What is Memory in Computer ?

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Memory

In the article “what is memory in computer”, we will discuss about memory, use of memory in computer, etc. Every digital processing system must have some device for storing digital information. Information is usually in the form of instruction, data or results which are coded in binary form. That part of a digital or microcomputer system that provides the facility to store data is called memory. Until some time ago, memory was mostly of magnetic type, but due to the unexpected development of semiconductor technology, it has become possible to make memory of different types and different sizes. Semiconductor memory is small in size, low in cost, high speed, high reliability. Their size can be increased as per requirement. Click here to read Read this article in Hindi

Uses of memory in microprocessor

In microprocessor systems, semiconductor memory is used to store data or information. Generally in microprocessor/microcomputer systems memory is used at the following levels-

1. Registers
2. Faster Prime Memory
3. Slower Prime Memory
4. Mass Storage Memory (Hard-disc)
5. Off-line Back-up Storage
In terms of speed of operation, the memory written at the top is faster than the memory written below it. For example, it takes 100 ns (nanosecond) to read a word of information from a fast primary memory, while it takes 10 ms (millisecond) to read a word from a hard disk (mass storage).

Although there are five levels of memory, many systems may have only three: (1) registers, (2) primary memory, and (3) mass storage.

Registers

Registers are located inside the CPU. The number of registers and their nature (type and numbers) are different in each microprocessor, but the amount of information that can be stored in them is limited. It ranges from a few hundred to a few thousand bits.

Primary memory

Registers on a microprocessor chip require space, so only a limited number of registers can be made available on the chip, usually in most systems this number remains less than required. Therefore, primary level memory is used to store programs and data. Primary memory is also multiple chips. The overall size of primary memory ranges from a few kilobytes in small systems to several megabytes in large systems.

Some microprocessor systems have an additional arrangement of primary memory. It has a large memory size, although its speed is slow. This additional memory is commonly found in supercomputers, for example the Cray X/MP class of machines.

Storage memory

In most systems, many programs and data are stored (resident) in the system so that they can be loaded into primary memory for execution immediately when needed. Such programs include compilers, assemblers, text editors and other useful programs such as pay roll data of a company etc. These types of programs require many megabytes of memory. Along with this, it is not necessary that programs and data should not be used frequently. Therefore, one or more storage devices are used to store this type of information. For example hard disk, floppy disk, and optical disk etc. Storage memory in a system can range from a few megabytes to several gigabytes. This type of storage memory is called on-line storage because all the information stored in it can be accessed although its access is slow.

Cache memory

In some systems it is possible that the primary memory may be much slower than the operating speed of the CPU. In this state, the CPU has to wait while sending or receiving data from the primary memory, which reduces the efficiency of the CPU. To prevent the CPU from operating at a reduced speed, cache memory is used. Cache is like primary memory but in speed it is somewhat faster than primary. Memory consists of high speed chips. Their value is also high. The size of the cache memory is in few kilobytes. In Motorola 68030, the cache is located on one of its CPUs. In some systems it is located on the same board with the microprocessor and primary memory.

Off-line back-up storage

While working on any system, it may also happen that we use all the storage memory available in the system and we do not have space left in any memory. What would you do in such a situation? There are many ways for this. The simplest method is to provide more storage memory. But after it ends, the same situation will happen again. So there is a limit to this type of on-line storage which depends on the financial condition of the programmer.

Another solution is to use a storage device in the system that can be removed, for example a removable hard disk or tape drive. Having such an arrangement, back-up operation can be done at a fixed time interval. In a back-up operation, data and programs that are less commonly used can be “saved” on a back-up tape or hard disk cartridge, and can be used when needed. Can be kept safe in the library. This type of storage is called off-line back-up storage. It is called off-line storage because the microprocessor cannot access it like other primary and on-line memory.

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