Do many arcade games come with EROMS?

[Scottacus]

From looking around it seems like many arcade games have UV erasable  EPROMS but one of my two Gorf ROM boards has ROMS that have no UV sight window and are labeled Midway on the top.  I assume that these are non erasable EROMs (not EEPROMs), is this the case and was this done frequently?

[MonMotha]

They are probably mask ROMs.  These are actual (semi-)custom ICs that are non-programmable, and hence non-erasable, ROMs made special with just the data the manufacturer wanted on them.  They were quite suitable for volume production as they were cheap in modest volume (cheaper than buying a bunch of EPROMs and programming them) and extremely reliable.  The downside is that there's long-ish lead time to get the masks set up, and there's absolutely no way to change any of the data once you commit to the mask set.

It's not uncommon to see a big bank of mask ROMs with a couple changed out for EPROMs that were distributed as patches/upgrades.  Sometimes one or two were distributed with the initial installation due to bugs/upgrades made after the mask freeze.  Some smaller releases that didn't have the anticipated volume to justify a mask ROM (which again needs modest volume) were distributed entirely on EPROMs.  In some cases, initial releases were made on EPROMs with subsequent volume production, once volume was known and program stabilized, done on mask ROMs to drive down cost.

There also exist OTP ROMs (aka PROMs).  These are One-Time-Programmable devices that generally are actually just EPROMs with no UV window.  You could in theory erase them by decapping them and exposing them to UV just like EPROMs, but it's not worth trying.  OTP devices are typically slightly cheaper than UV EPROMs because they can be easily put in plastic packages rather than expensive ceramic packages.

[Scottacus]

Thanks for the great answer, that was just what I wanted to know 

[lilshawn]

most games came with what's commonly known as PROMs or FPROMs OR OTPROMs (basically one time programmable read only memory.)

They where chosen because of their cost. they are cheaper to produce because they can be encapsulated in straight plastic like a regular IC chip. an EPROM needs to have a quartz window in a ceramic package built and a different type of die installed, this incurs a greater cost due to the extra processing that is required to produce them.

when you are making 1000's of games with sometimes upwards of 10 ROM chips on them, paying less for each of them begins to add up considerably.

PROM chips where superseded in the late 80's and early 90's to get the best of both worlds by EEPROMS (electronically erasable ROM) and soon after, Flash ROM. (cheap production costs, but electronically erasable so there was no need for the expensive to produce quartz UV window and ceramic packaging.)

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[Scottacus]

Thanks lilshawn, I really like your profile message about breaking and fixing stuff, oh so true for many of us!