Primary Storage, also known as main Memory, core memory,immediate access storage., provides capability to store input data, statements from current undergoing process, data resulting from processing, and data in preparation of Output.

The amount Of information that can be hold in primary memory is called as memory capacity. The capacity of the main memory is measured in kilo bytes (KB) or Mega bytes(MB).

The following are some characteristics of the primary storage:

•Fast Access . The central processing unit can transfer a data item to or from main memory in less than a billionth of a second. A typical access time is one sixteenth of a billionth of a second.

•Random Access: The access time for each item in main memory is the same , regardless of the order in which the item were stored or the location of each item in memory.

•Moderate capacity: Typically, small computers have main memory capacities ranging from 640 KB to 8 MB; capacities in the megabyte range has become common today. The trend in recent years has been for increasing the capacity.

The main function of different functional areas are:

1. Program storage area holds instruction from both system software and application software or programs, which enter the central processor from an input device.

2. Working storage area is analogous to a scratch pad, and is used to hold the data being processed as well as the intermediate results of such processing.

3. Input storage area temporarily holds data that have been read from an input device.

4. Output storage area holds the finished results of processing until released to the user.

Any storage unit of a computer is ranked according to the following criteria:

a. access time. b. storage capacity. c. Cost per bit storage.

All computers today uses semi-conductor elements in their primary storage sections.

Chips that employ metal oxide semi conductor(MOS) technology are usually used in the primary storage section. These primary storage components are often referred to as random access memory(RAM).

RAM is a read write memory . It is called random access because each separate location (address) inside the memory can be accessed as easily as any other location and takes the same amount of time.

One can access the memory at random and insert or remove data in any location at any time.

Ram is extremely fast and also can be expensive.

The storage cell circuits in dynamic RAM chips contain 1. a transistors that acts in much the same way as mechanical on or off light switch and 2. a capacitor that are capable of storing an electric charge.

Static RAM chips are also volatile storage devices, but as long as they are supplied with power , they need no special regenerator circuits to retain the stored data.

ROM provide permanent memory storage, i.e information is written permanently into the memory. Data can only be read from the memory but cannot be written there. It is a non volatile memory.

ROM are normally used to store information that the computer may need frequently for its own operation.

PROM(Program Read Only Memory). Instead of being installed when the chips are manufactured , the contents of PROM are stored electrically with a device called PROM programmer. Once it is programmed, its contents cannot be altered or erased.

EPROM(Erasable Programmable read only memory) chips are prom chips that can be erased and reused.

EEPROM(Electrically Erasable Programmable Read only memory) can be both erased and reprogrammed by applying suitable electric signal.

Besides primary storage where information and programs are stored for immediate processing , modern computer systems used additional types of storage known as secondary storage, backup storage or auxiliary storage.

Reasons- 1.Primary storage is highly expensive. 2.Limited size of primary storage the

computer can only accommodate limited number of programs and data.

But data in Auxiliary storage cannot be directly accessed but should be routed though primary memory for processing.

Virtual Storage is a useful processing techniques that has emerged with systems operating on more than one programs at a time. Large programs require sufficient storage to be available, which calls for virtual storage.

Virtual memory users allows them to act as if he or she ahs memory section of whatever size is needed to meet the program.

A very high speed memory is sometimes used to increase the speed of processing by making current programs and data available on the CPU at rapid rate.

A technique used to compensate the mismatch of operating speed of CPU and main memory is to employ an extremely fast , small memory between CPU and main memory. This type of memory is called buffer or cache memory.

1.The Level 1 cache memory is also known also Primary Cache Memory, and is attached with the CPU or Processor and is also it is used for temporary storage of Instructions and data organized in the blocks of 32 bytes. This type of Cache memory is also one of the fastest form of storage Memory used in Computer. Since because it's integrated with chip with a zero wait-state (delay) interface to the processor's execution unit, where it is limited in size. And This memory is also implemented using Static RAM (SRAM).

2. Today's most of the PCs are having with Level 2 Cache Memory to extent / bridge the processor / memory performance gap. This memory is also known as secondary Cache Memory and uses the same control logic as Level 1 cache memory do, and is also implemented in SRAM.Level 2 cache typically comes in two sizes, 256KB or 512KB, and can be found, or soldered onto the motherboard. The main Aim of Level 2 Cache Memory is to supply the stored information to the processor without any delay (wait-state).