Darren New <dne### [at] sanrrcom> wrote:
> It says that FLASH, being mass-produced, is cheaper than ROMs that you have
> to mask on a per-device basis.
>
> Even back in the days of VT100 terminals and TRS-80's, EPROMs were used
> instead of ROMs because it was cheaper, and nobody ever really expected to
> patch the fonts on a VT100 terminal.

It's a question of quantity.

As soon as the numbers grow big enough, it is more efficient to mass-produce
ROMs that you can just solder onto your board and go for it, than it is to add
in-system programming circuitry and have a production step to flash the
software into each and every individual device.

Provided you don't ever intend to replace the software on the devices.


For instance, the Amstrad CPC home computers came with genuine, custom-designed
ROMs, while expansion devices with built-in software typically came with
EPROMs.


For low-count program-once applications, chip manufacturers even offer "one-time
pogrammable EPROMs", which are straightforward UV-erasable EPROMs inside a
windowless casing, effectively making them PROMs. And I guess some even offer a
programming service. A big advantage of using these is that they're perfectly
compatible with their windowed siblings (but cheaper, and easier to handle in
production because you don't have to put stickers on them), so you can use the
windowed version during development where you'll definitely want to re-program
the things now and then, but the more cost-effective non-windowed one in the
final product, without ever worrying about potential differences in the
operational parameters.

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