Computer Systems - Registers

Starter…Discuss in pairs the definition of the following

• Control Unit• Arithmetic and Logic Unit• Registers• Internal clock• Internal buses• Logic gates

General-purpose Registers

General-purpose registers allow programmers to use them as they wish.

They are not given a specific role and R0,R1 etc. should not beconfused with a memory location also with anaddress of 1.

General-purpose registers are accessed with instructions such LOAD, STORE and ADD.

Dedicated RegistersThese are registers that have been assigned specific roles by the processor designer. Programmers may read or manipulate some but not all of these dedicated registers.

There are 5 registers in particular that you need to know…

Program Counter (PC) - an incrementing counter that keeps track of the memory address of which instruction is to be executed next.

Memory Address Register (MAR) - holds the address in memory of the next instruction to be executed

Memory Data Register (MDR) - a two-way register that holds data fetched from memory (and ready for the CPU to process) or data waiting to be stored in memory

Current Instruction register (CIR) - a temporary holding ground for the instruction that has just been fetched from memory

Accumulator Register (ACC) – holds the data result of a current calculation