If you already have a GX1 chassis with a power supply and all the required internal non-electronic hardware (including the riser bracket), you've just saved yourself about $40-$50 as of the time of this writing.  The required different (from GX1) components are (the cheapest available prices are listed below, mostly from eBay auctions, including shipping): GX110-compatible CPU ($5-$10 for 1GHz Coppermine) GX110 Socket 370 Motherboard ($15-$20) GX110 Riser Card that matches your chassis (SFF uses 2-slot PCI, LP uses 3-slot PCI, MidSize and Mini-Tower (MT) use 5-slot PCI, and MT also uses a 7-slot ISA/PCI) ($9-$25) PC100 non-ECC unbuffered unregistered low-density SDRAM if this is not what you already have on your GX1 ($5-$20) If using an LP chassis, you need the GX1 Slot 1 "case" 50mm fan to use as the CPU fan.  If a MidSize or MT chassis, you need the 80mm case fan shroud.
	Use a fast CPU so you don't waste your time, like a 1 GHz Coppermine or the Powerleap Tualatins for over 1 GHz.  You can find the Intel SL52R CPUs (1GHz Coppermine) on eBay for between $15-$20 and it will run on BIOS A09.  You can also find 1.3 and 1.4 GHz Socket 370 100 MHz FSB FCPGA-2 Celeron Tualatins on eBay and at Directron for $37 (1.3 GHz) as of this writing, but you must follow these restrictions: You must use a power converter adapter, either a Lin-Lin 370 "Slocket" (about $15 including shipping), a Powerleap PL-Neo/T Adapter ($50, which comes with or without the processor), or an Upgradeware adapter from Stratton Computer (USA, $30). Use no higher than BIOS A05, meaning if you are using a later version than you must change it before putting in the Tualatin. The Pentium III 133 MHz FSB Tualatins have FSB100 down-speed compatibility using the same BIOS restrictions, but they cost more and the 133 MHz FSB will down-speed to 100 MHz anyway on your GX110 motherboard.
	PC100 SDRAM is compatible on the GX1, so before buying new SDRAM make sure you need it.  PC66 and ECC SDRAM is compatible on the GX1, both of which cannot be used on the GX110.  Some of the 256MB PC133 SDRAM is downward compatible if the SDRAM has 16 chips, 8 chips on each side, but suppliers are no longer guaranteeing PC100 compatibility using the PC133, so when you shop on eBay watch what you are buying.  A compatible PC133 DIMM may also not be mixable with a PC100 DIMM (note it is standard practice when changing memory on a motherboard to use the same DIMM types).  The compatibility issue has to do with compatibility with the Intel 810e chipset on the GX110 which only operates on a 100 MHz FSB.  Even for PC100 SDRAM you must use low-density DIMMs.  Look for Micron-validated DIMMs here.  The Kingston part to use is KTD-OPGX1N/256 (the "N" is absolutely necessary and it means Non-ECC or No Parity).  Some of you may think that more memory is better, but if you are using W2K or XP then you don't need more than 320MB (256 + 64).  Of course, if you are using the computer as a development system (compiling, linking) or as a Windows server, the more memory the better.  The GX110 only has two DIMM slots compared with the GX1's three - an apparent change in product deployment on Dell's part when they decided to build different lines of machines as servers rather than have both as servers and workstations.  In any case, the GX110 functions well as a UNIX/BSD/Linux server with 512MB.
	The GX1s are all Slot 1 motherboards and more than likely you should upgrade using a Socket 370 GX110 motherboard (why bother with Slot 1 unless you have it already?).  This means you will have a different fan configuration, which leads to a conventional fan issue.  Dell uses a proprietary 3-pin audio plug look-alike (which are 4 pins) instead of a conventional fan and plug.

For the MidSize & Mini-Tower Units:

	You will have to get hold of a green fan shroud that only comes with the GX110 chassis.  I have been able to find a couple, because a lot of GX110s are being torn down for parts sales rather than keeping whole systems intact.  The only other solution is the same for the one below for the LPs.
	The units use a proprietary 80mm chassis fan, and here are two suppliers.  The fan plug on the 80mm MidSize fan is the same as the one on the LP & SFF SECC fan.

For the LP & SFF Units:

A CPU fan is used on the SECC heat sink, and this is the fan you need for a socket 370 CPU.  If you can't get hold of this or the 3rd-party replacement fan, then you can use a special power cable adapter that works using a conventional CPU fan without the motherboard fan plug, but that's bad because if the CPU fan fails the BIOS can't detect it and won't shutdown your PC before your CPU pops its cork.  The Optiplex fan also uses a variable-speed potentiometer that allows the BIOS to speed it up when the CPU gets too hot. This is really important if you are going to use the Tualatin Celeron because it runs hotter. If you don't believe me you can try a little experiment: using BIOS A05 put a Lin-Lin Adapter and Celeron 1.3GHz in an SFF, use the Optiplex fan on the heat sink, close the cover and power-up.  You will find the fan speed up and hum.  Then carefully remove the cover while it is on and blow directly through the heat sink (without spitting of course!!!) and you will hear the fan drop in speed dramatically.

The only other possible fan issue is that the SECC fan directs air flow straight-out the back of the chassis vent holes.  With Socket 370 all that hot air has to be pulled-out through the power supply to exhaust the chassis.  I don't think this is problematic, but if you are concerned you can always strap two conventional 40mm 12VDC CPU fans to the back vent holes and power it off the power supply using one of the cables discussed above.  This should be done if operating on an SFF with the Tualatin.  I haven't checked the fan speed with a Tualatin yet in an LP, but based on what is going on in the SFF I recommend it; the SECC fan really trucks on a Tualatin Celeron when the SFF chassis is closed up,  meaning it is operating at max speed (the noise level isn't good, either), but which I was able to prevent using two CPU fans exhausting out the back vent holes.  Note this should not be a problem in the MidSize and MT because the fan shroud and chassis fan take care of this issue.

Other Issues:

	Mods are necessary but doable when using a GX1 Front Power Control Panel (FCP) with a GX110 motherboard, and this is described on this web site.  The FCPs are hard to come by and are relatively costly, so it is cheaper just to do the mods.
	Although not a GX1 to GX110 upgrade issue, the Dell power supplies have a proprietary motherboard power cable that is convertible using a 3rd-party adapter cable when installing a conventional ATX power supply.  So, if you need a power supply, do NOT use a conventional supply without this adapter cable, else you will fry your motherboard.  There are also 3rd-party Dell power supply look-alikes for the MidSize and Mini-Towers, but once I run out of Dell P/Ss I'd rather use a conventional supply anyway because the adapter cable does the job, unless I can find one cheap on eBay, and a lot of them are still out there.  Keep in mind that unlike the motherboard, each chassis flavor of GX110 comes with its own style power supply, so unless you have spare power supplies for your SFF and LP chassis, don't spend too much money upgrading them.  The LPs use a 152W HP-145SNF supply and the SFFs use a 110W supply.  The 200W supplies have conventional form factors and conventional supplies can fit in a MidSize and Mini-Tower, as long as you remember to use the adapter cable.  I have not investigated how uniform Dell's power supplies are throughout their older and newer product lines, so before buying even a Dell power supply, make sure your part numbers are correct or get one specifically marketed for the GX1 or GX110.
	The GX110 onboard video has either 1MB or 4MB of Video RAM, so if you are going to run Google Earth you should also look for a 32MB PCI Video card (yeah I know Google says 16MB but I've already seen resource issues with a TNT2 16MB).  My favorite is (was!) the Pine SiS 315E 32MB DDR PCI ($25-$35) but it is no longer made (Pine isn't Pine anymore, either) and I have been hard-pressed to find it on distributor web sites or even on eBay (time to test another PCI replacement).  Be careful you don't get its AGP sister version because there is no AGP connector on the motherboard.  Hopefully you already have a good PCI video card in your old Dell already.  And this leads to another big issue: the older less power hungry SVGA PCI cards are being replaced in the market with the more power hungry higher memory equivalents, and this is going to be a problem with your SFF power supply running at 110W.  It may even be a problem with your LP supply at 152W.  Many of these more recent cards blatantly spec a 200W+ power supply as a requirement, which may or may not be CYA or reality.  It's up to you to test one and find out.
	More on GX110 PSUs.   The table below shows power requirements for 4 PSUs - the MidSize/MT GX110 PSU, the LP PSU, an unusual LP PSU replacement (!) normally designed for rack-mounting, and a very-much-older GXa MidSize PSU.  Note the Dell LP PSUs are heavy on +5VDC and +3.3VDC power but light on +12VDC (designed for hard drives).  PCI cards use +5V (one-notch) or both +5V and +3.3V (two notches).  It’s a good idea to get the 2-notch variety to take advantage of the +3.3VDC power available, allowing you to use the newer more power-hungry SVGA PCI cards.  In other words, don't assume your seemingly low-power PSU can't do the job in an LP, even if you have other PCI cards in your system.

GX110 PSU MID/MT     LP   I-Star TC-1U/25       GXa PSU