Introduction To Computer Architecture and Organization Part 2

From part 1 we learnt about Introduction To Computer Architecture and Organization. We described computer architecture as a set of rules and methods that describe the functionality, organization, and implementation of computer systems. This second part we are going to look at computer memory and the motherboard

Read also : Introduction to Computer Architecture Part 1

The MotherBoard

The main printed circuit board in a computer is known as the Motherboard. It is also known as System Board, Main Board or Printed Wired Board (PWB). It holds the processor, memory and expansion slots and connects directly or indirectly to every part of the PC. The type of motherboard installed in a PC has a great effect on system speed and expansion capabilities.

Motherboard Components
The motherboard holds all the major logic components of the PC. These components include:

  • The CPU
  • Main Memory (RAM)
  • Math Co-Processor
  • BIOS
  • CMOS memory
  • CMOS Battery
  • Level 2 cache RAM
  • CPU Clock
  • Expansion Bus
  • Chipset
  • Parallel printer port
  • Serial ports
  • Keyboard interface
  • Floppy disk controller
  • Hard disk controllers

CPU- Central Processing Unit It is also known as the microprocessor. It is the ‘brain’ of the computer, and it executes program instructions as well as performing mathematical and logical calculations.

Math Co-processor
Math co-processors are microprocessors that are optimized to execute complex mathematical calculations e.g. irrational numbers and arrays.

BIOS- Basic Input Output System
All motherboards include a small block of Read Only Memory (ROM) which is separate from the main system memory used for loading and running software. The ROM contains the PC’s Basic Input/Output System (BIOS).

The BIOS performs the following routines and functions:

  1. As soon as the machine is powered on, it inspects the computer to determine what hardware is fitted and then conducts some simple tests to check that everything is functioning normally – a process called the power-on self test (POST).
  2. If any of the peripherals are plug and play devices, the BIOS recognizes them and assigns their resources.
  3. Allows the PC’s set-up configuration to be viewed and edited. A user can choose an option to enter the Setup program and from there be able to view or edit the PCs hardware configurations.

CMOS- Complimentary Metal Oxide Semiconductor
Motherboards also include a small separate block of memory made from CMOS RAM chips, which is kept ‘alive’ by a battery (known as a CMOS battery) even when the PC’s power is off. This prevents reconfiguration when the PC is powered on.

CMOS devices require very little power to operate.

The CMOS is used to store basic information about the PC’s configuration: number and type of hard and floppy drives, how much memory, what kind and so on.

The other important data kept in CMOS memory is the time and date, which is updated by a Real Time Clock (RTC).
NB: The clock (RTC), CMOS RAM and battery are usually all integrated into a single chip. If the CMOS battery fails, all the CMOS configurations are lost.

Cache Memory
A small block of high-speed memory (RAM) that enhances PC performance by pre-loading information from the (relatively slow) main memory and passing it to the processor on demand.

Most CPUs have an internal cache (in-built in the processor) which is referred to as Level-1 Cache memory or primary cache.

This can be supplemented by external cache memory fitted on the motherboard. This is Level-2 Cache memory or secondary cache. Even though Level-2 cache is optional, it results in a major improvement in performance.

Expansion Buses
Buses carry signals, such as data, memory addresses, power and control signals from component to component.

A chipset is a group of small circuits that coordinate the flow of data to and from key components of a PC. This includes the CPU itself, the main memory, the secondary cache and any devices situated on the buses. The chipset also controls data flow to and from hard disks, and other devices connected to the IDE channels.

CPU Clock
The clock synchronizes the operation of all parts of the PC and provides the basic timing signal for the CPU.

Switches and Jumpers
DIP (Dual In-line Package) switches are small switches found on the circuit board that can be turned on or off just like a normal switch. They are very small and so are usually flipped with a pointed object such as a screwdriver, bent paper clip or pen top. Care should be taken when cleaning near DIP switches as some solvents may destroy them.


Memory is used to hold data and software for the processor. There is a variety of memory types, and often a mix is used within a single system. Some memory will retain its contents while there is no power, yet will be slow to access. Other memory devices will be high-capacity, yet will require additional support circuitry and will be slower to access.

Memory chips come in different sizes, with the width specified as part of the size description. For instance, a DRAM (dynamic RAM) chip might be described as being 4M×1 (bit-organized), whereas a SRAM (static RAM) may be 512K×8 (word-organized)

RAM stands for Random Access Memory. RAM is the “working memory” in the computer system. It is where the processor may easily write data for temporary storage. RAM is generally volatile, losing its contents when the system loses power. Any information stored in RAM that must be retained must be written to some form of permanent storage before the system powers down.

ROM stands for Read-Only Memory. ROMs are nonvolatile memory, requiring no power to retain their contents. The primary purpose of ROM within a system is to hold the code (and sometimes data) that needs to be present at power-up. Such software is generally known as firmware and contains software to initialize the computer by placing I/O devices into a known state.

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