A DESCRIPTIVE OVERVIEW OF PC COMPUTER HARDWARE
Is general term used to represent the physical and tangible component of the computer i.e. those component which can be seen and touched . It
includes:
- Input Unit
- output Unit
- Central processing unit
- Backing storage and auxiliary memory devices.
The electronic circuits consisting of resistors, capacitors, ICs main computer equipment( visually the keyboard, visual display unit and central processing unit) and its peripherals like floppy drives, joystick, printer, tracker ball ,graphic pad, plotters, digitizer, card reader, paper and magnetic tapes and disks, modems, interfaces terminals etc. are all examples of computer hardware . All input and output devices connected to computer are collectively known as peripherals.
INPUT UNIT
Input unit is actually a device which provides man to machine communication with computer. Input of any form is first converted into binary electronic signals which can be understood by CPU. This process is called digitizing.
Input may be linguistic, graphical, mechanical, audio, visual or audiovisual .Linguistic input is written program in computer’s programming languages which is inputted to computer either by typing on keyboard, or by floppy, magnetic tapes or CD, DVDs.
OUTPUT UNIT
Output unit works just in reverse manner of input units. We feed data into computer by typing on to the keyboard of computer. Similarly, information coming out of computer can be typed on the sheet of paper by an output unit known as printer, in a similar manner, as it happens is happens in teleprinters. Output coming from the CPU is in the form of electronic binary signals that needs conversion in a form, that can be easily understood by human being, i.e. graphical alphanumeric, audiovisual or in the form of human language. This function is performed by output units include, VDU, Plotter, printers, speech synthesizers, decoders, robots etc.
CENTRAL PROCESSING UNIT
CPU is totally electronic based and its function are to:
- Receive and store data into main storage memory.
- Control sequence of operations.
- Give command to all parts of the computer system.
- Carry out data processing and output the result.
The CPU assumes many different sizes in different computers. The CPU of mainframe computers are like large cup board and carry out millions of instructions in seconds The CPU of a microcomputer is much less powerful and is contained in a single chip.
This is actually the brain and heart of a computer. Data is processed here . It takes information from the input unit and process it accordingly to instructions . The instruction are given by programs. programs are written in languages which a computer can under stand. These are actually coded languages.
By data processing we means
- Making arithmetic calculation like addition , subtraction, multification, division and exponentiation etc.
- Making logical decision like comparing two values to find out which one geater.
- Manipulating alphanumeric
ARITHMETIC AND LOGIC UNIT (ALU)
The ALU is a section where all the arithmetic and logical functions are carried out. We know that every arithmetic operation required twooperands. The operation then process a result. This ALU, therefore, must be able to handle two data words and the result. 
This concept is dependent on the storage and processing techniques, which may vary , from model to model. Logical operation usually involve comparisons. Circuits an the ALU compare two values by subtracting one from another. For example, to determine whether number A is greater than number B , B is subtracted fro A and the sign of the result is determined . Depending on the sign of the result , the ALU does further operation. Alphabetic data also compared according to their assigned order sequence.
ALU comprises a number of accumulators and registers. It derives all the data from the main memory as directed by control unit based on program given to it. This data gets loaded into accumulators in ALU. For example , if numbers A and B are to be added the control unit selects number A from its address in memory and loads it into arithmetic unit, Then the value of B is selected and added to A in the arithmetic unit. The results are placed in the main storage(again under the direction of control unit ) or may be retained in the accumulators themselves for further calculation. Some logical operation of the ALU enable the computer to have the decision making quality.
CONTROL UNIT
The control unit direct all the operation inside the computer. It is known as nerve centre of the computer, because it controls and coordinates all hardware operation, i.e, those of the CPU and input-output devices. It performs following actions
It gives command to transfer data from input device to memory of arithmetic and logic unit. It also transfer result from ALU to memory and on to the output device for printing.
It stores the program in the memory, takes instruction one by one , understand them and issue appropriate commands to other units.
It fetches the required instructions from the main memory storage via memory data register(MDR) and places it in the control instruction register (CIR). Then it interprets the instruction in CIR and gets it executed by sending a command signal to the concerned hardware device. Memory data register is a special register which holds all data instructions temporarily, as they pass in and out of the main memory, Control instruction register is also a special register which holds machine instructions currently being interpreted by control unit.
MEMORY
Digital computer use the binary number system, which has two digit : 0 and 1. A binary digit is called a bit . Information is represented in digital computer I n groups of bits.
The bit is an elementary of Memory.
A group of 8 bit is called a byte and a group of 4 bit is called nibble.
One byte is the smallest unit which represents data. Other bigger units of memory are KB , MB and GB which has following relation:
1KB=1024Byte(210 Byte)
1MB=1024KB=024x1024bytes
1GB=1024 MB =1024 x 1024 x1024 bytes.
Memory of storage devices are two types:
- Internal Primary . or Main Storage or Immediate Access Storage (IAS).
- Auxiliary memory storage or backing storage.
INTERNAL MEMORY OR IMMEDIATE ACCESS STORAGE (IAS)
It is also called computer ‘s main or primary memory because like human it is able to
store information which can be recalled or accessed when required . The program of instruction s has to be stored in the main memory in order to make it work automatically. This memory forms an integral part of
ALU and is synthesized wholly by electronic components due to which its operation is extremely fast.
Any item of data or any instruction stored in the memory can be retrieved (called back) by the computer at lightning speed. Modern computer does this in few nanoseconds. Only a limited storage is provided as it is very costly. The rest of the program and data are kept in secondary storage devices also known as backing storage devices.
Internal memory of a modern computer is contained in silicon chips which are of two types
Read only memory (ROM)
Random Access Memory (RAM)
RAM CHIPS
RAMs are designed to act as short term memory, and therefore also known as volatile memory. A RAM holds information which is needed for particular operation. New information can be recorded, read and then rubbed out when no longer needed. But once the computer switched off, a RAM forgets everything.
ROM CHIPS
ROMs are Read Only Memories holds sets of instruction which tell the microprocessor to do. For instance, a ROM will tell the computer, how to recognize keys and which key is to be pressed and how to light up the screen.
Information stored in ROM can only be read. It can not be rubbed out or added to. It is permanently built in computer at the time of its production and therefore also known as firmware. ROM also holds the permanent data like trigonometric functions several variations of ROM are available.
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