Basic components of a computer system
Computers have been and will continue to be the fastest growing part of our lives ever, a hundred years ago the idea of a peice of machinery doing complex mathamatics more efficently and faster than any human could ever do was a dream held only by the most progressive minds of the time. Now computers are everywhere, you are probably reading this document on a computer, if not some barsted has copied my work and printed it out.
Only in 1981 did the first comercial PC ever come out (My year of birth incedentaly) when IBM brought out their first "Home" PC.
Now computers are used for everything, including:
The computer system can be broken down in to two definate components: Hardware and Software
Hardware is the solid parts of the computer such as the CPU, the memory, the monitor and the keyboard. These are all parts of the computer that you can pick up and move around.
Software is the programs that run on the system making it work, the program code is usaly stored on the hard disk where it can be accessed easily, but it can also be stored on flopy disks and in the memory.
The components of a computer can be further broken down, this is outlined in the diagram below:
Basic components of a computer system
The CPU is the centeral device which performs logical opperations on the data that is input from the input device. The input device can be a keyboard, mouse, graphics tablet or one of many other input devices. When the processor gets the data from the input device, it uses the information that is stored in the main memory and the auxiliary storage device to create some kind of output, this output could be in the form of a picture on a monitor or a print out from a printer. The main memory is a short term storage device which is fast to access, but it is limited because large amounts of memory cost money. The hard disk on the other hand is a large amount of perminant storage, it can store very large amounts of data for potentialy the life of the hard drive.
Memory and Hard disk space are measured in bytes which is a collection of 8 BITS (BInary DigiTS).
| 1 kilobyte | = | 1KB | = | 1,024 bytes | ||
| 1 megabyte | = | 1MB | = | 1,024 KB | = | 1,048,576 bytes |
| 1 gigabyte | = | 1GB | = | 1,024 MB | = | 1,073,741,824 bytes |
| 1 terrabyte | = | 1TB | = | 1,024 GB | = | 1,099,511,627,776 bytes |
There are 4 basic configurations plus one slightly diffent type of computer:
Software is the name for all of the programs and code that runs on a computer to make it do what the user or the programmer wants it to do, if you are reading this on the website there are probable 5 or more different peices of software running at the moment : The web browser, dialing software, virus scanner, opperating system. All of this software is stored on your hard disk in a code that the machine can read. Of course software is not written in this code it is written in a special programming language that is then compiled to make the machine code that is on your hard drive.
There are 5 basic catagories of software
General purpose applications software is software that is used for a general purpose, for example: a word processor, a spreadsheet, desktop publishing software, graphics packages and telecomunications software. These can be used for many puropses, like the word processor could be used to write a letter, type up an essa, build a webpage, and many more. You will almost certanly use these in part of your computing course.
Special purpose applications software is software that (strangley enough) is used for a special purpose this could be with in a company doing payroll, ticket booking, storing customer details or keeping business accounts. These fucntions could be replicated with general purpose applicatios software but they are often not as reliable or not quite what the company want for their computer system.
Programming Languages are the special languages that software is written in, they are often similar to engilish but they can also be very abstract and more like machine code. Some popular programming languages are C, Basic, Pascal, Perl. They all can be compiled to run on a computer with out the sipport of the development enviroment that they were created in.
Opperating systems are the layer between the software and the hardware of the computer. They exist because modern PC's use many different types of driver which need different commands and instructions to be sent to them, rather than writing different software for each of the different types of hardware the opperating system provides standardised access to the hardware. Common opperating systems include Microsoft Windows, Unix, Linux, SUN-OS and Mac-OS, which are all written to run on a certin platform with different peices of hardware.
Utility programs are like applications software but instead of having a use they provide an interface with the hardware on the system, for example a Disk Defragmenter looks at the hard disk of the machine it is run on and re organises it so that it performs better. Other utility programs include Scandisk - for checking a disk for errors, Anti-Virus - for scanning disk drives and memory for viruses and Memory Optimizers - for re organising memory much the same way as a disk defragmenter re-organises a hard disk.
As mentioned before general purpose application software performs a task based on what the user wants it to do. There are different basic types of applications software:
Word processing packages all have common features inlucding : text formatting, find and replace, graphics, spelling and grammar check, indexes and tables of contents and mail merge. In adition most modern word processing packages allow the use of scripts to automate task and customize the software, in this way the word processing package can become extendable.
Desktop publishing packages allow the user to arange text and graphics on a page as it would be printed out, this interface called a WYSIWYG (What You See Is What You Get) interface. Desktop publishing packages are often used to design magazines and newspapers because it is easy to apply a style to the text and arange it as you would like it to appear.
Spreadsheet packages are basicly a huge grid where you can enter values of your choice, you can refrence one cell from another therefore making calculations based on the contents of other cells. Spread sheets can be used for keeping company accounts and compiling results for scintific or research work. They can also be used as databases.
Graphics software these come in two basic types, the bitmap graphics packages which create a single layered image that is comprised of single pixels (Picture elements), the other type is a vector based graphics package which is based around draw ing shapes which can be resized and changed colour independantly which means they can be changes at a later date, vector based graphics are more flexable than bitmap based graphics but subsequently are less complicated.
Integerated packages are collections of software that will often be used together for example: a word processor a spreadsheet and presentation graphics package may be put to gether to make one integrated package. Integrated packages are often more flexable bacause the components of the package can often work together to get the best of all worlds.
The interface between the computer and the user is an important part of the system, if the user is unable to use the software then the software is as good as useless
The basic types of interface are:
Menu Interfaces : Full Screen Menus are used less in modern software application because inherently they take up a larga amount of screen space, space that could be used for other purposes such as text editing. They are used more in special purpose software applications because they need a display that makes choices obvious to the opperator, they are also used in software written for child because they are easier to use.
Menu Interfaces : Pull down menus are menus that are only visable when you click an area below the title bar of the application that the menu belongs to this is the main type of menu that is found in modern software applications because it is fairly obvious to use and you can fit a large number of options in a relativly small space.
Menu Interfaces : Pop-Up menus are used primarly to give quick access to common commands for a certain area of the screen, pop-up menus are invisible untill a certain event, such as a right click of the mouse button in a space on screen
WIMP interface stand for Windows, Icons, Mouse and Pull-down menus most modern software applications are based on this conceptual model, it provides easy access to common function twinded with asthetic simplicity of windows and icons.
Forms and Dialog boxes are a conveniant way of focusing the attention of the user on the form that they are required to do something to, the form or dialog box should show a title, not be too clutterd, the fields should be in logical sequence. All of these factors contribute to an efficent form.
Command driven interfaces are interfaces that require you to type a command to perform a function such as list the contents of a directory or format a floppy disk, these interfaces are simple but still effective. They are not used very much in modern computing because they require the user to know the commands to perform different opperations, but if you know the commands it can be very powerfull.
Speach input interfaces are in their infancy at the moment, speach recognition technology is not yet good enough to perform the required opperations that a modern computer system needs. In a perfect world you would be able to control your computer by speach recognition alone.
There are three diferent hireachial levels of business orginisation
Real-time processing is when a computer has to perform task sincronously with a external system such as a peice of machinery. This type of processing needs access to the resorces it needs such as file access and memory access.
Interactive processing is requiered when mutiple users need access to a file to make queries and update information, this poses a problem because if multiple users can access a file it runs a risk of double updating a database there for corrupting the file. The way this is solved is by locking the database so when one user is accessing it another can not.
Batch processing is when the machine used for data entry is not connected to the computer used for processing, for example a Telxon is used in a supermarket to scan in individual shelf tickets where the product is out of stock, it is then downloaded at a later date where it is processed and the book stock levels are updated. There is an instance where the machine used for data entry is used to process the data, this is when processing the data will take up a large amount of processor use, so there for the data is stored on the computer till it can be used.
Because batch processing is not done on-line errors in the data will not be noticed until the processing is done this means that other methods have to be employed to make sure that the data is correct. There are two basic ways of doing this, first is to validate the data and second is to verify the data.
Validation is the checking of data to a set of pre-defined rules there are a number of validation checks that can take place, these include :
Verification is where the data is checked by a human opperator, this could be the same person who entered the data in the first place in the form of an "Are you sure?" type question, or by a second opperator, where if the data entered dose not match an error is produced.