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Apollo Guidance Computer
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<p>The Apollo Guidance Computer (AGC) was a <a href="/facts/Digital_computer/SQe1aK05">digital computer</a> produced for the <a href="/facts/Apollo_program/IC1Ek1Ao">Apollo program</a> that was installed on board each <a href="/facts/Apollo_command_module/rfoTgzFx">Apollo command module</a> (CM) and <a href="/facts/Apollo_Lunar_Module/XtvQS5K5">Apollo Lunar Module</a> (LM). The AGC provided computation and electronic interfaces for guidance, navigation, and control of the spacecraft. The AGC was among the first computers based on <a href="/facts/Silicon/cgWx0hdr">silicon</a> <a href="/facts/Integrated_circuit/fjn6vg7C">integrated circuits</a> (ICs). The computer's performance was comparable to the first generation of <a href="/facts/Home_computer/CDEPVd1T">home computers</a> from the late 1970s, such as the <a href="/facts/Apple_II/se82CNvK">Apple II</a>, <a href="/facts/TRS-80/zNfQKxnQ">TRS-80</a>, and <a href="/facts/Commodore_PET/08R12Xk4">Commodore PET</a>. At around 2 cubic feet in size, AGC held 4,100 IC packages. </p><p>The AGC has a 16-bit <a href="/facts/Word_(computer_architecture)/2e5umRaj">word</a> length, with 15 data bits and one <a href="/facts/Parity_bit/peFp3Wau">parity bit</a>. Most of the software on the AGC is stored in a special <a href="/facts/Read-only_memory/P9QMuDLH">read-only memory</a> known as <a href="/facts/Core_rope_memory/fFDpRmJs">core rope memory</a>, fashioned by weaving wires through and around <a href="/facts/Magnetic_core/yojywmuo">magnetic cores</a>, though a small amount of read/write <a href="/facts/Core_memory/4TFIXSNd">core memory</a> is available. </p><p>Astronauts communicated with the AGC using a numeric display and keyboard called the DSKY (for "display and keyboard", pronounced "DIS-kee"). The AGC and its DSKY user interface were developed in the early 1960s for the Apollo program by the <a href="/facts/MIT_Instrumentation_Laboratory/prxprY9L">MIT Instrumentation Laboratory</a> and first flew in 1966. The onboard AGC systems were secondary, as NASA conducted primary navigation with mainframe computers in Houston. </p>