Q1. What is a computer? Explain its basic architecture along with the functioning of each of its subunits.
Ans. A computer is an electronic device that can perform a variety of operations in accordance with a set of instructions called program.
Figure: Basic Structure of a Computer
The input unit is formed by the input devices attached to the computer.
Examples of input devices and media are: keyboard, mouse, magnetic ink character reader (MICR), optical mark reader (OMR), optical character reader (OCR), joystick etc.
The input unit is responsible for taking input and converting it into computer understandable form (the binary code). Since a computer operates on electricity, it can understand only the language of electricity that is, either ON or OFF or high voltage or low voltage. That means a computer can understand two stages ON/OFF or High/Low voltage or the binary language that uses just two symbols: 1 for ON and 0 for OFF.
An input unit takes the input and converts it into binary form so that it can be understood by the computer.
Central Processing Unit (CPU)
The CPU is the control centre for a computer. It guides, directs and governs its performance. It is the brain of the computer. The CPU has two components which are responsible for different functions. These two components are its Control Unit (CU) and Arithmetic Logic Unit (ALU).
Arithmetic Logic Unit (ALU)
The ALU performs all the four arithmetic (+,-,*,/) and some logical (<,>,=,<=,>=,<>) operations. When two numbers are required to be added, these numbers are sent from memory to ALU where addition takes place and the result is put back in the memory. The same way other arithmetic operations are performed.
For logical operations also, the numbers to be compared are sent from memory to ALU where the comparison takes place and the result is returned to the memory. The result of a logical operation is either TRUE or FALSE. These operations provide the capability of decision-making to the computer.
Control Unit (CU)
The Control Unit (CU) controls and guides the interpretation, flow and manipulation of all data and information. The CU sends control signals until the required operations are done properly by ALU and memory. Another important function of CU is the program execution that is, carrying out all the instructions stored in the program. The CU gets program instructions from memory and executes them one after the other. After getting the instructions from memory in CU, the instruction is decoded and interpreted that is, which operation is to be performed. Then the asked operation is carried out. After the work of this instruction is completed, control unit sends signal to memory to send the next instruction in sequence to CU.
The control unit even controls the flow of data from input devices to memory and from memory to output devices.
The output unit is formed by the output devices attached to the computer. The output coming from the CPU is in the form of electronic binary signals which needs conversion in some form which can be easily understood by human beings that is, characters, graphical or audio visual. This function of conversion is performed by output units. Some popular output devices are VDU (Visual Display Unit), printer, plotter, speech synthesizer and coder etc.
The memory of a computer is more like a predefined working place, where it temporarily keeps information and data to facilitate its performance. When the task is performed, it clears its memory and memory space is then available for the next task to be performed. When the power is switched off, everything stored in the memory gets erased and cannot be recalled.
The memory of computer is often called main memory or primary memory.
The memory cell may be defined as a device which can store a symbol selected from a set of symbols.
Each of these cells is further broken down into smaller parts known as bits. A bit means a binary digit, that is, either 0 or 1. A number of bits together are used to store data instructions by their combination.
Figure: Memory cells
A bit is an elementary unit of the memory.
A group of 8 bits is called a byte and a group of 4 bits is called a nibble.
One byte is the smallest unit which can represent a data item or a character. Other units of memory are KB, MB, GB, and TB.
One KB (Kilobyte) means 210 bytes, that is, 1024 bytes. One MB (Megabyte) means 210 KB, that is, 1024X1024 bytes. One GB (Gigabyte) means 210 MB that is 1024X1024X1024 bytes. One TB (Terabyte) means 210 GB, that is, 1024 GB.
Since computer’s main memory (primary memory) is temporary, secondary memory space is needed to store data and information permanently for later use. Some most common secondary storage media are the floppy diskette, the hard disk and CD-RWs etc.. The secondary memory devices are also known as storage devices.