Nonvolatile ROM
ROM chips come in a few different types. Like all memory chips, ROM prices are based mostly on capacity, with a small price premium for speed. Some ROMs can retrieve data faster than others, and this might be worth a little extra money to someone building a fast system.
Masked ROM
The simplest and cheapest ROMs are called masked ROMs (MROMs). These chips are mass-produced with particular data bits already stored in them. Once the MROMs are made, the data can never be changed. This is usually the point: MROMs are good for mass-produced products like cars, in which the software for the antilock brake system should never be altered.
Because their data patterns are permanently set when the chips are built, MROMs are only made in large ...
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