Chapter 1. Computer System Overview

Chapter 1. Computer System Overview

Processor Register
A processor includes a set of register that provides a type of memory that is faster and smaller than main memory. The register in the processor serve two functions:
1. User Visible Registers
A user visible register may be referenced by means of the machine language that the processor executes and is generally available to all programs, including application programs as well as system program. Types of register that are typically available are data, address, and condition code registers.

Data Registers
Can be assigned to a variety of functions by the programmer. In come case, they are general purpose in nature and can be used with any machine instruction that performs operations on data. Often, however, there are restrictions. For example, there may be dedicated registers for floating-point operations and others for integer operations.

Address Registers
Contain main memory addresses of data and instructions, or they contain a partion of the address that is used in the calculation of the complete or effective address. These register may themselves be general purpose, or may be devoted to a particular way, or mode, of addressing memory. Examples include the following :

Index register
Index addressing is a common mode of addressing that involves adding an index to a base value to get the effective address.

Segment register
With semented addressing, memory is divided into segments, wicht are variable-length block of words.

Stack pointer
If there is user-visible stack addressing, then there is a dedicated register that points to the top of the stack.
2. Control and status register
A variety of processor registers are employed to control the operation of the processor. On most machines, most of these are not visible to the user. Some of the may be accesible by machine instructions executed in what is referred to as a control or operating system modes.

Of course,, different will have different register organizations and use different terminology. We provide here a reasonably complete list of register types, with a brief description.

1. Program Counter (PC) : Contains the address of the next to be fetched.
2. Instruction register (IR) : Contains the instruction most recently fetched.

Source :
William Stallings, “Operating Systems “Internals and Design Principles”, Fifth Edition, Pearson Education Internationl
Related Post :
Basic Elements
Processor Register
Intruction Execution
Interupts
The Memory Hierarchycal
Cace Memory
I/O Communication
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