Protection Hardware

Protection Hardware

Early mainframes, like the IBM 7090/7094, had no protection hardware, so they just ran one program at a time. A buggy program could wipe out the operating system and easily crash the machine. With the introduction of the IBM 360, a primal form of hardware protection became available and these machines could then hold various programs in memory at the same time and let them take turns running (multiprogramming). Monoprogramming was declared outdated.

At least until the first minicomputer showed up - without protection hardware - so multiprogramming was not possible. Although the PDP-1 and  PDP-8 had no protection hardware, finally the PDP-11 did, and this feature led to multiprogramming and eventually to UNIX.

When the first microcomputers were built, they used the Intel 8080 CPU chip, which had no hardware protection, so we were back to  monoprogramming. It wasn't until the Intel 80286 that protection hardware was added and multiprogramming became possible. Until this day, many embedded systems have no protection hardware and run just a single program.

Now let us look at operating systems. The first mainframes in the beginning had no protection hardware and no support for multiprogramming, so they ran simple operating systems that handled one manually loaded program at a time. Later they obtained the hardware and operating system support to handle multiple programs at once, and then full timesharing capabilities.

When minicomputers first appeared, they also had no protection hardware and ran one manually loaded program at a time, even though  multiprogramming was well established in the mainframe world by then. Gradually, they obtained protection hardware and the ability to run two or more programs at once. The first microcomputers were also capable of running only one program at a time, but later got the ability to multiprogram. Handheld computers and smart cards went the same route.

In all cases, the software development was dictated by technology. The first microcomputers, for instance, had something like 4 KB of memory  and no protection hardware. High-level languages and multiprogramming were simply too much for such a tiny system to handle. As the microcomputers developed into modern personal computers, they obtained the necessary hardware and then the necessary software to handle more advanced features. It is expected that this development will continue for years to come. Other fields may also have this wheel of reincarnation, but in the computer industry it seems to spin faster.


protection hardware, monoprogramming, multiprogramming