DRAM is used in the main memory
DRAM’s access speed is 50-70 nanoseconds
DRAM is less dense than SRAM
DRAM is volatile
DRAM is written to when you open up programs and data files
To erase DRAM you close the file or the program
The memory needs to be refreshed because the capacitors don’t hold charge
SRAM
SRAM is usually used for the cache
SRAM’s access speed is 15-30 nanoseconds
SRAM is more dense thn DRAM
SRAM is volatile
Writing to SRAM is block level
The memory doesn’t need to be refreshed because the capacitors hold there charge
ROM
ROM is used on the boot up sequence and in things where the memory doesn’t need to be changed i.e calculators
ROM is slow
ROM is non volatile
Data is wired into the ROM chip
You can’t erase the memory
PROM
PROM allows computer manufacturers to add their own data to the ROM chip
PROM is slow
PROM is non volatile
PROM is programmed by blowing the fuses in selected cells
You can’t erase the memory
EPROM
EPROM is used for testing
EPROM is slow
Uses 1 transistor per bit so has a high density
EPROM is non volatile
EPROM is programed by blowing the fuses in selected cells
EPROM uses an ultra violet light to repair the blown fuses and reprogram the chip
EEPROM
EEPROM is used on things like usb sticks and some BIOS systems because they can be updated
EEPROM is very slow
Uses more than 1 transistor per bit so is less dense than EPROM
EEPROM is non volatile
You write to EEPROM electrically
EEPROM is erased electrically
HOW MANY TRANSISTORS REQUIRED PER BIT?
SRAM – SRAM uses 4 transistors to keep a stable state
