Personal computers

1. Personal computers

2. Basic diagram of a computer Central processing unit (CPU) Memory unit ALU (Arithmetic Logic Unit ) Output device Input device Control unit

4. Central Processing Unit • is the part of the computer that carries out the instructions of a computer programme • is the unit that reads and performs programme instructions • is known as the brain of the computer • It consists of: • Memory Unit - also known as the primary storage or main memory. • stores data, programme instructions, internal results and final output temporarily before it is sent to an appropriate output device • consists of thousands of cells called storage locations • these cells are activated with off-on or binary digits(0,1) mechanism: a character either a letter or numerical digit is stored as a string of (0,1) binary digits ( BITS) • these bits are used to store instructions and data by their combinations

5. Arithmetic and Logical Unit (ALU) - the unit where all arithmetic operations (addition, subtraction, multiplication and division) and logical functions such as true or false, male or female are performed. • Once data are fed into the main memory from input devices, they are held and transferred as needed to ALU where processing takes place. • No process occurs in primary storage. Intermediate generated results in ALU are temporarily placed in memory until needed at later time. • Data may move from primary memory to ALU and back again to storage many times before the process is finalised.

6. Control Unit • acts as a central nervous system and ensures that the information is storedcorrectly and the programme instructions are followed in proper sequence as well as the data are selectedfrom the memory as necessary. • coordinates all the input and output devices of a system.

7. Computer • The hardware are the parts of the computer itself including the central processing unit (CPU) and related microchips and micro-circuitry(the circuits that an electrical or electronic device contains, considered as a single system), keyboards, monitors,and drives (hard, CD, DVD etc...). • Other extra parts called peripheral components or devices include mouse, printers, modems, scanners, cameras and cards (sound, colour, video) etc. • Together they are referred to as a personal computer.

8. Input and output devices • Keyboard - is used to type information into the computer or input information. • The most common for Latin based languages is the QWERTY layout (named for the first 6 keys). • The standard keyboard has 101 keys. • Notebooks have embedded keys accessible by special keys or by pressing key combinations (CTRL or Command and P for example). • Hand held devices have various and different keyboard configurations and touch screens. • Some of the keys have a special use. They are referred to as command keys.

9. Note:A disc refers to optical media, such as an audio CD, CD-ROM, DVD-ROM, DVD-RAM, or DVD-Video disc. A disk refers to magnetic media, such as a floppy disk, the disk in a computer's hard drive, an external hard drive. • Removable Storage and / or Disk Drives - All disks need a drive to get information off - or read - and put information on the disk - or write. • Each drive is designed for a specific type of discwhether it is a CD, DVD, hard disk or floppy. • Often the term ‘disk’ and ‘drive’ are used to describe the same thing but the disk is the storage device which contains computer files - or software - and the drive is the mechanism that runs the disk. • Digital flash drives use memory cards to store information - there are no moving parts. • Digital cameras also use Flash memory cards to store information, in this case photographs. • Hand held devices use digital drives, many also use removable or built in memory cards.

10. Mouse • Touch pads • Printers • Scanners • Monitors - The monitor shows information on the screen - outputting information. • When the computer needs more information it will display a message on the screen, usually through a dialog box. • The resolution of the monitor determines the sharpness of the screen. • Most desktop computers use a monitor with a cathode tube or liquid crystal display (LCD). • Most notebooks use a liquid crystal display monitor.

11. Modem - A modem is used to translate information transferred through telephone lines, cable, satellite or line-of-sight wireless. • Modem stands for modulate and demodulate which changes the signal from digital, which computers use, to analog, which telephones use and then back again. • Digital modems transfer digital information directly without changing to analog. • Modems are measured by the speed that the information is transferred. • The measuring tool is called the baud rate (the number of signal events, signal changes, or signal transitions occurring per second over an analog circuit, such as changes from positive voltage to zero voltage, from zero voltage to negative voltage, or from positive voltage to negative voltage. The baud rate can never be higher than the raw bandwidth of the channel, as measured in Hz). • Originally modems worked at speeds below 2400 baud but today analog speeds of 56,000 are standard. • Cable, wireless or digital subscriber lines can transfer information much faster with rates of 300,000 baud and up.

12. Cards - are components added to computers to increase their capability. • Sound cards allow computers to produce sound like music and voice. The older sound cards were 8 bit then 16 bit then 32 bit. • Graphic cards allow computers to produce colour. • The first colour cards were 2 bit which produced 4 colours [CGA]. • Next came 4 bit allowing for 16 [EGA and VGA ] colours. • Then came 16 bit allowing for 1064 colours and then 24 bit which allows for almost 17 million colours and now 32 bit and higher allow monitors to display almost a billion separate colours. • Video cards allow computers to display video and animation. Some video cards allow computers to display television as well as capture frames from video. • A video card with a digital video camera allows computers users to produce live video. A high speed connection is required for effective video transmission. • Network cards allow computers to connect together to communicate with each other. Network cards have connections for cable, thin wire or wireless networks.

13. Cables connect internal components to the Motherboard (mainboard, system board) - a board with series of electronic path ways and connections allowing the CPU to communicate with the other components of the computer such as the CPU and memory, and provides connectors for other peripherals.

14. Memory • Memory or storage capacity is one of the important components of a computer. • Any storageunit of a computer system is classified on the basis of the following criteria: • 1. Access time: This is the time required to locate and retrieve stored data from the storage unit inresponse to programme instructions. • 2. Storage capacity: It is the amount of data that can be stored in the storage unit. • 3. Cost per bit of storage.

15. Memory - one of the easiest pieces of hardware to add to a computer. It is common to confuse chip memory with disk storage. • An example of the difference between memory and storage would be the difference between a table where the actual work is done (memory) and a filing cabinet where the finished product is stored (disk). • To add a bit more confusion, the computer’s hard disk can be used as temporary memory when the programme needs more than the chips can provide. • Random Access Memory or RAM - the memory that the computer uses to temporarily store the information as it is being processed. • The more information being processed the more RAM the computer needs.

16. Units of memory • The computer stores a character in the storage cells with binary mechanism (the system only uses two digits: 0,1). • The basic unit of memory is a bit (the terms comes from an abbreviation of binary digit – 0,1). A bit is one of the eight binary digits that make up a byte. • To store a character, a computer requires 8 bits or 1 byte. This is called the word length of the storage unit. • The storage capacity of the computer is measured in the number of words it can store and is expressed in terms of bytes. The different units of measurement are:

17. Types of Memory Primary Memory ( Internal storage) Secondary Memory ( External storage) The primary memory which is faster (and hence expensive) is generally not sufficient for large storage of data. Additional memory, called the auxiliary or secondary memory is used. It is also referred as a backup storage as it stores large volume of data on a permanent basis which can be transferred to the primary memory whenever required for processing. Data are stored in secondary storage in the same binary codes as in the main (primary memory) storage. Some of the devices of secondary storages are (Floppy Disk), Hard Disk, CD-ROM, DVD and Flash drive. • Primary memory is also called internal memory and is an important part of acomputer. • It is the main area in a computer where the data is stored. • This memory can be quickly accessed by the CPU for readingor storing information. However, the storage of data and instructions inRAM is temporary, till the time the computer is running. • Primary memory is further classified into two types: 1. Random Access Memory (RAM) and 2. Read- Only Memory (ROM ) • RAM - also known as read/write memory as information can be read from and written onto it.

18. Advantages of computers • High speed:Computers have the ability to perform routine tasks at a greater speed than humanbeings. They can perform millions of calculations in seconds. • Accuracy: Computers are used to perform tasks in a way that ensures accuracy. • Storage:Computers can store large amount of information. Any item of data or any instructionstored in the memory can be retrieved by the computer at lightning speeds. • Automation:Computers can be instructed to perform complex tasks automatically (whichincreases the productivity). • Diligence:Computers can perform the same task repeatedly & with the same accuracy withoutgetting tired. • Versatility: Computers are flexible to perform both simple and complex tasks. • Cost effectiveness:Computers reduce the amount of paper work and human effort, therebyreducing costs.

19. Limitations of computers: • Computers need clear & complete instructions to perform a task accurately. • If the instructionsare not clear & complete, the computer will not produce the required result. • Computers cannot think. • Computers cannot learn by experience.