The Matrix, in the long-running British science fiction television series Doctor Who, is a massive computer system on the planet Gallifrey that acts as the repository of the combined knowledge of the Time Lords.
Access to the Matrix is obtained through an apparatus connected to or enclosing the head of the user or, physically, via Doors into which the user walks. The Matrix functions as a simulated reality, the physical laws of which an advanced user may bend or break.
The Matrix includes the Amplified Panatropic Computer Network, or APC Net, which contains the biological imprints (or bio-data extracts) of all Time Lords as well as the memories of dead Time Lords, storing them in an extradimensional framework of trillions of electrochemical cells. It also receives input from sensors contained in the TARDIS time machines piloted by Time Lords. As a result, the Matrix is not only a record of the past but can actually predict the future as well. The amount of knowledge in the Matrix, though vast, is not complete, and can be tampered with if given the right amount of access.
In the Doctor Who serial, The Deadly Assassin, the Matrix is the location for a battle between the Doctor and the titular assassin. The serial also explains that if a person dies while linked to the Matrix he dies in the real world as well.
Full access to the Matrix is given only to the President of the High Council of Time Lords through the use of the Crown of Rassilon, but limited access to its contents are guaranteed to other Time Lords. The Keeper of the Matrix holds the Key of Rassilon that grants access to the Seventh Door, which was thought legendary until the Doctor used the Key to access it in The Ultimate Foe.
Matrix is also the name of a Doctor Who spin-off novel by Mike Tucker and Robert Perry , in the BBC Past Doctor Adventures range, featuring the Seventh Doctor and Ace. (ISBN 0563405961)
