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What is "virtual memory"?

Virtual memory is a common part of most operating systems on desktop computers. It has become so common because it provides a big benefit for users at a very low cost.

Most computers today have something like 64 or 128 megabytes of RAM (random-access memory) available for use by the CPU (central processing unit). Often, that amount of RAM is not enough to run all of the programs that most users expect to run at once. For example, if you load the Windows operating system, an e-mail program, a Web browser and word processor into RAM simultaneously, 64 megabytes is not enough to hold it all. If there were no such thing as virtual memory, your computer would have to say, "Sorry, you cannot load any more applications. Please close an application to load a new one." With virtual memory, the computer can look for areas of RAM that have not been used recently and copy them onto the hard disk. This frees up space in RAM to load the new application. Because it does this automatically, you don't even know it is happening, and it makes your computer feel like it has unlimited RAM space even though it has only 32 megabytes installed. Because hard-disk space is so much cheaper than RAM chips, virtual memory also provides a nice economic benefit.

The area of the hard disk that stores the RAM image is called a page file. It holds pages of RAM on the hard disk, and the operating system moves data back and forth between the page file and RAM. (On a Windows machine, page files have a SWP extension.)

Of course, the read/write speed of a hard drive is much slower than RAM, and the technology of a hard drive is not geared toward accessing small pieces of data at a time. If your system has to rely too heavily on virtual memory, you will notice a significant performance drop. The key is to have enough RAM to handle everything you tend to work on simultaneously. Then, the only time you "feel" the slowness of virtual memory is in the slight pause that occurs when you change tasks. When you have enough RAM for your needs, virtual memory works beautifully. When you don't, the operating system has to constantly swap information back and forth between RAM and the hard disk. This is called thrashing, and it can make your computer feel incredibly slow.

 

3. Find the answers to the questions:

1. What is a common part of most operating systems on desktop computers?

2. Most computers today have something like 64 or 128 megabytes of RAM (random-access memory) available for use by the CPU, don’t they?

3. Can the computer with virtual memory look for areas of RAM that have not been used recently?

4. Why can virtual memory provide a nice economic benefit?

5. What is the key to handle everything you tend to work on simultaneously?

Complete the sentences.

1. Virtual memory has become so common because it …

2. If you load the Windows operating system, an e-mail program, a Web browser and word processor into RAM simultaneously, 64 megabytes is not enough …

3. The area of the hard disk that stores the RAM image is called …

4. Of course, the read/write speed of a hard drive is …

5. If your system has to rely too heavily on virtual memory, you will notice …

Match the following English words with their Ukrainian equivalents.

Монохромна система, графічний адаптер, крихітна точка, буфер обміну, палітра кольорів, переповнення пам’яті, розширення імені файлу, файл віртуальної пам’яті, прикладна програма, віртуальна пам’ять.

True or false statements.

1.Virtual memory is a common part of hardware of desktop computers.

2. Most computers today have something like 600 megabytes of RAM (random-access memory) available for use by the CPU.

3. The operating system deletes data from the page file and RAM.

4. When you have enough RAM for your needs, virtual memory works beautifully.

5. When you have enough RAM for your needs the operating system has to constantly swap information back and forth between RAM and the hard disk.

Translate from English into Ukrainian.

1. Virtual memory is a computer system technique which gives an application program the impression that it has contiguous working memory (an address space), while in fact it may be physically fragmented and may even overflow on to disk storage.

2. Systems that use this technique make programming of large applications easier and use real physical memory (e.g. RAM) more efficiently than those without virtual memory.

3. Virtual memory differs significantly from memory virtualization in that virtual memory allows resources to be virtualized as memory for a specific system, as opposed to a large pool of memory being virtualized as smaller pools for many different systems.

4. Note that "virtual memory" is more than just "using disk space to extend physical memory size" - that is merely the extension of the memory hierarchy to include hard disk drives.

5. Extending memory to disk is a normal consequence of using virtual memory techniques, but could be done by other means such as overlays or swapping programs and their data completely out to disk while they are inactive.

6. The definition of "virtual memory" is based on redefining the address space with a contiguous virtual memory addresses to "trick" programs into thinking they are using large blocks of contiguous addresses.

Translate from Ukrainian into English.

1.Віртуальна пам'ять – це загальна частина більшості операційних систем настільних комп'ютерів.

2. За допомогою віртуальної пам'яті комп'ютер може шукати зони оперативної пам'яті, які не використовуються, та копіювати їх на жорсткий диск.

3. Часто кількості оперативної пам'яті не вистачає для того, щоб запустити всі програми, які користувачі сподіваються використовувати одночасно.

4. Так як ємність жорсткого диску дешевше ніж чіпи оперативної пам'яті, віртуальна пам'ять також надає економічні переваги.

5. Коли у вас є достатньо оперативної пам'яті для виконання ваших задач, віртуальна пазять працює чудово.

II. Retell the text “What is ‘virtual memory’?”

III. Rendering.

Read the text and translate it using a dictionary.

Units of memory

Bits- basic units of memory. Information is processed and stored in computers as electrical signals. A computer contains thousands of electronic circuits connected by switches that can only be in one of the possible states: ON (the current is flowing through the wire) or OFF (the current is not flowing through the wire). To represent these two conditions we use binary notation in which 1 (one) means ON and 0 means OFF. This is the only way the computer can understand anything. Everything about computers is based upon this binary process. Each 1 or 0 is called a binary digit or bit.

Bytes and characters. 1s and 0s are grouped into eight-digit codes that typically represent characters (letters, numbers and symbols). Eight bits together are called a byte. Thus, each character in a keyboard has its own arrangement of eight bits. For example, 01000001 for the letter A, 01000010 for B and 01000011 for C.

The ASCII code. The majority of computers use a standard system for the binary representation of characters. This is the American Standard Code for Information Interchange, known popularly as ‘ASCII’ (pronounced ‘ask-key’). There are 256 different ways of combining 0 and 1 bits in a byte. So they can give us 256 different signals. However, the ASCII code only uses 128 bytes to represent characters.

The first 32 codes are reserved for characters such as the Return key, Tab, Escape, ect. Each letter of the alphabet, and many symbols (such as pronunciation marks), as well as the ten numbers, have ASCII representations. What makes this system powerful is that these codes are standard.

Kilobytes, megabytes and gigabytes. In order to avoid astronomical figures and sums in the calculation of bytes, we use units such as kilobytes, megabytes and gigabytes. One kilobyte is 1,024 bytes (2 10) and it is represented as KB, or more informally as K. One megabyte is equivalent to 1,024 KB, and one gigabyte is 1,024 MB.

We use these units (KB, MB, GB) to describe the RAM memory, the storage capacity of disks and the size of any application or document.



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