Memory Unit (MU)

The memory unit stores all instructions and data for the CPU. Memory Unit is an important part of the computer system. The storage device of a computer system is known as memory. Memory Unit can receive data, hold it and deliver according to the instructions from the control unit.

⇒ Memory is of two kinds (a) Primary and b) Secondary.

(a) Primary Memory: It is often referred to as the working memory or the main memory of a computer system. It is capable of sending and receiving data at a very high speed. It is temporary in nature i.e. Data stored in primary memory are lost when the computer is switched off. So it is also called volatile memory. Example of primary memory is RAM.

⇒ Primary memory is directly accessible to the CPU. It must be able to provide data very quickly.

⇒ The two basic kinds of primary memory are the Random Access Memory (RAM) and the Read Only Memory (ROM).

⇒ The RAM is a read/write memory.

⇒ The CPU can change the contents of the RAM at any time. In addition, RAM is volatile.

⇒ The RAM capacity greatly influences the computing ability of the computer. Capacity is usually measured in kilobytes and megabytes.

⇒ The ROM can not be altered.

⇒ A Informations is stored on the ROM at the time of its manufacture. The information might be in the form of crucial instructions that govern the working of the computer.

⇒ The ROM is non-volatile and retains its information even after the power is turned off.

⇒ The PROM (Programmable Read Only Memory), however, has the option of being programmed, i.e. the manufacturer of the computer may choose to load a program designed by his company into this PROM, and then the computer would use this PROM like any other ROM.

(b) Secondary Memory: It is used to store data for a long term. It operates at a much slower rate than primary memory. Secondary memory is permanent in nature, so it is also called non-volatile. It is also cheaper than primary memory.

⇒ Primary memory is fast but expensive. To reduce storage costs, computers also use secondary memory.

⇒ Common examples of secondary memory are floppy diskettes, hard (fixed) discs and magnetic tapes, CDs, DVDs, Memory Cards, USB Sticks etc.

⇒ It is not directly accessible to the CPU. Information is moved from the secondary memory to the primary memory first and then to the CPU.

⇒ A floppy diskette is a plastic disk coated with magnetic material.

⇒ Special devices known as disk drives are capable of reading from and writing to floppies using special magnetic ‘head’.

⇒ Any piece of information stored on a floppy diskette can be directly accessed.

⇒ Magnetic tapes are long plastic tapes coated with magnetic material.

⇒ Magnetic tapes can store far larger amounts of data than the floppy diskette. But a problem with magnetic tapes is that information can not be accessed directly as in the case of floppy diskettes.

⇒ The third type of medium, called fixed or hard disks, are more or less similar to the floppy diskette. But one hard disk drive contains several discs of a hard material.

⇒ Another popular storage medium is the compact disk (CD). Unlike the media described above, CDs are an ‘optical’ medium.

⇒ An optical medium is one where the properties of light is used for the medium to perform its basic functions.

⇒ Conventional CDs are made of a special kind of plastic.

⇒ The CD is read using a laser beam.

⇒ Secondary memory is much slower, but it is non-volatile and can be used to store information for long periods of time.

⇒ DVD drive is another optical drive which is same in size as CDs but is higher in storage capacity.

⇒ USB Flash drive also known as USB stick, USB, Flash Memory etc. are physically much smaller than optical drives with high storage capacity and are removable and rewritable in nature.

⇒ SD and Micro SD cards are very small in size but very high in capacity.

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