General Purpose Registers

Question

I am new to Computer Architecture.Can somebody help me in understanding the use of limited registers in processing of several complex applications. My question is there are fixed number of registers(For Example :: 80386 contains a total of sixteen registers) that are of interest to the applications programmer.

What happens if we want more registers( for example: to accommodate increased Stack size), are the addresses and data from registers written back to main memory ?.In multitasking environment, are the registers data and addresses of different applications moved from between main memory and back to register for processing ?

Does operating systems have special registers which does not interfere with application general purpose registers ?

And suggest any good resource for understanding such concepts for starters ?

Answer 1

Registers are the fastest memory in a computer. The instruction set of any particular cpu is written specifically for the register architecture. You are right that data/addresses must be backed to memory as more register space is used.

As far as a multitasking system goes, the scheduler generally has to save the execution context between tasks. This context involves the current state of the registers as well as other status bits (depending on the cpu).

A good first step would be to learn assembly programming. It is so close to the hardware that you will learn all of this stuff thoroughly. Once you have that, pick up an operating systems book to see how it is done at a higher level. Depending on your commitment (and curiosity), you could also read some of the source code for smaller real-time operating systems, such as FreeRTOS. Reading up on 8-bit microcontroller architectures is also nice, since they are simple. For example, AVR or HC08 are pretty straightforward architectures to learn. All of the info is free; you just have to read it. Enjoy.