A prototype is any version of a video game produced before the final, released game. In the case of a video game that was never commercially sold ("unreleased"), any version of such a game is a prototype.

A prototype can go by several different names like sample, dev cart, demo, alpha, beta, pre-release, preview, and review copy (among others). There has been a lot of debate on what makes a prototype a prototype, but just to reiterate, any version produced before the final game's release is a prototype according to my definition. Alpha refers to a considerably early build (or version) of a game, whereas beta refers to a game in a later stage of development nearing QA (Quality Assurance, i.e. bug testing) approval. I will go more into specific examples of prototypes in the next section. For now, though, let's begin by exploring why you should care about prototypes in the first place.

The greatest allure of collecting a prototype of a released game is the possibility of finding changes not seen in the final version.

These changes could mean experiencing early or not-yet-developed graphics and unpolished gameplay as in this Adventures in the Magic Kingdom prototype. In this prototype, the tile graphics on top of the Main Street, USA stores are not yet drawn; the title screen is crossed out; several sprites in the game are different or missing in cutscenes and such levels as Space Mountain; and some buggy gameplay exists in the Big Thunder Mountain Railroad level that can result in the train derailing and entering a field of zeroes before crashing into an undeveloped track.

At first glance, an incomplete version of a game like Adventures in the Magic Kingdom might not seem like much, but for someone like me, who grew up playing this game for hours on end and whose memories of visiting the Disney theme parks with my family remain a high point in my life, having this unique opportunity to view the game take shape is a very special thing, indeed.

And for anyone who is interested in the process of game development: Nothing beats putting a rough draft under a microscope, examining how a game is formed over time, especially a title coming from a big name company like Capcom.

Think of a game that has always fascinated you. What if there were elements removed or changed during the development of that game? How might have things turned out differently? Imagine if you were able to see how the game once was (or was meant to be). Now stop imagining because answers to those questions could be hiding in a prototype, just waiting to be found.

Playing a prototype of a released game could also mean witnessing firsthand something historically interesting like Nintendo's strict censorship back in the day, as is seen in this Princess Tomato in the Salad Kingdom prototype. In this version, you can buy a clay pot, abbreviated as "POT," in stores and choose to use it from the menu screen. The name of this item was later changed in the final version to "VASE," presumably because of the marijuana drug innuendo of buying and using pot. If Nintendo made Hudson Soft change something as small and innocent as a reference to a clay pot, imagine what other major game content in the vast NES library might have been muffled and censored, too.

In the case of prototypes of games never before released, it isn't hard to see why they are in such hot demand (and fetch much more money)—to be able to finally play a game that has been stored away for decades is a dream of any NES player.

These are only a few reasons why prototypes can be worth your time, money, and effort. Now let's take a look inside of a prototype to see how it functions.

Know your EPROMs.

The plastic Nintendo cartridges that we've all held in our hands act like protective shells for the circuit boards inside. These circuit boards are called PCBs (Printed Circuit Boards). The data found inside of the majority of prototype carts is stored on memory chips on the PCB called EPROMs. "EPROM" stands for Erasable Programmable Read Only Memory.

Masked ROMs... unmasked!

Game data found inside of nearly all regular, officially licensed Nintendo carts is stored not on EPROMs, but rather on memory chips on the PCB called Mask ROMs (or Masked ROMs/ROMs/MROMs). "MROM" stands for Mask Read Only Memory. From this point forward, Mask ROMs/Masked ROMs will be referred to as "MROMs" to differentiate them from the term "ROMs," which people confuse for ROM images, or the files you can download and play on emulators.

If I'm starting to lose you with all of the terminology, let's step back for a moment with an analogy.

If you're like me and enjoy burning CDs of your favorite music, think of MROMs as a CD+/-R, and EPROMs, as a CD+/-RW.

If you ever burned music before on a CD-R, you'll know that you're stuck with whatever songs you chose to put on the disc after the files have been copied. Even if later you have second thoughts about including Rick Astley's "Together Forever" on your Ultimate Club Mix track list, a CD-R can only be burned once—the music files are permenantly stored on the CD—and no amount of pointing out the irony of being stuck forever with "Together Forever" will ever change that.

If, instead, you opted to use a CD-RW to burn your music CD, you could have avoided any future regrets by placing the disc right back into your computer drive, removing Astley, and finding a better song. (Might I suggest Milli Vanilli's "Ma Baker" as a worthy substitute?)

EPROMs were the way that game developers removed their "Astley mistakes"—they gave developers the ability to test games still in development on an actual Nintendo system, allowing them at any time to transfer a newer or more complete version of the game for future bug testing. This continual process of copying (i.e. burning), testing, erasing, and re-copying data gave developers the means to update their games and try them out for as many times as was needed without having to throw away one-time use MROMs (the same way as you might have thrown away countless CD-Rs before investing in a drive compatible with CD-RW).

Unlike permanent MROMs, EPROMs were never meant to last for a very long time—they were temporary solutions for testing games or flashing them quickly to ship them out to gaming publications for previews and reviews before the mass-produced carts were manufactured.

Have you covered up your EPROMs today?

A sure way of visually differentiating an EPROM from an MROM is by seeing if there is a small square in the middle of the chip like the one above. This is called an EPROM window, and it's made of quartz crystal that makes it reflective like a hologram. Exposing this window over time to a certain amount of UV light (like the sun's rays) will gradually erase the game data stored on an EPROM.

Official Capcom sticker on an Adventures in the Magic Kingdom proto EPROM.

To prevent the game data from erasing, EPROMs on prototypes are often covered with an adhesive sticker to help block out UV light. Capcom, for example, had special company stickers of their own made and placed over EPROM windows.

EPROMs can also be erased over several years without any direct exposure to UV light. Just how long it takes for the data to erase under normal temperate conditions, without sunlight or other UV light to progress the erasure, is a discussion that has gone on for some time now. The slow erasing of data without exposing the EPROM to UV light is what as known as bit rot, and I will go more into that subject in a later section on why it is important to dump prototypes.

EPROMs are not unique to prototypes alone; they can be found on some other games, as well. Several pirated and unlicensed games, like all three of the Panesian pornographic titles, use EPROMs. (This means that, one day, Panesian collectors will be left with nothing but their own self shame.)

Test carts are examples of official, non-prototype Nintendo games using EPROMs. These were cartridges given to Nintendo Service Centers to help diagnose console and accessory problems.

In rare cases, there have even been reports of EPROMs being spotted in some officially licensed and released Nintendo carts.

Nintendo Power explains the PPU and the CPU with a cooking analogy. (Image source: RetroMags.com)

But back to the subject of prototypes: An EPROM in a prototype is commonly marked on the EPROM sticker to identify the chip as either PRG or CHR.

PRG stands for "program," and it's, well, the program behind a game that can be read by an NES system's CPU (Central Processing Unit).

CHR, on the other hand, stands for "character," and it's where all of the graphics in a game are stored to be read by an NES system's PPU (Picture Processing Unit).

When combined, they form like Voltron to give you the complete NES gaming experience. (Note that, for some games, there might only be one EPROM inside for the PRG, with the CHR being found on a RAM chip.)

I know all of this is a lot to take in if you're new to prototypes. You may wish to re-read this section again to make sure you have everything down. When you're ready to continue, the next section covers how to find and identify authentic NES prototypes.