Well for those who don't know, there exists extremely rare carts known as "Prototypes" which leaked from the video game industry when games were in their testing phase.
Not only they are interesting because they contain unpolished versions of games we know with sometimes significant differences.
However, for us they are also interesting because it can give us an idea of how people who were actually working on NES games worked back then. I know some people here don't give a damn, with the argument we are more equipped than they were, but personally I care a lot about how they actually did to make games.
After this amazing interview of Neil Baldwin we were able to learn a few things, in short that they used PCs to compile assembly, that this was horrendously slow, and that they had a card they could link to via some kind of parallel port.
Now let's analyze the pictures of boards found in prototypes cards that I was able to find on the net :
First let's start with the easier, those who are on Bootgod's database, on which we have the most detailed info about them :
http://bootgod.dyndns.org:7777/profile.php?id=2572
This prototype is made of a standard japanese CNROM board with a fami -> NES adapter. Since the game was developed in Japan, it made sense they used a board that they already used for the japanese version and used an adapter to get it on the NES.
Likely whoever developed this game had to compile their source, then remove EPROMs from their sockets, UV-light erase them, program them, and insert them back. Very tedious as opposed to assemble + run emulator on a modern PC.
Because boards with smaller ROMs are compatible with EPROMs, they could use the same boards for large runs of games and for internal testing though.
http://bootgod.dyndns.org:7777/profile.php?id=2694
This prototype is from Sunsoft, which used their own boards instead of Nintendo. Very likely the board is identical to what they used for large runs of games, it doesn't have anything special.
http://bootgod.dyndns.org:7777/profile.php?id=2708
This is a UNEPROM board (prototype specific). This time, they didn't use a fami -> NES converter, but directly a NES board, even though the game was developed by Capcom which is a Japanese company.
Again other than it's compatible with EPROMs, this board is nothing very different from a regular UNROM board. Maybe it also accepts 256 KB EPROMs (UOROM) ? It would make sense as the pinout is the same. Unfortunately the picture isn't detailed engough so we can't tell.
http://bootgod.dyndns.org:7777/profile.php?id=3795
This uses a SKEPROM board (prototype specific). A famicom board for a famicom prototype. Note that since this board doesn't have a circular hole, it wouldn't fit a NES case with a fami -> NES adapter.
Again it's almost like a regular SKROM board, with support of standard pinouts. There is circuitery for battery backup and PRG RAM, but it wasn't used in this game.
http://bootgod.dyndns.org:7777/profile.php?id=2950
This uses a TKEPROM board (prototype specific). It's the most interesting board around. This time it's definitely NOT close to a standard TKROM board.
It has silkscreens, which shows instructions how to use solder pads for different PRG and CHR sizes. Whoever uses this board is supposed to use multiple 128 kB EPROMs to make up the total size, which is why there is 4 slots for PRG ROMs and 2 for CHR ROMs. A 74HC139 adress decoder is used to control the enable lines of those chips.
Again there is circuitery for RAM and battery backup, and this time it's used.
On the back of the board, there is two wires connectings to PRG ROM's A17 and A18 lines. Apprently they modified the board so that they could put a 512 kB EPROM instead of using 4 128 kB EPROMs. Nevertheless the game that is in uses 128 kB, and the EPROM that's on the board is a 27C1000 which is 128kB.
On the back of the board, there is no silkscreen, but there is more instructions about how to use solder pads written in negative on the solder mask. Apparently it says "PRG : ??? Type / JEDEC TYPE". and "CHR : ??? Type / JEDEC Type". So maybe the other type is the same as the regular TKROM boards ?
Because they have all those solder pads, it makes sense they would use this board not only for TKROM games but for all MMC3 games.
Now there is also pics of a Mega Man 3 and Mega Man 4 prototypes form this site.
It shows that they used multiple 128 kB EPROMs to get to the desired PRG/CHR ROM sizes, but also that Mega Man 4, which uses CHR-RAM, can also fit a TKEPROM board. Likely they had a jumper configuration for that or cheated with wires. Mega Man 4 have PRG RAM installed, even if the game didn't used it (at least the final version didn't).
http://kevtris.org/mappers/mmc1/NES_SKEPROM.jpg
This SKROM board, from Kevin Horton, is a MMC1 development board. Surprisingly, it is a quite different from the japanese SKROM board. For some reason it has support for 4 lockup chips (USA, England/Oceania, Contiental Europe, Asia). It has provisions for PRG RAM and battery backup, but this wasn't used here (the final game is SLROM). So chances are that this generic board were used not only for SKROM games, but for many MMC1 games.
The wire connects CPU R/W from the cart edge to the MMC1. No idea why they added it (did they cut the line accidentally ?), but it shows developpers sometimes were dealing directly with wires.
Eventually, this thread is a goldmine for prototype pics.
In addition to some non-NES stuff, and to what was already shown above, we can see :
http://i113.photobucket.com/albums/n223/mrmark0673/nintendo/100_0270.jpg
A Mega Man 2 proto which uses a fami -> NES adapter. The board is HVC-SNROM-TEST-01 ! It uses a 3-mil wide CHR-RAM chip instead of most commonly seen 6-mil wide ones, a surface mounted (!) PRG-RAM chip (Mega Man 2 doesn't use it), and two 128 kB EPROMs, with a surface mounder adress decoder (likely 74HC139). Has circuitery for battery backup, unused here.
http://i113.photobucket.com/albums/n223/mrmark0673/nintendo/100_0990.jpg
This ones uses a normal NES-TSROM board, modified with wires to accept EPROMs. Which leads me to suspect it's fake, but since the guy has real prototype why fake one ? Or maybe someone else made a fake and sold it as a prototype for an amazing price ? We'll never know...
A few others prototypes on the theads uses apparently modified standard boards as well.
http://i113.photobucket.com/albums/n223/mrmark0673/nintendo/100_1240.jpg
The right part of the image is (if the label on the cart is true...) a SKWEPROM board, which apparently allows for 2x128 KB PRG ROM (Bases Loaded II effectively uses 256 kB PRG ROM).
http://i113.photobucket.com/albums/n223/mrmark0673/Protos/100_1617.jpg
This appears to be an AOEPROM boards. With 2x128 KB PRG ROMs again, the two chips on the left are likely a 74HC161 and a 74HC?? which is used both as an adress decoder and a bus-conflicts preventer.
You can bet Rare used almost exclusively this board when developing games, with their insane fidelity to mapper 7.
http://i113.photobucket.com/albums/n223/mrmark0673/Protos/100_1625-1.jpg
Another one with a fami -> NES converter. Apparenty it's a SMEPROM board, it's functionally like SGROM but with 2x128 KB of PRG ROM again. The address decoder is made with resistor/diode/transistor logic instead of using a 74xx chip !
Wow this was long, and hopefully interesting.
Not only they are interesting because they contain unpolished versions of games we know with sometimes significant differences.
However, for us they are also interesting because it can give us an idea of how people who were actually working on NES games worked back then. I know some people here don't give a damn, with the argument we are more equipped than they were, but personally I care a lot about how they actually did to make games.
After this amazing interview of Neil Baldwin we were able to learn a few things, in short that they used PCs to compile assembly, that this was horrendously slow, and that they had a card they could link to via some kind of parallel port.
Now let's analyze the pictures of boards found in prototypes cards that I was able to find on the net :
First let's start with the easier, those who are on Bootgod's database, on which we have the most detailed info about them :
http://bootgod.dyndns.org:7777/profile.php?id=2572
This prototype is made of a standard japanese CNROM board with a fami -> NES adapter. Since the game was developed in Japan, it made sense they used a board that they already used for the japanese version and used an adapter to get it on the NES.
Likely whoever developed this game had to compile their source, then remove EPROMs from their sockets, UV-light erase them, program them, and insert them back. Very tedious as opposed to assemble + run emulator on a modern PC.
Because boards with smaller ROMs are compatible with EPROMs, they could use the same boards for large runs of games and for internal testing though.
http://bootgod.dyndns.org:7777/profile.php?id=2694
This prototype is from Sunsoft, which used their own boards instead of Nintendo. Very likely the board is identical to what they used for large runs of games, it doesn't have anything special.
http://bootgod.dyndns.org:7777/profile.php?id=2708
This is a UNEPROM board (prototype specific). This time, they didn't use a fami -> NES converter, but directly a NES board, even though the game was developed by Capcom which is a Japanese company.
Again other than it's compatible with EPROMs, this board is nothing very different from a regular UNROM board. Maybe it also accepts 256 KB EPROMs (UOROM) ? It would make sense as the pinout is the same. Unfortunately the picture isn't detailed engough so we can't tell.
http://bootgod.dyndns.org:7777/profile.php?id=3795
This uses a SKEPROM board (prototype specific). A famicom board for a famicom prototype. Note that since this board doesn't have a circular hole, it wouldn't fit a NES case with a fami -> NES adapter.
Again it's almost like a regular SKROM board, with support of standard pinouts. There is circuitery for battery backup and PRG RAM, but it wasn't used in this game.
http://bootgod.dyndns.org:7777/profile.php?id=2950
This uses a TKEPROM board (prototype specific). It's the most interesting board around. This time it's definitely NOT close to a standard TKROM board.
It has silkscreens, which shows instructions how to use solder pads for different PRG and CHR sizes. Whoever uses this board is supposed to use multiple 128 kB EPROMs to make up the total size, which is why there is 4 slots for PRG ROMs and 2 for CHR ROMs. A 74HC139 adress decoder is used to control the enable lines of those chips.
Again there is circuitery for RAM and battery backup, and this time it's used.
On the back of the board, there is two wires connectings to PRG ROM's A17 and A18 lines. Apprently they modified the board so that they could put a 512 kB EPROM instead of using 4 128 kB EPROMs. Nevertheless the game that is in uses 128 kB, and the EPROM that's on the board is a 27C1000 which is 128kB.
On the back of the board, there is no silkscreen, but there is more instructions about how to use solder pads written in negative on the solder mask. Apparently it says "PRG : ??? Type / JEDEC TYPE". and "CHR : ??? Type / JEDEC Type". So maybe the other type is the same as the regular TKROM boards ?
Because they have all those solder pads, it makes sense they would use this board not only for TKROM games but for all MMC3 games.
Now there is also pics of a Mega Man 3 and Mega Man 4 prototypes form this site.
It shows that they used multiple 128 kB EPROMs to get to the desired PRG/CHR ROM sizes, but also that Mega Man 4, which uses CHR-RAM, can also fit a TKEPROM board. Likely they had a jumper configuration for that or cheated with wires. Mega Man 4 have PRG RAM installed, even if the game didn't used it (at least the final version didn't).
http://kevtris.org/mappers/mmc1/NES_SKEPROM.jpg
This SKROM board, from Kevin Horton, is a MMC1 development board. Surprisingly, it is a quite different from the japanese SKROM board. For some reason it has support for 4 lockup chips (USA, England/Oceania, Contiental Europe, Asia). It has provisions for PRG RAM and battery backup, but this wasn't used here (the final game is SLROM). So chances are that this generic board were used not only for SKROM games, but for many MMC1 games.
The wire connects CPU R/W from the cart edge to the MMC1. No idea why they added it (did they cut the line accidentally ?), but it shows developpers sometimes were dealing directly with wires.
Eventually, this thread is a goldmine for prototype pics.
In addition to some non-NES stuff, and to what was already shown above, we can see :
http://i113.photobucket.com/albums/n223/mrmark0673/nintendo/100_0270.jpg
A Mega Man 2 proto which uses a fami -> NES adapter. The board is HVC-SNROM-TEST-01 ! It uses a 3-mil wide CHR-RAM chip instead of most commonly seen 6-mil wide ones, a surface mounted (!) PRG-RAM chip (Mega Man 2 doesn't use it), and two 128 kB EPROMs, with a surface mounder adress decoder (likely 74HC139). Has circuitery for battery backup, unused here.
http://i113.photobucket.com/albums/n223/mrmark0673/nintendo/100_0990.jpg
This ones uses a normal NES-TSROM board, modified with wires to accept EPROMs. Which leads me to suspect it's fake, but since the guy has real prototype why fake one ? Or maybe someone else made a fake and sold it as a prototype for an amazing price ? We'll never know...
A few others prototypes on the theads uses apparently modified standard boards as well.
http://i113.photobucket.com/albums/n223/mrmark0673/nintendo/100_1240.jpg
The right part of the image is (if the label on the cart is true...) a SKWEPROM board, which apparently allows for 2x128 KB PRG ROM (Bases Loaded II effectively uses 256 kB PRG ROM).
http://i113.photobucket.com/albums/n223/mrmark0673/Protos/100_1617.jpg
This appears to be an AOEPROM boards. With 2x128 KB PRG ROMs again, the two chips on the left are likely a 74HC161 and a 74HC?? which is used both as an adress decoder and a bus-conflicts preventer.
You can bet Rare used almost exclusively this board when developing games, with their insane fidelity to mapper 7.
http://i113.photobucket.com/albums/n223/mrmark0673/Protos/100_1625-1.jpg
Another one with a fami -> NES converter. Apparenty it's a SMEPROM board, it's functionally like SGROM but with 2x128 KB of PRG ROM again. The address decoder is made with resistor/diode/transistor logic instead of using a 74xx chip !
Wow this was long, and hopefully interesting.