Functional Components

Functional Components of Computer

The computer is the combination of hardware and software. Every task given to a computer follows an Input- Process- Output Cycle (IPO cycle). It needs certain input, processes that input and produces the desired output. The input unit takes the input, the central processing unit does the processing of data and the output unit produces the output. The memory unit holds the data and instructions during the processing.

The block diagram of basic computer organization is shown below:-

Input Unit

It consists of input devices that are attached to the computer. These devices take input and convert it into binary language that the computer understands. Some of the common input devices are keyboard, mouse, joystick, scanner etc.

Central Processing Unit (CPU)

The main component to make a computer operate is the computer chip or microprocessor. This is referred to as the Central Processing Unit (CPU). It is also known as Brain of computer. It performs arithmetic and logic operations. The CPU (Central Processing Unit) is the device that interprets and executes instructions. The CPU has three main components which are responsible for different functions – Arithmetic Logic Unit (ALU), Control Unit (CU) and Memory registers.

Arithmetic and Logic Unit (ALU)

It is one of main components of the CPU. This is where all arithmetic & logic operations are done. Arithmetic calculations include addition, subtraction, multiplication and division. Logical decisions involve comparison of two data items to see which one is larger or smaller or equal.

Control Unit (CU)

How many times have you kept a book open with your eyes fixed on it and not read a single word? This happens because the control unit of brain doesn’t allow your eyes to provide an input at a given point of time.

“A control unit is that part of computer, which makes the ALU and Memory work in synchronization with the data. It is responsible for carrying out all the instructions stored in the program. It decodes the fetched instruction, interprets (understands) it and sends control signals to input/output devices until the required operation is done properly by ALU and memory.”

Memory

It is the location where data & instructions are stored. They can be retrieved from memory whenever required .Memory is used to

1. Hold the data received from input device temporarily & ready it for processing.
2. Hold data that has been processed & the intermediate results generated within.
3. Hold the finished results of processed data, until released to output devices.
4. Hold the system software & application software in use.

Data is stored in memory as bytes. A byte is made up of eight bits. A bit is the smallest unit of memory. Other units of memory are Kilobytes (KB), Megabytes (MB), Gigabytes (GB) and so on… which we will study later on.

Memory can be classified into two groups.

1. Main Memory
2. Secondary Memory

• Main Memory

Memory attached to the CPU is used for storage of data and instructions and is called internal memory. During processing, it is the internal memory that holds the data. The internal memory is divided into many storage locations, each of which can store data or instructions. Each memory location is of the same size and has an address. With the help of the address, the computer can find any data easily without having to search the entire memory. The internal memory is also called the Primary memory or Main memory. There are several different types of main memory.

1. Random Access Memory (RAM)

 It is a volatile memory which means when power is turned off, all the contents are destroyed. Most modern semiconductor volatile memory is either Static RAM or Dynamic RAM.

SRAM retains its contents as long as the power is connected and is easy to interface to but uses six transistors per bit.

DRAM is more complicated to interface to and control and needs regular refresh cycles to prevent its contents being lost. However, DRAM uses only one transistor and a capacitor per bit, allowing it to reach much higher densities and, with more bits on a memory chip, be much cheaper per bit. SRAM is not worthwhile for desktop system memory, where DRAM dominates, but is used for their cache memories.

 SRAM vs DRAM

1. SRAM is static while DRAM is dynamic
2. SRAM is faster compared to DRAM
3. SRAM consumes less power than DRAM
4. SRAM uses more transistors per bit of memory compared to DRAM
5. SRAM is more expensive than DRAM
6. Cheaper DRAM is used in main memory while SRAM is commonly used in cache memory

2. Read Only Memory (ROM)

It is a non-volatile memory which means it retains the stored information even if the power is turned off. ROM is of four types:-

1. Masked ROM (MROM)
2. Programmable ROM (PROM)
3. Erasable Programmable ROM (EPROM)
4. Electrically Erasable Programmable ROM (EEPROM)

3. Cache Memory

Cache memory is random access memory (RAM) that a computer microprocessor can access more quickly than it can access regular RAM. As the microprocessor processes data, it looks first in the cache memory and if it finds the data there (from a previous reading of data), it does not have to do the more time-consuming reading of data from larger memory. It is of two types:-

L1 cache is on the same chip as the microprocessor.

L2 is usually a separate static RAM (SRAM) chip.

• Secondary Memory

Secondary memory is needed to store data and information permanently for later use. Some of the secondary storage devices are Cassette Tape, Magnetic tape, Floppy disk, Memory Card, Pen drives, External Hard disk etc.

Output Unit

The output unit consists of output devices that are attached with the computer. It converts the binary data coming from CPU to human understandable from. The common output devices are monitor, printer, plotter etc.

Interconnection between Functional Components

The interconnection between the functional components of a computer can be done in many ways. In microcomputers we generally see a Common Bus Architecture as shown in the figure below. As we have seen before that a computer consists of input unit that takes input, a CPU that processes the input and an output unit that produces output. All these devices communicate with each other through a common bus. A bus is a transmission path (set of conducting wires) over which data or information in the form of electric signals, is passed from one component to another in a computer. The bus can be of three types – Address bus, Data bus and Control Bus.

The address bus carries the address location of the data or instruction. The data bus carries data from one component to another and the control bus carries the control signals. As shown in the figure below, the system bus is the common communication path that carries signals to/from CPU, main memory and input/output devices. The input/output devices communicate with the system bus through the controller circuit. This controller circuit helps to manage various input/output devices attached to the computer.

Fig. Common Bus Architecture