Memory Memory is the part of the computer system that is used to store data or instruction temporarily and permanently. Once data is store...

 Memory

Memory is the part of the computer system that is used to store data or instruction temporarily and permanently. Once data is stored in a location in the memory, it remains there until it is replaced by other data.

1. Primary Memory

Primary Memory is the computer memory which is directly accessed by the CPU. It is also known as main memory, primary storage or internal memory. It holds data for processing. It holds data after it is processed waiting to be sent to an output or storage device.

Features

• It is directly accessible to the CPU
• It is usually volatile memory except the ROM
• It is usually expensive and faster to r/w operation than secondary memory.
• It is normally used for smaller storage.
• It is a semiconductor memory.

Types of Primary Memory

i. RAM (Random Access Memory)

RAM is the read/write memory of the computer i.e. both, the information can be written into the RAM and read from the RAM. It is volatile memory i.e. it stores data or information as long as the power supply is on when the power supply goes off, the stored content in the RAM will be lost.

Types of RAM

• SRAM (Static Random Access Memory) : 
• DRAM (Dynamic Random Access Memory) : 

Differences between SRAM and DRAM

S.N	SRAM	S.N	DRAM
1.	SRAM stores data or programs as long as the power supply is 'ON' state.	1.	DRAM loses its stored information in a very short time even though the power supply is 'ON' state.
2.	It has a higher speed compared to DRAM	2.	It has lower speed than SRAM.
3.	It stores bit as voltage.	3.	It stores bit as a charge.
4.	It is expensive in cost.	4.	It is cheaper in cost.
5.	It is usually available in a smaller storage capacity of a few MB.	5.	It is usually available in large storage capacity of few GB.

ii. ROM (Read Only Memory)

Read Only Memory is a type of storage medium that permanently stores data on personal computer (PC) and other electronic devices. It can be used only to perform the read operation, it does not have writing capabilities. It is non-volatile memory.

Types of ROM

• PROM (Programmable Read Only Memory) : The user can write data in a PROM only once. User can store permanent programs, data or any kind of information in a PROM.

• EPROM (Erasable Programmable Read Only Memory) : The data stored in EPROM can be erased by exposing it to ultraviolet light. It is used to store programs, which are permanent but need frequent updating.

• EEPROM (Electrical Erasable Programmable Read Only Memory) : It can be erased and reprogrammed on the byte by byte basis. Either a single byte or the entire chip can be erased in one operation.

Differences between RAM and ROM

S.N	RAM	S.N	ROM
1.	RAM stands for random access memory.	1.	ROM stands for read-only memory.
2.	It allows both read and write operations.	2.	It allows only to read operation.
1.	It is volatile in nature i.e. data are lost when the power supply is switched off.	1.	It is non-volatile in nature and used for permanent storage.
2.	It usually has a higher memory space than ROM.	2.	It usually has less memory space than RAM
2.	Types of RAM are SRAM and DRAM.	2.	Types of ROM are PROM, EPROM and EEPROM.

iii. Cache Memory

Cache memory is special, high speed, and expensive semiconductor memory placed between RAM and CPU. Cache memory is the fastest system memory, required to keep up with the CPU as it fetches and executes instructions. The fastest portion of the CPU cache is the register file, which contains multiple registers.

2. Secondary Memory

Secondary storage is any storage device designed to retain data and instructions in a relatively permanent form. It is non-volatile, that is stored data and instructions retain even if the power supply is cut off. It is also called as auxiliary memory or back-up memory.

Features

• It is called the auxiliary, external or backup memory.
• It is not directly accessible to CPU
• It is used for storing data and programs permanently.
• It is usually non-volatile memory.
• It is normally used in a larger storage capacity.

Types of Secondary Memory

i. Magnetic Memory

Magnetic memory is the storage of data on a magnetized medium. Magnetic storage uses different patterns of magnetisation in a magnetizable material to store data and is a form of non-volatile memory.

Types of Magnetic Memory

• Magnetic tape : 
• Magnetic disk : 

Types of Magnetic disk

• Hard Disk
• Floppy Disk

ii. Optical Memory

Optical memory is a removable disk on which data is written and read through the use of laser beams. A laser beam is a concentrated narrow beam of light, focused and directed on a particular location to read or write data.

Types of Optical Memory 

• CD (Compact Disk)
• DVD (Digital Versatile Disc)
• BD (Blue-ray Disk)

iii. Flash Memory

Flash memory is an electronic non-volatile computer memory storage medium that can be electrically erased and reprogrammed. Flash memory is an EEPROM form of computer memory and thus does not require a power source to retain the data.

Types of Flash Memory

• Memory chip
• Pen drive

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