Information borrowed from
|In the science fiction Stargate universe, a DHD (for Dial-Home Device) is an Ancient machine used to control a Stargate. DHDs are pedestal-shaped with a round inclined control panel on top consisting of two concentric circles of "keys" and a translucent red (Milky Way) or blue (Pegasus) hemisphere in the center; the 38 or 36 keys represent the corresponding symbols (or glyphs) on the rim of the Stargate with the central hemisphere serving to engage the Stargate. When a DHD is present the gate will not simply activate even if the inner ring is spun in the correct combination as shown in the Stargate film. This likely serves as a fail safe to ensure that the correct address was entered. It also serves to allow for "quick dialing" which allows the gate to activate without waiting for the inner ring to spin. The DHD also provides power for the Stargate and appears to have a complex programming interface with it that is not normally needed by the operator.|
|It appears that originally every Stargate had its own DHD, located directly in front of the Stargate and facing it. However, over time some DHDs have been damaged or lost. This presents a difficulty for Stargate travellers, as it is still possible to dial in to a Stargate that lacks a DHD but dialling out again is much more difficult.||
Several episodes have hinged upon SG
teams becoming stranded on worlds without functioning DHDs, having to
improvise lightning rods or other such power sources and manually dialling the
Stargate's symbol ring. One of the primary functions of the MALP
that is sent to new Stargates before any SG team is to confirm the presence of
a functioning DHD.
According to Dr. Zelenka, dialing an address leaves a small imprint on the control crystals of the DHD, so about fifty addresses can be recovered from a DHD from someone with the proper equipment; however, this gives no indication of the order in which the addresses were dialed and no guarantee can be made as to the accuracy of the recovered addresses.
DHDs are not the only methods of dialing Stargates. There are 2 other ways that a Stargate has been seen to be dialed:
|EARTH & THE MILKY WAY DHDS|
|Earth's Stargate was missing its DHD when first discovered, requiring Stargate Command to develop its own native dialling system (or 'MacGyver our own' as Sam puts it in "Children of the Gods"). This resulted in Stargate misbehavior from time to time, since most of its detailed interfaces and safety features could not be reverse-engineered.||
Earth's DHD had not been destroyed, however, merely lost; the Nazis removed it
from Egypt during World War II and the Soviet Union subsequently captured it at
the end of the war. It passed
into the possession of the Russians after the Soviet Union's fall. After the Russians recovered the American primary Stargate from the Pacific Ocean when it was lost in the crash of Thor's starship Beliskner, they set up their own Stargate exploration program using the DHD to secretly "override" the backup Stargate the SGC was using whenever Russian SG teams were scheduled to dial back to Earth. The backup Stargate's DHD was still with it when it was found in Antarctica, and was used briefly by NID operatives to conduct covert technology raids through the backup Stargate, but it has since run out of power and ceased to function. The Antarctic gate and DHD are thought to have been the oldest known, possibly among the earliest that were constructed by the Ancients.
The American Stargate program eventually suffered a mishap that their makeshift dialing interface was unable to correct, with Teal'c becoming "trapped" in their Stargate's data buffer after the wormhole connection was severed when a ship destroyed the Stargate that the Earth Stargate was connected to. The Americans eventually made a bargain to exchange some of the information their more-successful Stargate program had gained for the Russian DHD, which was able to retrieve Teal'c alive. The DHD was (spectacularly) burned out in the process, however, leaving Earth with no remaining known DHDs.
The Milky Way DHDs have sparked numerous discussions as the design and
operation of the device has resulted in contradiction throughout the SG-1
series. In the Milky Way, the Dial-Home-Device contains 38 of the 39 symbols on
the Stargate, meaning there is always a missing glyph on each DHD. This missing
glyph however is not the point of origin for the planet. It has been confirmed
that the missing glyph on numerous DHDs differs based on where each Stargate is
positioned in the galaxy. The glyph that is hidden under the pedestal of the
Stargate, unseen along with the two chevrons, cannot be dialed by that DHD.
This means that only certain addresses can be reached from certain positions in
the galaxy. The only way to intervene and reach all destinations in the Milky
Way is to manually dial the gate and use an external power source, for example:
|PEGASUS GALAXY DHDS|
|In the series Stargate Atlantis, an expedition to the Pegasus galaxy discovers another Stargate network along with extensive remnants of Ancient civilization. Conventional DHD pedestals are found in most worlds of the Pegasus Galaxy, with mainly cosmetic differences from DHDs in the Milky Way due to the fact that the Pegasus DHDs are newer, and obviously feature a different coordinate system specific to that galaxy. The primary differences are that both the keys and the central hemisphere in the Pegasus Galaxy are blue, the sound produced by dialing a Pegasus DHD is more||
of a buzzing than a swishing, and that gate-dialing is much faster, likely due
to the fact that, unlike the Stargate on Earth and its galaxy, these Stargates
do not dial manually. In addition, the DHD keys are made of a reflective,
glass-like material. The Wraith
also travel through Stargates in small spacecraft called darts
and have some means of remote-dialling them in a manner similar to Ancient
The Atlantis DHD is more
similar to the Earth's dialing computer than an actual DHD, and looks more like
a set of crystal panels. A similar DHD is also used on Puddle
Consequently, the Atlantis DHD also has an extra control-crystal allowing
the dialing of an eighth chevron during the dialing sequence and is the only
DHD in the Pegasus galaxy capable of dialing Earth. This was probably a
security measure set up by the Ancients so that not everyone could dial into
another galaxy, such as the Wraith
from dialing into Earth.
|PUDDLE JUMPER DHDS|
The Puddle Jumper
DHDs are very similar to the Atlantis DHD with the exception of the extra
control-crystal. The ships DHD is used for travel through an orbital Stargate
possibly in conjunction with a Stargate Power Node since orbital Stargates have
no constant DHD. These DHDs seem to be tailored to their counterpart galaxy
since the Puddle Jumpers from Atlantis have the Pegasus set of glyphs where as
the Gate Ship in Stargate SG-1 had the Milky Way set. However, it may be that
the Jumpers possess a sort of 'universal' DHD that tailors itself to the gate
system in question, as a Jumper from Atlantis has been seen activating a gate
from the Milky Way.