So like if I have an extra computer laying around, I can basically turn it into an arcade machine, and have it run games a lot better than it should because of it. This is Steam games in particular.
2 Answers
Back in the day, with extremely limited resources, and mostly standard systems, it was possible. You knew you had a 8086 processor, a fairly standard set of video outputs
Many games would boot directly off a disk. With modern machines the benefits are limited to say the least - especially when you're talking about steam.
Nowadays, the hardware stack, right down to the processor needs drivers for full functionality. A bootable game would need a fairly comprehensive kernel, drivers... etc.
Since most arbitrary games run on windows or linux, to run such games, your hypothetical kernel would need to support the APIs these games support. OpenGL is fairly common, and if you had a video driver that supports it, porting is plausible. DirectX is trickier.
At the end of the day your directly bootable game would have a good chunk of a proper, common OS running underneath it.
Amusingly, modern consoles are often x86 or at least general purpose systems (running variants of powerpc, or I guess ARM or MIPS), they do run cut-down, specialized versions of standard OSes - Sony uses Freebsd, MS uses a Windows varient and so on.
So, practically speaking, there's no modern system I know of that does what you want. You need an underlying OS to run Steam (linux or windows) - and even steamos is debian running steam as its main UI. You'd need to roll in/write basically an entire OS (a non trivial task!) and drivers to get everything to work.
In theory, you could start off an extremely minimal install of windows or linux, carefully pare down the system for the drivers you need, streamline the boot process and so on. Steamos is an example of that. You could also find tools to remaster a windows install to be more minimal, though with modern systems, I suspect the time spent would be considerable, and the utility minimal.
1You can't "boot" into a game. Games are just programs running on an operating system, and usually require "tons of resources". That being said, for Steam there is the option of SteamOS:
6SteamOS is a Debian-based Linux operating system by Valve Corporation and is the primary operating system for Valve's Steam Machine video game console. It was released alongside the start of end-user beta testing of Steam Machines in December 2013.
