Central Processing Unit (CPU)Central Processing Unit (CPU)Central Processing Unit (CPU)Central Processing Unit (CPU)

1. Chapter 1
Introduction to Computer Organization &
Architecture

2. Computer Architecture vs. Computer Organization
The fundamental distinction between these two concepts is crucial.

3.  Computer Organization is the physical implementation and operational
structure of a computer system.
 It explains how the hardware components are arranged and work
together to implement the architecture,.
 including control units, data paths, memory technologies, and buses.
Computer Organization
•Organization → How the computer is built

4.  Refers to the way hardware components are connected and controlled
 Explains how instructions are executed at the hardware level
Includes ALU operations, control signals, and data movement
 Concerned with physical implementation of the system
Example: How registers connect to the ALU inside the CPU

5. Computer Organization – Key Focus Areas
 Control unit design and operation
 Data paths between registers and ALU
 Memory access mechanisms
 I/O interfacing techniques
 Timing and synchronization of operations

6.  Computer Architecture is the conceptual design and functional
specification of a computer system as seen by the programmer.
 It defines what the system does
 including the instruction set, data types, registers, addressing modes,
and overall system behavior.
 Specifies addressing modes and data
representation
Computer Architecture

7.  It is Independent of hardware technology
Example: x86 instruction set used by Intel processors
 Defines instruction formats and instruction set
 Describes attributes of a computer visible to
programmers
•Architecture → What the computer does

8. Computer Architecture – Programmer’s
View
 Instruction set architecture (ISA)
 Number and type of registers
 Supported data types (integer, floating point)
 Addressing modes such as direct and indirect
 System calls and exceptions

9. Feature Computer Architecture (The "What") Computer Organization (The "How")
Definition
The functional behavior and design
principles of a computer system as seen
by a programmer.
The physical realization of the
architecture, including how the
hardware components are connected
together and the control signals.
Focus
Instruction Set Architecture (ISA),
Addressing Modes, Data Types,
Memory Addressing Techniques, I/O
Mechanisms.
Control Signals, Interfaces between
components, Memory Technology (e.g.,
DRAM vs. SRAM), Peripherals.
Analogy
The blueprint of a house (the design
and functionality).
The construction of the house (the
selection and connection of materials).
Change
Does not change often (e.g., the x86
instruction set is constant).
May change frequently (e.g., upgrading
from a hardwired control unit to a
microprogrammed one).

10. Basic Computer System Components
A digital computer system is primarily composed of multiple distinct
functional units that work together to process information.
Each unit performs a specific task
All units work together to execute programs
Communication occurs via system buses

11. Main Components – Description
Input Unit: Accepts data and instructions
CPU: Processes data and controls operations
Memory: Stores programs and data
Output Unit: Displays results
Bus: Transfers data and control signals

12. Input Unit
Keyboard,
mouse, scanner
CPU
ALU + Control
Unit
Main Memory
RAM / ROM
Output Unit
Monitor,
printer
Computer System Block Diagram

13. A. Central Processing Unit (CPU)
 Often referred to as the "brain" of the computer.
 Function: Executes instructions, performs arithmetic and logical
operations, and controls all other parts of the system.
 Key Sub-components (covered in Chapter 3):
 ALU (Arithmetic Logic Unit): Performs calculations (+, -, *, /) and logical
operations (AND, OR, NOT).
 Control Unit (CU): Directs the sequence of operations, fetches instructions, and
issues control signals to all other units.
Controls overall operation of the computer

14.  Registers: Small, high-speed storage locations within the CPU used to hold
data, addresses, and instructions temporarily during execution.
Components of CPU
 Arithmetic Logic Unit (ALU)
 Control Unit (CU)
 Registers
 Internal buses
 Clock circuitry

15. CPU Example
 Instruction: ADD R1, R2
 Operands fetched from registers
 ALU performs addition
 Result stored back in register
 Control unit manages the steps

16. CPU Internal
Architecture
Control Unit
Instruction control
& timing
ALU
Arithmetic & logic
operations
Registers
Fast temporary
storage
Internal Bus
Data
movement

17. B. Memory
Function: Stores both data and the program instructions required for
processing.
Primary Memory (Main Memory):
Volatile (loses data when power is off).
Fast access speed.
Examples: RAM (Random Access Memory)
 Secondary Memory:
 Non-volatile (retains data when power is off).
 Slower access speed, but higher capacity.
 Examples: Hard Disk Drives (HDD), Solid State Drives (SSD)

18.  Memory stores data and instructions
 Provides data to CPU during execution
 Speed of memory affects performance
 Different types exist based on speed and cost
Memory System

19. Types of Memory
 Registers – fastest, smallest
 Cache memory – high-speed buffer
 Main memory – RAM
 Secondary memory – HDD, SSD
 Non-volatile vs volatile memory

20. Memory Example
 Program loaded from disk to RAM
 Instructions copied to cache
 Registers hold operands
 CPU executes instruction
 Result written back to memory

21. Memory Hierarchy (Labeled)
Registers
Fastest, inside
CPU
Cache
High-speed buffer
RAM
Main memory
Secondary Storage
Permanent storage

22. Function: Provide the means for the computer to communicate with the
outside world (users and other devices).
 Input Devices: Allow data entry into the computer (e.g., keyboard, mouse,
scanner).
 Output Devices: Display or transfer processed data out of the computer (e.g.,
monitor, printer, speaker).
C. I/O Devices (Input/Output Devices)
 I/O Controllers: Specialized hardware interfaces that manage the
communication between the CPU and the various I/O devices.

23. Input and Output Devices
 Enable interaction with external environment
 Input devices supply data
 Output devices present results
 Controlled using I/O modules
 Slower than CPU operations

24. I/O Example
Keyboard sends data to CPU
I/O controller buffers input
CPU processes data
Result sent to monitor

25. I/O Subsystem
Input Devices
Keyboard,
mouse
I/O Controller
Buffering &
control
CPU
Processing
Output Devices
Monitor, printer

26. D. Buses
 Function: A set of electrical conductors (wires) that
interconnect the major components of the computer system,
enabling the transfer of data and control signals.

27. System Buses
Provide communication pathways
Shared among system components
Reduce wiring complexity
Critical for performance

28. Types of System Buses
(covered in Chapter 7):
 Data Bus: Carries the actual data being transferred. It is bidirectional.
 Address Bus: Specifies the source or destination of the data (e.g., a memory
location or an I/O port). It is unidirectional (from CPU to memory/I/O).
 Control Bus: Carries control and timing signals to synchronize the operations
of the attached devices.

29. Types of System Buses
 Data Bus – carries data
 Address Bus – carries addresses
 Control Bus – carries control signals
 Bus width affects speed
 Clock synchronizes bus operations

30. Bus Example
 CPU requests memory read
 Address placed on address bus
 Control bus signals READ
 Data returned via data bus
 Operation completed in clock cycles

31. System Bus Structure (Labeled)
Data Bus
Data transfer
Address Bus
Location selection
Control Bus
Read/Write & timing

32. End of Chapter one
Thanks