I am learning a lot by reading this thread and I'm sure many others have too - thanks to all that have contributed! Another thread I also read is https://pinside.com/pinball/forum/topic/help-burning-a-stern-rom#post-4592642.

I have some follow-up questions, mainly surrounding terminology in stating size of a chip, size of a ROM image file, and corresponding pinball manufacturer documentation.

When someone refers to an EPROM or PROM only by size, say "a 512K EPROM", does the number represent Kbits or Kbytes? One example would be Stern SB157 that discusses using a "blank 512K EPROM" to update the sound OS on a Whitestar board. I looked at the biosv8.u8 file for that sound update, and Windows shows the file as 128KB (bytes) in size on my hard drive, so it would seem that Stern must have meant a chip of 512Kbytes in size, not 512Kbits. So, a 27C010 chip. But that doesn't make sense as the chip at U7 is physically smaller than a 27C010 chip. U7 (the location where the sound update chip would temporarily be installed) is described in the LOTR manual as "27256 / 27512, CPU Sound, 512K". Both of these chips would be the correct physical size for the socket at U7, so Stern must have been talking about a 512kbit EPROM after all. But neither a 27256 or 27512 chip can hold a 128Kbyte file, so I'm still missing something here. Perhaps the 128KB file size I see for the biosv8.u8 file on my hard drive is not the correct way to identify the actual size of the image in the file?

Here is another example, just in case there was something uniquely odd about the example above. If I look at the directory entry for a ROM file extracted from a zip file on my computer, and that file is shown as 128KB (KB means bytes in this case) on disk, then how does that relate to the size chip needed to burn that file to an EPROM? For example, the CPU file in the LOTR 10.0 or 10.02 zip files both result in an extracted file that is 128KB as stored on disk. The readme file says "Game ROM 1M". The LOTR manual shows U210 as "27C040 CPU Game, 1MB. The PinWiki chart shows the 27C040 as a 4Mbit / 512Kbytes chip. Why would Stern say 1MB in the manual? Would one use a 27C040 chip and just multiply the software file as many times as necessary (quadruple it) to fill the 27C040? Could one instead use a 27C010 and burn the image without multiplying it to fill the 27C010?. What about a 27C020, could that chip be used with a doubled software file? Was Stern thinking to the future in specifying a 27C040 chip, so future games could have significantly bigger code and still run on this board? Or by specifying a 27C040 chip do they for some reason really want that size chip to be used and not a smaller chip? Or was there a typo in the Stern manual and they should have said "27C010 CPU Game, 1MB"?

The Stern manual's documentation for U7 puzzles me for another reason. The PinWiki chart shows 27256 as a 256Kbit chip, and 27512 as a 512Kbit chip, so these are different size chips. Could Stern really have used either chip in U7 even though the diagram also says 512K, or is this really always a 27512 512Kbit chip?

And finally, the Stern manual's documentation for U37, U36, U21 and U17 also puzzles me for a different reason. These are described in the manual as: "M27C04000I-12FI, Voice ROM x, 8MB". PinWiki shows the 27C040 as 4Mbit chip, but Stern lists as 8MB on the diagram. What chip type is really used in these locations, a 27C040 4Mbit chip or a 27C080 8Mbit chip? I guess I could understand if the "8MB" had been a size smaller than the specified chip (could multiply the image to fill the chip), but 8MB is larger than the specified chip size! The actual image files seem to be only 1MB, so perhaps the 8MB shown in the Stern manual is a typo?

Thanks for adding some clarity!

And another quick follow-up question. Some of the labels on EPROMs seem to fall right off with just a touch. Some are stuck on there really well. What do you recommend to safely use to remove the labels that are stuck on quite well? Would GooGone work ok, or would that damage the chip? According to this thread http://www.vcfed.org/forum/archive/index.php/t-57315.html, not much would damage these chips so I'm thinking of using Goo Gone followed up by alcohol to remove any residue.

Playing with my new GQ-4x4, and UV EPROM eraser. Interesting how different EPROMs take different amount of times to erase. I have to say that the most difficult one to erase out of the 20 I have erased so far was a National NM27C040. No idea why, but this one made 3 trips thru the eraser with increasing times before it would test as blank, final trip in the eraser was for 1 hour!

That is also true of the GQ-4x4 that i just bought. You must install the USB 3.0 driver manually. Go to http://download.mcumall.com to get what you need. I think this YouTube video can also help you:

In case the link stops working, you can search for "How To: Burn, Read, and Erase Pinball EPROMS with GQ-4X". In this video, he takes a GQ-4X4 out of the package, gets it ready for use and burns an EPROM.

Got it, and that Wikipedia chart looks super useful. I will pay attention to the image file size, and pick an EPROM that can handle that size, or larger with the same pin count package.

Using this info has now helped me identify why I'm having trouble figuring out in advance how to burn a U7 Bootflash EPROM to update the Sound OS on my LOTR before installing the LOTR LE 10.02 CPU code in preparation for adding a shaker. The file image I was intending to use to burn the U7 Bootflash EPROM is named BIOSv8.u8 and is 128KB in size. I got that file per this Pinside reference: https://pinside.com/pinball/forum/topic/how-to-install-shaker-motor-in-lotr-standard-edition/page/5#post-3080604. That must not be the correct file because a 128KB file would require a 1Mbit chip or larger, but a 1MB chip is not the correct pin count package (too big) to fit into the 28 pin socket at U7. So, I will start the search again for the correct image file for the U7 Bootflash EPROM, and when I find that then I can burn it to a 28 pin EPROM of the appropriate size (or larger including repeat copies to bulk up the file image).

Unless this is indeed the correct file, and there is a different reason why it shows at 128KB on my computer's hard drive?

How do the Checksums work for EPROMs? I just noticed that the checksum calculated by the GQ-4x4 for a given image file changes based on what Device you select. It varies for size of EPROM, and even more interesting for the same size EPROM the checksum differs between different EPROM manufacturers. For a particular file I have, when I select AMD AM27512 the GQ-4X4 software displays a checksum value of 00A68ED5, but when I select ST M27512 the GQ-4X4 software displays a checksum value 00FC9040. Why is that?

Hmm, it may be because I was erroneously looking at a file too large to fit on the target EPROM. Using another file, 64KB in size, I get exactly the same calculated checksum values when selecting either the AMD AM27512 EPROM as the Device, or the ST M27512 as the Device, which seems normal.

That is good to know. I wish I had taken screen shots to show what I observed before. But looking again now using the same file as before I am indeed getting identical checksums from compatible EPROMS by different manufacturers. Not sure why I didn't see this when checking earlier, but I will chalk it up to "user error" of some kind. Thanks Quench!

That does make sense, and I did see the truncate message. I'll make it a habit to select the Device (chip) first, and then load the file.