Quoted from Nusilor:
Sorry was just looking at the data sheet for a 27c1024. they are 16x64kbit 16 address pins(including a0). So will only break down in to 8K(64kbit)chunks. That is in a 4k slot. I believe it will break down in to 32 in a 2k
In choosing a chip, you should stick to 8 bit chips (Chips with D0-D8) as using higher width chips such as 16 bit chips (D0-D15) will be wasteful, in terms of usable storage. Remember, this era of pinball machines are only 8 bits wide and so the excess data pins on the wider chip will go unused.
You also need to think about timing/response time and handshaking signals of the chip you choose. They must match the 2716 and 2732 chip specification and be at least as fast as that.
No matter the size of the chip, they will always break down into 2K chunks using A0-A10. 4K chunks would need A0-A11. 8K chunks A0-A12, etc. Any extra address lines on the chip you choose should each be routed (in order) to a DIP switch.
The bigger the chip, the more chunks you get. System 7 boards (in system 7 mode) need 4K chunks. A system 7 board in system 6 or earlier mode will need 2K chunks. System 6,4,3 also need 2K chunks.
For those that don't quite know how to decide, I'm likely going with an SST39SF040 (512k x 8 bits) when I do start putting some pre-programmed adapter boards up for sale. In the mean time, if you decide on a different chip that works please feel free to chime in, and post your design for others if you like.
Here's where you can get the 39SF040 from digikey (digikey part# SST39SF040-70-4C-PHE-ND) in Canada:
Don't forget to use a chip that your chip programmer supports, and use a socket on your adapter board - you'll need to quickly remove the chip to program it with newer versions of ROMs HINT: Make your life easy and use a ZIF socket!