Category:SSEM: Difference between revisions

 

Each storage address could hold either a signed 32-bit integer (using two's complement for negative values) or an instruction word. Unlike most later digital computers, the SSEM's binary notation has the least significant bit first: 1 is one, 01 is two, 001 is four, etc. In an instruction word, the leftmost five bits stored the address of the operand and bits 13-15 stored the instruction itself. The operand was always a storage address and never an immediate value, even in the case of jumps: the jump target needed to be stored in a separate word, to which the jump would refer. The instruction set consisted of:

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<td><tt>000 <operand> to CI</tt></td><td>load the number stored at address <tt>operand</tt> into the Current Instruction register. CI would then be incremented, so this is equivalent to <tt>goto store[operand] + 1</tt></td>