That is really hard to answer. Wikipedia says "Over 80" Cray-1s were sold, so they weren't all that common, despite being the iconic representation of a supercomputer.

The answer is different for each machine. There are emulators for some of the older machines. See http://simh.trailing-edge.com/ and http://simh.trailing-edge.com/links.html for some.

Here's an HP-2000 emulator:

1. Telnet to mickey.publicvm.com (yes, telnet)

2. Slowly alternate CTL-J and CTL-M until you see a “PLEASE LOG IN” message.

3. Enter “HEL-T001,HP2000,1″ . The resulting output includes:

    Try exe-castle.b300, exe-kingdm.g100, exe-spawar.r500
    To play the 1975 version of Oregon Trail type exe-oregon
    To play the 1978 version of Oregon Trail type exe-ore2
    To hunt the Wumpus, type exe-wumpus

Then "exe-oregon"

  DO YOU NEED INSTRUCTIONS  (YES/NO)?YES

  THIS PROGRAM SIMULATES A TRIP OVER THE OREGON TRAIL FROM
  INDEPENDENCE, MISSOURI TO OREGON CITY, OREGON IN 1847.
  YOUR FAMILY OF FIVE WILL COVER THE 2000 MILE OREGON TRAIL
  IN 5-6 MONTHS --- IF YOU MAKE IT ALIVE.

  YOU HAD SAVED $900 TO SPEND FOR THE TRIP, AND YOU'VE JUST
     PAID $200 FOR A WAGON.

This is bullshit. I immediately died of pneumonia, even after spending amply on food and oxen.

Added to http://rationalwiki.org/wiki/Fun:Real_Gamers

Haha. After a really stressful day, this made me laugh out loud. Thanks.

Who's gonna preserve that stuff? Even if you have the media, it's non-trivial to play it and get the data off of it. Moreover, the actual owners of it, the almost rush to end of life stuff when they can, they don't want to carry the legacy and they OWN it.

Back in the 70s and early 80s it was like the 'hey day' of alternative hardware and software. There were dozens and dozens of systems, all with their own micro architecture, there are probably a bunch that are completely defunct, even if you had working hardware the software might be extinct. Wang, Kaypro, CDC, there were bunches of them...

The real warning shot this should be to everybody is for your personal media. The video and photos of your family. If you don't actively take part in archiving them (like regularly checking in on them, backing them up, copying them to new media, etc..) it is very possible, some would say likely that in 20, 30, maybe 50 years, you won't even be able to read the stuff. It's already a real chore to play a VHS tape.

"Who's gonna preserve that stuff?" There are dedicated groups attempting to do what they can, getting the word out so that more eyes can scan the landscape and sight historical ephemera to be preserved helps too:

http://www.computerhistory.org/groups/spg/ https://archive.org/details/software

My list which has many items still to be found:

http://www.retrocomputingtasmania.com/home/projects/spg

While I assume there was an official Cray operating system for the Cray-1, in those days it was not unusual for the buyer of such a system to write their own OS, particularly in the DOE/DOD/NSA which is who bought most of them.

it's a real problem. other engineering disciplines have it too - "we don't have the prints anymore" is common in manufacturing - but you can always take apart and measure a mechanical device. reverse engineering software is much more difficult. that's one advantage of open source software, it's easy to archive. we should try to archive bug trackers and mailing lists too.

In this case it's not about reverse engineering - the actual binaries don't exist anymore either. I'm quite impressed that they've found a way of reading those old disk packs, just hope someone finds one with the right stuff.

The great irony of the Information Age is nothing will be remembered.

Then how was John Titor able to reboot society with an IBM 5100.