2. Display the BIOS version and copyright notice in upper middle screen. You will see a large sequence of numbers at the bottom of the screen. This sequence is the BIOS identification line.

3. Display memory count. You will also hear tick sounds if you have enabled it (see Memory Test Tick Sound section).

4. Once the POST have succeeded and the BIOS is ready to call the operating system (DOS, OS/2, NT, WIN95, etc.) you will see a basic table of the system's configurations:

· Main Processor: The type of CPU identified by the BIOS. Usually Cx386DX, Cx486DX, etc..

· Numeric Processor: Present if you have a FPU or None on the contrary. If you have a FPU and the BIOS does not recognize it, see section Numeric Processor Test in Advanced CMOS Setup.

· Floppy Drive A: The drive A type. See section Floppy drive A in Standard CMOS Setup to alter this setting.

· Floppy Drive B: Idem.

· Display Type: See section Primary display in Standard CMOS Setup.

· AMI or Award BIOS Date: The revision date of your BIOS. Useful to mention when you have compatibility problems with adaptor cards (notably fancy ones).

· Base Memory Size: The number of KB of base memory. Usually 640.

· Ext. Memory Size: The number of KB of extended memory.

In the majority of cases, the summation of base memory and extended memory does not equal the total system memory. For instance in a 4096 KB (4MB) system, you will have 640KB of base memory and 3072KB of extended memory, a total of 3712KB. The missing 384KB is reserved by the BIOS, mainly as shadow memory (see Advanced CMOS Setup).

· Hard Disk C: Type: The master HDD number. See Hard disk C: type section in Standard CMOS Setup.

· Hard Disk D: Type: The slave HDD number. See Hard disk D: type section in Standard CMOS Setup.

· Serial Port(s): The hex numbers of your COM ports. 3F8 and 2F8 for COM1 and COM2.

· Parallel Port(s): The hex number of your LTP ports. 378 for LPT1.

· Other information: Right under the table, BIOS usually displays the size of cache memory. Common sizes are 64KB, 128KB or 256KB. See External Cache Memory section in Advanced CMOS Setup.

AMI BIOS POST Errors

During the POST routines, which are performed each time the system is powered on, errors may occur. Non-fatal errors are those which, in most cases, allow the system to continue the boot up process. The error messages normally appear on the screen. Fatal errors are those which will not allow the system to continue the boot-up procedure. If a fatal error occurs, you should consult with your system manufacturer or dealer for possible repairs. These errors are usually communicated through a series of audible beeps. The numbers on the fatal error list correspond to the number of beeps for the corresponding error. All errors listed, with the exception of #8, are fatal errors. All errors found by the BIOS will be forwarded to the I/O port 80h.

· 1 beep: DRAM refresh failure. The memory refresh circuitry on the motherboard is faulty.

· 2 beeps: Parity Circuit failure. A parity error was detected in the base memory (first 64k Block) of the system.

· 3 beeps: Base 64K RAM failure. A memory failure occurred within the first 64k of memory.

· 4 beeps: System Timer failure. Timer #1 on the system board has failed to function properly.

· 5 beeps: Processor failure. The CPU on the system board has generated an error.

· 6 beeps: Keyboard Controller 8042-Gate A20 error. The keyboard controller (8042) contains the gate A20 switch which allows the computer to operate in virtual mode. This error message means that the BIOS is not able to switch the CPU into protected mode.

· 7 beeps: Virtual Mode (processor) Exception error. The CPU on the motherboard has generated an Interrupt Failure exception interrupt.

· 8 beeps: Display Memory R/W Test failure. The system video adapter is either missing or Read/Write Error its memory is faulty. This is not a fatal error.

· 9 beeps: ROM-BIOS Checksum failure. The ROM checksum value does not match the value encoded in the BIOS. This is good indication that the BIOS ROMs went bad.

· 10 beeps: CMOS Shutdown Register. The shutdown register for the CMOS memory Read/Write Error has failed.

· 11 beeps: Cache Error / External Cache Bad. The external cache is faulty.

Other AMI BIOS POST Codes

· 2 short beeps: POST failed. This is caused by a failure of one of the hardware testing procedures.

· 1 long & 2 short beeps: Video failure. This is caused by one of two possible hardware faults. 1) Video BIOS ROM failure, checksum error encountered. 2) The video adapter installed has a horizontal retrace failure.

· 1 long & 3 short beeps: Video failure. This is caused by one of three possible hardware problems. 1) The video DAC has failed. 2) the monitor detection process has failed. 3) The video RAM has failed.

· 1 long beep: POST successful. This indicates that all hardware tests were completed without encountering errors.

If you have access to a POST Card reader, (Jameco, etc.) you can watch the system perform each test by the value that's displayed. If/when the system hangs (if there's a problem) the last value displayed will give you a good idea where and what went wrong, or what's bad on the system board. Of course, having a description of those codes would be helpful, and different BIOSes have different meanings for the codes. (could someone point out FTP sites where we could have access to a complete list of error codes for different versions of AMI and Award BIOSes?).

BIOS Error Messages

This is a short list of most frequent on-screen BIOS error messages. Your system may show them in a different manner. When you see any of these, you are in trouble - Doh! (Does someone has any additions or corrections?)

· "8042 Gate - A20 Error": Gate A20 on the keyboard controller (8042) is not working.

· "Address Line Short!": Error in the address decoding circuitry.

· "Cache Memory Bad, Do Not Enable Cache!": Cache memory is defective.

· "CH-2 Timer Error": There is an error in timer 2. Several systems have two timers.

· "CMOS Battery State Low" : The battery power is getting low. It would be a good idea to replace the battery.

· "CMOS Checksum Failure" : After CMOS RAM values are saved, a checksum value is generated for error checking. The previous value is different from the current value.

· "CMOS System Options Not Set": The values stored in CMOS RAM are either corrupt or nonexistent.

· "CMOS Display Type Mismatch": The video type in CMOS RAM is not the one detected by the BIOS.

· "CMOS Memory Size Mismatch": The physical amount of memory on the motherboard is different than the amount in CMOS RAM.

· "CMOS Time and Date Not Set": Self evident.

· "Diskette Boot Failure": The boot disk in floppy drive A: is corrupted (virus?). Is an operating system present?

· "Display Switch Not Proper": A video switch on the motherboard must be set to either color or monochrome.

· "DMA Error": Error in the DMA (Direct Memory Access) controller.

· "DMA #1 Error": Error in the first DMA channel.

· "DMA #2 Error": Error in the second DMA channel.

· "FDD Controller Failure": The BIOS cannot communicate with the floppy disk drive controller.

· "HDD Controller Failure": The BIOS cannot communicate with the hard disk drive controller.

· "INTR #1 Error": Interrupt channel 1 failed POST.

· "INTR #2 Error": Interrupt channel 2 failed POST.

· "Keyboard Error": There is a timing problem with the keyboard.

· "KB/Interface Error": There is an error in the keyboard connector.

· "Parity Error ????": Parity error in system memory at an unknown address.

· "Memory Parity Error at xxxxx": Memory failed at the xxxxx address.

· "I/O Card Parity Error at xxxxx": An expansion card failed at the xxxxx address.

· "DMA Bus Time-out": A device has used the bus signal for more than allocated time (around 8 microseconds).

If you encounter any POST error, there is a good chance that it is an HARDWARE related problem. You should at least verify if adaptor cards or other removable components (simms, drams etc...) are properly inserted before calling for help. One common attribute in human nature is to rely on others before investigating the problem yourself. Please don't be a politician (Aide-toi et le ciel t'aidera).

Standard CMOS Setup
You should have your current setup options written down ON PAPER somewhere, preferably taped to the inside or the outside of the case. CMOS memory has a tendency to get erased as the battery gets old, or become inaccessible if you forget the password. Especially remember the hard disk settings; they are the most important.

If you have warm-booted the computer (via CTRL-ALT-DEL) to go into the CMOS setup, the BIOS routine to handle the "Print Screen" key will probably be installed. You can display each screen of the CMOS setup and press SHIFT-PRINT SCREEN to get a printed copy directly. There are several good CMOS saver programs out on the market, including the PC-Tools and Norton recovery programs. They allow a user to save a copy of the CMOS registers to a file in case the battery dies, or if they messed around with the settings, etc.

· Date (mn/date/year) and Time: To change the date and time of the system clock. Do not expect your computer to keep tract of time as accurately as an atomic clock, or even a wrist watch! Depending of the quality of the motherboard expect to loose (or gain) several seconds per month. On rare occasion you will need to setup the clock in BIOS Setting as all operating systems allow to change these settings within their environments.

· Daylight Saving: Allows the clock to automatically adapt to the daylight saving scheme which is removing one hour on the last Sunday of October and adding one hour on the last Sunday of April.

· Hard disk C type: The number of your primary (master) hard drive. Most of the time this number is 47, which means that you must specify the drive specs according to your hard drive manual.

· Cyln: The number of cylinders on your hard disk.

· Head: The number of heads.

· WPcom: Write Precompensation. Older hard drives have the same number of sectors per track at the innermost tracks as at the outermost tracks. This means that the data density at the innermost tracks is higher and thus the bits are lying closer together. Starting with this Cyl# until the end of Cyl#s the writing starts earlier on the disk. In modern HDs (all AT-BUS and SCSI, Small Computer Systems Interface) this entry is useless. Set it either to -1 or max Cyln (a common value is 65535). For IDE (Integrated Device Electronics) hard drives it is not necessary to enter a WP cylinder. The IDE HDD will ignore it for it has its own parameters inboard.

· LZone: The address of the landing zone. Same as WPcom. Used in old HDs without an auto-parking feature (MFM, Modified Frequency Modulated, or RLL, Run Length Limited). Set it to 0 or max Cyl#.

· Sect: The number of sectors per track. It is often 17 for MFM and 26 for RLL HDD. On other types of drives, it will vary.

· Size : This is automatically calculated according the number of cylinders, heads and sectors. It is in megabytes and applies this formula: (Hds * Cyl * Sect * 512) / 1048.

EIDE specifications. With the growing capacity of hard disks on desktop computers, a redefinition of IDE specifications was necessary. The old IDE specification only supported drives up to 528 megabytes, which is the Normal partition setting. In 1994, the EIDE (Enhanced IDE) protocol was designed and now all new motherboards support it. This new protocol uses the LBA (Logic Block Addressing) system which considers logic blocks instead of heads, cylinders and sectors. If your BIOS does not support LBA, several hard disk manufacturers provide drivers to trick the BIOS. You will also find a Large partition setting that can accommodate drives up to 1024 cylinders, but do not support LBA. Unfortunately, many large implementations don't work correctly for drives of over 1GB (there's no good reason why it wouldn't work for much larger drives though). Note that 1024 cylinders native is 528MB. The 528MB limit is the 1024 cyl / 16 head / 63 sector limit.

· Hard disk D type: The number of your secondary (slave) hard drive. Same procedure than above. Jumpers must be set for an hard drive to perform as slave. Please refer to your hard drive manual. You might also want to refer to the hard disk data file frequently posted to comp.sys.ibm.pc.hardware.storage

Several of the PCI motherboards can now accommodate up to four IDE drives: Primary Master, Primary Slave, Secondary Master and Secondary Slave.

· Floppy drive A: The type of floppy drive installed for drive A. Frequent configurations are 1.44 MB (3 1/2 inches), or 1.2 MB (5 1/4). Newer systems have also a 2.88 MB (3 1/2) setting.

· Floppy drive B: The type of floppy drive installed for drive B.

· Primary display: The type of displaying standard you are using, and in case of systems with two video adapters the primary one. The most frequent is VGA/PGA/EGA. Modern computers have VGA (Video Graphics Array). If you have an older black/white display select Mono or Hercules, if your Video adapter card is text only, select MDA.

· Keyboard: Installed. If "not installed" this option sets the BIOS to pass the keyboard test in the POST, allowing to reset a PC without a keyboard (file server, printer server, etc.), without the BIOS producing a keyboard error. As a system administrator, you can uninstall the keyboard as a supplementary security procedure to prevent people messing up with the server.

Changing Your Password

Enable you to change the active password. The default is no password.

Remember your password!!! Write it down somewhere!!! Ask yourself: Do I really need to set a password to access my system and/or the BIOS? (is your brother / sister / kid / employee / colleague that dangerous?) If security is of some minor concern to you, disabled recommended. Why not only password protect (or encrypt) some critical files (personal finances - things the IRS should not see, juicy love letters, pornographic images (the thing that Internet is most used for), customer information databases, etc...)? If you lose your password, you will have to erase your CMOS memory (see the FAQ ). Some systems allow you to choose when the password is needed to change the CMOS settings, to boot the machine, etc.

Auto Configuration

All recent motherboards have now an auto-configuration setting leaving much of BIOS setup problems out of the user's hands, such as Bus Clock Speed and Wait States. On the majority of cases it will do just fine. But you must remember, it is not an optimization of your system's performances, but a set of efficient settings that will insure a good result. You will have to Disable this setting if you want to alter the BIOS yourself, otherwise your settings will be ignored. On some systems, you may get supplementary performances by improving over auto configuration settings, but on others auto configuration is all you will ever need.

Auto Configuration with BIOS Defaults

The BIOS defaults may not be tuned for your motherboard/chipset, but give a reasonable chance of getting into POST. Usually these settings are a good start to fine tune your system. If you did something wrong and don't know what, select this. It will replace your BIOS settings by default values. You will have to start all over again. Be sure to know your system's configuration. This option does NOT alter the date, hard disk and floppy disk configurations in the Standard CMOS setup, so in general you can expect your system to boot without problems after selecting this.

Auto Configuration with Power-on Defaults

When powering on, the BIOS puts the system in the most conservative state you can think of. Turbo off, all caches disabled, all wait states to maximum, etc... This is to make sure that you can always enter BIOS setup. Useful if the settings obtained by selecting AUTO CONFIGURATION WITH BIOS DEFAULTS fail. If the system does not work with these values, it's time to panic: the problem may be hardware-related (DIP switches, cards not inserted properly or worst, something broken).

Exiting BIOS

There are two ways to exit BIOS settings.

· Write to CMOS and Exit: Save the changes you made in the CMOS. You must do that to permanently keep your configuration. Several users say they changed the CMOS setup but forgot to exit with this one! A common source of error.

· Do Not Write to CMOS and Exit: If you are not sure of the changes you made in the CMOS settings, use this option to exit safely.

Advanced CMOS Setup

May vary according to your system, BIOS version and brand. Some functions may not be present or the order and name may be different (particularly for different BIOS brand). Know EXACTLY what you are doing. Some configurations may keep your computer off from booting. If that's the case: Switch the power off. Turn your computer on WHILE keeping the DEL key pressed. This is supposed to erase the BIOS memory. If it still doesn't boot, consult your motherboard manual. Look for a "forget CMOS RAM" jumper. Set it. Try it again. If it still doesn't boot, ask a friend or post to a computer hardware newsgroup. You are permitted to panic.

· Typematic Rate Programming: Disabled recommended. It enables the typematic rate programming of the keyboard. Not all keyboards support this! The following two entries specify how the keyboard is programmed if enabled.

· Typematic Rate Delay (msec): 500 ns recommended. The initial delay before key auto-repeat starts, that is how long you've got to press a key before it starts repeating.

· Typematic Rate (Chars/Sec): 15. It is the frequency of the auto-repeat i.e. how fast a key repeats.

· Above 1 MB Memory Test: If you want the system to check the memory above 1 MB for errors. Disabled recommended for faster boot sequence. The HIMEM.SYS driver for DOS 6.2 now verifies the XMS (Extended Memory Specification), so this test is redundant. It is thus preferable to use the XMS test provided by HIMEM.SYS since it is operating in the real environment (where user wait states and other are operational).

· Memory Test Tick Sound: Enabled recommended. It gives an audio record that the boot sequence is working properly. Plus, it is an aural confirmation of your CPU clock speed/Turbo switch setting. An experimented user can hear if something is wrong with the system just be the memory test tick sound.

· Memory Parity Error Check: Enabled recommended. Additional feature to test bit errors in the memory. All (or almost all) PCs are checking their memory during operation. Every byte in memory has another ninth bit, that with every write access is set in such way that the parity of all bytes is odd. With every read access the parity of a byte is checked for this odd parity. If a parity error occurs, the NMI (Non Maskable Interrupt), an interrupt you mostly cannot switch off, so the computer stops his work and displays a RAM failure) becomes active and forces the CPU to enter an interrupt handler, mostly writing something like this on the screen: PARITY ERROR AT 0AB5:00BE SYSTEM HALTED. On some motherboards you can disable parity checking with standard memory. Enabled to be sure data from memory are correct. Disable only if you have 8-bit RAM, which some vendors use because it is 10% cheaper. If you own a Gravis Ultrasound Soundcard (GUS), it's imperative that this is enabled; otherwise the Sound Blaster emulation won't work(!).

Note: Be sure to have memory chips of the same speed installed. It is not uncommon to have system crashes simply because memory SIMMS are of different speed. Faster memory will not adapt itself to the speed of slower memory. 60 ns and 80 ns SIMMS will surely make your system crash and yourself wonder what is the problem (I know).

· Hard Disk Type 47 RAM Area: The BIOS has to place the HD type 47 data somewhere in memory. You can choose between DOS memory or PC BIOS (or peripheral card) memory area 0:300. DOS memory is valuable, you only have 640KB of it. So you should try to use 0:300 memory area instead. There may be some peripheral card which needs this area too (sound card, network card, whatever). So if there are some fancy cards in your PC, check the manuals if they're using the 0:300 area. But in most cases this will work without checking. This is redundant if BIOS is shadowed (maybe not in very old BIOSes). The RAM area can be verified by checking address of int41h and int46h. These are fixed disk parameters blocks. If they point to the BIOS area, BIOS made modification of parameters before mapping RAM there.

· Wait for <F1> If Any Error: When the boot sequence encounter an error it asks you to press F1. Only at 'non-fatal' errors. If disabled, the system prints a warning and continues to boot without waiting for you to press any keys. Enabled recommended. Disabled if you want the system to operate as a server without a keyboard.

· System Boot Up Num Lock: Specify if you want the Num Lock key to be activated at boot up. Some like it, some do not. MS-DOS (starting with 6.0, maybe earlier) allows a "NUMLOCK=" directive in config.sys, too; if someone turns the BIOS flag off but has NUMLOCK=ON in their configuration file, they may be a bit perturbed.

· Numeric Processor Test: Enabled if you have a math coprocessor (built in for the 486DX, 486DX2, 486DX3 and Pentium - 586 - family). Disabled if you don't (386SX, 386DX, 486SX, 486SLC and 486DLC). If disabled, your FPU (Floating Point Unit, if present) isn't recognized as present by the system and will therefore significantly decrease the performance of your system.

· Weitek Coprocessor: If you have Weitek FPU, enable. If you have not, disable. This high performance FPU has 2-3 times the performance of the Intel FPU. Weitek uses some RAM address space, so memory from this region must be remapped somewhere else.

· Floppy Drive Seek at Boot: Power up your A: floppy drive at boot. Disabled recommended for faster boot sequence and for reduced damage to heads. Disabling the floppy drive, changing the system boot sequence and setting a BIOS password are good techniques for adding some security to a PC.

· System Boot Sequence: What drive the system checks first for an operating system. C:, A: recommended for faster boot sequence, or to not allow any user to enter your system by booting from the FDD if your autoexec.bat starts with a login procedure. A:, C: if the person who uses the computer is someone who don't knows how to setup CMOS. Because if something fails and a boot floppy won't work, many users won't know what to do next. However, be careful. You had better know this setting is turned on and be prepared to turn it off if your hard disk boot track becomes corrupted, but not obviously absent, since you otherwise won't be able to boot from floppy. Also, it's easy to fool yourself into thinking you booted from a known virus-free floppy when it actually booted from the (virus-infested) hard drive.

· System Boot Up CPU speed: Specify at what processor speed the system will boot from. Usual settings are HIGH and LOW. HIGH recommended. If you encounter booting problems, you may try LOW. You may also change the CPU speed with Ctrl-Alt +.

· External Cache Memory: Enabled if you have external cache memory (better known as L2 cache memory). This is a frequent error in CMOS setup as if Disabled when you have cache memory, the system performance decreases significantly. Most systems have from 64K to 512K of external cache. It is a cache between the CPU and the system bus. Different operating systems may address different levels of cache memory. For instance, DOS and Windows can address up to 64K at one time while Windows 95, OS/2 and Windows NT can address larger memory spaces. So, don't buy 256K of cache is you are using a DOS environment with less than 8MB of memory. It will not improve much the performance of your system. If Enabled when the system does not have cache memory, the system will freeze most of the time.

· Internal Cache Memory: Enable or disable the internal cache memory of the CPU (better known as L1 cache memory). Disabled for 386 and Enabled for 486 (1 to 8KB of internal CPU cache). If the CPU does not have internal cache, the system may freeze if enabled.

In many AMI and AWARD BIOSes, the two previous options are implemented either as separate Internal and External Enable/Disable options, or as a single option (Cache Memory : Disabled/Internal/Both).

· CPU Internal Cache: same as above.

· Fast Gate A20 Option: A20 refers to the first 64KB of extended memory (A0 to A19) known as the "high memory area". This option uses the fast gate A20 line, supported in some chipsets, to access memory above 1 MB. Normally all RAM access above 1 MB is handled through the keyboard controller chip (8042 or 8742). Using this option will make the access faster than the normal method. This option is very useful in networking and multitasking operating systems.

· Turbo Switch Function: Enables or disables the turbo switch. Disabled recommended.

· Shadow Memory Cacheable: You increase speed by copying ROM to RAM. Do you want to increase it by cacheing it? Yes or no - see Video BIOS Area cacheable. Yes recommended for MS-DOS and OS/2. Linux and other Unix-like operating systems will not use the cached ROMs and will benefit from the additional available memory if they are not cached.

· Password Checking Option: Setup password to have access to the system and / or to the setup menu. Good if the computer is to be shared with several persons and you don't want anyone (friends, sister, etc.) to mess up with the BIOS. Default password: AMI (if you have AMI BIOS). Award: BIOSTAR or AWARD_SW for newer versions (Note: I even know a computer store that kept standard AWARD BIOS configuration with their systems because they didn't know what the default password was!).

· Video ROM Shadow C000, 32K: Memory hidden under the "I/O hole" from 0x0A0000 to 0x0FFFFF may be used to "shadow" ROM (Read-Only Memory). Doing so, the contents of the ROM are copied into the RAM and the RAM is used instead, which is obviously faster. Video BIOS is stored in slow EPROM (Erasable Programmable Read-Only Memory) chips (120 to 150ns of access time). Also, ROM is 8 or 16 bit while RAM 32 bit wide access. With Shadow on, the EPROM content is copied to RAM (60 to 80ns of access time with 32 bit wide access). Therefore performance increases significantly. Only sensible on EGA/VGA systems. Enabled recommended. If you have flash BIOS (EEPROM), you can disable it. Flash BIOS enables access at speeds similar to memory access so you can use the memory elsewhere. However, flash BIOS is still only accessing it at the speed of the bus (ISA, EISA or VLB). On systems where the BIOS automatically steals 384K of RAM anyway, it shouldn't hurt to enable shadowing even on flash ROM. One side effect is that you will not be able to modify the contents of flash ROM when the chip is shadowed. If you reconfigure an adapter which you think might have flash ROM, and your changes are ignored, or of course if it gives you an error message when you try to change them, you'll need to temporarily disable shadowing that adapter. On (S)VGA you should enable both video shadows. Some video cards maybe using different addresses than C000 and C400. If it is the case, you should use supplied utilities that will shadow the video BIOS, in which case you should disable this setting in the CMOS. Video BIOS shadowing can cause software like XFree86 (the free X Window System) to hang. They should be probably be disabled if you run any of the 386 unixes.

Some cards map BIOS or other memory not only in the usual a0000-fffff address range, but also just below the 16MB border or at other places. The BIOS (for PCI buses only?) now allows to create a hole in the address range where the card sits. The hole may be enabled by giving an address, then a size is requested in power of 2, 64k - 1MB.

· Adaptor ROM Shadow C800,16K: Disabled. Those addresses (C800 to EC00) are for special cards, e.g. network and controllers. Enable only if you've got an adapter card with ROM in one of these areas. It is a BAD idea to use shadow RAM for memory areas that aren't really ROM, e.g. network card buffers and other memory-mapped devices. This may interfere with the card's operation. To intelligently set these options you need to know what cards use what addresses. Most secondary display cards (like MDA and Hercules) use the ROM C800 address. Since they are slow, shadowing this address would improve their performance. An advanced tip: in some setups it is possible to enable shadow RAM without write-protecting it; with a small driver (UMM) it is then possible to use this 'shadow RAM' as UMB (Upper Memory Block) space. This has speed advantages over UMB space provided by EMM386.

· Adaptor ROM Shadow CC00,16K: Disabled. Some hard drive adapters use that address.

· Adaptor ROM Shadow D000,16K: Disabled. D000 is the default Address for most Network Interface Cards.

· Adaptor ROM Shadow D400,16K: Disabled. Some special controllers for four floppy drives have a BIOS ROM at D400..D7FF.

· Adaptor ROM Shadow D800,16K: Disabled

· Adaptor ROM Shadow DC00,16K: Disabled

· Adaptor ROM Shadow E000,16K: Disabled. E000 is a good "out of the way" place to put the EMS page frame. If necessary.

· Adaptor ROM Shadow E400,16K: Disabled

· Adaptor ROM Shadow E800,16K: Disabled

· Adaptor ROM Shadow EC00,16K: Disabled. SCSI controller cards with their own BIOS could be accelerated by using Shadow RAM. Some SCSI controllers do have some RAM areas too, so it depends on the brand.

Some SCSI adapters do not use I/O-Addresses. The BIOS address range contains writable addresses, which in fact are the I/O-ports. This means: this address must not be shadowed and even not be cached.

· System ROM Shadow F000, 64K: Same thing as Video shadow, but according to the system BIOS (main computer BIOS). Enabled recommended for improved performance. System BIOS shadowing and caching should be disabled to run anything but DOS (Windows).

On older BIOS versions the shadow choices are in 400(hex)-byte increments. For instance, instead of one Video ROM Shadow segment of 32K, you will have two 16K segments (C400 and C800). Same thing for Adaptor ROM Shadow segments.

· BootSector Virus Protection: It is not exactly a virus protection. All it does is whenever your boot sector is accessed for writing, it gives a warning to the screen allowing you to disable the access or to continue. Extremely annoying if you use something like OS/2 Boot Manager that needs to write to it. It is completely useless for SCSI or ESDI (Enhanced Small Device Interface) drives as they use their own BIOS on the controller. Disabled recommended. If you want virus protection, use a TSR (Terminate and Stay Resident) virus detection (Norton, Central Point, etc...). Scan by Macfee is also a good idea. Available on most FTP servers, it is a shareware.

Advanced Chipset Setup

Configurations may vary according to your system, BIOS version and brand. So, some setting may be present on your computer, some may not. Be sure of what you are doing!

· Automatic Configuration: Allows the BIOS to set automatically several important settings (e.g. Clock divider, wait states, etc.). Very useful for newbies. Disabled recommended if you want to play around with the settings. If you have some special adapter cards, you will also have to disable this option.

· Keyboard Reset Control: Enable Ctrl-Alt-Del warm reboot. Enabled recommended for more control over your system.

Refresh

· Hidden Refresh: Allows the RAM refresh memory cycles to take place in memory banks not used by your CPU at this time, instead or together with the normal refresh cycles, which are executed every time a certain interrupt (DRQ0 every 15 ms) is called by a certain timer (OUT1). Every time it takes 2 to 4 ms for the refresh. One refresh cycle every ~16 us refreshes 256 rows in ~ 4ms. Each refresh cycle only takes the equivalent of one memory read or less, as CAS (Column Address Strobe) is not needed for a refresh cycle. Some RAM can do it, some not. Try. If the computer fails, turn it off. Enabled recommended. There are typically 3 types of refresh schemes: cycle steal, cycle stretch, or hidden refresh. Cycle steal actually steals a clock cycle from the CPU to do the refresh. Cycle stretch actually delays a cycle from the processor to do the refresh. Since it only occurs every say 4ms or so, it's an improvement from cycle steal. We're not really stealing a cycle, only stretching one. Hidden refresh typically doesn't stretch or steal anything. It's usually tied to DTACK (Data acknowledge) or ALE (Address Latch Enable) or some other signal relating to memory access. Since memory is accessed ALL of the time it is easy to synchronize the refresh on the falling edge of this event. Of course, the system performance is at its optimum efficiency, refresh wise since we're not taking clock cycles away from the CPU.

· Slow Refresh: Causes RAM refresh to happen less often than usual, around four times. This increases the performance slightly due to the reduced contention between the CPU and refresh circuitry, but not all DRAM memories necessarily support these reduced refresh rates (in which case you will get parity errors and crashes). It also saves power, a good opportunity for laptop computers. Enabled recommended

· Concurrent Refresh: Both the processor and the refresh hardware have access to the memory at the same time. If you switch this off, the processor has to wait until the refresh hardware has finished (it's a lot slower). Enabled recommended.

· Burst Refresh: Performs several refresh cycles at once. Increase the system performance.

· DRAM Burst at 4 Refresh: Refresh is occurring at Bursts of four, increasing the system performance.

· Hi-speed Refresh: Refreshes are occurring at an higher frequency, which is improving the system performance. Of course, not all types of memory can support it and Slow Refresh is preferred.

· Staggered Refresh: Refresh is performed on memory banks sequentially. The advantages are related to less power consumption and less interference between memory banks.

· Slow Memory Refresh Divider: The AT refresh cycle occurs normally every 16 ns, straining the CPU. If you can select an higher value, such as 64 ns, you will increase the performance of your system.

· Decoupled Refresh Option: Enables the ISA bus and the RAM to refresh separately. Because refreshing the ISA bus is more slow, this causes less strain on the CPU.

· Refresh Value: The lower this value is, the best the performance.

· Refresh RAS Active Time: The amount of active time needed for Row Address Strobe during refresh. The lower the better.