The components of a computerThe components of a computer

Types of computerTypes of computer

MicrocomputersMicrocomputers- desktop, laptop, notebook and palmtop personal computers (PCs)- desktop, laptop, notebook and palmtop personal computers (PCs)- used in businesses, schools/colleges and homes- used in businesses, schools/colleges and homes- cost from a few hundred pounds to a few thousand - cost from a few hundred pounds to a few thousand

MinicomputersMinicomputers- often used as multi-user systems, with 100’s of workstations or - often used as multi-user systems, with 100’s of workstations or

terminals attached to a central minicomputer, e.g. EPOS. terminals attached to a central minicomputer, e.g. EPOS.- cost from £10,000 to about £150,000.- cost from £10,000 to about £150,000.

Mainframe computersMainframe computers- used by large organisations which may have 1000’s of terminals, often - used by large organisations which may have 1000’s of terminals, often

remoteremote- cost ££ hundreds of thousands- cost ££ hundreds of thousands

SupercomputersSupercomputers- largest category of computer used mostly by scientific & industrial - largest category of computer used mostly by scientific & industrial

research departments, NASA, the Weather Centre, stock exchangesresearch departments, NASA, the Weather Centre, stock exchanges- cost ££ millions- cost ££ millions

Computers can be categorised into four types

CPUCPU

Controls the transmission of data from input devices to memoryControls the transmission of data from input devices to memory

Processes the data held in main memoryProcesses the data held in main memory

Controls the transmission of information from main memory to output Controls the transmission of information from main memory to output devicesdevices

How CPUs work?How CPUs work?

A microprocessor -- also known as a CPU or central processing unit -- is a complete computation engine that is fabricated on a

single chip.

• Using its ALU (Arithmetic/Logic Unit), a microprocessor can perform mathematical operations like addition, subtraction, multiplication and division. Modern microprocessors contain complete floating point processors that can perform extremely sophisticated operations on large floating point numbers.

• A microprocessor can move data from one memory location to another.

• A microprocessor can make decisions and jump to a new set of instructions based on those decisions.

Clock SpeedClock Speed

To synchronize the steps of the fetch-decode To synchronize the steps of the fetch-decode

execute cycle, all processors have an internal execute cycle, all processors have an internal

clock which generates regularly timed pulses. clock which generates regularly timed pulses.

All activities of the fetch-decode-execute All activities of the fetch-decode-execute

Cycle must begin on a clock pulse.Cycle must begin on a clock pulse.

Word SizeWord Size

The number of bits that the CPU can The number of bits that the CPU can process simultaneously. Normally groups process simultaneously. Normally groups of 8, 16, 32, 64, 128 bit words are processed of 8, 16, 32, 64, 128 bit words are processed as a unit during input, output and logic as a unit during input, output and logic instructions.instructions.

Word size is a major factor in determining Word size is a major factor in determining the speed of a processor.the speed of a processor.

Bus SizeBus Size

Buses are the lines along which data is Buses are the lines along which data is transmitted. This data can be in the form of transmitted. This data can be in the form of data and instructions as well the addresses data and instructions as well the addresses of the data and the instructions.of the data and the instructions.

The width of a data bus determines how The width of a data bus determines how many bits can be transmitted many bits can be transmitted simultaneously and the maximum address simultaneously and the maximum address which can be referenced.which can be referenced.

Bus Size con’tBus Size con’t

For 8 bits 2For 8 bits 28 8 – 1 = 255 – 1 = 255 i.e. 0 to 255 which is 256 locations.i.e. 0 to 255 which is 256 locations.

An An address busaddress bus (that may be 8, 16 or 32 bits wide) that (that may be 8, 16 or 32 bits wide) that sends an address to memory sends an address to memory

A A data busdata bus (that may be 8, 16 or 32 bits wide) that can (that may be 8, 16 or 32 bits wide) that can send data to memory or receive data from memory send data to memory or receive data from memory

An An RDRD (read) and (read) and WRWR (write) line to tell the memory (write) line to tell the memory whether it wants to set or get the addressed location whether it wants to set or get the addressed location

A A clock lineclock line that lets a clock pulse sequence the processor that lets a clock pulse sequence the processor

A A reset linereset line that resets the program counter to zero (or that resets the program counter to zero (or whatever) and restarts execution whatever) and restarts execution

Instruction SetInstruction Set

Instructions in machine language are in the Instructions in machine language are in the form of binary codes, with each different form of binary codes, with each different processor using different codes for the processor using different codes for the instruction set supported by its hardware. instruction set supported by its hardware.

The instruction set for a typical computer The instruction set for a typical computer

includes the following types of instructions:includes the following types of instructions: Data TransferData Transfer Arithmetic OperationsArithmetic Operations Logical OperationsLogical Operations Test and Branch InstructionsTest and Branch Instructions

Main memoryMain memory

Instructions and data are held in main memory, which is divided into Instructions and data are held in main memory, which is divided into millions of individually-addressable storage units called millions of individually-addressable storage units called bytesbytes. .

One byte can hold one character, or it can be used to hold a code One byte can hold one character, or it can be used to hold a code representing, for example, a tiny part of a picture, a sound, or part of a representing, for example, a tiny part of a picture, a sound, or part of a computer program instruction. computer program instruction.

The total number of bytes in main memory is referred to as the The total number of bytes in main memory is referred to as the computer’s computer’s memory sizememory size. Computer memory sizes are measured as . Computer memory sizes are measured as follows:follows:

1 Kilobyte (Kb)1 Kilobyte (Kb) == 1000 bytes (to be exact, 1024 bytes)1000 bytes (to be exact, 1024 bytes)1 Megabyte (Mb)1 Megabyte (Mb) == 1,000,000 (1 million) bytes1,000,000 (1 million) bytes1 Gigabyte (Gb)1 Gigabyte (Gb) == 1,000,000,000 (1 billion) bytes1,000,000,000 (1 billion) bytes1 Terabyte (Tb)1 Terabyte (Tb) == 1,000,000,000,000 (1 trillion) bytes1,000,000,000,000 (1 trillion) bytes

Random Access Memory (RAM) Random Access Memory (RAM)

‘‘Ordinary’ memoryOrdinary’ memory

Used for storing programs which are currently running and data which is Used for storing programs which are currently running and data which is being processed. being processed.

This type of memory is This type of memory is volatilevolatile - it loses all its contents as soon as the - it loses all its contents as soon as the machine is switched off. machine is switched off.

Read Only Memory (ROM)Read Only Memory (ROM)

Non-volatile, with contents permanently etched into the memory chip at Non-volatile, with contents permanently etched into the memory chip at the manufacturing stagethe manufacturing stage

Used for example to hold the Used for example to hold the bootstrap loaderbootstrap loader, the program which runs , the program which runs as soon as the computer is switched on and instructs it to load the as soon as the computer is switched on and instructs it to load the operating system from disk into memory. operating system from disk into memory.

PROMPROM

Short for Short for pprogrammable rogrammable rread-ead-oonly nly mmemory,emory, a a memory chip on which on which data can be written only can be written only once. Once a once. Once a program has been written onto a has been written onto a PROM, it remains there forever. Unlike PROM, it remains there forever. Unlike RAM, , PROMs retain their contents when the PROMs retain their contents when the computer is is turned off. The difference between a PROM and a turned off. The difference between a PROM and a ROM ( (rread-ead-oonly nly mmemory) is that a PROM is emory) is that a PROM is manufactured as blank memory, whereas a ROM manufactured as blank memory, whereas a ROM is programmed during the manufacturing process. is programmed during the manufacturing process.

To To write data onto a PROM chip, you need a data onto a PROM chip, you need a special special device called a called a PROM PROM programmer or or PROM burner. The process of programming a PROM burner. The process of programming a PROM is sometimes called burning the PROM. PROM is sometimes called burning the PROM.

An An EPROM (erasable programmable read-only (erasable programmable read-only memory) is a special type of PROM that can be memory) is a special type of PROM that can be erased by exposing it to ultraviolet light. Once it is erased by exposing it to ultraviolet light. Once it is erased, it can be reprogrammed. An erased, it can be reprogrammed. An EEPROM is is similar to a PROM, but requires only electricity to similar to a PROM, but requires only electricity to be erased. be erased.

What is an EPROM?What is an EPROM? EPROM(Erasable Programmable Read EPROM(Erasable Programmable Read

Only Memory) can be programmed and Only Memory) can be programmed and erased enabling them to be re-used. erased enabling them to be re-used. Erasure is accomplished using an UV Erasure is accomplished using an UV (Ultra Violet) light source that shines (Ultra Violet) light source that shines through a quartz through a quartz erasingerasing windowwindow in the in the EPROM package.EPROM package.

Acronym for Acronym for eerasable rasable pprogrammable rogrammable rread-ead-oonly nly mmemoryemory, and , and pronounced pronounced ee-prom,ee-prom, EPROM is a special type of EPROM is a special type of memory that that retains its contents until it is exposed to ultraviolet light. The retains its contents until it is exposed to ultraviolet light. The ultraviolet light ultraviolet light clears its contents, making it possible to its contents, making it possible to reprogram the memory. To reprogram the memory. To write to and erase an EPROM, you to and erase an EPROM, you need a special need a special device called a called a PROM programmer or PROM or PROM burner. burner.

An EPROM differs from a PROM in that a PROM can be An EPROM differs from a PROM in that a PROM can be written to only once and cannot be erased. EPROMs are used written to only once and cannot be erased. EPROMs are used widely in widely in personal computers because they enable the because they enable the manufacturer to change the contents of the PROM before the manufacturer to change the contents of the PROM before the computer is actually shipped. This means that is actually shipped. This means that bugs can be can be removed and new versions installed shortly before delivery. removed and new versions installed shortly before delivery.

What is an EEPROM?What is an EEPROM?Pronounced Pronounced double-ee-promdouble-ee-prom or or e-e-prom,e-e-prom, short short for for electrically erasable programmable read-electrically erasable programmable read-only memoryonly memory. EEPROM is a special type of . EEPROM is a special type of PROM that can be erased by exposing it to an that can be erased by exposing it to an electrical charge. Like other types of PROM, electrical charge. Like other types of PROM, EEPROM retains its contents even when the EEPROM retains its contents even when the power is turned off. Also like other types of power is turned off. Also like other types of ROM, EEPROM is not as fast as , EEPROM is not as fast as RAM. EEPROM . EEPROM is similar to is similar to flash memory (sometimes called (sometimes called flash EEPROMflash EEPROM). The principal difference is that ). The principal difference is that EEPROM requires data to be written or erased EEPROM requires data to be written or erased one one byte at a time whereas flash memory allows at a time whereas flash memory allows data to be written or erased in data to be written or erased in blocks. This . This makes flash memory faster. makes flash memory faster.

What is a Flash EPROM?What is a Flash EPROM? AA flash flash EPROM is similar to an EEPROM EPROM is similar to an EEPROM

except that flash EPROMs are erased all at except that flash EPROMs are erased all at once while a regular EEROMs can erase one once while a regular EEROMs can erase one byte at a time. byte at a time. In- circuitIn- circuit writing and erasing is writing and erasing is possible because no special voltages are possible because no special voltages are required. To accomplish in-circuit operation, required. To accomplish in-circuit operation, you have to write special application software you have to write special application software routines. Flash EPROMs are also called routines. Flash EPROMs are also called nonvolatile memorynonvolatile memory....

Cache MemoryCache Memory

Very fast memory used to improve the speed of a computer, Very fast memory used to improve the speed of a computer, doubling it in some cases doubling it in some cases

Acts as an intermediate store between the CPU and main Acts as an intermediate store between the CPU and main memorymemory

Stores the most frequently or recently used instructions and Stores the most frequently or recently used instructions and data for rapid retrieval data for rapid retrieval

Generally between 1Kb and 512KbGenerally between 1Kb and 512Kb

Much more expensive than normal RAMMuch more expensive than normal RAM

Memory Cache speeds up a computer by storing data the computer has recently used. There are 2 types :

Internal & External

External Cache

If the computer cannot find what it needs in the Internal Cache, it looks in the external cache. This is usually located on the Motherboard. In some CPU chips the External cache is built in.

Internal Cache

When the computer needs data it first looks in the Internal cache. This is located on the CPU chip and provides the fastest way for the computer to get data.

Space on a hard disk used to temporarily store data and swap it in and out of RAM as needed.

Virtual memory

Motherboard

This is the main circuit board that all of the other internal components connect to.

The CPU and memory are usually on the motherboard. Other systems may be found directly

on the motherboard or connected to it through a secondary connection.

For example, a sound card can be built into the motherboard or connected through PCI (Peripheral

Component Interface).

Auxiliary StorageAuxiliary Storage

Hard disksHard disks- - all standalone PCs have in-built hard diskall standalone PCs have in-built hard disk- typical capacity for Pentium PC is >= 40 Gb - typical capacity for Pentium PC is >= 40 Gb - used for storing software including the operating system, - used for storing software including the operating system,

other systems software, application programs and dataother systems software, application programs and data Floppy disks Floppy disks - thin sheet of mylar plastic in hard 3½” casing - thin sheet of mylar plastic in hard 3½” casing

- capacity 1.44Mb- capacity 1.44Mb CD-ROM CD-ROM - holds about 700Mb- holds about 700Mb Zip disks Zip disks

- hold up to 250Mb - hold up to 250Mb

Power supply

An electrical transformer regulates the electricity used by the computer.

Hard disk

This is large-capacity permanent storage used to hold information such as programs and documents.

Operating system

This is the basic software that allows the user to interface with the computer.

Integrated Drive Electronics (IDE) Controller

This is the primary interface for the hard drive, CD-ROM and floppy disk drive.

Peripheral Component Interconnect (PCI) Bus

The most common way to connect additional components to the computer, PCI uses a series of slots on the motherboard that PCI cards plug into.

SCSI

Pronounced "scuzzy," the small computer system interface is a method of adding additional devices, such as hard drives or scanners, to the computer.

Graphics card - This translates image data from the computer into a format that can be displayed by the monitor.

Sound card

This is used by the computer to record and play audio by converting analog sound into digital information and back again.

AGP

Accelerated Graphics Port is a very high-speed connection used by the graphics card to interface with the computer.

                             

                                                                                                 

                                                                                               

                               

Parallel Port

Serial PortsUSB Ports

SERIAL PORTConsidered to be one of the most basic external connections to a computer, the serial port has been an integral part of most computers for more than 20 years. Although many of the newer systems have done away with the serial port completely in favor of USB connections, most modems still use the serial port, as do some printers, PDAs and digital cameras. Few computers have more than two serial ports.

If you have a printer connected to your computer, there is a good chance that it uses the parallel port. While USB is becoming increasingly popular, the parallel port is still a commonly used interface for printers. Parallel ports can be used to connect a host of popular computer peripherals:

• Printers

• Scanners

• CD burners

• External hard drives

• Iomega Zip removable drives

• Network adapters

• Tape backup drives

Parallel Ports

The goal of USB is to end all of these headaches. The Universal Serial Bus gives you a single, standardized, easy-to-use way to connect up to 127 devices to a computer.

Just about every peripheral made now comes in a USB version. A sample list of USB devices that you can buy today includes:

Printers Scanners Mice Joysticks Flight yokes

Digital cameras Webcams Scientific data acquisition devices

Modems Speakers Telephones Video phones

Storage devices such as Zip drives Network connections

Connecting a USB device to a computer is simple -- you find the USB connector on the back of your machine and plug the USB connector into it.

Universal Serial Bus (USB) Ports

The rectangular socket is a typical USB socket on the back of a PC.

A typical USB connector, called an "A" connection

A typical "B" connection

Input and output devicesInput and output devices

Input devicesInput devices

- - KeyboardKeyboard- mouse- mouse- barcode readers - barcode readers - Scanners- Scanners

Output devicesOutput devices

- printer- printer- plotter- plotter- VDU- VDU

Can you name some others?Can you name some others?