Notes on Section: Background
Aims
- background knowledge - enabling understanding and appreciation of material.
- knowledge of various components of typical computer and their functions.
- leading to how personal computers developed.
Hardware = case and contents (hard drive, processor, motherboard, graphics card, soundcard, modem, network card etc) - physical parts of computer.
Peripherals = monitor, printer, keyboard, scanner, speakers etc.
Software = programs and applications.
Software can be written in a variety of programming languages.
Programming language>expresses instructions>computer responds.
Three Basic Types of Software
1/. Operating Systems.
- act as foundation upon which programs and applications can run.
- first thing visible after switching on computer..
- allows you to tell computer what you want it to do.
- examples include Windows, MS-DOS, Unix, Linux, BeOs, Mac OS.
2/. Languages.
- used by developers to write new software programs.
- examples include Basic, C, Assembler, Pascal, C++, Visual Basic and Java.
3/. Applications.
- allow user to perform activities on computer.
- applications are programs written for specific purpose.
- examples include word processors (MS Word), spreadsheets (Excel), databases (Access), graphics packages (Photoshop & Corel Draw) etc.
How a computer represents information.
- lowest level - turns on or off millions of tiny switches called transistors.
- transistors can only be in one of two states - ON or OFF.
- example - light switch - either ON or OFF.
- states of ON or OFF represented by numbers 1 and 0.
In Mathematics - number system with only two digits referred to as BINARY
In Mathematics - number system with ten digits (0-9) is called denary.
The BINARY system is the smallest number system that can be used to provide information.
It is useful to think of BINARY in terms of columns (eg. 64, 32, 16, 8, 4, 2, 1)
- computer functions by manipulating 1s and 0s.
- possible to represent any letter of alphabet or any character by assigning a binary code to it.
- International Alphabet Number 5 (IA-5) - agreed representation of text.
- computer knows what to do with data because it has instructions from program (operating system or application).
- program instructions themselves are binary representations.
Difference between DATA and INSTRUCTIONS
- DATA is the current information the computer program is working with (numbers, text etc).
- INSTRUCTIONS are what the computer does with the data (eg clicking on 'save' button will always save data).
BIT-MAPPING
- Images can be represented using a technique called 'bit-mapping'.
- divides an image up into thousands of cells.
- allocates a value to each cell.
- if image in black and white, each cell will have a value of 1 (black) or 0 (white).
- colour can be represented by allocating more information to each cell.
- this information indicates the proportion of red, green and blue values (RGB).
- wide spectrum of colours available by varying relative values of RGB.
SOUND
- sound can also be represented in binary.
- sound (like images) can be divided up into different segments.
- each segment allocated an appropriate binary value.
- sound can be reproduced from binary code.
SUB SECTION:-
ANALOGUE AND DIGITAL
- ANALOGUE - analogous or parallel - an analogous object or signal is one which is similar to the original in its form.
- uses physical variables which include length, weight, and voltage.
- these are all natural variables which can be found in the natural world.
- an analogue signal can take any value within a specified range.
- DIGITAL - using digits (numbers 0-9).
- computers operate on data in a binary form - which is digital i.e. 1s and 0s.
- digital used to refer to anything that handles data in digital form i.e. clock, TV etc.
- a digital signal is restricted to set values - called 'discrete' values since each must be distinct from the other with no overlap.
Analogue to digital conversion.
- digital computers need system to reproduce analogue signals like sounds and pictures.
- system called 'analogue to digital conversion'.
- enables computer to divide analogue signals into digital codes for accurate representation.
Benefits of digital devices:-
1/. Reliability.
- difficulty in reproducing an analogue signal
- it can have any value within specified range
- how to you know you have reproduced correct signal?
- digital signal can only have a set value
- much easier to reproduce exactly.
- transmitting analogue signals through telephone network - results in degradation of signal.
- signal is boosted or amplified - incorrect or corrupted values in signal also amplified.
- transmitting digital signals through telephone network - signal suffers no degradation.
- signal is regenerated so result is faithful copy of original because of use of discrete values.
2/. Manipulation.
- digital systems have become more popular.
- related to increase in speed and power of microprocessors and falling prices.
- microprocessors deal quickly and reliably with binary data.
- ability to use microprocessors in small devices like cameras etc.
- analogue signals - text, images, sounds - manipulated easily as binary data by a microprocessor.
- ease of manipulation very important and powerful.
- makes working with digital systems very attractive.
Bits and Bytes
- 1s and 0s = binary digits - bits for short.
- 'bits' too small for practical use - groups of 8 bits are called a byte.
- 'byte' is basic unit or 'building block' used by computer - often used in groups of bytes.
- due to eight bits in a byte - eight and its multiples are very important in computing.
- numbers 8, 16, 32 and 64 appear a lot in varying contexts in computing due to properties of 'bytes'.
KEY POINT:-
- basing your entire system on only two digits may seem limiting
- but these two digits can be used to represent almost anything.
KILOBYTE:- 2 to the power of 10 bytes - actually 1024 bytes - close enough to be given prefix 'kilo' (thousand).
MEGABYTE:- 2 to the power of 20 (or 1 Kb squared) - actually 1,048,576 bytes - close enough to be given prefix 'mega' (million).
GIGABYTE:- 1000 (a thousand) megabytes.
Manipulating Data.
- people don't naturally work in binary - manipulating 1s and 0s.
- more productive means of controlling computer's actions is required.
- development of programming languages.
- first language known as Assembler - operates a quite a low level in computer.
- takes commands - converts them to binary which computer can interpret as actions.
- Assembler tells computer where to move data and what to do with it.
- newer programming languages operate at higher level than Assembler.
- their development has made task of programming much simpler.
A 'chunk'of information is called a WORD.
- 'words' can be eight bits (a byte), 16 bits, 32 bits and, soon, 64 bits.
- 'words' are basic unit of information manipulated by computer when performing an action.
The components of a computer.
Microprocessor:-
- key to personal computer is silicon chip called microprocessor.
- microprocessor is 'brains' of computer and carries out most of computing.
- mainframes had different circuit board for each function.
- core of mainframe - three separate units linked to form Central Processing Unit (CPU)
1/. Arithmetic and Logic Unit (ALU) - unit does actual work - 4 basic maths functions plus comparison capabilities.
2/. Control Unit - controls flow of data from memory into ALU and other devices.
3/. Memory.
- Microprocessor combines ALU and Control Unit on one silicon chip (sometimes called 'computer on a chip').
- memory is separate to microprocessors in microcomputers.
- other microprocessors control graphics card, modem and other devices.
- CPU microprocessor housed on circuit board called 'motherboard'.
- motherboard also has clock chip - acts as metronome to synchronise actions of computer.
- ROM chips (Read Only Memory) important programs (BIOS) supplied with computer - needed for its basic functions - cannot be altered.
Input-Output Devices:-
- devices used to enter data into computer and for computer to output data.
- called input/output devices or I/O DEVICES
- examples - keyboard and mouse for input.
- examples -monitor and printer for output.
- data for devices sometime passes through slot-in circuit board (a card) which plugs into slot in motherboard.
- a card performs functions such as converting data to form usable by that particular device.
RAM (Random Access Memory):-
CPU also sends and receives data via RAM - computer's memory - (Random Access Memory).
- RAM consists of chips similar in construction to CPU.
- memory stores all data computer is currently using together with programs it needs to work with this data.
- limit to amount of data RAM can hold - contents are usually lost when computer is switched off.
Data Storage Devices:
- microprocessor needs to read from and write to a permanent data storage device.
- usually a hard disk drive.
- other permanent data storage devices are CD-ROM (these disks cannot be written to).
- optical disks, tape storage, zip disks, CD-R and CD-RW, and floppy disks (all of these can be read-only or re-writeable except CD-R which can only be written to once.)
Buses:-
- microprocessor connected to cables - referred to as 'buses' from Latin 'omnibus' meaning 'for all'.
- microprocessor uses 'buses' to receive and send data to storage and other devices.
The power of computers lies in the speed with which they perform the switching of transistors and their reliability in doing it. Computers typically operate millions of switches each second.
The power of a computer is combination of two factors:-
- the complexity of the tasks it can perform at any one time.
- the speed with which it can do them.
Factors influencing rate and complexity:-
1/. Microprocessor used for the CPU.
- successive generations of chips have more and more transistors placed on them.
- more transistors = chips can be programmed to perform more tasks = increase in complexity.
- more complex tasks would have required another circuit board in previous computers.
- now performed by additional transistors on microprocessor.
Additional benefits from development of microprocessor chips:-
- increased number of transistors on chip makes possible new methods of improving memory usage and speed of performance - leads to improvements in successive generations of microprocessors.
- Intel's 80286 microprocessor chip allowed computer to use method called 'virtual memory'.
- means computer could utilise section of hard disk as if it were RAM.
- computer able to act as if it had more memory than was physically present on the motherboard.
- Intel's later 80486 microprocessor chip - maths co-processor built into chip.
- maths co-processor - chip dedicated to doing complex maths.
- complex maths (floating point numbers) difficult for computer to perform.
- previously required separate chip and special software.
2/. Clock speed.
- each action of CPU occupies one cycle (although most modern CPUs can perform several tasks in the same cycle).
- greater number of cycles per second = faster computer.
- 1 million megaherz (Mhz) means one million cycles per second.
- first computers were about 4Mhz - latest ones are in excess of 1000 Mhz.
3/. Size of 'words' used by microprocessor and buses.
- computers sometimes referred to as '32 bit' or '64 bit' machines.
- means size of the 'words' that the microprocessor and buses can manipulate.
- larger the word - more information it can contain.
- 32 bit word can contain twice the data of a 16 bit word. (64 bit word twice that of 32 bit word).
Benefits of increasing size of word
- improves complexity (more data can be manipulated)
- improves speed (same time to interpret each word)
- sometimes 32 bit processor is hamstrung by 16 bit buses which slows down data processing.
- RAM acts as the computer's working memory.
- it contains information needed for current session.
- various operating system commands.
- programs currently running.
- current display configurations.
- data being used.
- increase in amount of RAM = increase in amount of data it can store at any one time.
- improves complexity of computer - able to run programs involving lots of data handling.
- enables computer to run several programs simultaneously.
- increases speed of computer because it avoids swapping data to and from virtual memory.
Result:-
- ability to run more complex programs (detailed graphics, simulation software with complex maths functions)
- programs work much faster.
- multitasking with more programs open simultaneously.
Mainframes
- dominant form of computing before microcomputers.
uses:-
- used by large companies, public authorities, universities - data handling tasks.
1/. File maintenance
- maintaining records
- need to be accessed by different people in real-time
- updated with batches of data
- necessary to have data stored centrally
- accessible to those who need data.
- examples -sales, credit card status, payroll details, social security details, health records, stock inventory etc.
2/. Simulations
- physical and engineering problems require complex computer simulations to enable solving.
- require intensive mathematical work.
- use mainframe's computational power.
- examples - weather forecasting, accurate calculations of positions of astronomical bodies.
- many minicomputers or workstations now used for this type of problem.
3/. General purpose
- many universities use mainframe as general purpose computing facility.
- users can be given own space on mainframe to store files.
- different departments can use resources to perform department-specific tasks.
- examples - predicting bird populations (Biology Dept), calculating metal stress (Engineering Dept).
- general growth in mainframes has slowed - now in decline.
- smaller computers have become more powerful.
- mainframes still required by many institutions to perform large data handling tasks.
- central mainframe computer holds data centrally for many different people to access.
Minicomputers
- powerful, special-purpose computers.
- originally viewed as small mainframes.
- developed increasing power.
- replaced mainframes for many functions.
- typically cost hundreds of thousands of pounds.
uses:-
1/. Plant Control.
- industrial plants require central computing facility.
- data is collected from various sensors.
- appropriate actions are taken on data input - example - pressure or temperature regulation.
2/. Network Control.
- central computer provides storage space for programs.
- controls network of computers using special network software.
- central network computer called 'server'.
- computers that access 'server' are called 'clients'.
- server computers can also act as interface to Internet - accepting messages, hosting email and web facilities.
- powerful PCs can also be used to perform these functions.
3/. Databases:
- minicomputers can hold central databases of records which appropriate people can access.
- increasingly taking this maintenance role over from mainframes.
Changing roles of computers:-
- most heavy duty computing is now performed by minicomputers.
- growth of networking has brought increase in role of minicomputers.
- large software companies provide specialist software for client-server computing.
- examples - Novell who provide networking software, Oracle who supply database software.
Workstations
- powerful computers based on specialised microprocessors.
- can be thought of as powerful PCs for specialist tasks.
- use a special type of microprocessor called a R.I.S.C. chip.
- R.I.S.C. = Reduced Instruction Set Computing.
- technology (developed at IBM) removes many complex instructions from microprocessor.
- result is a set of basic instructions which perform tasks very quickly.
- increases speed and power of microprocessor particularly in numerical problems.
- workstation market dominated by SUN microsystems.
- typically cost between tens and hundreds or thousands of pounds.
- typically part of a networking system.
uses:-
1/. C.A.D. (Computer Aided Design) and C.A.M. (Computer Aided Manufacturing).
- growth industries since the mid 1980s.
- allow engineers to design complex machine parts without producing an actual physical model.
- complex 3D graphics require a lot of computing power and good quality video capabilities.
2/. Animation.
- similar to CAD/CAM.
- animation requires a lot of processing power.
- lots of complex calculations need to be performed quickly.
- ideally suited to RISC technology.
3/. Simulations.
- simulations of processes require considerable computing power.
- example - behaviour of an industrial plant.
4/. Multitask programming.
- any complex programming deemed to require more power than offered by a PC.
- requirement to perform several tasks simultaneously.
Personal Computers
- range of microprocessor-based computers.
- used by individuals - hence 'personal computer'.
- initially stand-alone machines.
- increasingly connected to a network.
- ideal for tasks requiring individual computing power.
uses:-
1/. Word processing - production of complex and attractive documents using word-processing software like MS Word.
2/. Spreadsheets - creation of mathematical models particularly for use in financial planning.
3/. Desktop Publishing - creation of profession-quality graphic design work - examples - magazine layouts, posters, book covers, newsletters etc.
4/. Games - led to increased computing power, good quality graphics and complex gameplay abilities in personal computers.
5/. Accessing the internet - enabling email, website creation, web browsing.
6/. Servers - many powerful PCs used as servers to control network of client computers.
Results:-
- tasks once performed by mainframes have been taken over by minicomputers.
- development of networking has provided increased role for minicomputers as servers.
- Personal Computers - new type of individual computer usage
- activities once performed by hand - now carried out on computer.
- increase in power of PCs - now used for tasks reserved for minicomputers and even mainframes in the past.