Types Of Computer Memory

Memory:-

A memory is just like a human brain. It is used to store data and instructions. An essential component of every computer is its memory. Without memory there could be no computers as we now know them. Memory is used for storing both instruction to be executed and the data.The memory is divided into large number of small parts called cells. Each location or cell has a unique address, which varies from zero to memory size minus one. For example, if the computer has 64k words, then this memory unit has 64 * 1024 = 65536 memory locations. The address of these locations varies from 0 to 65535.

There are three types of memory:-

Cache Memory
Primary Memory/Main Memory
Secondary Memory

Cache Memory:-

Cache memory is a very high speed semiconductor memory which can speed up the CPU. It acts as a buffer between the CPU and main memory. it is used to hold those parts of data and program whit are most frequently used by CPU. IT is made up of high speed Static R.A.M.

when a processor needs to read or write a data, it first checks in the cache memory. If the processor finds the data in cache memory it is known as "hit", and if the processor does not finds the data it is known as "miss".

Cache Memory

Advantages of Cache Memory:-

Cache memory is very much faster memory as compared to main memory/primary memory.It is the fastest memory in computer.
It stores the program that can be executed within a short period of time.
It consume less access time as compared to main memory/primary memory.
It stores data for temporary use.

Disadvantages of Cache Memory:-

Cache memory is very expensive compared to main/primary memory and secondary memory.
It has limited capacity.

Primary Memory/Main Memory:-

Primary memory is known as main memory of computer. Primary memory holds those data and instruction on which the computer is currently working. It has a limited capacity and data is lost when power is switched off.It is made up of a semiconductor device.It is faster than Secondary memory.It is the memory without which a computer can't run.

Features of Primary Memory/Main Memory:-

It is usually a volatile memory.
Data is lost in case power is switched off.
It is the working memory of the computer.
Faster than secondary memories.
As said in the above line that computer cannot run without the primary memory.

Primary Memory/Main Memory is divided into two subcategory-

RAM- Random Access Memory
ROM- Read Only Memory

1.RAM- Random Access Memory:-

RAM is also called as read-write memory or main memory or primary memory.
The program and data that the CPU requires during execution of a program are stored in this memory
It is a volatile memory as the data looses when the power is turned off.
RAM is father classified into two types-

a. SRAM-Static Random Access Memory

b. DRAM-Dynamic Random Access Memory

RAM

a. SRAM-Static Random Access Memory:-

It is constructed of circuits that is similar to flip-flop that stores the binary information.
Holds its contents as long as power is available.
It is very expensive as compared to DRAM.
It is faster than DRAM.
It consumes more electricity or power than DRAM.
It generates more heat compared to DRAM.
SRAM Is used as Cache memory.

b. DRAM-Dynamic Random Access Memory:-

It consists of only one transistor and one capacitor per bit, the capacitor leaks electricity.
It requires a recharge in every milli-seconds to maintain its data.
It is inexpensive as compared to SRAM.
It is slower than SRAM.
It consumes less electricity or power than SRAM.
It generates less heat compared to SRAM.
DRAM is used as primary memory/main memory.

DRAM Refreshing- DRAM uses a single capacitor and single transistor per bit. The transistor is turned on to charge the capacitor, but the capacitor leaks off over a time measured in milli-second. Therefore, it must be regularly refreshed (thousands times a second) to ensure that the data is not lost.

2.ROM- Read Only Memory:-

It stores crucial information essential to operate the system, like the program essential to boot the computer.
It is non-volatile.
Used in embedded system or where the programming needs not to be changed.
ROM is further classified into four types-

a. MROM-Masked Read Only Memory

b. PROM-Programmable Read Only Memory

c. EPROM-Erasable Programmable Read Only Memory

d. EEPROM-Electrically Erasable Programmable Read Only Memory

a. MROM-Masked Read Only Memory:-

The very first ROMs were hard-wired devices that contained a pre-programmed set of data or instructions. These kind of ROMs are known as masked ROMs, which are inexpensive.

b. PROM-Programmable Read Only Memory:-

It can't be reprogrammed. Once programmed, the data and instruction in it cant' be changed.

c. EPROM-Erasable Programmable Read Only Memory:-

It can be reprogrammed. To erase data from it, expose it to Ultra-Violet rays.To reprogram it erase all the previous data.

d. EEPROM-Electrically Erasable Programmable Read Only Memory:-

The data can be erased by applying electric field, no need of UV rays.

Secondary Memory:-

This type of memory is also known as external memory or non-volatile. It is slower than the main memory. These are used for storing data/information permanently. CPU directly does not access these memories, instead they are accessed via input-output routines. The contents of secondary memories are first transferred to the main memory, and then the CPU can access it. For example, disk, CD-ROM, DVD, etc.

Hard Disk(secondary memory)

Secondary Memory

Features of Secondary Memory:-

These are magnetic and optical memories.
Computer may run without the secondary memory.
It is used for storage of data in a computer.
It is known as the backup memory.
It is a non-volatile memory.
Slower than primary memories.
Data is permanently stored even if power is switched off.

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