Possibly the most recognisable of Time Lord technology is the TARDIS, the ‘vehicle’ for traveling in space and time. The Doctor’s TARDIS permanently looks like a police box, but other fully functioning TARDIS’s have chameleon circuits that adapt to any era they are in, camouflaging the TARDIS to look like a standard object for that time zone.
Most notable instances of this have been The Master’s TARDIS which has camouflaged itself as a Cupboard, a stone pillar and a Wardrobe on several occasions. The inside of the TARDIS can be huge, some can even be city sized, and though this is limited be the amount of power that the TARDIS can generate. All TARDIS’s draw their power from a captured Black Hole, which can feed them unlimited power for an Infinite period of time.
One of the most interesting characteristics of a TARDIS is the fact that they are not built, rather grown and are sentient creatures in their own right. TARDIS’s are quite capable of movement, and even interstellar flight, though this does put an enormous strain on the TARDIS as its normal movement is to simply fade from one area of Space and Time and enter the time vortex, reappearing in another Space and Time.
When The Doctor’s companions or enemies first encounter the TARDIS’s strange ‘Tesseract’ ability of warping space-time to fit the outside over the inside, they are understandably quite baffled. This feature of the TARDIS’s is possibly its most famous feature and can be explained quite easily using mathematics and Four Dimensional Engineering.
One of the most famous examples of theoretical four dimensional engineering is a ‘Hypercube’, or a ‘4D cube’.
This can be easily explained using a dimension that exists away from normal three dimensional space, and is only accessible to a fraction of three dimensional space. This is the theory behind the TARDIS, that the inside of the TARDIS is on another dimension, or realm, and the TARDIS itself only acts as a door to that dimension.
Another amazing fact of the TARDIS is that it regenerates with The Doctor, to a new ‘face’ or style with each new Doctor. This has been a running theme through the TV show and the Comic’s as each new Doctor appears, the TARDIS has a new, but familiar feel to it to match the new Doctor’s personality and appearance.
Almost all TARDISes were able to blend in with their surroundings because of a mechanism called the "chameleon circuit", or "camouflage unit". Some later models seemed to regularly allow the pilot to choose a desired exterior, overriding what would have been "natural" for the surroundings. (DW: Time and the Rani, Time-Flight) In fact, the Doctor's TARDIS seemed to have both abilities, were the chameleon circuit operational. Long before he met Ian and Barbara, the First Doctor landed on Iwa, where the TARDIS quite easily posed as a boulder in that planet's desert. Likewise, on Quinnis, the Doctor was unhappy when the TARDIS landed in a bazaar and she decided to turn into a market stall, complete with a striped awning. However, the Fourth Doctor showed Adric how the TARDIS could be changed to the shape of an Egyptian pyramid, implying that he could override the chameleon circuit's "automatic" functionality. In any case, the defining characteristic of the Doctor's TARDIS was that its chameleon circuit had broken after assuming the shape of a 'Police Box' in 1963 London. It had been working up until it landed in I.M. Foreman's junkyard. The Doctor's granddaughter stated that the TARDIS had previously appeared as a sedan chair and an ionic column, and both she and the Doctor expressed surprise that it had not changed form when they traveled to a new destination.
The interior dimensions are considerable bigger than the exterior shell would suggest, though even an approximate size of the interior has yet to be determined. So far only two rooms have been seen; The Control Room and the TARDIS Wardrobe, this is vastly different to the previous seen TARDIS' as in previous Doctor's TARDIS we have seen bedrooms, various living rooms and study areas and even an Olympic sized swimming pool, though this was jettisoned prior to the "City of Death" storyline..
The TARDIS projects a telepathic field which translates all spoken and written languages for recognized operators and companions. This field does not function if the operator is incapacitated or near death and only works on languages which the TARDIS has knowledge of.
There was a library inside the TARDIS. Known books included Jane's Spaceships , Every Gallifreyan Child's Pop-Up Book of Nasty Creatures From Other Dimensions ), The Time Machine by H. G. Wells , The Murder of Roger Ackroyd by Agatha Christie (first printing, signed, with last page missing), War and Peace, The Wonderful Wizard of Oz and The I-Spy Book of British Birds. The console room also incorporated a library at the end of the Seventh Doctor's life and the beginning of the Eighth Doctor's. By the time the Eleventh Doctor was recovering from regeneration after-effects, the books in the library were ruined when the pool had fallen into it after crash-landing. However, it can be assumed that the TARDIS repaired the library and the Doctor began replacing the books.
The Doctor kept some of the clothes from his previous regenerations, as well as clothing for other people in the TARDIS wardrobe. Some of these clothes were picked up along the way, or even left behind by prior travelling companions. It contained clothing from various times and environments, to suit the time and place the TARDIS' occupant(s) found themselves. This proved useful on numerous occasions for the Doctor's companions, many of whom left on their travels without taking many clothes of their own. At least some of the clothes had pockets that were bigger on the inside.
The cloister room was related to the cloister bell, which sounded when disaster was imminent. When the TARDIS interior went through a metamorphosis, the cloister room became a grand and gothic room with an interface with the Eye of Harmony. When the main console room was converted into a paradox machine to maintain the effects of a paradox, the bell rang continuously. (DW: Last of the Timelords) It rang when the TARDIS was in extreme danger with occupants in it after the matrix has been removed and a malevolent lifeforce possessed it.
The holding ring was a storage area of the TARDIS which let the Doctor preserve certain rooms. When Lucie, Susan and Alex investigated it, the ring contained the rooms of many of his former companions, preserved as they had been the last time the companion were in the TARDIS. The rooms were saved in chronological order, suggesting that Susan was indeed the Doctor's first companion. Susan later teased her grandfather, calling his habit of saving rooms overly sentimental. He suggested that the ring was one of the few ways his time-travelling life allowed him to put down roots. After Susan, Alex and Lucie departed the TARDIS for new adventures on Earth, the Doctor reconsidered the wisdom of keeping so many rooms in stasis. Insisting to himself he needed to look towards the future, he deleted all the rooms on the holding ring — "except that one".
The TARDIS had a swimming pool which was used by Leela. However, she referred to it as "the bathroom". It was later jettisoned due to leakage. It was replaced some time afterward, and, following the TARDIS's crash after the Doctor's tenth regeneration, the water from the swimming pool fell into the library. After the TARDIS fixed itself, the swimming pool had been relocated to keep the library from being ruined again, but the Doctor did not know where it was at the time. He revealed he had found it when he offered to swim a few laps to give Amy and Rory some privacy. Later, to save River Song after she had jumped off a New York skyscraper, the Doctor had Amy and Rory open all the doors leading to the pool to soften River's landing in the sideways TARDIS. However, the Doctor said he got rid of it to "Give the TARDIS a bit of welly" when going outside the universe.
As TARDISes were intelligent, the Doctor's TARDIS also developed a personality. It was called "sentimental" by the Eighth Doctor and "stupid" by. Though intelligent, it was generally unable to communicate in words with the Doctor, relying on other means. Even when the TARDIS did not take the Doctor where he wanted to go, it took him where it felt he needed to be.
The TARDIS displayed a prejudicial fear of the time-locked Jack Harkness. It showed a similar hostility to Charley Pollard when she began to travel with the Sixth Doctor, apparently due to the paradoxical nature of her very existence. This resulted in the TARDIS 'refusing' to protect Charley from viruses as it had protected his previous companions.
The TARDIS displayed a feminine personality when her matrix was temporarily transferred into the humanoid body of Idris. While in this form, she thought Rory was "pretty" and stated that she actually chose the Doctor as a travelling companion. She also referred to the TARDIS remains in a junkyard as "her sisters," implying that all TARDISes were female. The TARDIS referred to the Doctor's previous companions as "strays" and did not know the names of Amy and Rory, dubbing them "the orangy girl" and "the pretty one". She did, however, seem to be somewhat familiar with Earth culture, once comparing the Doctor's efforts to build a working TARDIS console to "a nine-year-old trying to rebuild a motorbike in his bedroom", though she was puzzled by the Doctor's reference to fish fingers. When asked her name by the Doctor, she chose to be called Sexy because that's what he called her in private (she later introduced herself to Rory and Amy by this name); she also expressed fondness for being called "Old Girl". Just prior to Idris' body being destroyed and the TARDIS' consciousness reverting to what it was, the TARDIS shared a tearful "hello" with the Doctor and was heard to utter the words "I love you" as the shell of Idris disappeared.