In the article ‘What’s the “Scroll Lock” key on my computer for?’, http://www.straightdope.com/mailbag/mscrolllock.html , Una Person describes what the Scroll Lock key does, but fails to explain what it’s for. The answer is actually pretty straight forward. It’s there to provide compatibility with IBM mainframe terminals. IBM 3270 terminals were the deluxe terminal of choice for IBM mainframes at the time the first IBM PC was created. Both the Scroll Lock and the SysReq keys are present on IBM 3270 terminals. These keys were presumably provided so that IBM PCs could act as 3270 terminal emulators. In fact, IBM release IBM 3270 terminal emulator adapter cards for IBM PCs shortly after the first PCs shipped.
I don’t really know what these keys did on a 3270 terminal – I never used them much, and I remember really struggling with the user interface, which was a little strange, to say the least. I imagine Scroll-Lock acted as described in Una’s article. I don’t know what SysRq did. The premise of the 3270 terminal – which was radically different from other terminals in this period – was that the terminal should provide all local editing, and should – as much as possible – send information to the mainframe (or the front end IBM system 1 computers) in batches, instead of keystroke at a time. This strategy was neccessary to allow a multi-million dollar IBM 360 or 370 mainframe with less horsepower than a modern desktop computer to simultaneously host 100 users in a “time-sharing” environment.
To find out what these keys are really supposed to do, you would probably have to dig among the thousands of pages of documentation on IBM’s Systems Architecture strategy papers – IBM’s early grand vision of how mainframes and personal computers should co-exist in peace and harmony.
Personally, the one button I would really to see on modern PCs is the explosive power off button. IBM mainframes and minicomputers had a big round red “Stop” button on their front consoles that triggered an explosive charge on the outputs of the system’s power supply. The theory – as I understood it – was that if the system seriously malfunctioned, flicking a switch just wasn’t good enough to protect a multi-million dollar computer system; you had to blast those leads off the power supply in order to shut down the system as quickly as possible.