This document defines computer instructions and discusses their format, operations, and types. It begins by defining an instruction as an order given to a processor by a program. Instructions contain operation codes and operands. There are different types of instruction set operations like data transfer, arithmetic, logical, and program control. Instruction formats can have register, memory, or immediate operands. Instructions sets are classified as either Complex Instruction Set Computer (CISC) or Reduced Instruction Set Computer (RISC) depending on the number of instructions. The basic instruction cycle that a CPU performs is fetch, decode, and execute.

1. Computer Architecture
Instruction
J. Rama
AP-SS/ECE
KIT, Coimbatore.

2. OUTLINE
• Definition of Instruction
• Instruction Format
• Instruction set Operations
• Types of Operands

3. Define Instruction
• Is a word giving order to a computer processor by a
computer program is called Instruction.
• Its Vocabulary is called Instruction set.

4. Format of an Instruction
An Instruction contains two fields: Operation code
(OPCODE) and Operands
Example: Consider an instruction
add a, b, c
Opcode Operands
This instruction instructs to perform addition
OPERATION with OPERANDS “b” and “c”.
Also loads the result in “a”.

5. Instruction Set Operations
• Data Transfer Operation
• Arithmetic Operation
• Logical Operation
• Input Output Operation
• System Control Operation
• Program Control Operation

6. Examples of Instruction set
• Data Transfer Instruction
• MOVE, LOAD
• Arithmetic Instructions
• ADD, SUB, MUL, DIV
• Logical Instructions
• OR, AND, SHIFT, ROTATE

7. Examples of Instruction set Contd.,
• Input Output Instructions
• IN, OUT
• System Control Instructions
• Program Control Instructions
• Unconditional Branching
• Conditional
• Sub-routine call
• Interrupt handling

8. Operands
• Specifies data that is to be operating on or
manipulated, the data itself.

9. Types of Operands
• Register Operand
eg.,
• Memory Operand
eg., lw $t0,8($s3) # Temporary reg $t0 gets A{8}
• Immediate or Constant Operand
eg., addi $s3,$s3,4 # $s3 = $s3 + 4
add a, b, c
sub d, a, e

10. Classification of Instruction set
There are two types:
Complex Instruction Set Computer (CISC)
Reduced Instruction Set Computer (RISC)

11. CISC
• Contains more number of instructions
• to compute complex instructions in the most
efficient way, it was later found that many small,
short instructions could compute complex
instructions more efficiently.

12. RISC
• Contains less number of instructions
• Frequently used in programs
• The performance of RISC processors is often two to
four times than that of CISC processors because of
simplified instruction set.
• This architecture uses less chip space due to reduced
instruction set.

13. Instruction Cycle
• Basic operation cycle of a computer is
 Fetch
 Decode
Execute
• Simply FDX
• This cycle is repeated continuously by CPU, from bootup
to shut down the computer.

14. THANK
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