The MATRIX

One of the greatest achievements of the Time Lords is the APC Net--the Amplified Panatropic Computations Network. It is located in the Capital, and is a masterpiece of exitonic engineering, consisting of billions of artificial brain cells. When a Time Lord is dying, his mind can be linked to the Net, and his knowledge duplicated into the system. The combined knowledge of innumerable Time Lords exist within this unit. It serves to monitor life in the Capital, and to perform many computational functions. It may also analyze events and predict forthcoming events.

It did, for example, predict the impending assassination of the President by the Master (though the Master diverted this prediction to the Doctor alone). It also predicted a potential future in which the Daleks become sole masters of the Universe.

It is possible for a still-living mind to be connected to the Matrix--the "landscape" within the APC Net. There are two legal ways for this to be accomplished. One is through the input that scans the dying brains. This is quite painful, however, and not every one can survive it. The second method id through the head-band worn by the President of the Time Lords, using which he can safely commune with the Net, and draw on its vast supply of knowledge to aid him in his decisions. His mind becomes permantently a part of the Matrix in this fashion, and thus when he dies, his knowledge lives on. The mind-patterns of all previous Presidents of the Time Lords are thus a part of the APC Net. It is simply a matter of being able to access them. This record stretches back to the earliest known period of the Time Lords' history, including that of Rassilon.

There are illegal ways into the Matrix, of coursse.  The Master used one such connection for his puppet, Goth.  The Valeyard knew of another, the half-legendary seventh entrance.

The Matrix contains all the knowledge accumulated by the Time Lords.  It can be entered mentally only by a person acclimatized to it, and access is generally limited to the President of the High Council.  Even then, he must be mentally and physically alert in order to safely enter the APC Net, which places a great drain on his faculties.   The Matrix can also reject people who are mentally incompatible with it.  On the other hand, the Matrix has been invaded numerous times by other Time Lords: the Master, Omega, and the Valeyard.  Even aliens have managed to penetrate it, as in the case of the Vardans.  Once again, it would seem that the Time Lords' "facts" are quite mutable: despite their claim that only the President can enter the Matrix, this is quite clearly untrue.

The Bio Scan data of all living Time Lords is held inside the Matrix.   Theoretically it is accessible only to the President of the Council.  On the other hand, both Councillor Hedin and the Master have stolen the Doctor's data from it.   It is simply a matter of knowing (or deducing) the correct codes to gain access.

Originally, the Bio Scans (then called Data Extracts or DEs) were separate from the Matrix, but they proved to be too susceptible to interference and change.  As a result, they were then adapted into the APC Net.  This did not make them all that much safer in fact, but undoubtedly it made the Time lords breathe a little easier.

The Time Lords scan the reaches of space and time, accumulating information at a rate far greater than any minds could comprehend.  Scanning beams are thus linked into the Matrix, and all of the information gathered by the scans is stored within the Matrix.   Generally speaking, this is a safe process, but on one occasion it almost spelled the doom of the Time Lords.  One such scanning beam touched down upon the home world of the Vardans.

Though a humanoid race, the Vardans possess the ability to transform themsleved and travel down the broadcast wavelengths, including those of thought.  When the scans touched their world, several Vardans managed to trace back along the path and invade the Matrix.  They then sought to enlist the aid of a renegade Time Lord in order to invade Gallifrey physically.  They made a grave error in their choice, selecting the Doctor.  Though he played along with their plans, he managed to shield his true thought from them. He used his robotic companion, K9, to link with the Matrix and search it for information and the point of entry by the Vardans.

Once he found this, K9 could then activate the rejection of the Vardans from the Matrix, and trigger a time bubble about their home world.  The Vardans thus remain sealed within their home planet forever.

The Valeyard seized control of the Matrix in his attempt to kill the Doctor and the members of the Ultimate Court of Appeal.  During this time, we were shown a new figure, the Keeper of the Matrix.  Though his precise function was never made clear, he seems to have been a recent appointment, whose job was to ensure that only authorized persons had access to the Matrix.  He didn't perform his task at all well, since both the Master and the Valeyard had their own channels of entry, and both manipulated the Matrix as they wished.  The Doctor managed temporarily to freeze the Matrix, trapping the Master.  The Valeyard, however, used his own connection with the Matrix to take over the body of the Keeper.

We are also told in this tale that the Matrix has not merely the ability to predict the future, but actual knowledge of it.  Presumably it has been upgraded in the intervening years, and can now collect data from the future time streams.  The Time Lords have also recently placed collecting devices within each TT Capsule (including the Doctor's, which they didn't bother to tell him about).  These "bugs" have a fair range, and can collect information and transmit it back to the Matrix on Gallifrey for recording and evaluation.  In the Doctor's case, it provided the "evidence" used in his trial.  This information had, of course, been severely edited before it was presented as evidence.