Unit of Data Measurement / ( C.P.U, M.U, Input/Output)

Unit of Data Measurement / ( C.P.U, M.U, Input/Output)

• The basic elements of Computers that can signal a 1 or a 0 are called flip-flops. It is a simple electrical device and can either be a ‘0’ or a ‘1’, which means that the flow of current is either inward or outward.
• Modern Computers use a very tiny set of flip-flops known as a register. The most important characteristic of these registers is that the binary digits can be stored in them using certain voltages.
• The entire independent circuits can be designed on a small piece of a semi conductor material like silicon.
• Silicon is obtained from sand and is a poor conductor of electricity. But, by chemical processes, the surface and the enterior of a silicon ‘chip’ are modified to give it electronic capabilities. Such miniature circuits are called Integrated Circuits (IC).
• By 1971, engineers were able to put a few component switches – necessary to build a complete Computer on a single chip of silicon. This tiny silicon chip was called the microprocessor.
• Because the Computer is a binary machine, it performs mathematical operations using the binary number system.
• The binary number system is similar to the decimal system where we use ten digits, 0, 1, 2, 3…. 8, 9 to represent all numerical values. The only difference is in the number of digits used.
• The Computer converts all decimal numbers into binary numbers or combinations of bits. They by acting upon individual bits, it can perform the required mathematical operation addition, subtraction etc.
• The internal circuits that can perform mathematical operations on bits are usually made of two or more logic gates. Logic gates are components that generate a 1 or a 0 depending on the input.
• The three basic logic gates are AND, OR and NOT.
• A Computer is organized into three basic units:
  1.  Central Processing Unit (CPU)
  2.  Memory Unit (MU) and
  3.  Input / Output Unit 

1. Central Processing unit (CPU)

The CPU is the part of a Computer that performs the main function of information processing. The memory unit stores data. The Computer supplies processed information back to the users using special output devices.

• The Central Processing Unit or CPU,  is the most important part of the compute. It is called the brain of the Computer. It makes all the required calculations and processes data.

The CPU can be divided into three main components:
(a) ALU  (b) CU and  (c) Registers.

a. The Arithmetic and Logic Unit (ALU):

ALU performs all the mathematical and logical operations on the information supplied to the CPU.

b. Control Unit (CU):

This unit directs the working of the CPU. It fetches instructions (Programs) from the memory and according to the instructions, controls the flow of data between the ALU and other parts of the Computer.

c. Registers:

Registers are storage locations that hold instructions or data while the CPU is using them. The registers consist of flip-flops and the registers used by the CPU are the fastest memory elements in the Computer. In contrast, the memory unit holds instructions and data before or after the CPU processes these.

Main attributes of CPU

a. Data Width:

It refers to the number of bits of data that can be manipulated within the CPU at one given time.

• The data width of a Computer is also called its word size.
• Computers have data widths ranging from 8 to 64 bits.
• A higher data width means the CPU is capable of processing data faster. A CPU with a higher data width is more powerful.

b. Address Range:

Address range refers to the amount of memory that can be directly read or written by the CPU.

c. Clock Speed:

The speed of CPU is known as Clock Speed. The Computer is essentially composed of tiny devices that can be put on or off to indicate 1 or 0.

• At any moment several thousand such devices change their state. To synchronize the change of all these components the CPU uses an internal clock.
• With every tick of this clock all switches that need to change their position do so in perfect harmony.
• The larger number of ticks per second the faster is the speed of the CPU.
• The ticks per second of the internal clock are measured in megahertz and gigahertz.
• Hertz is a unit of frequency.
• 1 MHz = 1 million ‘ticks’ per second, 1 GHz = 100 MHz
• Higher the clock-speed, faster the Computer.

2. Memory Unit (MU)

The memory unit stores all instructions and data for the CPU. Memory Unit is an important part of the Computer system. The storage device of a Computer system is known as memory. Memory Unit can receive data, hold it and deliver according to the instructions from the control unit.

• Memory is of two kinds: (a) Primary and (b) Secondary.

1. Primary Memory:

It is often referred to as the working memory or the main memory of a Computer system. It is capable of sending and receiving data at a very high speed. It is temporary in nature i.e. Data stored in primary memory are lost when the Computer is switched off. So it is also called volatile memory.

Example of primary memory: RAM & ROM

• Primary memory is directly accessible to the CPU. It must be able to provide data very quickly.
• The two basic kinds of primary memory are the Random Access Memory (RAM) and the Read Only Memory (ROM).
• The RAM is a read/write memory.
• The CPU can change the contents of the RAM at any time. In addition, RAM is volatile.
• The Ram capacity greatly influences the computing ability of the Computer. Capacity is usually measured in kilobytes and megabytes.
• The ROM cannot be altered.
• Informations is stored on the ROM at the time of its manufacture. The information might be in the form of crucial instruction that govern the working of the Computer.
• The ROM is non-volatile and retains its information even after the power is turned off.
• The PROM (Programmable Read Only Memory), however, has the option of being programmed, i.e. the manufacturer of the Computer may choose to load a program designed by his company into this PROM, and then the Computer would use this PROM like any other ROM.

2. Secondary Memory:

 It is used to store data for a long term. It operates at a much slower rate than primary memory. Secondary memory is permanent in nature, so it is also called non-volatile. It is also cheaper than primary memory.

• Primary memory is fast but expensive. To reduce storage costs, Computers also use secondary memory.
• Common examples of secondary memory are floppy diskettes, hard (fixed) discs and magnetic tapes, CDs, DVD’s Memory Cards, USB Sticks etc.
• It is not directly accessible to the CPU. Information is moved from the secondary memory to the primary memory first and then to the CPU.
• A floppy diskette is a plastic disk coated with magnetic material.
• Special devices known as disk drives are capable of reading from the writing to floppies using special magnetic ‘head’.
• Any piece of information stored on a floppy diskette can be directly accessed.
• Magnetic tapes are long plastic tapes coated with magnetic material.
• Magnetic tapes can store far larger amounts of data than the floppy diskette. But a problem with magnetic tapes is that information cannot be accessed directly as in the case of floppy diskettes.
• The third type of medium, called fixed or hard disks, are more or less similar to the floppy diskette. But one hard disk drive contains several discs of a hard material.
• Another popular storage medium is the compact disk (CD). Unlike the media described above, CDs are an ‘optical’ medium.
• An optical medium is one where the properties of light are used for the medium to perform its basic functions.
• Conventional CDs are made of a special kind of plastic.
• The CD is read using a laser beam.
• Secondary memory is much slower, but it is non-volatile and can be used to store information for long periods of time.
• DVD drive is another optical drive which is same in size as CDs but is higher in storage capacity.
• USB Flash drives also known as USB stick, USB, Flash Memory etc. are physically much smaller than optical drives with high storage capacity and are removable and rewritable in nature.
• SD and Micro SD cards are very small in size but  very high in capacity.

3. Input /Output

• There has to be a physical channel that permits users to supple informations to the Computer.
• Devices that permit users to supple information to the Computer are called ‘input’ devices.
• Input unit enables us to enter (or ‘Input’) data into a Computer. The common input devices are keyboard and mouse.
• Similarly, a physical channel that permits a Computer to convey the processed information to the outside world. Devices that permit such a function are called ‘output’ devices.
• Output unit enables the Computer to show us the result and the information that we want. The common output devices are monitor, printer and speakers.
• Input and output devices are indispensable, but are not a part of the CPU. They are also called peripheral devices, suggesting that they lie on the periphery of the CPU.
• These devices are also called an interface, because they translate informations for man and machine.
• The most popular input device used in contemporary Computers is the keyboard.
• Another way to input information into a Computer is to use an Optical Mark Reader (OMR). Optical Mark Reader are capable of reading specially prepared forms. These forms have a provision for black marks to be made using a pen or a pencil in a specific position.
• Most competitive examination that deal with a large number of students usually use this system.
• Banks use another input device called a Magnetic Ink Character Reader (MICR).
• Special numbers are written on bank cheques using magnetic ink and in a particular style to write different numbers. The MICR passes over the words or characters, examines the shape of the magnetic field created by the character, and is thus able to recognize it.
• Barcodes are often imprinted on products in merchandise stores. A bar code consists of several parallel vertical line of different thickness that represent the binary digits.
• The bits form a code that can be used to identify the object ton which the bar code is imprinted. A bar code reader is used to read the bar codes by detecting the bars by using light.
• The bar code can represent information like the price of the product or its date of expiry etc.
• Menu-driven programs, where the user sees the host of on-screen choices, sometimes use another input devices called the mouse.
• The mouse is a pointing device. It can be gripped in the palm of the hand and moved over a horizontal surface. The motion of the mouse can be monitored by the Computer in different ways.
• The movement is measured and transmitted to the Computer. This generates a corresponding movement of an on-screen marker called a cursor from one option to another.
• To select an option, the user presses one of the mouse’s buttons.
• Another, input device is a digital camera. A digital camera has a circuit that is sensitive to light.
• The two most common devices are the Visual Display  Unit (VDU) and the printer.
• A Visual Display Unit (VDU) uses a cathode ray tube to display informations.
• To represent any character, VDU illuminates a particular pattern of these dots. These dots are also known as pixels, a short form for picture-elements.
• Printers print characters on paper or other similar medium.
• Printers come in three popular versions  : dot matrix printers, ink-jet printers and laser printers.
• Dot matrix printers print characters in the form of combinations of very tiny dots. The printing head aligns its ‘pins’ to match a particular pattern of dots.
• Ink-jet printers spray jets of ink on to the paper to print any character. The characters are absolutely smooth as ink is sprayed in a continuous flow.
• Laser printer, uses a laser beam to actually ‘burn’ the characters on to the paper.
• We need to issue the Computer a detailed sequence of instructions that it needs to follow to operate upon any data. Such a sequence is called a program.
• A program may directly be written to the RAM or may be stored in some form of secondary memory.
• It may be transferred from the secondary memory to the RAM as the when required.
• Execution of a program means that data is moved around in the CPU according to a well-detailed sequence by the programme.
• Computer programs are written using special languages called programming languages.
• There are several programming languages. Each language has its own ‘grammar’ called its syntax.