Computer Generations Overview

Computer Generations

• First generation computers (1940s) used vacuum tubes for logic and memory.
  • The Colossus was the first computer (1943-1944).
  • The ENIAC (Electronic Numerical Integrator And Computer) was the first general-purpose computer (1943-1946).

Von-Neumann Architecture

• Introduced in 1945 by John von Neumann.
• Stored-program computer: Instructions are stored in the same memory as the program.
  • Components:
    • Memory unit: Stores instructions and data.
    • Arithmetic logic unit (ALU): Performs calculations and logic operations.
    • Control unit: Manages the flow of instructions.
    • Input–output (I/O): Facilitates communication with external devices.

Second Generation Computers

• Used transistors (1950s).
• Transistors are solid-state silicon devices invented at Bell Labs (1947).
• They offered significant advantages over vacuum tubes, including smaller size, lower power consumption, and greater reliability.

Third Generation Computers

• Marked by the invention of the integrated circuit (IC) (1958).
  • Microelectronics era.
  • The IC allowed for the miniaturization of electronic circuits, leading to more powerful and compact computers.

Later Generations: Large-Scale Integration (LSI)

• LSI (and later VLSI and ULSI) refer to the increasing density of components on integrated circuits.
• LSI: 1,000 – 10,000 components per chip
• VLSI: 10,000 – 1 million components per chip
• ULSI: > 1 million components per chip

Decimal and Binary Notations for Size Terms

• Standardized to resolve ambiguity:
  • Ki = 210 (1,024)
  • Mi = 220 (1,048,576)
  • Gi = 230 (1,073,741,824)
  • K = 103 (1,000)
  • M = 106 (1,000,000)
  • G = 109 (1,000,000,000)

CISC vs. RISC Architectures

• Both represent different approaches to instruction set design.
• CISC (Complex Instruction Set Computer):
  • Uses fewer assembly lines and more complex instructions.
  • Example: Intel X86 Architecture.
• RISC (Reduced Instruction Set Computer):
  • Uses a smaller, highly optimized set of instructions.
  • Example: ARM Architecture.

Intel x86 Architecture (CISC)

• Dominant architecture for PC computers.
• Features:
  • Backward compatibility: Programs written for older versions can run on newer versions.
  • Over 500 instructions in its instruction set.

ARM Architecture (RISC)

• Developed by ARM Holdings.
• Known for high-performance, low-power consumption, small size, and low cost.
• Widely used in embedded systems.
• It is estimated that billions of embedded computer systems are produced each year.

Computer Architecture vs. Computer Organization

• Architecture: Focuses on the parts visible to programmers, such as instruction sets, data types, I/O mechanisms, and memory addressing modes.
• Organization: Deals with the hardware details transparent to the programmer, such as control signals, interfaces between components, and memory technology.

Computer Functions

• Data Processing: Processing diverse data formats, including numerical calculations and logical operations.
• Data Storage: Storing data for future retrieval.
• Data Movement: Transferring data between various components.
• Control: Managing the execution of instructions and overall system operations.

CPU Performance

• Affected by Instruction Count, Clock Cycles per Instruction (CPI), and Clock Cycle Time.
• Execution Time: Calculated as Instruction Count × CPI × Clock Cycle Time.
• MIPS (Millions of Instructions Per Second): A common measure of performance.
• Clock Rate: The reciprocal of Clock Cycle Time.

Units of Measurement for CPU Performance

• Execution Time: Time taken to complete a task, expressed in seconds.
• Instruction Count: Number of instructions executed.
• CPI (Clock Cycles per Instruction): Average number of clock cycles per instruction.
• Clock Cycle Time: The duration of one clock cycle.