Computer Organisation and Architecture

BASIC COMPUTER
ORGANIZATION AND
DESIGN


Instruction Codes, Computer Registers,
Computer Instructions , Timing and Control ,
Instruction Cycle , Memory Reference
Instructions , Input-Output and Interrupt ,
Complete Computer Description , Design of
Basic Computer , Design of Accumulator Logic

, Instruction Codes
 The organization of the computer is defined by its internal
registers, the timing and control structure, and set of
instructions that it uses.
 The internal organization of a digital system is defined by the
sequence of microoperations it performs on data stored in its
registers.
 A program is a set of instructions that specify the operations,
operands, and the sequence by which processing has to
occur.
 A computer instruction is a binary code that specifies a
sequence of microoperations for the computer.
 Instruction codes together with data are stored in memory.
 The computer reads each instruction from memory and
places it in a control register.

, Instruction Codes
 A group of bits that tell the computer to perform a specific
operation (a sequence of micro-operation)

 Micro-operation usually divided into operation code, operand
address, addressing mode, etc.

, Operation code
 The operation code of an instruction is a group of bits that
define such operations as add, subtract, multiply, shift and
complement.

 The number of bits required for the operation code of an
instruction depends on the total number of operations
available in the computer.

 The operation code must consist of at least n bits for a given
2n (or less) distinct operations.