Each character and digit in the computer corresponds to the code from 0 up to 255.

The hexadecimal system allows writing 1 byte in two digits from 00 up to FF.

One byte contains number from 0 up to 255.

The computer works with numbers in the binary system and uses only two digits 0 and 1.

The computer works only with Digital data.

Some general notes

To learn as the computer works, it is necessary to know some main concepts and rules:

To process any information with computer it is necessary to present this information in the digital form, to input it into the computer, to process, to convert to the usual format and to output from the computer. For example, if you want to process music, it is necessary to convert it to digital form and to input into the computer. After that it can be changed, supplemented or modified. And then it is necessary to convert it back to the sound form and to output from the computer. Similarly you should work with photos, video and other information.

Any number of the decimal system can be presented in binary sort. For example:

0 0000

1 0001

2 0010

3 0011

4 0100

5 0101

6 0110

7 0111

8 1000

9 1001

10 1010

11 1011

12 1100

13 1101

14 1110

15 1111

Etc.

3. Bit is an item of information, which represents number 0 or 1 (yes / no, on/off).

The binary system is used in a computer, as it is easiest for realizing technically. And it is most reliable, as has only two stable conditions ("yes" / "no" and never - " may be ").

4. The computer works with 8 bits one time, which are named as byte
(1 byte = 2⁸ bits).

0 00000000

......

255 11111111

This system is used only for compact writing of the binary system.

0 00000000 00

1 00000001 01

2 00000010 02

3 00000011 03

4 00000100 04

5 00000101 05

6 00000110 06

7 00000111 07

8 00001000 08

9 00001001 09

10 00001010 0A

11 00001011 0B

12 00001100 0C

13 00001101 0D

14 00001110 0E

15 00001111 0F

16 00010000 10

17 00010001 11

.........

255 11111111 FF

7. One kilobyte = 2¹⁰ bytes = 1024 bytes.

8. One Megabyte = 2¹⁰ kilobytes = 1024 kilobytes.

0-127 designate the international (English) coding, and 128-255 - national (Cyrillic).

There are some standards of the coding of characters ASCII, ANSI, KOI, Windows etc.

Structure of PC hardware

Personal computer includes a lot of hardware components.

The most important part of PC is the system unit.

The system unit is only house for many cards of your computer. There are:

· Power supply. This unit gives energy to all others units in PC.

· The motherboard is the most important card in PC. All others cards and units of PC are connected each other through motherboard.

· CPU (the central processing unit) is the brain of PC and set in motherboard. CPU looks like little chipset with big cooler and many gold connectors.

· The memory chipset is set in motherboard too. It is special little card for getting CPU instruction and commands. All programs, which we use, must be loading to this chipset for all time when your computer is working.

· The next important card in motherboard is Video card. It is special device for creating and sending text and images to the monitor.

· System unit as a rule has 3 kinds of drivers. Floppy driver – the device for saving little volume of information on floppy disks. HDD – the device for saving big volume information inside system unit for long time. CD-ROM – the device for using CDs. Sometime system unit has a zip-driver – the device for big volume floppy disks (about 100Mb).

· Now many PCs have Sound Blaster inside system unit. It is device for making and getting sounds and music with external speakers.

· All motherboards have many empty plugs for connecting with others devices. Such as internal modem, TV tuner, SCSI adapter, network adapter, scanner card and many others.

On the backside of system unit you can see a many different plugs for connecting your PC with others external devices. Such as monitor, keyboard, mouse, printer, modem, scanner, network and others.

Another hardware component of your computer looks like a TV. It's called a monitor.

Text and images are generated by your computer and displayed on its screen.

The monitor is very important device for user. Because the results of your job, your eyes and your health depends on quality of monitor.

There are many different monitors. When you choose the monitor you should know general characteristics of it. There are:

· Type of screen (CRT, DualScan, Active matrix, LCD, TFT and others).

· Size of screen (from 14 inch to 27 inch).

· Size of screen dot (0.20 mm, 0.24 mm, 0.28 mm, 0.31mm).

· Horizontal frequency (from 60 Hz to 160 Hz).

You communicate with your computer as a rule using one of two devices. There are keyboard and mouse.

You can type information and instructions into your computer using a keyboard, which looks like a set of typewriter keys.

Or, you can use a pointing device, such as a mouse, to select and move items that are displayed on the monitor's screen.

There are printers, modems, speakers and many others Peripherals in PC.

A printer produces a paper copy of the information displayed on your screen or contained in a document.

Laser, ink and matrix printers are used now for PC.

Laser printer is the best for modern office.

· Laser printer makes the best quality pictures. But this printer is a not cheap and printing only black/white picture. The colour laser printer now is very expensive.

· Matrix printer is the cheapest in use. But quality of its copy is not well.

· Ink printer is the best for home. This printer is not very expensive, but has a good quality. It can make a colour pictures with good quality. But inks for this printer are not cheap. That’s why, this printer is not good for big volume printing.

A modem connects your computer to the other computer or to the Internet over a telephone line. There are external or internal modems. The most important characteristic of modem is the communication speed. There are 14,4 28,8 33,6 56Kbit/sec modems. For Internet modem with 56k speed is the best, because you have to pay money for worktime in Internet. You should chose.

Audio can be heard through internal or external speakers. There are many kinds of Sound Blaster and Speakers for Computers Games and for professional work with music.

It is very comfortable to use scanner with PC. It is device for input to computer the images and pictures. If you have a special program, you can use scanner for input texts without keyboard. As a rule, scanner can input colour pictures.

Now we can use Notebooks or Pocket PC. As a rule these computers are very comfortable to use, but more expensive. It is easy to take these PC to the business tripe or when you are travelling. Notebook works with standard software and could be used as an ordinary PC. Pocket PC needs special software and can’t be connected with peripherals by cables. For linking Pocket PC with other devices you can use USB,Bluethooth or Infrared connections.

The History.

The history of development of computer science and computer equipment starts many centuries ago. As soon as man has learned to count, at once he wanted to do it faster and more correctly with special methods and tools.

However, for the first time concept of an analytical Machine has appeared only in first half of XIX century. The English mathematician Charles Babbage has offered to construct the computer with punched cards for the programs.

But the creation of the computer was not possible, because it was too difficult for engineering of that time. The first computers were created on the basis of electromagnetic relays in the 40-th years of XX century.

However, these computers worked slowly and not reliably.

In 1945 in USA the computer was created on the basis of electron tubes. It worked fast and reliably. But the input of the easy program to it took some days. Because it was need to connect many wares with each other.

Then famous mathematician Jon von Neumann in 1945 has formulated main principles of a computer work, which are used even today.

Principles of the computer work by von Neumann:

Each computer should contain the following devices:

1. Arithmetic-logic unit.

2. Control unit.

3. Storage device (memory).

4. Peripherals for input-output of the information.

All computer memory should consist of the numbered cells, which are accessible to any device of the computer.

In the beginning the peripheral loads the program and data into the memory.

The control unit reads commands from memory and fulfils them. If it is necessary, control unit can refer data for fulfil the arithmetic and logical operations into the ALU. The result of fulfil is located in memory or is output to the peripheral.

After that the control unit executes the next command from memory. The computer is working until the all commands will be fulfilled or the peripheral will give the stop command.

In 1949 the Englishman Wilks has created the first computer on a von Neumann's principle.

Even from these principles it is clear, that the power of the computer can be increased with 3 main factors:

1. The time of the execution 1 command, which depends on clock rate (frequency) of the computer.

2. Size of the RAM, which limits a size of the program and given executable to the computer.

3. Optimization of the control unit work.

The progress in all three these directions have allowed to provide huge growth of productivity of modern computers.

In further development of computers was depended on development of electronic technologies first of all.

The computer of Wilks occupied some huge halls and floors.

Such computers costed many millions dollars.

With appearance of transistors the computers of steel more reliable and are less on a size and cheaper. In 1965 the Digital Equipment corporation has built the computer by a size about a small refrigerator, which costed about 20 000 dollars.

In 1968 the first computer on integrated circuits (chips) was created. In it the whole transistor assembly and the units were fulfilled on the one silicon crystal.

In 1970 the Intel corporation has issued the first microprocessor (Intel-4004), which was looked like a small chip and had power of the processor block of a mainframe computer.

In 1973 the more powerful processor Intel-8008 has appeared.

And in 1974 the legendary processor Intel-8080 has appeared which long time was the standard for the computer industry.

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