MEMORY

Memory is the part of the computer that holds data and instructions for processing. It stores program and instructions or data for only as long as the program they pertain to is in operation.

TYPES OF MEMORY

(a)    PRIMARY MEMORY: This is the memory that can be directly accessed by the CPU which constantly interact with it, retrieves data stored therein, goes through instructions and execute them as per the requirement. All the information, data and application are loaded there in uniform manner. Example is RAM (Random Access Memory) which is volatile (temporary) but fast form of memory.

 Apart from the main large capacity RAM, there are two subs – layers of the primary memory.

(i)                 Processor registers within the processor, which are one of the fastest forms of data storage

contain a word of data (usually 32 or 64 bits).

(ii)               Processor cache, which is meant for enhancing the performance of the computer. It links the

fast register to slower main memory. Cache memory loads the duplicated information that is

used most actively. It is much faster than the main memory but relatively can store limited

data.

USES OF PRIMARY MEMORY

The primary storage unit is used for the following activities:

(i)                 For input and output operations.

(ii)               For manipulation of text and calculation operations.

(iii)             For logical or comparison operations.

(iv)             For storage and retrieval operations.

EXAMPLES OF PRIMARY MEMORY

(i)                 RAM chip provides volatile storage, but as long as it is supplied with power, it needs no special regenerator circuits to retain the stored data.

(ii)               ROM chip retains the stored data when the power supply is cut. So, unlike RAM chips, ROM chips are not volatile. ROM chip only read and it does not accept instruction from the users.

Types of ROM

(a)    Programmable Read Only Memory (PROM): It allows a chip to be programmed by the user for converting critical and lengthy operations into micro programs that are fused into a chip.

(b)   Erasable Read Only Memory (EROM): It can be erased and reprogrammed. It needs to be removed and expose to ultraviolet light for some time before it can accept any new content.

(c)    Electrical Erasable and Programmable Read Only Memory (EEPROM):  It can be reprogrammed with special electrical pulses.

SECODARY MEMORY

Secondary memory or storage is the non – volatile memory that stored externally from the computer. A secondary – storage medium is usually used for the storage of large amount of data or for permanent or long – time storage of data or programs. It is also used for storing backups.

Secondary storage media can be ranked according to the following:

(i)                 Retrieval speed: This is the time it takes to locate and retrieve the stored data.

(ii)               Storage capacity: This is the ability to store data.

(iii)              Cost per bit of capacity.

TYPES OF SECONDARY MEMORY

(i)                 Magnetic Disk: This is a Mylar or metallic platter on which electronic data are stored. The

data are recorded as tiny invisible magnetic spots on its iron oxide coating.

The access time for data stored on a magnetic disk is determined by the seek time i.e. the time required for positioning read/write head over the paper track and search time i.e. the time required or spinning the required data under the head. Once the data have been accessed, they are copied from the disk to the processor for processing. The transfer rate depends on the density of the stored data and rotational speed of the disk.

Magnetic Disk came in two categories which are:

(a)    Fixed disk or Hard disk: It is made from materials such as aluminum instead of Mylar.  The input/output device used to transfer data to from a hard disk called dish drive. Hard disk may be permanently installed in a drive or in form of removable disk.

Forms of Fixed disk or hard disk

1.      Larger permanent sealed metal disk (14 – inch) which is used in larger systems and minicomputer.    

2.      Larger metal disk in removable cartridges (14 – inch) which is used in mini sized and larger systems.

3.      Rigid disks permanently housed in Winchester drives. It comes in 9, 8 and 5¼  inches size.

4.      3½ inch disks currently used in PC’s, servers and small ones in Notebooks and other device.

(b)   Floppy Disk: These disk are available in three sizes which are:

1.      8 inch portable floppy (flexible) disk.

2.      5¼ inch portable floppy disks.

These two diskettes are individually packaged in protective envelopes.

3.      Compact floppy disk measuring less than 4 inches in diameter.

OPTICAL TECHNOLOGY STORAGE

This involves the use of laser beams i.e. highly concentrated beams of light. It comes in form of:

(a)    Optical laser disk which could be Compact Disk Recordable (CD – R), Compact Disk Rewriteable (CD – RW) or Digital Versatile Disk (DVD) or flash  which the data stored in it can be read by CD – ROM drives, CD – RW drives, DVD – ROM drives or DVD – RW drives and Flash drive respectively.

Differences between primary and secondary memory

	Primary storage devices	Secondary storage devices
1	These devices are temporary.	These devices are permanent.
2	These devices are expensive.	These devices are cheaper.
3	These devices are faster, therefore expensive.	These devices connect via cables and are slow, therefore cheaper.
4	These devices have less storage capacity.	These devices have high storage capacity.
5	These devices refer to RAM, ROM etc.	These devices refer to FDD, HDD etc.