Advent Calendar 05: Backwards Combat-ibility

Greetings, and welcome to Advent Calendar 2022! This year we're being self-indulgent and rambling about video games.

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I hope you're all having a happy winter holiday season. Let the nerd rambling commence!

My parents broke down and bought a Super Nintendo the Christmas they wanted to play Final Fantasy II (IV in Japan) and were annoyed that the new machine was not backwards compatible with NES carts. It wasn't necessarily a silly thing to expect. Microcomputer games sometimes had a version for 8K and 16K machines on one disk or tape; I remember a lot of PC games had 5.25" and 3.5" diskettes in the same box, to account for whatever drive you had. And on the console end, a big selling point of the Atari 7800 was its ability to play your existing library of 2600 games.

They would not have run into the same problem if they'd gone with a Sega Genesis, where a reasonably inexpensive accessory called the Power Base Converter allowed you to play 8-bit Sega Master System games on your shiny new 16-bit console. It was an easy trick to pull off, because while the Genesis had a blazing fast 7.6MHz Motorola 6800 processor for all of your sick new graphics needs, it used the brain of a Master System, a Zilog Z80, as its sound controller. All the PBC did was short a couple of wires to direct the CPU requests to the sound chip and voilá! Your Master System games were communicating with a chip that spoke their language.

This technique has been used to great success in quite a number of consoles. Nintendo used a Gameboy Color CPU as the tone generator in its Gameboy Advance handhelds that doubled as a way to play GB/GBC games, and straight up built a DS into their 3DS consoles specifically for DS compatibility. Their Wii console was essentially an upgraded GameCube, and played GC discs, and the easily-forgotten WiiU was based on Wii architecture. Sony pulled a similar trick in its Playstation 2 consoles, where a stripped-down Playstation board was used to handle controller input.

A more interesting case is the Playstation 3. Moving from the original Playstation to the PS2 took Sony from a CPU compatible with a pretty widely-used instruction set to an entirely custom chip, the Emotion Engine, which was compatible with basically nothing else. The PS3's Cell processor and architecture not only strayed farther from industry standards, but was not particularly close to the Emotion Engine either. The ability to play PS1 games was a very popular feature of the PS2, so to maintain backwards compatibility on the PS3, early "fat" 60GB deluxe models contained actual PS2 hardware that handled discs from the previous generation. 

This was an expensive feature in an already very expensive console. It was not a surprise to anyone when Sony opted to implement PS2 compatibility in software in later models instead. PS1 games were already handled via software emulation, and that worked reasonably well, but a PS1 was a bear of very little brain when compared to PS3, whereas the PS2... well, there were some issues. Most games worked mostly fine. A few games were a disaster. Behold:

Microsoft took an entirely different approach, where they effectively ported a lot of popular games to their new hardware and used your old discs as a "proof of purchase" that let you download the new versions. Which is great, until they decide to stop hosting the ports. Microsoft has historically been pretty pig-headed about their ideas (see: the 'always-on Kinect' controversy) so I doubt they'll ever provide first-party native support for previous generations of games. Sony has also ditched direct compatibility; the Playstation 4 has only a Blu-Ray drive, which can physically read DVDs but doesn't recognize the format of PS2/PS3 discs, and can't see PS1 CDs at all. PS4 and PS5 play previous games through a subscription service that gives access to some, but definitely not all, of the past library.