PDP-10 Instruction Set

One of things that eased writing PDP-10 Assembler code was the symmetry of its instruction set. While detractors often claimed the -10 had more no-ops than any other system, that cost was fairly minor, as there was plenty of space for opcodes and I'm sure it eased instruction decoding in the discrete transistor architecture used in the PDP-6 and first PDP-10.

The symmetry lead to a nifty one page summary of the instruction set. Once you learned what the instructions did, all you needed was this page:

For example, you often want to load the left half of a register with a count or address. The usual choice was:

However, this would always zero the low half. To set just the top half: which means "Halfword Right to Left Immediate" - take the right half of the effective address and put it in the left half of the register. HRLZI functioned the same as MOVSI, but the latter was easier to read. All 64 possible halfword instructions were implemented.

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Last updated 2002 Jan 6.