Each number in IAS is represented by a sign bit and a 39-bit value. Each instruction consists of an 8-bit operation code (opcode) specifying the operation to be performed and a 12-bit addressas shown in picture
So, why does instruction word has left and right side, do they corelate, can one side be executed and other not?
why does instruction word has left and right side
It’s not actually sides, it’s 2 independent instructions. They are packed this way to save half of the space used by code.
The machine addresses 40-bit words. The instruction set is so simple, and addressable memory is so small, that it’s possible to keep 2 instructions per word.
do they corelate
Usually they run sequentially.
can one side be executed and other not?
Sometimes. If the first instruction is a jump (conditional or not), the machine will not execute the second one because it jumps instead. Similarly, jumps have 2 forms/each, one form jumps to the second instruction of the target address, when that happens, execution goes to the second instruction and the machine won’t execute the first one.
