Memory

Computer memory is any physical device capable of storing data or information temporarily or permanently. In a computer system there are two types of memory areas:

• Primary memory(storage)
• Secondary memory(storage)

Primary memory(storage)

This is the category of computer storage often called main memory.

It has three functions :

1. Stores all or part of the program that is being executed.
2. Stores the operating system programs that manage the operation of the computer.
3. Holds data that the program is using.

Modem primary storage devices include:

• RAM
• ROM

Random-access memory (RAM)

• It is used for the short-term storage of data or program instructions.
• It is volatile. Its contents will be lost when the computer’s electric supply is disrupted by a power outage or when the computer is turned off.
• It is a memory chip that can be read from and written to by the processer.
• The more RAM a computer has, the faster it responds.

There are two types of basic RAM chips:

1.Dynamic RAM (DRAM)

• It is the most common type.
• It must be re-energized constantly

2.Static RAM (SRAM)

• It is faster and more reliable than DRAM.
• It doesn’t have to be re-energized as often as DRAM.

Newer type: magnetoresistive RAM (MRAM).

Read-only memory(ROM)

• It can only be read from; cannot be written too.
• ROM chips come from the manufacturer with programs already burned in, or stored.
• It is used in general-purpose computers to store important or frequently used programs such as
• computing routines for calculating the square roots of numbers.
• It is a memory chip that stores permanent data and instructions.
• It is a non-volatile memory, it is not lost when the computer power is turned off.

There are three types of RAM they are:

1. Firmware: it is manufactured with permanently written data, instruction, or information.
2. PROMC(programmable read memory): chip onto which a programmer can write permanently.
3. EEPROM(electrically erasable programmable read-only memory): it is a type of PROM containing a microcode programmer can erase.

Secondary storage

• It is used for relatively long-term storage of data outside of the CPU.
• Secondary storage is non-volatile and retains data even when the computer is turned off.
• Most technologies are magnetic disks, optical disks, and magnetic storage. Storage is the place of holding data, instructions, and information for further use. A storage medium is a physical material used for storage.
• The storage medium is non-volatile contents are retained when power is off.
• Memory is volatile it holds data and instructions temporarily.

There are various types of secondary memory or storage devices, are magnetic disk, optical disk, magnetic tape, etc.

A. Magnetic disk

It permits direct access to individual records so that the datastore on the disk can be directly accessed regardless of the order in which the data were originally recorded.
Disk storage is often referred to as a direct access storage device (DASD).
There are two kinds of magnetic disk:

1. Floopy Disk

• It is a portable, inexpensive storage medium that is also called distal. (thin, circular, flexible frim, enclosed in 3.5 wide plastic shell).
• The device that reads from and writes to a floppy disk is called a floppy disk drive.

2. Hard disk

• It is a high-capacity storage system.
• It consists of several inflexible, circular patterns that store items electronically.
• Its components are enclosed in an airtight, sealed case for protection.
• The track is a narrow recording band that forms a full circle on a disk.
• Sectors stores up to 512 bytes of data.
• Formatting prepares a disk for use and marks bad stores as unusable.

B. Optical disk

• It is also called compact disks or laser optical disks as it uses laser technology to store data at densities
• many times greater than those of magnetic disks.
• The most common optical disk system used with PCS is called CD-ROM(compact disk read-only memory)
• It is a flat, round, portable metal discs made of metal plastic and lacquer.
• It can be read-only or read and write.
• In an optical disk, a tract is divided into evenly sized sectors that store items in them.

There are two types of optical disk, they are:

1. CD-ROM (Compact Disk Read-Only Memory)

• Its contents cannot be erased or modified.
• Typically it holds 650MB to 1GB data.
• It is commonly used to distribute multimedia and complex software.

2. DVD-ROM (Digital Versatile Disk-ROM or Digital Vide Disk-ROM)

• It stores databases, music, complex software, and movies.
• Its contents can be erased or modified.
• The high-capacity disk is capable of storing 4.7GB to 17GB.
• The computer must have a DVD-ROM drive or DVD player to read DVD ROM.

C. Magnetic Tape

• Magnetic tape is an older storage technology that is still used for the secondary storage of a large volume of information.
• The tape is a magnetically coated plastic ribbon capable of storing large amounts of data at low costs. It is primarily used for backup.
• Its advantages are its inexpensiveness, irrelative stability, and ability to store very large quantities of information.
• Its disadvantage is it sequentially stores data and its relative slowness compared to the speed of secondary storage media.