Primary Memory

 Primary / Main Memory

This memory unit which communicates directly with the CPU and is connected to each computer is called primary or main memory. Primary memory is divided into many small parts which are called Location or Cell. A certain bit called word length can be stored in each location. The word length in the computer can be of 8, 16, 32, 64 bits. The speed of primary memory is fast but its storage capacity is limited and the price is high. Primary memory is usually temporary memory. Register, Cache Memory, RAM, ROM are examples of primary memory. To store data in the location is called write and to receive data from the location is called read. Primary memory is mainly electronic or semiconductor memory. Integrated circuits are used in these, which are made of silicon chip. The credit for its development goes to J. s. goes to Kilby. Silicon chips are mainly made of gallium arsenide.

Primary memory is classified into three parts-

A) Volatile Memory (Temporary Memory) : - The memory unit in which the stored data is destroyed when the power supply is turned off. It is called Volatile Memory.

Following are the types of Volatile Memory-


1. Dynamic Random Access Memory (DRAM) : - It is also called DRAM in short. The most common of RAM is DRAM and it needs to be refreshed frequently. Refresh means here to electrically charge the chip. It refreshes about thousands of times in a second and every time it refreshes it erases the previous content. Due to its quick refresh feature, this RAM is slow compared to other RAM.

2. Synchronous DRAM :- This type of chip is much faster than normal DRAM. The reason for its fast speed is that it runs according to the clock speed of the CPU. Therefore, for this reason, it transfers data faster than other DRAM.

3. Static RAM :- Static RAM is less refreshed. As a result, SRAM is faster and more expensive to store data than DRAM. They are used for specific purpose computers.

B) Cache Memory : - The speed of receiving data from memory is much less than the data processing speed of CPU. Cache memory is used to remove the speed mismatch between memory and processor. It is an extremely fast memory between the primary memory and the CPU. Where frequently used data and instructions are stored. Due to the fast speed of the cache memory, the speed of the processor increases.
Cache memory is directly connected to the CPU. The system bus does not have to be used to carry information from the cache memory to the CPU. Hence the data transfers at a faster rate. Cache memory acts as a buffer between CPU and main memory. Generally, the size of the cache memory used in the computer can be from 256 kb to 4 mb.

Cache Memory

C) Non-Volatile Memory (Permanent Memory) : - The memory unit in which the data remains even when the power supply is turned off. called permanent memory.

Following are the types of non-volatile memory-

1. Read Only Memory (ROM) : - It is a permanent electronic memory in which the stored data and information itself is not destroyed and cannot be changed. Information in ROM is also filled at the time of creation and the computer can only read them. Cannot change these. The information remains in the ROM even when the power supply of the computer is turned off.
ROM is made from semiconductor devices. Therefore it is also called Electronic or Semiconductor memory. ROM is used to store programs and data of a permanent nature. The necessary information to start the computer such as instruction set and system boot program is stored in ROM. ROM contains the BIOS which runs the POST (Power on Self Test) program when the computer is turned on.
2. Programmable Read Only Memory (PROM) : - This is a special type of ROM, in which user-friendly data is programmed by a special process. There are thousands of diodes in PROM. The desired information is recorded by fusing them with high voltage. Once programmed, it behaves like a normal ROM.
3. Erasable Program Read Only Memory (EPROM) : - With the help of ultraviolet rays on this type of ROM, a new program can be written by deleting the old program. For this the EPROM has to be removed from the circuit. It is also called Ultravoilet EPROM.
4. Electrically Erasable Programmable Read Only Memory (EEPROM) : - Without removing this type of ROM from the circuit, a new program can be written by removing the old program with the help of high electric potential on it. It is mainly used in research.
Currently, the use of EEPROM as auxiliary memory is increasing. Pendrive is a good example of this. This type of electronic memory is being used in many modern devices like- Digital camera, Laptop, Smartphone, Mobile phone etc. It is a cheap device and it has the ability to keep data safe even in extreme conditions.