Tuesday, 9 July 2019

Multics (1969)

Artists rendition of early MIT Multics system
Launched July 1969

These days the computer you possibly interact with most often is your smartphone, and that is most likely to be an Android or iOS device. Both those operating systems are related, descended from the Unix operating system developed during the early 1970s.

Unix-like operating systems are not just found on smartphones – they are everywhere from web servers and huge mainframes to embedded devices and smart TVs. Over the decades it has been around, the influence of Unix is almost universal with only Microsoft’s Windows operating system offering any competition at all.

But what came before Unix? Just as your ARM-powered smartphone is spiritually descended from the 8-bit BBC Micro, Unix itself was borne out of another project: Multics.

Originally a project between General Electric (GE), Bell Labs and MIT. GE sold its computing business early on to Honeywell and Bell Labs dropped out. After five years of development, Honeywell released the first version of Multics to general users running on Honeywell 6000 series mainframes – with the Multics versions later named the DPS-8.

Multics was arguably the world’s first modern operating system, a highly-secure multi-tasking and multi-processor system it was also fault tolerant and the hardware could be reconfigured while the system was still in use. Multics also introduces the now-standard hierarchical file system, supported the concept of “daemons” (system processes that carry out tasks, in Windows these are called “services”). Multics also allowed every part of the system to be accessed as if it were a file, and introduced the concept of dynamic linking – Windows users would recognised these as being the ubiquitous DLLs we see today.

I kept hold of this manual for 30 years.
Just for this blog post.


It was highly advanced, secure and pretty user-friendly. But it was not really a success. Multics was limited to running on certain types of hardware - expensive hardware. A typical installation would cost several million dollars, back in the days that several million dollars was a lot of money. And in an attempt to be sophisticated, it was maybe too sophisticated.

So where does Unix fall into all this? Two engineers working for Bell Labs in the early days were Ken Thompson and Dennis Ritchie who didn’t like the over-sophistication of Multics but did like some of the features – notably the file system and command line. Instead of making a computer system that could run on expensive multiprocessor mainframes, they designed something that would run on cheaper single processor minicomputers. They called it Unix, a play on the word Multics… Unix was for uniprocessor computers, Multics for multiprocessor ones.

In some ways Unix was similar to Multics, but in most fundamental ways it was completely different, because Kernighan and Ritchie could see where the design decisions of Multics were leading it to be an expensive niche product. At its heart, Unix is the antithesis of Multics.

Unix grew and evolved from its roots on the DEC PDP-7 to run on a huge variety of hardware. The match the choice in hardware, a wide variety of different versions of Unix were created. Somewhere along the way the Unix-like Linux and Mach operating systems were created which in turn spawned Android and iOS. Unix wouldn’t have been Unix without the influence of Multics.

Multics itself continues in development until the mid-1980s. Not long after that, Honeywell sold its computer business off to Groupe Bull. Despite all this, Multics hung around with the last system being shut down in October 2000. 31 years of history isn’t bad for something that wasn’t really considered a success.

Today, Multics memorabilia is pretty rare and it’s unlikely anyone has a complete system in their attic. However, the OS was open sourced some years ago and as a result there are some simulators available for you to try. If you are interested in learning more about this historic operating system, the Multicians.org website is utterly comprehensive and details just about everything you would ever want to know.

Image credits: MIT, Conrad Longmore

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