GE-635

The GE-635 was a transistor mainframe computer; the largest of the GE 600 series‎ family. It is notable mostly for being the design base of the GE-645, a descendant created for the Multics project (after IBM refused to add necessary features such as virtual memory to the System 360). The Dartmouth Time Sharing System, where BASIC was developed, also ran on the GE-635.

The basic overall architecture of the GE-635 was inherited by the later Multics systems: it was a tightly-coupled multi-processor, with all the CPUs sharing access to a collection of multi-port memory modules. I/O activities were handled by Input/Output Controller modules, similarly sharing access to the memory modules.

The GE-635 was intended for multi-programming; a CPU operated in either Master mode, in which there were no limitations on its operation, or Slave mode, in which base and bounds type memory management applied.

The GE-635 was a 36-bit machine, as was common for scientific computers in that period. The CPU included a single double-width accumulator, and eight index registers (18 bits wide; the size of addresses in the GE-635). The Program Counter was also 18 bits.

The GE-625 was identical to the GE-635; they differed only in the speed of the main memory.

External links

• GE-635 System Manual
• GE-635 Programming Reference Manual - 1964 edition
• GE-635 Programming Reference Manual - 1969 edition
• The GE-635s at Project MAC and BTL
• Starring the Computer - GE-635 - images of GE-635's used as props