Primary Storage Devices.
Primary storage devices stock nonvolatile data in computers. The memory unit is the internal memory of the computer this can temporarily store computer programs and data during execution parts of main memory may contain permanently stored instructions that tell what to do when a computer is turned on.
Primary storage devices are internal to the system and are the fastest. Naturally, primary storage devices have an example of all the data and applications currently in use or being managed. The computer gets and retains the data and files it in the primary storage device until the process is completed or data is no longer required.
As the main memory unit is located inside and has the direct link with other components so access to data and instructions is very. Fast Process of entering data in memory is called writing and a process of retrieving data from memory is called reading.
Today, we are using semi – conductor memories These are semiconductor integrated circuits designed to function as memory chips the two most common forms of semiconductor memories are:
1. ROM (Read Only Memory).
2. RAM (Random Access Memory).
READ ONLY MEMORY.
The name gives the idea we can only red this memory we can not write anything in this memory This basically contains messages and instructions from the manufacturer like how to start computer check every part of. memory, when the machine is turned on it, works under:
The control of from which performs the below mentioned important functions.
- Displays messages from the manufacturer.
- Runs the Power-On-Self-Test (POST) which checks the memory keyboard drives printers and all attaches equipment.
- Searches for an operating system. if it finds an operating system the control would be transferred to that operating system then the machine starts working under the control of then operating system if no operating system is supplied then the ROM will hang the machine and we will not be able to work.
- Loads the Basic Input Output System (BIOS) which works with the microprocessor for controlling the inputs and Outputs. That is why sometimes ROM is known as ROM BIOS.
This part is unchangeable and non-volatile. Several types of ROMS are available like PROM EPROM.
- Programmable Read Only Memory (PROM).
This can be programmed by the user but only once. No further alteration is possible.
- Erasable Programmable Read Only Memory (EPROM).
This is also programmable. But you can use it more than once. It has a transparent window covering the whole circuitry You can remove that chip from the circuit and expose it to ultraviolet light this process erases the contents of the chip and then you can reprogram it.
- Electrically Erasable Programmable Read Only Memory (EEPROM).
The contents of EEPROM can be erased electrically you don’t need to remove it from the circuit as with EPROM Once The contents are erased it can be reprogrammed.
RANDOM ACCESS MEMORY
This part of main memory temporarily stores data and programs and holds them till the execution. This is the user accessible area where the program and data of the user are stored temporarily this is volatile memory that means if there is any power failure or you turn off the power the computer will forget the contents it had in its mind ( memory unit ) This is also called read and write memory We call it random or direct because any piece of data available inside the memory can be accessed directly / randomly.
There are several kinds of memories available to us like conventional base memory extended memory special purpose memories.
· Conventional RAM or the Base Memory
The first 640 KB of the total memory of the computer system is called conventional ram or the base memory.
· Extended memory.
All the memory above the conventional memory (first 640 KB) is the extended RAM.
· Special – purpose memories.
Register Buffer And Cache are the special purpose memories These memories are vital to moving data in and out of the main memory and to processing the data.