I was looking in a friends warranty coverage for his car and one of the things I noticed was PROM (programmabe read only memmory). Now IIRC from computer class (and I do)ROM is NOT progammable or it wouldn’t be ROM just “M” that’s like having a washable permanent marker. So does anyone know what it means?
Formerly known as Nec3f on the AOL SDMB
If I understand it correctly, PROM is only reprogrammable at the factory, using some kind of ultraviolet light. Hey, failing that it’s easy to look this up on Yahoo, which I would do if it weren’t 12:59 am.
programmable, reprogrammable (even if it can only be done at the factory) it’s still not READ-ONLY. Seems like an oxy-moron
Formerly known as Nec3f on the AOL SDMB
At last, a use for my obsolete hardware geek knowledge! <g>
Anyway, PROM is indeed Programmable Read Only Memory. The thing is, it becomes read-only AFTER you’ve programmed it; so it’s not really an oxymoron. Programming the earliest PROMS amounted to blowing teeny little fuses on the chip surface, which is a little tricky to undo. After you found something that worked for you, you made a map of what data you wanted encoded on the chip and sent that to the chip maker, along with an order for about a gazillion of 'em, and they made up your order with the fuses pre-blown at the factory (Actually, the chip maker just didn’t bother putting the wire at locations you specified as blown). Other variants you might see around include EPROM (Erasable Programmable Read Only Memory; you expose the chip [which is under a clear quartz window] to UV light, which erases it), and EEPROM, Electrically Erasable PROM.
Who knew the Grail wasn’t dishwasher safe? – MST3K
So that explains it. PROM and ROM are basically the same. They are only progammabe in a sense but really they are both just chips with something hardwired into them.
Formerly known as Nec3f on the AOL SDMB
First they had just plain ROMs (read-only memory). OEMs (orginal equipment manufacturers) sent the information to the maker of the ROMs, who put the data/programs in them. In contrast to RAMs (random-access memory), the contents programmed into these devices remained there after power was removed.
Then came P(rogrammable)ROMs – ROMs received by the OEM, who could then program them once only with an electrical instrument.
Then came E(rasable)PROMs, which the OEM could erase with UV light and reprogram.
Next there were EPROMs that could be erased electrically and were called E(electrically)EPROMs.
Thereafter came flash EEPROMs. I had flashed out by then, so I kind of forget their claim to flame, but I think it revolves about very quick reprogrammability without an erase phase. I believe they are the most common at present.
I think there are some other types also these days.
Ordinary “memory” is, of course, RAM (random-access memory). Of course, all the kinds of ROM (read-only memory) are just as random-access as RAM, but RAM came before all of the above, and the name was used to distinguish it from other, earlier (but still used) types of “volatile” (contents lost when power removed) memory, such as the linear, two-port shift registers, sometimes called FIFOs (first-in-first-out), LIFOs (last-in-first-out), or shift registers with “parallel” outputs from certain or all register cells.
Ray, retired electronics engineer (Memories are made of this. . .but I forget why. Well, actually biological memory is different. It is content-controllable and follows what is known to date about natural-neural-network theory.)
{{{Thereafter came flash EEPROMs. I had flashed out by then, so I kind of forget their claim to flame, but I think it revolves about very quick reprogrammability without an erase phase. I believe they are the most common at present.}}}—NanoByte
FlashROM, or Flashable ROM is simply another name for EEPROM, and can be identified by device numbers conforming to the series 28xxxx or 29xxxx device numbers.
In most instances, firmware code is written to the device at or about the time of incorporation into the consumer product, and the end user is given the ability to update all or aportion of the installed firmware code via a manufacturer-supplied software routine. Most contemporary US Robotics/3Com modems utilize this technique to provide for an easy upgrade path for their customers.
Additionally, your very own motherboard probably has this technology to provide for BIOS (Basic Input-Output System) updates. This is necessary to keep pace with the rapidly changing technology as it relates to computer components, peripherals, etc. In this case, the “chip” is generally block programmable.
Block programmability allows pre-defined areas of the chip (which are not programmed with firmware instructions) to be selectively programmed with code, without disturbing the existing contents of the chip. Support for the silicon steppings of the Pentium family of microprocessors is particularly dependent upon this feature.
–Kalél
(The Original EnigmaOne)
Common ¢ for all ages.