What Is DRAM ,SRAM ,PROM And EPROM Explain In Detail

DRAM :-

• Short for Dynamic Random Access Memory, DRAM is one of the most commonly found memory modules in PC compatible personal computers and workstations. 
• DRAM was first invented and patented by Robert Dennard in 1968 and first released commercially by Intel in October1970. 
• DRAM stores its information in a cell containing a capacitor and transistor; because of this design, these cells must be refreshed with new electricity every few milliseconds allowing the memory to keep its charge and hold the data as long as needed.

• Above, is an example of a 512MB DIMM computer memory module with eight DRAM integrated circuits on the visible side of the module.

Note: This type of memory is a volatile memory and if the computer is powered off, the information within the memory is lost.

SRAM :-

• Short for Static RAM, SRAM is computer memory that requires a constant power flow in order to hold information. 
• Although quicker thanDRAM, SRAM is much more expensive and requires more power; therefore, it is commonly only used in cache and video card memory.

PROM :-

• Alternatively referred to as a FPROM (field programmable read-only memory) or OTP (one-time programmable) chip, PROM orProgrammable ROM is short for Programmable Read Only Memoryand is a computer memory chip first developed by Wen Tsing Chow in1956 that is capable of being programmed once after it has been created. 
• Once the PROM has been programmed, the information written is permanent and cannot be erased or deleted. 
• A good example of a PROM in a computer is the computer BIOS in early computers.
• When the PROM is created it ships with all bits reading as "1" and during the programming any bit that needs to be changed to a 0 is etched or burned into the chip using a device known as a gang programmer. 
• Below is an example of a gang programmer from Advin that programs multiple ROM chips at one time.

• If a PROM has been programmed and has an error or needs updated the chip is discarded and a new PROM is created and replaces the old chip. 
• A variation of the PROM is an EPROM, which is a PROM that can be erased and reporgrammed without being replaced.

EPROM :-

• Short for Eras able Programmable Read-Only Memory, ERPOM is a memory chip that was invented by Dov Frohman in 1971while at Intel that can only be read from. 
• If exposed to ultraviolet light an EPROM can be reprogrammed if needed, but otherwise does not accept or save any new data. 
• Hardware manufactures use EPROM when it may be needed that the data contained on the EPROM needs to be changed. 

                                               

• An EPROM chip is distinguishable by a small quartz crystal (not glass) circle window that exposes the chip so that can be reprogrammed. 
• In the picture shown on this page is an example of an Intel 8048 made by NEC and is an example of an EPROM chip.
• Today, EPROM chips are not used in computers and have been replaced by EEPROM chips.