Transmat

Transmat — short for particle matter transmission (TV: The Armageddon Factor) — was a common technological form of instantaneous transport. It was a subset of methodologies described as teleportation.

History
This technology was available to time-travelling species such as Time Lords (TV: The Five Doctors) and the Daleks. (TV: Remembrance of the Daleks)

In the second half of 20th century, it was known to the civilisation which Mawdryn and his crew belonged to (TV: Mawdryn Undead). Sontarans handled it at the beginning of the 21st century. (TV: The Sontaran Stratagem)

After the end of the Cyber-Wars, it was used by humans on the space station Nerva Beacon (TV: Revenge of the Cybermen) and by an unspecified civilisation on the planet houseing the Hedgewick's World of Wonders. (TV: Nightmare in Silver)

Transmats were still in use in the 49th century on human colonies. (AUDIO: Shockwave)

This technology was somehow involved in a series of conflicts called the Transmat Wars during the 51st century. (COMIC: The Keep)

During the Fourth Great and Bountiful Human Empire (about year 200.000), it was used on the Earth space station Satellite Five, indeed controlled by the Daleks. (TV: Bad Wolf)

Forms
Transmats existed in two forms. Commonly, both types seemed designed to move no more than three people at a time, suggesting either a built-in safety feature or simply a hard limit of the technology. (TV: The Daleks' Master Plan, The Ark in Space, Silence in the Library / Forest of the Dead)

Close-ended transmats
This form of transmat required a transmission/reception station at either end of the journey. The traveller entered the station where their molecular structure was scanned and stored for transmission, at which point their body was disintegrated into its component atoms (TV: The Mutants onwards). They typically functioned at interplantary distances, but ones powerful enough to cross the gulf between stars at trans-luminal speeds existed (PROSE: Love and War).

While some systems transferred this physical component to the reception station, the complexity involved meant that in most cases only the structural data recorded prior to disintegration was transmitted, with a new physical form being constructed from a matter source at the other end. (PROSE: Down)

Open-ended transmats
This represented a significant advancement in transmat technology, as it entailed the ability to remotely scan and manipulate the molecular structure of objects. It was typically the product of a higher species. For instance, Time Lords had at their disposal a "power-boosted, open-ended transmat beam" able to send the Master into the Death Zone. (TV: The Five Doctors)

An open ended transmat may acquire the object to be transferred at either end of the process. It's possible that an open-ended transmat beam was actually a form of wormhole projection, warping space-time to allow the scanning and disassembly/reassembly to take place without having to expend the energy that would be required to make a breach through which an object could physically pass, but it is also possible dimensions like hyperspace were used for transmatting objects over vast distances. It is possible that the Transmat engines used by the pirate planet of Zanak used an open ended hyperspace conduit to travel through space. Romana did mention that Zanak "dropped out of the space dimension" in order to scavenge and mine planets. This implied that other dimensions were often used in transmat technology.

Open-ended transmats could complete transfer trans-luminal speeds. Human examples have spanned interstellar distances in a matter of a few days or even hours (TV: The Daleks' Master Plan), while a Dalek transmat beam moved its victim across the distance between Earth and the edge of its solar system in mere moments. (TV: Bad Wolf)

Other variants utilised a travel capsule that might have enhanced the capacity of the system's matter conversion through providing additional computing power in addition to providing protection should the location being transmatted to was hazardous. (TV: Mawdryn Undead)

Durability
A Sontaran version of the technology, though disrupted by the Doctor's sonic screwdriver, proved easily repairable. Similarly the deployment of the T-Mat system was at least partially predicated on the ease of repairing the systems. (TV: The Sontaran Stratagem)

Some 40,000 years later, the refugees of the Nerva Beacon were able to utilise a transmat to repopulate the Earth after being freed from suspended animation. Admittedly benefiting from vast technological and scientific advances, they were still able to use receiver stations that, despite spending thousands of years unattended on a planet scoured clean by solar flares, remained largely functional with the only noticeable defect being a drifting of the reintegration point (TV: The Ark in Space).

Weaknesses
Transmat capsules could damage organic structures if they were not properly maintained. (TV: Mawdryn Undead) The greatest vulnerability of transmat technology rested in the fact that it was reliant upon the beam being successfully transmitted from the point of disintegration to that of reintegration. Signal degradation would have proved catastrophic or even fatal. Certain advanced species — such as Time Lords — however possessed the knowledge and technical ability to intercept and even redirect transmat beams to new destinations apparently greatly distant from those actually intended. (TV: Genesis of the Daleks)

It was generally inferred that anyone's first journey on a transmat was particularly uncomfortable, often resulting in vomiting or headaches. (COMIC: Endgame) Even subsequent trips could have been discomforting, inducing disorientation and amnesia. (TV: Bad Wolf)

Other references
Shockeye mistook the materalisation of the Doctor's TARDIS for a transmat. (TV: The Two Doctors)

The Eleventh Doctor thought that Brian Williams sneaked aboard the TARDIS via a transmat. Rory Williams soon revealed to the Doctor that Brian was his father, Brian having been with Rory and Amy Pond when the TARDIS materialised around them. (TV: Dinosaurs on a Spaceship)

Behind the scenes
Although teleportation technology had already been employed in the show (p.e. TV: The Evil of the Daleks), the transmat concept was introduced during the tenure of the Fourth Doctor, since TV: The Ark in Space.