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Юриспунденкция

Moor’s law

For thirty years, the speed of processor clocks have approximately doubled every 18 month and we can expect this trend to continue for the next decade until physical limits are reached.

Processors have registers. Each of them may hold a computer word. The registers operate at the speed of the processor.
It means that in each clock cycle a register may be read or written. However the processor operates much faster than the main memory. In order to prevent the processor being slowed down by reading or writing from the main memory, the cache is inserted between main memory and processor. Whenever the processor issues a request for a memory location, the cache loads a sequence of words containing this location from the main memory and holds it locally for further use. The cache operates at processor speed. When the cache becomes full, it writes words (line), which have not been used for a long time back into main memory.

Cache and main memory are coupled by the system bus, a communication unit which combines multiple system devices.

The program executed by the processor is stored in the main memory. It consists of a sequence of machine instructions each of which is encoded in a computer word.

The program counter is a special processor register, which holds the address of the next instruction to be executed.

The operation of the processor is a continuous cycle of the following steps coordinated by the control unit:

· fetch the instruction referenced by the program counter from the main memory;

· decode the instruction and increment the program counter to reference the next instruction in sequence;

· execute the instruction.

This operation principle is called the von Neumann architectureafter John von Neumann who invented the concept in 1945.

CPUs come in different types and speeds. Intel, Cyrix, and AMD are the three main manufacturers of CPUs. Intel is the market leader, and will probably stay that way for quite some time. The Cyrix and AMD offerings are usually comparable to the latest Intel CPUs, however, performance is usually slightly below that of Intel. It is recommended buying one step behind the latest technology. It is here that you find the best value for your money. The newest technology is always the most expensive, and when a new chip comes out, the previous model always drops in price. It’s advisable not to buy anything more than two steps behind the latest technology. Technology changes quickly, and you don’t want to buy a computer that will become outdated too quickly.

CPU types

It is absolutely beyond one’s reach to give specific information regarding CPUs because this information has a tendency to get outdated within a few months. It means that if we give you an appropriate advice now, when making this book, it might have been «old fashioned» by the time the book will be issued. Hence, the general advice given above is more timeless.

Processor speed is indicated after the brand of the chip. For example a Pentium II 400 runs at 400 MHz. MHz stands for Megahertz, which put simply, is how fast the computer runs. The higher the MHz, the faster the computer. There are many speeds available: Pentium III, Pentium IV and so on.

New, faster processors are always in development, and as faster processors become available many of the slower processors are phased out.

Which processor is best

A basic rule of thumb is to buy as good processor as you can afford. If you can afford a CPU with the newest technology, then by all means, buy that. The processor is the hardest and most expensive part of a computer to upgrade. Most of the other components can be easily upgraded. This means that the most important decision in buying a computer is choosing the processor.
Of course, you may not need the fastest processor available. If the only thing you are using your computer for is typing school papers, then even the simplest processor will do just fine. If you are going to use it for playing multimedia games, designing graphics, or running multiple applications, then you should get at least Pentium IV. As stated previously, the best value is usually one level behind the newest technology.

RAM (Memory)

RAM, Random Access Memory, is commonly referred to as memory. Memory is measured in Megabytes, abbreviated MB. This is the second most important decision for your PC purchase. RAM is used by the computer as a temporary storage area for the things it is using. Any data that you are using or inputting is temporarily stored in the RAM, where it can be manipulated and used by the computer. The more RAM you have, the faster the computer can perform tasks. RAM is easily upgradeable.

Bus speed

It’s worth to remember the faster the bus, the faster the CPU can communicate with other parts of the computer.

Cache

Cache is another type of memory, which is similar to RAM. Cache is used by the computer to move data between the RAM and the CPU faster. Hence, the faster the cache, the better.

Motherboard

The motherboard is the circuit board which everything in the computer plugs into. The CPU, RAM chips, and cache all plug into the motherboard. Three main considerations in a mother board are – bus type, number of expansion slots, and number of RAM slots. Expansion slots are used for holding cards, such as video cards or sound cards. RAM slots are where the RAM chips plug into. With both types of slots more is better. The more slots you have, the more room you have for expansion.

Case

One of the smaller and easier choices in your computer system is the type of case to get. The two types of cases available are the tower and the desktop. A desktop case fits nicely underneath the monitor. The tower case can be put on the floor to clear up some room on your desk. Tower cases usually have an extra disk drive bay, but unless you are planning on adding several more drives, this is not a big concern. Basically, it is just a matter of preference.

Disc drives

Hard drive

The hard drive is where the most of programs are stored. The hard drive is inside the computer. Hard drives come in many different sizes, up to 60 gigabytes and more. The more programs you have, the more disc space you need. It’s especially essential for multimedia programs. Once again, more is better.

Floppy disc drive

It’s a standard device and every computer comes with
a floppy disc drive. They are the usual way of putting information on to the hard drive. They also allow you to save information on a disc, which is an easy way to transport files and data between different computers. A 3.5’’ disc can hold 1.44 megabytes of data.

CD ROM drive

Most computers now come standard with a CD ROM drive. All the programs come on CD because they can hold over
500 megabytes of data on a single disk. A CD ROM drive reads data from a CD. The CD ROM drives come in several different speeds. If the speed is low the video and sound are more likely to be a bit jumpy. The faster a CD ROM can read a CD the smoother the video and sound becomes. Hence, faster is better. CD writers are also available now. CD writers allow you to write information to a CD. Once written, these CDs can be read by any CD ROM drive.

Another very important product to note is a CD rewritable (CD RW). It is a CD drive that can read and write to a CD. It can be used as a floppy disc but its memory is much more larger, up to 700 megabytes.

DVD drive

The latest in mass storage is the DVD drive. DVD stands for digital video disk. A dual layer, dual sided version of this disk can hold up to 17 gigabytes. Since this technology is relatively new these devices are quite expensive. Nevertheless DVD will soon replace the CD.

There are several types of high capacity devices which are not very wide spread, e.g.:

Tape Backup drive is mainly used for backing up all of the files on your hard drive. They can hold a lot of information, but they are not much good for anything except backing up files. The reason for this is that it is slow to access data from a tape. It is very useful if you have important files that need to be saved in case your computer crashes. Most computer systems do not come with tape drives because most people don’t have a large amount of data that needs to be backed up.

Zip Drive is removable storage similar to a floppy drive. A Zip disk can hold about 100 and much more megabytes of data. It is faster than the ordinary floppy drive but slower than a hard drive. This is a good alternative to the tape backup if you do not have a lot of files to back up. A zip disk can hold an entire program, yet it is not much bigger than a floppy disk.

Input devices

Input devices are parts of the computer that let you input information and data into the computer. The keyboard, mouse, joystick, scanner, and camera are examples of input devices. Disc drives and modem can also be used as input devices.

Keyboard

Using the keyboard is the primary way of inputting data into many of computer programs. Keyboards are usually described by the number of keys they have. Picking a keyboard is just a matter of preference.

Mouse

A mouse can have two or three buttons. A two-button mouse is usually a standard. It can accomplish any task. It’s possible to get three-button mouse. The software that comes with it allows to program the middle button to do certain tasks e.g.
to use it as a double click. Pushing the middle button once is more convenient than to double click another button.

Alternative to this mouse is a mouse without ball and cable,
the optical radio wireless mouse. As it has no ball there is no need to clean it. The absence of mechanical parts means longer life span of the mouse. It has 5 programmable buttons; it makes navigation on the Internet easier. Of course, it’s up to you, which mouse to buy.

Joystick

The joystick is essential for all the computer games.

Scanner is useful for copying written page or picture directly into the computer. Scanner is more useful for business. It comes in black and white or color. There are three types of scanners: hand scanners, page scanners and flatbed scanners. A hand scanner is dragged across the page being scanned. A page scanner feeds paper through it similar to a printer, but instead of printing, it scans in whatever is on the paper. A flatbed scanner looks and works like a copy machine. It is more common and wide spread.

Output devices

Output devices are the parts of computer that let you see what you are doing. The main types of output devices are monitor, video card, printer, sound card and modem.

Monitor

Several sizes of monitor are available; more common are
17-19 inch monitors. Which size to choose depends on your own preference. Be sure your monitor displays not less than 256 colors. One other thing to look for is the dot pitch.

Basically the dot pitch describes how sharp the picture will be. The lower the number of the dot pitch, the sharper the image will be.

Liquid crystal displays (LCD) of different size are also available but they are more expensive.

Video cardis the part of the computer that sends the images to the monitor. Video cards usually contain their own memory chips. This memory helps the computer to load images fast. Hence, the more memory contains video card the better.

Printer allows to make hard copies of documents. There are basically three different kinds of printers available: dot matrix, ink jet or bubble jet, and laser printer.

The dot matrix printer consists of a head with a row of pins that strikes the ribbon as it moves across the page. A dot matrix printer cannot give you the same high quality as that of an ink jet or a laser printer, but they are still popular because of their low cost.

Ink jet printers are the next step up. They squirt little droplets of ink onto the paper. The ink dries almost instantly and the quality is almost as good as a laser printer. Ink jet printers are the most feasible for printing in color.

Laser printers produce the best quality print. These printers are the most expensive, but since they offer very good quality they are usually the top choice of business.

Sound cardallows computer to reproduce music, sound, and voice. This is a definite necessity if you work on multimedia subjects. If you are using your computer for business, then you may not need a sound card.

Modemis used to send faxes or get on the Internet. It also allows the computer to communicate with other computers through the telephone lines. Modems are available in different speeds. The more speed the better.

With all the money you invest into your computer system, it would be destroyed by a power spike. It is a UPS that will help you. UPS stands for uninterrupted power supply. It protects against surges and power outages. It contains a battery backup, which will keep
your computer running for a short time after the power goes out. If the power goes off you will have enough time to save the file and turn off the computer before the battery runs out.

<== попередня сторінка	\|	наступна сторінка ==>
Fig. 1 Basic Computer Architecture	\|	No doubt, you read this text attentively and remember every detail.

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