The guidance computer is a general-purpose digital machine with a basic word length, in parallel operations, of 15 bits with an added bit for parity checks. The instruction code includes subroutines for double and triple operations. Memory cycle time is 11.7 microseconds with a single addition time of 23.4 microseconds. The 'core rope', used for the fixed memory, has a capacity of about 36,864 words with an erasable memory (of ferrite core planes) of 2,048 words. The processor is formed from integrated circuits (ICs). The total computer weight is 29.5 kg. The fixed memory contains programmes, routines, constants, star and landmark co-ordinates and other pertinent data. The erasable memory acts as an intermediate store for results of computations, auxiliary programme information, and variable data supplied by the G&N and other systems of the spacecraft.
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