This document discusses computer instruction sets. It defines an instruction set as the complete collection of instructions understood by a CPU in either binary machine language or symbolic assembly language. An instruction typically contains an operation code and references to operands and results. There are different types of instructions for tasks like data transfer, arithmetic, logic, and control flow. Instructions can be classified as zero-address, one-address, two-address, three-address, or four-address depending on the number of operands. Complex instruction set computers have many generalized instructions while reduced instruction set computers have fewer simpler instructions that can execute faster.

1. INSTRUCTION
SETS
DEEPAK SHARMA
12KSSB6031
BCA 5th SEM

2. What is an Instruction Set?
• The complete collection of instructions that are
understood by a CPU
• Machine language: binary representation of
operations and (addresses of) arguments
• Assembly language: mnemonic
representation for humans, e.g.,
OP A,B,C (meaning A <- OP(B,C))

3. Elements of an Instruction
 Operation code (opcode)
 Do this: ADD, SUB, MPY, DIV, LOAD, STOR
 Source operand reference
 To this: (address of) argument of op, e.g.
register, memory location
 Result operand reference
 Put the result here (as above)
 Next instruction reference (often implicit)
 When you have done that, do this: BR

4. Simple Instruction Format
(using two addresses)

5. Instruction Types
 Data transfer: registers, main memory, stack or
I/O
 Data processing: arithmetic, logical
 Control: systems control, transfer of control

6. Data Transfer
• Store, load, exchange, move, clear, set, push, pop
• Specifies: source and destination (memory,
register, stack), amount of data
• May be different instructions for different (size,
location) movements.

7. Input/Output
 May be specific instructions, e.g. INPUT, OUTPUT
 May be done using data movement instructions
(memory mapped I/O)
 May be done by a separate controller (DMA): Start
I/O, Test I/O

8. Instruction format
 An instruction is normally made up of a combination of an operation code
and some way of specifying an operand, most commonly by its location or
address in memory. A computer has a variety of instruction code formats.
The control unit in CPU interprets each instruction code and provides the
necessary control functions needed to process the instruction. There are 5
types of computer instructions. They are:
 Four address instruction
 Three address instruction
 Two address instruction
 One address instruction
 Zero address instruction

9. Complex Instruction Set
Computer [CISC]
 A computer with a large number of instructions is called Complex
Instruction Set Computer. In CSIC architecture it is very essential that a
single machine instruction for each statement that is written in a high
level language must be provided.
 FEATURES:
 Variable length instruction formats are used.
 The instructions provide direct manipulation of operands residing in
memory.
 A large number of instructions about 100 to 200 are provided.
 A large variety of addressing modes about 5 to 20 are provided
 Instructions performing specialized tasks are used infrequently

10. Reduce Instruction Set
Computer
 Computer that uses fewer instructions with simple constructs so that
they can be executed much faster within the CPU without having to
use memory often is called RISC.
 FEATURES:
 It has relatively fewer instructions.
 There are relatively fewer and simple addressing modes.
 Memory access is limited only to load and store instructions.
 All instructions are carried out using the registers of the CPU.
 Instructions are easily decodable.
 Instruction format is of fixed length.

11. Logical
 Bitwise operations: AND, OR, NOT, XOR, TEST,
CMP, SET
 Shifting and rotating functions, e.g.
 logical right shift for unpacking: send 8-bit
character from 16-bit word
 arithmetic right shift: division and truncation for
odd numbers
 arithmetic left shift: multiplication without
overflow

13. Types of Operand
 Addresses: immediate, direct, indirect, stack
 Numbers: integer or fixed point (binary, twos
complement), floating point (sign, significand,
exponent), (packed) decimal (246 = 0000 0010
0100 0110)
 Characters: ASCII (128 printable and control
characters + bit for error detection)
 Logical Data: bits or flags, e.g., Boolean 0 and 1

14. THANK YOU