MIT PDP-10 'Info' file converted to Hypertext 'html' format by Henry Baker

Memory

In programming the PDP-10 it is convenient to imagine that your program occupies contiguous virtual memory locations from 0 to some maximum address. All memory locations are equivalent for most purposes (but some operating systems reserve some of your space for their own purposes).

Accumulators

Sixteen memory locations (addresses 0 to 17 - note that addresses will appear in octal) are distinguished by their use as general purpose registers (also called accumulators or index registers). Most PDP-10 instructions address one memory operand and one accumulator (so-called "one and a half address" architecture). This means that nearly all instruction affect some accumulator. These registers are actually implemented in high speed solid state memory rather than in slower core. For any purpose where it is convenient to do so, a user may reference an accumulator as memory.