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Introduction to Computer System Architecture

Computer System

• A computer system consists of:

  • CPU (Central Processing Unit)

    • Electronic circuitry that executes instructions comprising a computer program

    • Also called a central processor, main processor or just processor

  • Cache Memory

    • Special-purpose, high-speed memory that holds frequently used data

  • Main Store (Memory)

    • Memory holds the bulk of working data

  • Secondary Store

    • Disk drives or CD-ROMs that archive large quantities of data so cheaply

  • Input/Output Devices (Peripheral Devices)

    • Devices designed to read information into or out of the memory unit upon command from the CPU

  • Bus

    • Communication system that transfers data between components inside a computer, or between computers

      • Common connection point

      • A bunch of wires that have a protocol associated with it depending on the bus type

    • The expression covers all related hardware components (e.g., wire, optical fiber, etc.)

    • The term bus is shortened form of the Latin omnibus, and historically also called data highway.

What is a Computer?

• In a broad sense, the term computer refers to any entity which could perform some type of calculation.

Two Types of Digital Computer Architectures

von Neumann Architecture

• Named after John Von Neumann.

• Has single storage system (memory) for storing data as well as program(set of instructions) to be executed.

• Has only one address bus and data bus between processor and memory.

  • This is the cause of the "von Neumann bottleneck".

• Processor needs two clock cycles to complete an instruction.
  (Pipelining the instructions is not possible with this architecture.)

  • In the first clock cycle the processor gets the instruction from memory and decodes it.

  • In the next clock cycle the required data is taken from memory.

• Slow

Harvard Architecture

• Named after the relay based old computer "Harvard Mark I".

• Has two separate memories for storing data and program(set of instructions).

  • This solves the "von Neumann bottleneck" of the von Neumann architecture.

• Processor can complete an instruction in one cycle if appropriate pipelining strategies are implemented.

  • In the first stage of pipeline the instruction to be executed can be taken from program memory.

  • In the second stage of pipeline data is taken from the data memory using the decoded instruction or address.

  • Most of the modern computing architectures are based on Harvard architecture, but the number of stages in the pipeline varies from system to sytem.

• Fast

Factors That Affect Performance

• Algorithm

• Programming language, compiler

• Architecture of the application

• Processor and memory

• Input/Output

• Operating System

Terminology

• Algorithm

  • A finite list of well-defined instructions that carries out an operation to solve a particular problem.

    e.g., Calculating a function or performing a given task

• Program

  • A set of computer instructions that implements an algorithm.

  • An instance of an algorithm expressed in a certain way and intended for solution on a certain machine.

  • May contain more information than is expressed by the algorithm, because the program has to set up an appropriate environment.

• Pseudocode

  • Falls between an algorithm and a program.

  • An algorithm expressed in ad-hoc programming-like language.

  • Purpose is to allow the writer to demonstrate an algorithm to reader without demanding that the reader know a specific high-level language in detail.

  • Since it does not have a specific syntax like any of the programming languages and thus cannot be executed on a computer.