Computer memory

 Introduction to various types of  memories and their features.

            Definition of Computer memory: Memory is storage part in computer. It is storing the data information, programs during processing in computer.  It stores data either temporarily or permanent basis. Memory used to important role in saving and retrieving data.

        Types of memory- Mainly computer have two types memory

1. Primary memory/Volatile memory
2. Secondary memory/ Non-Volatile memory

• Primary memory: Primary memory is also known as main memory or may also refers to internal memory of computer. It is directly accessible by CPU. 

Primary memory is the memory through which data information & programs are stored in temporary.

There are two types memory:

• RAM
• ROM

1. RAM: means Random Access memory. Ram is a semi-conductor depended memory. It can read & write data from CPU or other hardware device. It stores data temporarily. It loses data when the system is turned off.

There are two types of Ram:

• Static ram
• Dynamic ram

 Static Ram: It does not need to be refreshed frequently, so the data is stored for a long time. SRAM uses 6 Transistors for each memory cell. The memory cell doesn't refresh frequently due to the high number of transistors present in cell. SRAM accesses the data very speedily so SRAM  is Costlier than DRAM.

Dynamic Ram: lifetime of data in DRAM is very less. Data is about 4 millisecond. DRAM is stored in memory Cell, each consists of a transistor or a Capacitor pair. DRAM memory cell is refreshed every few milliseconds to retain data in memory. DRAM is less expensive than SRAM. 

     2.  ROM: Stand for Read only memory: It can only read the data. It store the data permanently. It is a non-Volatile memory. 

ROM are three types of memory:

• PROM
• EPROM
• EEPROM

                PROM: Programmable Read Only Memory. This memory is store the data permanently. PROM is a memory chip. In which data can be programmed only once, hence the program is known as one time programmable memory.

                EPROM: Erasable Programable Read Only Memory

In this, permanently stored data can be deleted with the help of Ultraviolet waves.

               EEPROM: Electricity Erasable Programmable Read Only Memory 

               EEPROM is a type of non-volatile memory used in computer. EEPROM is a user-modifiable ROM. It can be erased and reprogrammed by electrical voltage.

            Secondary Memory: Secondary memory is  non-volatile memory. It is not directly accessed by the computer. Secondary memory refers to storage device, such as hard drives.

eg: HDD, FDD, Pen Drive, DVD, CD, USB Flash Drive.

Differences between Primary and Secondary Memory 

S.N.	Primary memory	Secondary memory
1	Primary memory is temporary	Secondary memory is permanent
2	Primary memory is directly accessible by Processor/CPU	Secondary memory is not directly accessible by CPU
3	Nature of Parts of Primary memory varies. RAM- volatile in nature. ROM- Non-volatile	It’s always Non-volatile in nature
4	Primary memory devices are more expensive than secondary storage devices	Secondary memory devices are less expensive when compare to primary memory devices
5	The memory devices used for primary memory are semiconductor memories	The secondary memory devices are magnetic and optical memories
6	Primary memory is also known as Main memory or Internal memory	Secondary memory is also known as External memory or Auxiliary memory
7	Examples: RAM, ROM, Cache memory, PROM, EPROM, Registers etc	Examples: Hard Disk, Floppy Disk, Magnetic Tapes etc