Computer Architectures

  Computer Architectures The CPU A CPU is a processing circuit that can calculate, store results and makes algorithmic decisions. It is this latter factor that sets computers apart from calculators. There are different CPU types, including: register machines accumulator machines stack machines A very simple processor could be  Jorvik-1 , an accumulator machine: The program counter is a register showing the current location in a set of instructions and the accumulator is where values are stored before and after computation. An example set of instructions for this machine may be: Hexadecimal number Assembler equivalent Description 31 ADD A 03h This is 0011 0001, so add 0011 and incremement the pc by 1 F1 SUB A 01h Subtract (this is only possible if the accumulator understands signed numbers) 05 BRANCH 05h The accumulator is not affected, but the pc increases by 5 01 NOP No operation, just continue to the next step (this can be useful for timing purposes) 11 INC A Increment (real...