Why A Computer Needs Two Types Of Memory
§ 6. Computer memory
The main topics of the paragraph:
internal and external memory;
structure of the internal memory of the computer;
media and external memory devices.
Internal and external memory
When working with information, a person uses not only his knowledge, but also books, reference books and other external sources. In Chapter 1, “Man and Information,” it was noted that information is stored in a person’s memory and on external media. A person can forget the learned information, and the records are stored more reliably.
The computer also has two types of memory: internal (operational) and external (long-term) memory.
Internal memory is an electronic device that stores information while it is powered by electricity. When you disconnect the computer from the network, information from the RAM disappears. Program during its execution is stored in the internal memory computer. The rule formulated refers to the Neumann principles. It is called the principle of a stored program.
External memory is various magnetic media (tapes, disks), optical disks. Saving information on them does not require constant power supply 1.
1 In modern computers, there is another type of internal memory, which is called read-only memory. ROM. This is non-volatile memory, information from which it can only be read.
In fig. 2.3 shows a diagram of a computer device with two types of memory. Arrows indicate the direction of information exchange.
Computer internal memory structure
All computer devices do a certain job with information (data and programs). But how does the information itself appear on a computer? To answer this question, “look” inside the computer memory. Internal memory structure computer can be arbitrarily depicted as shown in Fig. 2.4.
The smallest memory element in a computer is called a memory bit. In fig. 2.4 each cell represents a bit. You see that the word “bit” has two meanings: a unit of measurement of the amount of information and a particle of computer memory. We show how these concepts are related.
Each memory bit can currently hold one of two values: zero or one. The use of two characters to represent information is called binary encoded.
Data and programs in computer memory are stored as binary code.
One character of the two-character alphabet carries 1 bit of information.
One bit of memory contains one bit of information.
The bit structure determines the first property of the computer’s internal memory. discreteness. Discrete objects are made up of individual particles. For example, sand is discrete, as it consists of sand grains. The “grains” of computer memory are bits.
The second property of the computer’s internal memory is addressability. Eight consecutive bits of memory form a byte. You know that this word also means a unit of information equal to eight bits. Therefore, in one byte of memory one byte of information is stored.
In the internal memory of the computer, all bytes are numbered. Numbering starts from scratch.
The serial number of a byte is called its address.
The principle of addressability means that:
Writing information to memory, as well as reading it from memory, is done at addresses.
Memory can be thought of as an apartment building, in which each apartment is a byte, and the apartment number is an address. In order for the mail to reach its destination, you must specify the correct address. That is how, at addresses, the processor accesses the internal memory of the computer.
Media and external memory devices
External memory devices are devices for reading and writing information to external media. Information on external media is stored as files. What is it, you will learn more later.
The most important external memory devices on modern computers are magnetic disk drives (NMD), or disk drives.
Who doesn’t know what a tape recorder is? We are used to recording speech, music, and then listening to recordings on a tape recorder. Sound is recorded on the tracks of a magnetic tape using a magnetic head. Using the same device, magnetic recording is again converted into sound.
NMD acts like a tape recorder. The same binary code is written to the tracks of the disk: the magnetized section is one, the non-magnetized one is zero. When reading from a disk, this record turns into zeros and ones in bits of internal memory.
A recording head is brought to the magnetic surface of the disk (Fig. 2.5), which can move along the radius. During operation, the HDD rotates. In each fixed position, the head interacts with the circular track. It is on these concentric tracks that binary information is recorded.
Another type of external media is optical disks (their other name is laser disks). They use not a magnetic, but an optical-mechanical method of recording and reading information.
First came laser discs, on which information is recorded only once. It is not possible to erase or overwrite it. These discs are called CD-ROM. Compact Disc-Red Onlum Method, which means “compact disk is read-only”. Rewritable laser discs, the CD-RW, were later invented. On them, as on magnetic media, stored information can be erased and recorded again.
Media that the user can remove from the drive is called removable.
The largest information capacity of removable media possess laser discs such as DVD-ROM. discs. The amount of information stored on them can reach tens of gigabytes. On discs, full-length movies are recorded, which can be viewed using a computer, like on TV.
Briefly about the main thing
The computer includes internal memory and external memory.
An executable program is stored in internal memory (principle of a stored program).
Information in computer memory is in binary form.
The smallest element in the internal memory of a computer is a bit. One bit of memory stores one bit of information: a value of 0 or 1.
Eight consecutive bits form a byte of memory. Bytes are numbered starting from zero. The serial number of a byte is called its address.
In the internal memory, writing and reading information occurs at addresses.
External memory: magnetic disks, optical (laser) disks. CD-ROM, CD-RW, DVD-ROM.
Questions and Tasks
1. Try to explain why the computer needs two types of memory: internal and external.
2. What is the “stored program principle”?
3. What is the discrete discrete internal memory property?
4. What are the two meanings of the word “bit”? How are they related?
5. What is the property of addressability of the internal memory of a computer?
6. What are the external computer memory devices.
7. What types of optical discs do you know?
I. Semakin, L. Zalogova, S. Rusakov, L. Shestakova, Computer Science, Grade 8
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