Flash Read Only Memory
Flash-ROM is a type of ROM memory chip. ROM memory is a type of integrated circuit containing a program inside. This program cannot be modified during its usage, hence the name ”read-only“. Another characteristic of ROM memories is that their contents aren’t lost when the power goes off, contrary to what happens to RAM memories.
You can erase Flash-ROM contents electrically, allowing its erasing and programming to be done even with the chip installed in the circuit (if the circuit was built to support these functions, of course). So it is easier to erase and reprogram this type of ROM memory, since it doesn’t need to be removed from the circuit or exposed to ultraviolet light, as it happens with EPROM chips.
The difference between Flash-ROM and EEPROM is that on Flash-ROM is not possible to erase just one given address inside the memory chip and reprogram just one piece of data, i.e. on Flash-ROM you need to erase the entire memory even when you need to change just one value inside of it.
It is important to notice that even though some ROM memories can have their contents erased and be reprogrammed, this doesn’t transform these memories from ROM to RAM, because the recording procedure on ROM memories takes a lot of time, contrary to RAM memories where storing data is really fast.
On the PC this kind of circuit is used as the main ROM memory, where BIOS, Post and setup programs are stored.
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Figure 1: BIOS is stored in a Flash-ROM memory.