The document discusses basic concepts of computer hardware components and addressing modes. It explains that addressing modes determine how operands are accessed during instruction execution, and can include implied, immediate, register, register indirect, auto increment/decrement, direct, indirect, relative, indexed, and base register modes. It also defines instruction set architecture as specifying the registers, memory interaction, and alignment requirements for an assembly language programmer.

1. DISCOVER . LEARN . EMPOWER
BASIC CONCEPTS & COMPUTER
HARDWARE COMPONENTS
University Institute of Engineering
DEPARTMENT OF COMPUTER SCIENCE
& ENGINEERING
Bachelor of Engineering (Computer Science & Engineering)
Subject Name: Computer Organization & Architecture
Subject Code: 21CST-252

2. • The way the operands are chosen during execution of an instruction is determined by the addressing mode.
• Mode fields is used to locate operands.
• If instruction contains an address field, it may be a register or a memory address.
• If more than one address field, each field is associated with its own mode.
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ADDRESSING MODES

3. • Implied Mode- operands are specified implicitly in the instruction itself. E.g. “Increment Accumulator”
• Immediate Mode- the address field contains the operand itself instead of the address of the operand.
• Register Mode- the address field contains the address of a CPU register which contains the operand.
• Register Indirect Mode- the address field contains the address of a register which holds the memory address of the
operand. Advantage : fewer bits required to represent a register than a memory word.
• Auto increment or Auto decrement –
• similar to register indirect mode except that the value of the register is incremented or decremented after it has
been used to access memory. Usually used to refer to a table of data.
• Direct Address mode-
• the address field contains the memory address of the operand.
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TYPES OF ADDRESSING MODES

4. • Indirect Address Mode-
• the address field contains the address of the memory location that contains the operand.
• Relative Addressing Mode-
• the address of the program counter is added to the address field to get the address of the operand.
• Usually used in branch type instructions.
• Lesser no. of bits to represent the relative address than compared to the full memory address.
• Indexed Addressing Mode-
• The content of an index register is added to the address part of the instruction in order to obtain the
effective address.
• Useful in case of an array.
• Base Register Addressing Mode-
• The content of a base register is added to the address part of the instruction in order to obtain the effective
address.
• The difference with Indexed addressing mode is in its use.
• Used for relocation of programs in memory.
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TYPES OF ADDRESSING MODES
(CONTD.)

5. • Defines any aspects of the processor that an assembly language programmer needs to know, in order to write a
correct program
• Specifies:
• The registers accessible to the programmer, their size and the instructions in the instructions set that can
use each register
• Information necessary to interact with the memory
• Certain microprocessors require instructions to start only at specific memory locations; this alignment
of the instructions will be part of the instruction architecture
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INSTRUCTION SET ARCHITECTURE

6. REFERENCES
• Reference Books:
 J.P. Hayes, “Computer Architecture and Organization”, Third Edition.
 Mano, M., “Computer System Architecture”, Third Edition, Prentice Hall.
 Stallings, W., “Computer Organization and Architecture”, Eighth Edition, Pearson Education.
• Text Books:
 Carpinelli J.D,” Computer systems organization &Architecture”, Fourth Edition, Addison Wesley.
 Patterson and Hennessy, “Computer Architecture” , Fifth Edition Morgaon Kauffman.
• Reference Website
 https://www.geeksforgeeks.org/computer-organization-and-architecture-tutorials/
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