Memory Unit

 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.



a.    Primary Memory

b.   Secondary 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



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.



(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 may contain micro program that causes the machine to perform certain operations such as starting the computer. 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

(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.

Options RAM ROM
Accessibility In reference with the processor, the information stored in the RAM is easily accessed The processor cannot directly access the information that is stored in the ROM. In order to access the ROM information, first the information will be transferred into the RAM and then it gets executed by the processor
Working type Both the read and write operations can be performed over the information that is stored in the RAM The ROM memory only allows the user to read the information. User cannot make any changes to the information
Storage RAM memory is only used to store the temporary information ROM memory is used to store permanent information and cannot be deleted.
Speed The accessing speed of RAM is faster, it assist the processor to boost up the speed. Speed is slower in comparison with RAM, ROM cannot boost up the processor speed
Data preserving Electricity is needed in RAM to flow to preserving information Electricity is not needed in ROM to flow to preserving information.
structure The RAM is a chip, which is in the rectangle form and is inserted over the mother board of the computer ROMs are generally the optical drivers, which are made of magnetic tapes.
Cost The price of RAMs are comparatively high The price of ROMs are comparatively low
Chip size Physically size of RAM chip is larger than ROM chip Physically size of ROM chip is smaller than RAM chip
Types The RAM memory is categorized into two types they are the: Statistic RAM (SRAM) and Dynamic RAM (DRAM) The ROM memory is categorized into three types, they are: PROM (Programmable Read Only memory), EPROM  (Erasable Programmable Read Only memory)  and EEPROM (Electrically Erasable Programmable Read Only memory)


/ASSESSMENT The teacher summarizes the lesson and allows student to ask questions to clear doubts.

Assessment :

1.    Define computer memory

2.    State types of memory we have and describe them.

Student are allowed to give corrections to the assessment given by the teacher, while the teacher support s them in order to guide them.



Make a research online about secondary storage devices and uses



See also

Central Processing Unit





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