Memory Devices

chapter 3

Memory Devices

MEMORY: Primary & Secondary:-

Memory unit is that component of a computer system, which is used to store the data, instruction and information before, during and after the processing by ALU. It is actually a work area (physically a collection of integrated circuit) with in the computer. where the CPU stores the data and instruction. It is also known as a main/primary/Internal memory. It is of the following three types:-
a)Read only memory (ROM pronounced as “Ra-Om”)
b)Random access memory (RAM pronounced as “Ra-aem”)
c)Complementary metal oxide semiconductor memory (CMOS)
We will discuss about (these memory units in the subsequent sub – section. Primary memory (especially RAM) stores the data, instructions and information temporarily during processing by CPU. When the computer is switched off, this memory gets erased. How does a computer store the data, information and software permanently so that they can be retrieved when ever required certainly, there must be some storage devices used with microcomputers.
Some of the common storage devices are.
a)Floppy disk
b)Hard disk
c)Magnetic optical disk
d)Magnetic tape
e)Compact disk
These storage devices are also called secondary memory devices.
Random Access Memory (RAM):- Random access memory is an important component of memory unit. It is used to store data instruction during the execution of programs. RAM is temporary and is erased when the computer is switched off. RAM is a read/write type of memory, and thus can be read and written by the user/programmer. As it is possible to randomly use any location of this memory, therefore, this memory is known as random access memory. The memory capacity of RAM varies from 640 kb to several megabytes (1 megabyte =1024 kb) with different models of PC.
Types of RAM:- There are two types of RAM used in PCs-Dynamic and static RAM. The difference b/w these two types of RAM used are describe.

  •  The information stored in Dynamic RAM has to be refreshed Every few milli seconds otherwise It is erased.
  •  D-RAM has higher storage Capacity.
  •  It is provides lesser speed to the Computer.
  •  It is cheaper.

Read only Memory: – Read only memory is an essential component of the memory unit we know that the memory unit. We know that the computer, being a machine, itself has no intelligence or memory unit and requires instructions which are given by man whenever the computer is switched on, it searches for the instruction. The memory, which has these essential instructions, is known as Read Only Memory. The memory is permanent and is not erased when the system switched off. As appears with its home, it is read type of memory i.e., it can be read only and not be written by user / programmer. The Memory capacity of ROM varies from 64 KB by 256 KB (1 Kilobyte = 1024 byte) depending on the model of computer Rom contains a number of programs (set of instruction). The most important programs of ROM is the Basic input Output System (BIOS, Pronounced as “bye – so”) which activities the hardware (physical components of computer) Such as keyboard, monitor, Floppy disk etc. in communicate with the system and application software (set of instruction or programs).
Types of ROM: –                                                                                                                                                                                                                            There are many types of ROM available for micro computers like Mask Rom, PROM, EPROM, EEPROM and EAPROM.
i.Mask ROM: – It is the basic ROM chip. In this type of ROM, the information is stored at the time of its manufacturing later on.
ii.PROM: – PROM stands for Programmable Read Only Memory. In this type of ROM, the information is stored by programmers after its manufacturing. It also cannot be altered or erased later on.
iii.EPROM: – EPROM stands for Erasable Programmable Read Only Memory. In this type of ROM it is similar to PROM but its information can be erased later on by ultra violet light and it can be re programmed.
iv.EEPROM: – EEPROM stands for electrically erasable Programmable Read Only Memory. It is similar to EPROM, but its information can be erased by using a high voltage current.
v.EAPROM: – EAPROM stands for Electrically Alternate Read Only Memory. As compared to EPROM and EEPROM, the information stored in EAPROM can be altered later
Complementary Metal Oxide Semiconductor Memory:-
Complementary Metal Oxide Semiconductor (CMOS) memory is used is store the system configuration, date, time and other switched on, BIOS matches the information of CMOS with the peripheral devices Mismatching.
Compact Disk Read Only Memory:-
Compact Disk (CD) is the latest storage device, used to store data, information and software which can be read only and not be changed or erased. It is an optical read only memory. Made-up of a resin. Therefore, it is actually called as Compact Disk Read only memory. However The information is stored on CDS by using on expensive drive, Called CD- Rom drive. Now-a-days compact disks are very popular storage devices for microcomputer because a large number of software including Multimedia, audio and graphics software are available only on these disks. Compact Disk can store a large volume of data (up to 630 MB) which is almost the same as a storage capacity of a 640 MB Hard Disk.
Worm: – Write once Read Many is a type of compact disk which can be recorded only once and not erased. It can store more data than a CD-ROM, generally measured in gigabytes.