Types of RAM and ROM

Types of RAM :- There are two types of RAM. These are Static RAM and Dynamic RAM.

Static RAM :- It consists of internal flip-flops that store the binary information. Stored information remains valid as long as power is applied to the unit. Static memory, consisting of static RAM chips are memory consisting of circuits capable of retaining their state as long as power is applied.

Dynamic RAM :- A Dynamic RAM loses its stored information in a very short time (a few milliseconds) even though in a dynamic memory cell in the form of charge on a capacitor and this charge can be maintained only for a very few milliseconds. As the charge on the capacitors leak away as a result of normal leakage, the capacitor gets turned off after the few milliseconds. So, to retain the cell information for a much longer time, the cell's content must be periodically refreshed to restore the capacitor charge to its full value.

Read Only Memory (ROM) :- ROM is a permanent type memory. ROM is used for storing programs that are permanently resides in the computer and the contents are written into at manufacturing time. ROM is needed for storing an initial program called a bootstrap loader or BIOS (Basic Input-Output system). The bootstrap loader is a program whose function is to start the computer software operating when power is turned on. ROM remains unchanged after power is turned off and on again.

A read-only memory (ROM) is a memory unit that performs the read operation only. It does not have a write capability. This implies that the binary information stored in a ROM chip is made permanent during the hardware production of the unit and can not be altered by writing different words into it.

ROM may be of the following types :-

PROM (Programmable ROM) :- PROM's contents are decided by the user ie, data can be loaded by the user. It is used for research and development purpose.

EPROM (Erasable PROM) :- EPROM chip allows the stored data to be erased and new data to be loaded. The contents of EPROM chip can be erased and reprogrammed. The chip's contents are erased by UV light. It is used for software developing purpise and also used in research & development purpose.

EEPROM (Electrically Erasable PROM) :- EEPROM chips do not have to be removed from the circuit board for erase. The contents of EEPROM can be both erased & programmed electrically. In this type of chip different voltages are needed for reading, writing and erasing the stored data. It is used for research and development purpose.

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