Computer Memory

                                                       Computer Memory

 

 

Memory :-

  

Computer Memory is internal storage area in the computer used to store the data and programs  either temporarily or temporarily.

A computer memory can be broadly divided into two groups.

 1.Primary memory :-

                  The memory that holds the data and the programs that are currently executing.

 

2.Secondary memory:-

                  The memory that holds the data and the programs that are not executing currently in use and provides long term usage.

Difference Between the primary(main ) memory and Secondary memory:-

Primary Memory:-

It is more expensive.

It is faster and more efficient than Secondary memory.

Directly accessed by the CPU.

It is volatile(Stores the data only when power is on) in nature.

Storage  Capacity is limited.

It has no moving parts.

The memory is power independent.

The memory is integrated circuit based.

It consumes less power.

It stores data temporarily.

Secondary memory:-

It is Cheaper.

It is lower and less efficient.

Can not be accessed by the CPU.

It is Non-volatile in nature.

It has large storage capacity.

It has moving parts.

The memory is power independent.

The memory is magnetic or optical based.

It consumes more power.

It stores data permanently.

These Days Computers use different types memory which can be organized as hierarchy around the CPU.The memory at higher level in the memory hierarchy has less capacity to store data,is more expensive, and is fastest access.

                                                             Memory hierarchy

                                                        

     1.CPU Register:-

                        

               CPU Registers are located inside the Processors and are therefore directly accessed by the CPU.Registers are the fastest all forms of computer  data storage. 

    2.Cache Memory:-

   Cache memory is intermediate form of storage between the CPU registers and The Primary memory.

It is used to  store the data and instructions that is used frequently to execute programs.

By using Cache memory ,it improves the overall system speed and increase the performance of the computer.

Using the cache memory to store data and instructions that are frequently used to execute programs ,avoid the accessing the primary memory frequently.

 Working of the cache memory:-

 

 The program is being is executed and CPU want to read the data or instructions,then it follows the    following steps: 

1.The CPU first checks the whether the data which is needed to execute program contains in the Cache  memory or not.

2.If it is there it takes form the cache memory,if it's not it copy that data from the primary storage (main memory ) into  CPU Registers as well as in the cache memory also.

3.When the same data or instruction is needed,the CPU reads it from cache memory instead of main memory.

      3.Primary Memory:-

Primary memory is also called as Secondary memory or internal storage.

This memory is directly accessed  by the CPU.

Any data that has to be operated by the CPU is stored in the primary memory.The CPU continuously read the instruction stored in primary memory and executes them.

There are two types of primary memory.They are

1. Random Access memory(RAM).

2. Read Only memory(ROM).

3.1.Random access memory(RAM):-

  

• It is volatile storage area with in the computer .
• It stores the data temporarily.
• The information is stored in the RAM is loaded from the computer hard disk.The data related to operating system and applications that are currently being executed by the processor.
• RAM is called random access because it access the data directly if memory address is known.
• When the RAM is full,computer system performs at low speed.
• If the RAM is full with multi applications ,It is searches for all the empty memory locations

       There are tow types of RAM.

1.Static RAM:- SRAM is made of flip-flops between 0 and 1 without using the capacitors.

It  occupies more  space and expensive than DRAM.It requires four to six transistors to store one        bit.These memory is often used as cache memory.These memory is used in household appliances          and cars.

  

2.Dynamic RAM:-   DRAM is made of transistors and Capacitors.It uses one transistor to store                 information between 0 and 1.

 The advantage of SRAM and DRAM is very cheap.

3.2.Read only memory(ROM):-

    

        ROM data contains permanent data.It is Non-Volatile.so it stores the data when the computer is              turned off.

       ROM chips include 

     1.PROM(Programmable read only memory)

     2.EPROM(Erasable Programmable read only memory)

     3.EEPROM(Electrically Erasable Programmable read only memory).

4.Secondary Memory:-

         

     The Secondary memory is also called External memory or Auxiliary memory.It differs from primary memory.It stores the data when the computer is turned off.

The data in secondary memory is organized into files and directories.The file system is also provides the information about owner of the file,access information ,access time and other information.

Example of Secondary memory are magnetic tape,hard disks,compact disks,USB flash drive,memory card,etc,,

  

magnetic tape:-

hard disk:-

USB flash drive:-