Rather than stored on a hard drive like the operating system, which is easily writable/modifiable by the user, this crucial, small central piece of code is stored on the CPU on a chip of Read-Only Memory (the read-only part is why this sort of code is often called firmware rather than software). But the CPU itself needs a little bit of programmed code in order to work – it has to be able to both understand and give instructions. This ensures your computer has at least some basic functionality even if your operating system were to get corrupted or some piece of hardware were to truly go haywire (see this other post).
It also has a CPU, central processing unit, which is commonly analogized to the “brain” of the computer: it coordinates all the different pieces of your computer, hardware and software alike: operating system, keyboard, mouse, monitor, hard drive (or solid state drive), CD-ROM drive, USB hub, etc. So you know your computer has a hard drive, where your operating system and all your files and programs live. This is the first thing that can start to throw people off. For the rest of us, there’s WinWorld, providing disk image files for all your abandonware OS needs. If you still have the original installer CD lying around, great! You can still use that. These used to come on bootable CD-ROMs, or depending on the age of the OS, floppy disks.
You’ll need the program that installs the desired operating system that you’re trying to recreate/emulate: let’s say, for example, Mac OS 8.5. We’ll go over these in more detail in a minute.
There are several free and open-source software options for emulating legacy Mac systems on contemporary computers.
In particular, while each Mac emulator has some pretty good information available to troubleshoot it (if you’ve got the time to find it), I’ve never found a really satisfying overview, that is, an explanation of why you might choose X program over Y. That’s also not something that to hold against them in the least, mind you – when you are a relatively tiny, all-volunteer group of programmers keeping the software going to maintain decades’ worth of content from a major computing company that’s notoriously litigious about intellectual property….some of the details are going to fall through the cracks, especially when you’re trying to cram them into a forum post, not specifically addressing the archival/information science community, etc.
The tinkering enthusiast communities that come up with emulators for Mac systems, in particular, are not always the clearest about self-documentation (the free-level versions of PC-emulating enterprise software like VirtualBox or VMWare are, unsurprisingly, more self-describing). I elided much of the technical process of setting up a legacy operating system environment in an emulator, since my focus for that post was on general strategy and assessment – but there are aspects of the technical setup process that aren’t super clear from the Emaculation guides that I first started with. Last fall I wrote about the collaborative technical/scholarly process of making some ’90s multimedia CD-ROMs available for a Cinema Studies course on Interactive Cinema.