MEMORY UNIT

What is a Memory?

Memory is storage part in computer. It is store the data, information, programs during processing in computer. It stores data either temporarily or permanent basis. Memory used to important role in saving and retrieving data.

- Definition of Computer Memory

The computer memory is the storage where data, programs and information are stored. The two main types of memory are:

1. Primary storage / Main memory

2. Secondary storage / Auxiliary memory

1. Primary Memory / Main Memory–   Primary memory is internal memory of the computer.  It is also known as main memory and Temporary memory. Primary Memory holds the data and instruction on which computer is currently working. Primary Memory is nature volatile. It means when power is switched off it lost all data. For this reason, the main memory is also called Immediate Access Storage (IAS).

Types of Primary Memory

Primary memory is generally of two types.

a. Random Access Memory (RAM)

b. Read Only Memory (ROM)

1. RAM (Random Access Memory) – It stands for Random Access Memory.RAM is known as read /writes memory where the CPU reads and writes to as often as required. It generally refereed as main memory of the computer system. It is a temporary memory, they are volatile. The information stored in this memory is lost as the power supply to the computer is switched off. That’s why RAM is also called “Volatile Memory”

- Types of RAM –   RAM is also of two types:

a) Static RAM- Static RAM also known as SRAM, retains stored information as long as the power supply is ON. SRAM are of higher coast and consume more power .They have higher speed than

b) Dynamic RAM– Dynamic RAM also known as DRAM, its stored information in a very short time (a few milliseconds) even though the power supply is ON. The Dynamic RAMs are cheaper and moderate speed and also they consume less power.

2. Read Only Memory (ROM) – It stands for Read Only Memory. ROM is a Permanent Type memory. Its content are not lost when power supply is switched off. Content of ROM is decided by the computer manufacturer and permanently stored at the time of manufacturing. ROM cannot be overwritten by the computer. It is also called “Non-Volatile Memory”. The data cannot be changed and the operating boot sector records are stored inside the ROM

- Types of ROM - ROM memory is in three types namely 

a) PROM (Programmable Read Only Memory) - PROM is a programmable memory chip that can be programmed by the user. it is PROM chips to write data once and read many. Once chip has been programmed, the recorded information cannot be changed. PROM is also non-volatile memory.

b) EPROM (Erasable Programmable Read Only Memory) - EPROM chip can be programmed time and again by erasing the information stored earlier in it. Information stored in EPROM exposing the chip for some time ultraviolet light.

c) EEPROM (Electrically Erasable Programmable Read Only Memory) - The EEPROM is programmed and erased by special electrical waves in millisecond. A single byte of a data or the entire contents of device can be erased.

SECONDARY STORAGES

Secondary Memory / Non Volatile Memory – Secondary Memory is an external memory of the computer. It is also known as Auxiliary memory and permanent memory. It is used to store the different programs and the information permanently. Secondary Memory is nature non volatile. It means data is stored permanently even if power is switched off.

Examples of secondary storage media include:

• Recordable Optical Disk (CDs and DVDs)

• Floppy Disks

• Magnetic (Hard) Disk

• Magnetic Tapes

• Pen Drive

• Winchester Disk and so on

Each one of these types of media must be inserted into the appropriate drive in order to be read by the computer. While floppy disks and removable disks are rarely used anymore, CDs and DVDs are still a popular way to save and transfer data.

Brief explanation of some secondary storage media

Internal hard disk

The hard disk is a spindle of magnetic disks, called platters, that record and store information. Because the data is stored magnetically, information recorded to the hard disk remains intact after you turn your computer off. This is an important distinction between the hard disk and RAM, or memory, which is reset when the computer's power is turned off.

The hard disk is housed inside the hard drive, which reads and writes data to the disk. The hard drive also transmits data back and forth between the CPU and the disk. When you save data on your hard disk, the hard drive has to write thousands, if not millions, of ones and zeros to the hard disk. It is an amazing process to think about, but may also be a good incentive to keep a backup of one’s data.

USB Drive

A USB flash drive, usually portable and rewritable, is a type of flash memory storage device that plugs into a computer's USB port. Flash drives are more expensive than hard drives with the same storage capacity.

Floppy Disks

Floppy disks are a storage medium made of a thin magnetic disk. They were widely used from the 1970s to the early 2000s. On the 3 1⁄2-inch microfloppy, common from the late 1980s onward, storage capabilities ranged from the standard 1.44 MB to 200 MB on some versions.

CD-R

A CD-R, a type of recordable CD, is an optical secondary storage device invented by Sony and Philips. It is also known as a WORM -- write once read many -- medium. They are used for recording, storing, and playing, audio, video and any other information in digital form.

DVD-R

A DVD-R, a type of recordable DVD, has a storage capacity of usually 4.1 GB. There is also an 8.54-GB dual-layer version, called DVD-R DL.

Magnetic Tape

Magnetic tape has been in use for more than 50 years. Modern magnetic tape is packaged in cartridges or cassettes and is used for storing data backups, particularly in corporate settings. The average amount of storage is 5 MB to 140 MB for every standard-length reel, which is 2,400 feet.

Assignment

Write out in a Tabular form four (4) differences between primary and secondary storage.