24February2017

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Hardware and System Software | Typical Computer System | Primary Memory

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Chapter No.5th

1. Typical Computer System:

1.1. Computer Architecture:

Computer Architecture means the combination of different hardware components/parts within the computer system. Computer Architecture is the way to organize the main components and connect them to obtain a complete computer system. There are four main components of a computer system.

  1. Processing Unit.
  2. Primary Memory.
  3. Secondary Memory
  4. Input/Output Peripherals.

In addition to these basic components of a working computer system, there are buses, ports and cables that provide interconnections among the components. The block diagram of a typical computer system is shown below.

The block diagram of a typical computer system is shown below.

Main Memory is directly connected to the Processor. Due to this reason Main Memory especially RAM is called online to the processor. The other components are called Peripherals that include Input / Output and Secondary storage devices. These peripherals are indirectly connected to the Processor through RAM and are called offline to the processor.

1.1.1. Processor:

This part of the system unit is also called CPU which stands for Central Processing Unit. System Unit is a complete box containing Processor or CPU, mother/main board, main memory, hard disk drive, floppy disk drive and buses. The system unit also contains buses on its rear side for connecting to the external Input/Output devices. A CPU is generally a single microprocessor made from a semi conducting material, usually silicon, with millions of electrical components on its surface. A CPU itself is a combination of different components.

Its main parts include ALU (Arithmetic and Logic Unit), CU (Control Unit), and a combination of different general purpose and special purpose storage locations called Registers. ALU is responsible for performing ordinary arithmetic operations (like Addition, Subtraction, Multiplication, Division and Modules) along with logical or comparison operations (such as Less than, Greater than, Equal to, Not equal to, Less or Equal, Greater or Equal, And, OR and NOT).

The Control Unit (CU) acts in the way similar to the human nervous system to monitor and control the different components of a computer system during their functions. Registers provide storage space to hold the data temporarily in order to be processed.

Microprocessors, also called silicon chips, are typically embedded in a protective casing. The wires radiating from the silicon chip above connect to short metal legs that are soldered into integrated circuit boards.

1.1.2. Floating-Point Processor:

It is also called a numeric coprocessor, a math coprocessor, and a floating-point unit. A coprocessor (processor additional to the main system microprocessor) that performs calculations using floating-point numbers, as opposed to integers (whole numbers). Adding a floating-point processor to a system can speed up math and graphics functions (graphics work is generally math-intensive) dramatically with programs that are designed to recognize and use it. Except for the Intel 80486 and the Motorola 68040, both the Intel 80x86 and the Motorola 680x0 families of microprocessors have companion floating-point processors.

A new type of hardware called cache memory is also introduced that is a small amount of storage within the processor. Cache Memory stores frequently accessed data or program instructions for the purpose of speeding a computer system's performance.

The speed of processing is usually measured in Mega Hertz (MHz) or Giga Hertz (GHz). Up to 2.8 GHz of processors are readily available in the market for Pentium 4.

1.1.3. Main Memory:

Main Memory is also called Primary or Internal or Real Memory. Main Memory operates at the highest speed and can be accessed directly by the central processing unit (CPU. Internal memory is contained on computer chips and uses electronic circuits to store information.

There are two types of Main memory:

1.1.3.1. RAM

RAM is an acronym for Random Access Memory. Semiconductor-based memory that can be read and written by the microprocessor. The storage locations can be accessed in any order. RAM is volatile. RAM must be provided with a constant power supply. If the power is interrupted then the data is lost. Thus RAM can be used only as a temporary storage.

1.1.3.2. ROM

ROM is an acronym for Random Access Memory. A memory that contains instructions or data that can be read but not modified. To create a ROM chip, the designer supplies a semiconductor manufacturer with the instructions or data to be stored; the manufacturer then produces one or more chips containing those instructions or data. Because creating ROM chips involves a manufacturing process, it is economically viable only if the ROM chips are produced in large quantities.

1.1.4. Secondary Memory

This is also called Mass Storage, Auxiliary Memory and External Memory. This memory is slower than the Main memory as it involves mechanical motion techniques during storage and retrieval of data. This memory is larger in size than Main memory but the processor is unable to access it directly due to its offline link with the processor. This means that the data from secondary storage must be loaded into RAM before the processor starts processing it. The main memory links the secondary memory to the processor.

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