Various Types of Memories used by the Computer System
Depending on the characteristics and functionality of it. One has to have a clear understanding of these memories types of understand the working of the computer memory. Some of the commonly available memory types are follows:
Magnetic Core Memory: This is the memory which uses small magnetic cores with wires running through then and electric current which flows through the wire, which generates magnetic field. Depending on the direction of current and magnetic field, data is represented. But this form of memory is bulky; this problem has been overcome by newer Technologies, such as semiconductor based memory like RAM and ROM.
Random Access Memory (RAM): While a program is being executed it requires data, this data while is required which execution of the program is stored in RAM. The data stored in RAM is volatile that is when there is a power failure; the data is the RAM is lost. Whenever new data is stored in RAM, the previous data is erased. Thus, RAM is used to store data and programs temporally. The capacity of the RAM is one of the major factors for faster working of the computer.
Read Only Memory (ROM): Some programs are always required to run the machine. These types of program if stored in RAM are lost as it is volatile memory, so they have to be stored in non volatile storage i.e., that device in which data is not erased when there is power failure or it is switched off. ROM provides that non volatile storage, therefore all those programs are stored in it. ROM usually contains the Bootstrap Loader Programs, which loads the operating system (O.S.) into the memory. As this program is stored in ROM, it starts as soon as the computer is switched ON and makes the computer ready to load OS program in the memory. As ROM is read only memory, the contents of ROM cannot be changed but for specialized use contents of ROM can be reprogrammed using special circuits. Theses ROM’s are known as Programmable Read Only Memory (PROM). Once the PROM is programmed by the user, they cannot be altered with.
Erasable Programmable Read Only Memory (EPROM): EPROM is that can be erased and reprogrammed to do this, it has to be removed from the processor and exposed to ultra violet rays for some time, then it can accept new contents.
Electrical Erasable and Programmable Read Only Memory (EEPROM): EEPROM can be reprogrammed using special electrical Pulses.
Secondary Memory (Secondary Storage Media)
As the contents of RAM or temporary, if the data and programs are to be stored permanently, secondary memory is used. Floppy Disc, Hard Disc, Magnetic Tapes CD’s etc, is some of the secondary memory devices.
Cache Memory: This is very high speed memory which is used to store portion of program from main memory temporarily. The cache memory very expensive, but it is very fast. The data is transferred automatically between the buffer and primary storage, so that buffer is usually invisible to the user.
Bubble Memory: This memory is Non Volatile Memory, but it is not that widely used when compared to semiconductor memory as it is expensive and slower. This memory is built on a thin piece of mineral garnet, where certain sections are subjected to the magnetic field which result in polarization which produces bubble like areas and thus data is represented as presence or absence of these bubbles.