What exactly is an 'eprom' ?

[winds]

I always see this word used when talking about game cartridges. I have a feeling it's a chip that holds the rom data, but i'm a little confused on what it is.
Do any real, commercial games use eproms? Or are they only used for protos/hacks/demos/beta games? If that's true, what do other cartridges use instead of an eprom? Is there an advantage to using an eprom? How long do eproms last?
Sorry for the million questions, i've just been confused about this for a while.
Thanks!

[Hatta]

EPROM is erasable programmable rom. Most games are made with mask roms, which have the data permanently written on them at fabrication time. So yeah, it's mostly for prototyping, hobbyist stuff. You can get an eprom that's a drop in replacement for most mask roms. The major advantage is that they're writable. Once they're written they're pretty stable, I'm sure there's a limit to how many times you can rewrite an eprom though.

[Ziggy]

You're right, it's a chip that holds ROM data. I've read that some commercial carts DO use EPROM, but that it's a very rare thing. Any cart you're gonna get (NES, SNES, Genesis, etc) will have mask ROMs. They're like OTP (One Time Programmable) EPROMs only the data is permanently sealed in the chip. I like to compare it to burned and hard pressed discs (burned discs can wear out eventually while hard pressed disc should last a very long time) but I've heard mask ROMs are suppose to last until a nuclear war. Anything short of getting struck directly by lightening, a mask ROM should last forever.

EPROMs, EEPROM, and flash chips can suffer bit rot. Bit rot is basically when the chip starts to loose it's data. It sort of "leaks" out. Most chips garuntee 10 years shelf life, but take the NES College-something or other- Championship cart that sold on eBay recently. It had a bunch of EPROMs on it, and that cart was made in 1992 (right?) so it's almost 20 years old and still works.

The only advantage to using an EPROM is, unless it's an OTP, is that you can erase and reprogram it. EEPROMs (electric erase programmable read only memory) can be erased electrically and reprogrammed. That's why you'll see them on proto carts and whatnot. An official cart, that gets an official production, will have tons of mask ROMs made up. Otherwise mask ROMs would be too expensive to use. And you wouldn't want to use a mask ROM anyways for a proto cart being that you can't erase them. Likewise, you wouldn't use an EPROM on a finished product.

All arcade PCBs that I've seen use EPROMs though. I guess so they can update the game at any time without a massive headache. So Street Fighter II can get turned into Turbo with the swap of a few EPROMS (then I guess CAMPCOM would reuse the EPROMs). Your computer's BIOS will be on an EPROM too (since you can upgrade it).

And just so you know, a lot of people refer to the mask ROM on a cart as an EPROM (not really knowing the difference). That being said, you might also hear people refer to something as an EPROM, EEPROM, or mask ROM incorrectly.

[Mod_Man_Extreme]

It's actually spelled EEPROM with EPROM the common misspelling.

Basically it stands for:

E:lectrically
E:rasable
P:rogramable
R:ead
O:nly
M:emory

As mentioned above they're basically for hobbyists and prototyping as after about 5-15 years the data on them begins 'bit-rotting' away as the electrons inside escape.

Commercial cartridges as also mentioned above use MASK ROM's which are 100% permanent and will outlive you, your kids, your grand kids and more unless physically destroyed by some external force. Basically only a hammer or other hard object smashing them to bits or by rusting away from storage in an environment prone to corrosion.

EDIT: Ziggy beat me to the punch with a longer more thought out version of what I was trying to convey.

[Ziggy]

Well EPROMs and EEPROMs are confused with good reason, they're basically the same thing. I believe that most EPROMs have an EEPROM counterpart. The only real difference, from a user point of view, is how they're erased. EPROMs, of the erasable variety (as oppose to OTP), have a little window that when exposed to ultra violet light will erase the data. EEPROMs are erased electrically (hence the name). Other than that, they're pretty much the same thing. They share the same form factors and pinouts.

But both have been replaced by flash memories. Flash memory is cheaper to produce (I think) and is smaller, faster, et cetera, et cetera. They're even more durable (wiki states that along with being more tolerable to temperatures and pressures they can even survive being submerged in water). ST and AMD (and probably others) even make flash memory that's compatible with (E)EPROMs so that you can use the newer technology with older stuff.

Which reminds me, if you wanna know more about memory, look up the wiki pages for EPROM, EEPROM and flash memory. In fact, the first few paragraphs of the wiki page for flash memory is comparing it to EEPROM.

@ Mod Man: All that being said, if you remember when we were talking about EPROMs in repros and such suffering from bit rot, I've opted to use flash memory whenever possible because it's a lot more durable (among other reasons).

[Duane Dibbley]

CAMPCOM

Is that the Boy Scout version of Capcom?

[winds]

Wow, thanks guys! Definitely helped clear up most of my confusion.
Now another question haha, I bought a proto recently with an eprom inside. How would I go about backing this up before bit rot takes over. Is there a cheap way?

[Mod_Man_Extreme]

Wow, thanks guys! Definitely helped clear up most of my confusion.
Now another question haha, I bought a proto recently with an eprom inside. How would I go about backing this up before bit rot takes over. Is there a cheap way?

I'll be honest and say I don't know jack about how to back up or dump carts, but just out of curiosity what proto did you buy?

[Anapan]

There's this thingy
http://kevtris.org/Projects/copynes/index.html
I heard about a USB universal eeprom reader-writer by a company called Topwin that was fairly cheap when I looked for one but I don't know if it'd work for NES chips (tho it should cause it supports thousands of types...)

[Ivo]

CAMPCOM

Is that the Boy Scout version of Capcom?

I'd just like to state that I fancy this sort of jokes. But really, CAMPCOM makes CAMPs instead of CAPs.

Also, on the more serious side, good explanations everyone else.

Ivo.