The Lowdown on ROM
Fundamentally, there are 3 basic types of ROM and they include:
- ROM itself
- PROM (Programmable Only Memory), which can only be written to once
- EPROM, which can be erased using UV light and reprogrammed using a pulsed voltage
(There is another type of ROM, which is identical to EPROM, apart from the fact that it can be electrically erased under software control).
In essence, ROM chips are quite different from RAM, as they use a diode to create a 1 and then break the connection to form a 0. Usually, ROM is created from hard wired logic and the data is encoded into the silicon inside, in the same basic way as a processor. It is created with to perform a very specific function, which cannot be altered, with good reason.
One common misconception is that only RAM is able to access data in a random way, but that isn’t true. ROM can also access data in the same way, it just can’t be written to.
The benefits of ROM lie in its permanence. Once the relevant data has been stored there, regardless of power supply, it will always be there (unless drastic action is taken, like taking an axe to it!). This non-volatile nature of ROM is shared by another component inside a computer, the hard disk
Another benefit is that ROM is very hard to tamper with the information stored inside, which means you’ll never get a virus altering code in a ROM module.
The BIOS on computers is the most prevalent way that ROM is used in the modern age and it is just as vital to the overall operation as any other components. Inside the BIOS you’ll find a lot of important data (which is permanent and not erased when power is lost) that pertains to boot up sequences and the operation of all of the hardware inside a modern laptop or PC.