The emulator's page actually runs a Linux emulator first, which then you can use to call up the SimH project's PDP-11 emulator, passing it a boot.ini file containing bootstrap instructions. After booting into Unix v4 proper, you'll be greeted with a familiar prompt so you can log in as the "root" user.
As the old saying goes, though: beware, there be dragons here. You'd think that much like the kid in Jurassic Park, you could find your way around it because it's a Unix system, but there's no shortage of proverbial grues just waiting to eat you.
First off, you can forget about most of your commands or aliases to them. For starters, ll is short for ls -la, so you better get used to typing the whole thing. Likewise, chdir was the Old English form of cd. And while the usual cat can output files like you'd expect, editing them is a process, as there's no nano. Brother, hold on, as there ain't no vi either — you use ed and enjoy viewing files a few lines at a time and humbly requesting for substitutions (ex: s/one/two).
Additionally, as you'll quickly figure out, the navigation shortcuts like arrow keys simply do not exist. The screen was treated like a roll of paper, and in order to go back one character you have to erase it with the "#" character, with one of them meaning "go back one character".
If you want to kill the entire line, Ctrl+C won't save you, only typing "@" and hitting Enter will do. You can click this link if you want a deep technical dive on the vicissitudes of emulating PDP hardware and Unix.
The backend of emulation comes by way of the Linux-native SimH emulator that's running inside the almost-magical JSLinux emulator, with a barebones version of Alpine Linux. Incidentally, JSLinux can also get you going with FreeDOS and even Windows 2000. That ought to trigger more than a couple waves of nostalgia.
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Bruno Ferreira is a contributing writer for Tom's Hardware. He has decades of experience with PC hardware and assorted sundries, alongside a career as a developer. He's obsessed with detail and has a tendency to ramble on the topics he loves. When not doing that, he's usually playing games, or at live music shows and festivals.