Memory in Computers
   

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Broadly the main memory can be directed into two parts

RAM (Random Access Memory)

  

ROM (Read only Memory)

  
 

RAM (Random Access Memory)

The RAM Chips in a Computer can be of two basic types:-

Dynamic RAM (DRAM)

  

Static RAM (SRAM)

  
   

 

Dynamic RAM

  

In dynamic RAM a transition and a capacitor is used to store a electric charge electric charge depends upon the switching action of the transistor. This storage Capacity of dynamic. RAM makes is differences then static RAM. a volatile memory and has less density then static memories. A  dynamic RAM Stores a bit of information in the cell storage.The special dynamic RAM consist of a metal oxide semi conductor field effect transistor (MOSFET). The various types of DRAM are as under:
  EDO DRAM  
  In a DRAM cells discharge refreshing of cell after certain time. The EDO DRAM solves this problem, it keeps the data valid till the next signal pass to the cells. It is made possible by using a dual pipe line architectures which allows to charge and discharge the cell simcelateneously.
  SDRAM (Synchronous DRAM)  
 

In EDO RAM the memory bus speed was unit due to it artitecture and design. In SDRAM this problem was solves and the memory buses speed are designed capable of high speed of memory bus speed. These memory can operate upto or equal to CPU Speed.
  RAM BUS DRAM (RD RAM)  
 

In RD RAM the address bus is divided into two groups (16 bit each for transisting the data packets) This qualify of RAM makes it difference from other. The Ram bus protocol does not multiplex or share control information on the data bus.
  Double Data Rate (DDR)  
 

This type of memory is similar to S.D. Ram but it does two operation per clock cycle. This DRAM doubles the memory band width due to doubling of data rate. So it is the fastest memory among all above of the memory. It is also called high band width memory.

Static RAM

 

Static RAM are the group of flip flop cells of information the RAM store the information remain valid as long as the power is supplied without any regenerator circuit to refreshed the cell. Static RAM takes more space for the storage as compared to Dynamic RAM. These are easier to use and have shorten read and write compared to Dynamic RAM.
     

ROM (Read Only Memory )

ROM is non-volatile memory the contents of memory do not erased when the power is switched off. It performs read operation only. Information cannot be charged or over written. The categories of ROM are as follows :-

Programmable Read only Memory (PROM)

  

Erasable Programmable Read only Memory (EPROM)

  

Electrically Erasable PROM (EEPROM)

  
PROM  

PROM stands for Programmable read only memory It is a ROM that can be programmed to record information using a facility known as PROM programmer. Once the chip has been programmed, the recorded information cannot be changed. In a PROM chips only PROM programmer can write instruction they are made by PROM programmer and user cannot makes any changes these behaves as ROM.

EPROM

stands for Erasable Programmable Read only Memory. It is another type of ROM that can be erased and the chip can be reprogrammed to record different information using a PROM program facility. Erasure is achieved by exposing to ultra violet light. When an EP ROM is in use, information can only be read and the information remains on the chip until It is erased. Types of EPROM:
 

- U PROM (Ultra Violet PROM)

  
 

- EA PROM (Electrically Alterable PROM)

  
EE PROM  

EEPROM stands for Electrically erasable programmable read only memory. This type of ROM can be programmed and erased by electric signals. It contents as EPROM memory does, and protrudes an easy means to load and store temporary or permanent inform of ROM memory. Information loaded in this memory can be retained for many year without any power supplied.
     
   

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  Contributed by: Jwala Pd. Singh, Batch - 0604A, Aptech Shaktinagar