I have zero firsthand knowledge, but I saw some devs talking about devkits once.
Apparently everyone working on the game should ideally have a devkit. But if you're trying to make a launch game for the platform, then maybe you were only able to buy one handmade prototype dev kit, and you consider yourself lucky to get that much. So then your entire team crowds around the dev kit and tries to figure out how it works as a communal activity. The instructions are sometimes handwritten in Japanese, and are just a collection of "Oh, you need to know this. Oh shit, you need to know this too!" without very much in the way of structure or editing or streamlining. Eventually people figure out what kind of work can be done on their PCs back at their desks, but everything they make needs to be tested through the dev kit, so people start lining up to try and get a turn at using the dev kit. Maybe there's some more work you can do on your PC, but if you don't know if the thing you're doing is correct, then you're just wasting your time running down the wrong road. So there's a HUGE bottleneck as people try to get on the devkit. The lack of devkits at this point is literally costing your company money through lost productivity.
Eventually your boss is able to buy a second devkit, and a third, and a fourth. Eventually some important people get to work with their own dedicated dev kit, but there are always some people sharing a dev kit, because dev kits are expensive, and the lowest-ranking people at the company aren't worth the expense. You can just go share with Steve. Two people can share a dev kit without tripping over each other that much.
And each new dev kit that your company picks up is better and more refined than the ones that were bought earlier. So the first dev kits become the worst dev kits, the ones that nobody wants to work on. Unless you have just been promoted from sharing a dev kit to having your own dev kit. They might drop the old piece of junk on your desk, but it's your piece of junk now, which makes it amazing.
I know a lot of people who worked on Atari Jaguar development, and the stories they've told me about the Jag SDK are honestly amazing, in all the bad ways. Documentation is an enormous part of an SDK, the actual hardware part is pretty rote. Being real, the hardware here is basically massively overpriced, no way was Saturn debugging hardware worth $70k in 1995, but they were the only game in town. The SGI workstation.... yeah, that was probably worth $100k, but the hardware to debug a saturn? No way. All a debugger really needs to do is be able to issue a non-maskable interrupt to the CPU to halt execution, read the registers, dump memory, and probably have a way to upload things to the console. Most retail consoles have some vestigial form of this built in already.
What really separates SDKs are the tools and resources and documentation. Microsoft has basically been the king of this world since around 1995, that is what this old meme is about:
People focus on him being sweaty and goofy in the video, but miss what the presentation actually was. Microsoft went
all in on building world-class tools for their platforms, amazing documentation, stuff like that. Valve currently does similar stuff with their development libraries. I'd say Microsoft and Valve are pretty much the best in class in this field today.
Part of the reason the Saturn was so much harder to develop for than the Playstation was because Sega's SDK shipped with poor documentation, often in japanese, with poor tools. So much had to be remade by hand from devs. By contrast, Sony shipped an amazing, easy to use C compiler and SDK, with tons of english documentation, that made working with the PSX a snap. Consider this -- to this day, there is still no real homebrew Playstation dev kit, primarily because the official tools were so advanced and great. Even today, if you want to make playstation homebrew, your best bet is to grab a PSX SDK. By contrast, there are tons of Sega open source devkits out there, because as time went on, the cross products Megadrive dev kit, for example, was long in the tooth compared to, say, a modern UMDK.
Anywho, back to the Jaguar: It basically shipped with
no documentation. The Devkit itself was full of bugs, the hardware itself actually did not work correctly. For example, the atari jaguar actually has a super advanced controller port, it works like a parallel port and can do all sort of two way communication. Known as the Atari Advanced Joystick port, it was honestly one of the most advanced communication protocols on any console for many, many years. EXCEPT, the early launch Jaguars had a hardware bug which made reading in two directions from the joystick near impossible. So the very feature of the joystick ports, wouldn't reliably work between revisions of the console, so no dev could ever use it. On top of this, different revisions of the console actually run at different speeds. Certain games will run faster on certain consoles.
So when you got a Jaguar SDK, they dump a very bare bones system, with no documentation, that didn't work, and told developers to "make it work" and pump out games in like 6 months time. Insane that
any jaguar games ever got made.