(and what is it anyway?) Part I Bob Eager History of UNIX – Part I1

An overview What is UNIX? loosely speaking, it’s a computer operating system operating systems are the programs that ‘run’ computers examples of other operating systems are Windows, MacOS X, etc. Is it new? no, it first saw the light of day in the very early 1970s but it has changed and grown a lot since then Do many people use it? many millions! Can I run my Windows programs on it? sometimes, but that’s not the point – there are free alternatives History of UNIX – Part I2

UNIX is actually a trademark, although it’s used informally for: UNIX derivatives : FreeBSD, OpenBSD, NetBSD, etc. UNIX lookalikes (wannabes!): ‘Linux’ systems in all their many incarnations ‘real’ UNIX™ systems (i.e. those that can legally use the name): MacOS X (Apple) Solaris (Sun, now Oracle) HP-UX (Hewlett-Packard, or HP) AIX (IBM) History of UNIX – Part I3

so really, it’s merely a name applied to a specification of a system but since they all look similar, they get called ‘UNIX’! many versions available (mostly open source and free) user friendly (ish), but picky about its friends! although much more friendly (less hostile?) than it used to be for example, it now has a graphical user interface… …but the real power lies in the original ‘command line’ originally, UNIX worked entirely at the command line and still does, if you want it that way real UNIX users mostly use the command line – it’s very fast and productive here’s a sample… History of UNIX – Part I4

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UNIX features originally based around a textual command prompt now provides a graphical user interface in fact, many different graphical user interfaces take your pick – some of the GUIs are excessively bloated! multi-user proper security makes it harder to do accidental damage... remote access via network (or hardwired) extensive networking support very rich set of features and applications So, how did it all start? History of UNIX – Part I6

Phase I – the mini systems UNIX was internally developed by researchers at Bell Laboratories in the USA, in the late 1960s/early 1970s Ken Thompson, Dennis Ritchie, and others (picture soon) the initial system (First Edition) was on a spare PDP-7 (an 18-bit machine), and it was capable of building programs, and text processing – this was between 1969 and 1971 by 1973, it had been rewritten in a new language called C. This had developed from a previous Bell Labs language called B - which was in turn based on a language called BCPL BCPL was developed at the University of Cambridge, UK, in the mid 1960s – a completely typeless language, much more ‘dangerous’ than C! in 1975, Sixth Edition UNIX was released to academic and research institutions - it arrived at Kent in July 1975, being the first system in England, if not the UK History of UNIX – Part I7

Kent’s copy of Sixth Edition arrived on three exchangeable disks of 2.4MB each: History of UNIX – Part I8

Here’s the drive it fitted into: History of UNIX – Part I9

at Kent, Sixth Edition UNIX ran on a Digital Equipment Co (DEC) PDP-11/40; a 16 bit machine with 112kB of memory (costing tens of thousands of pounds) this supported 6 simultaneous users (most of the CS students at the time!) if you want to try running this version, a free licence is now available disk images and a PDP-11 simulator are available – more later the Kent system ran for over 5 years before it was replaced by a VAX (see later) History of UNIX – Part I10

What was this PDP-11? made by the Digital Equipment Corporation of Massachusetts one of the most successful minicomputers of all time at one point, Kent probably had at least ten of them Bob owns four! 16 bits, memory from about 56kB up to 2MB or so (mostly at the low end) many possible peripherals some in big cabinets, some in deskside towers Now for some historical pictures…. History of UNIX – Part I11

Hardware – a PDP-11/40 CPU! This was in a full height rack (6 feet high), modules 19 inches wide…this is just the CPU and memory History of UNIX – Part I12

More hardware! A big PDP-11 (actually, two), with Ritchie and Thompson using it: History of UNIX – Part I13 Dennis Ritchie Ken Thompson

In the previous picture, note the main I/O device – the teletype; this ran at 10 characters/second, in upper case only: History of UNIX – Part I14

Students needed long term storage (as we use USB sticks today); the equivalent was the DECtape, storing 300kB or so of data: History of UNIX – Part I15

just about small enough to carry around in a (large) pocket… History of UNIX – Part I16

a micro PDP-11! deskside size often used for word processing circa mid 1980s Bob has one of these... History of UNIX – Part I17

Seventh Edition UNIX appeared in 1979, and included various enhancements. It was a very tight squeeze except on more expensive PDP-11s (which supported an operating system area of 120kB instead of 56kB) at about the same time, an interesting derivative was UNIX 2.9BSD, a modified version developed by staff (and, largely, graduate students) at the University of California at Berkeley (the Berkeley System Distribution, or Berkeley Software Distribution) included networking again a very tight fit! Kent didn’t have an expensive PDP-11, so never really used these a great deal it is said that only two important things came out of Berkeley at that time: BSD and the drug LSD – and that this is no coincidence! History of UNIX – Part I18

Bell Labs also produced ‘Mini-UNIX’, which ran on really small PDP-11s and supported (effectively) just one user with some limitations (no real pipes, for example) (~1978) still on the PDP-11 series, but low end ones this was limited simply because it ran on machines with the minimum amount of memory, and no memory management hardware at all really just a feasibility project, although fun to look at but it was possible to do real work on it History of UNIX – Part I19

UNIX source code was not meant to be shown to undergraduates, but someone actually used it to teach operating systems… this was a man called John Lions, at the University of New South Wales, Australia he went further, and in 1977 had the UNIX kernel source code made into a book, with his own companion volume as a ‘commentary’ on the code probably one of the most interesting computer science/operating systems publications ever produced it was circulated internally in UNSW, and also sold to UNIX licensees unfortunately, Bell Labs/AT&T were not happy, and essentially had the books rationed to one per company/institution after the first print run was sold; by 1978 they were completely unavailable despite the books being under copyright, “they must be the most frequently photocopied books in the whole area of computer science” History of UNIX – Part I20

they were finally republished as a single volume in 1996 – see link on website later History of UNIX – Part I21

UNIX was (and is) written mostly in the C language; here’s a sample: /* * Switch to stack of the new process and set up his segmentation registers. */ retu(rp->p_addr); sureg(); /* * If the new process paused because it was swapped out, set the stack level to the * last call to savu(u_ssav). This means that the return which is executed * immediately after the call to aretu actually returns from the last routine which * did the savu. */ /* * You are not expected to understand this. */ if(rp->p_flag&SSWAP) { rp->p_flag =& ~SSWAP; aretu(u.u_ssav); } /* * The value returned here has many subtle implications. * See the newproc comments. */ return(1); History of UNIX – Part I22 comments code

yes, C looks a bit like Java, but pre-dates it by decades! the C ‘look’ has been adopted by many other languages C is a very low level language, and allows the programmer to do pretty well anything even if it’s dangerous even if it makes no sense at all which is why it’s fun… UNIX systems are written almost entirely in C a few hundred lines, at most, may be written in assembler, to interface with the hardware in other words, the innermost layer of our operating system kernel History of UNIX – Part I23

Next time… we’ll look at: the progress of UNIX to bigger systems political and commercial differences the hairy guy true hackers the PC embedded UNIX systems what you’ll be doing next History of UNIX – Part I24