I am doing my bachelor's degree at a university. In a written assignment, the professor posted the task: "Name three PC operating systems".

Well, I went on an included a variety of OSes (Linux, Windows, Mac OS X) and including Unix & Solaris. Today I received a mail from my professor saying:

Unix is not a PC operating system. Many Unix-variants are not PC-hardware compatible (like AIX & HP-UX. About Solaris: there was one PC-compatible version...)

I am kind of suprised: Even if many Unix-variants are PowerPC based and have a different bit-order – Those don't stop being PCs now, right?

The question was given in a written assignment! It was not a question that came up during the lecture!

Due to the original task being in German, I'll include it just to make sure nobody suspects an error in the translation.

Frage: Nennen Sie 3 PC-Betriebssysteme.
Antwort: Unix ist kein PC-Betriebssystem, viele Unix-Varianten sind nicht auf PC-Hardware lauffähig (AIX, HP-UX). Von Solaris gab es mal eine PC-Variante.

  • 9
    Windows in various incarnations, OS/2, various DOS's (not just the MicroSoft ones either), BeOS, Linux, FreeBSD, NetBSD, OpenBSD, and I know I've missed some. The problem with "Unix" is that it is ill-specified, but then so is "PC". Mar 28, 2012 at 23:19
  • 18
    Your prof is just plain wrong. There have been several versions of Unix that ran on "the PC" (don't know if there are any currently), and versions of Windows that run on non-PC devices. But his point is possibly that you should be parroting back what he said in the lecture, when you were either asleep or absent. Mar 29, 2012 at 1:18
  • 75
    I think your professor should learn that "communicating badly and then acting smug when you're misunderstood is not cleverness." xkcd.com/169 Mar 29, 2012 at 1:32
  • 5
    @ott, the Y2K bug was a real issue. The reason it wasn't worse was because it was taken very seriously. Mar 29, 2012 at 9:58
  • 10
    You professor needs to define specifically what they mean by PC and what they mean by UNIX. Because both are vague and ambiguous. Many people say UNIX and actually mean UNIX-like because UNIX is a trademarked brand and requires certification to be able to use the term. And everyone uses PC to generally mean Windows compatible.
    – user22908
    Mar 29, 2012 at 13:07

13 Answers 13


Without a hard definition of what a "PC" is, your assignment question is a lake of ambiguity. I used an AT&T 3B1 no later than 1987, which unequivocally ran UNIX and was marketed as a "UNIX PC".

  • 81
    +1 for being able to smack down professorial hair-splitting with unshakable old-school cred.
    – octern
    Mar 29, 2012 at 3:31
  • 16
    This is a certified "UNIX PC". It even says so on the case!
    – unixman83
    Mar 29, 2012 at 6:40
  • 3
    Do you own this? does it still run? Mar 29, 2012 at 9:47
  • 17
    I think it does run, but he has to manually translate the high-low voltages into bits using a yellow multimeter.
    – Jake
    Mar 29, 2012 at 10:47
  • 10
    I want a three button mouse like that one. Also, is that a list of positive numbers on the wall? You know, that's not the most appropriate thing to be learning by rote...
    – naught101
    Mar 29, 2012 at 12:06

It would depend on your definition of 'PC operating system' and subsequently on your definition of a personal computer itself. If the first refers to operating systems that run only on personal computers, you might as well rule out every imaginable one, including Windows, which also runs on mobile phones, PDAs, server machines, supercomputers and a bunch of other non-PC machinery. To my knowledge, there are no operating systems meeting this strict criterium, as part of the PC's definition may be in its use. An OS will or will not support a machine regardless of that.

Even a more objective, hardware-only classification will fail. There is no unambiguous set of PC hardware. You will need a more specific term, such as 'x86-64 architecture', but those are not necessarily the same. For instance, your professor's example of AIX not being compatible with PC hardware is false. AIX supports the PowerPC platform which is uncommon, but perfectly usable in PCs.

Any answer to a question as vague as 'name three PC operating systems' can be shot down.

  • Your answer appeared after I submitted mine, but you make some interesting points that mesh with mine, so I upvoted your answer as a good one, too. I think my point about PC=IBM-PC might explain the professor's confusion, although I think he was wrong. Mar 28, 2012 at 23:09

I have two explanations for this:

  1. The task was supposed to name three PC-only operating systems
  2. Strictly put, Unix is not exactly an operation system - it's a family of operation systems, derived from the first one developed in 1969, and is not a PC operating System.
  • 5
    For point number 2, unix.org, the owner of the unix trademark and certification standards might disagree. Also, you can still download Unix V7, the final AT&T version of Unix. Mar 28, 2012 at 23:46
  • 2
    "Strictly put, Unix is not exactly operation system - it's a family of operation systems." If you were to answer something more specific, like OpenBSD or FreeBSD (both UNIX variants), that might net you a more positive result.
    – zpletan
    Mar 29, 2012 at 2:54

If your professor is one who simply makes up his own definitions (or one who doesn't believe in Wikipedia being the ultimate source of truth), you're basically at his/her mercy.

Otherwise, point him/her to these Wikipedia entries (or possibly their German counterparts):

A personal computer (PC) is any general-purpose computer whose size, capabilities, and original sales price make it useful for individuals, and which is intended to be operated directly by an end-user with no intervening computer operator.

An operating system (OS) is a set of programs that manage computer hardware resources and provide common services for application software.

Unix (officially trademarked as UNIX, sometimes also written as Unix) is a multitasking, multi-user computer operating system [...].

If you both agree to the assumption that Wikipedia can be believed, then Unix is definitely an OS for PCs.

  • If I'd try to prove anything to any of my professors using a wikipedia article, they'd kick me out of the course. (at least figuratively speaking) "not a scientific source".
    – Baarn
    Mar 31, 2012 at 11:32
  • @WalterMaier-Murdnelch: Hence the disclaimer. However, you can always at least use the sources quoted in Wikipedia to make your point. And if any prof or teacher won't accept that, they need to be told that it's about time to step into the 21st century. The Internet may be full of useless stuff, but if you know where and how to look, there are many great and authoritative sources as well. And Wikipedia does try to hold itself to high standards, give them some credit. Apr 1, 2012 at 7:13

Your professor may have a different definition of a "PC" than you - which is not to say he is correct. Originally, PC simply meant "Personal Computer", and did not have any specific architecture. But his use of "PC Hardware" sounds like he is using a different definition that only includes IBM Intel-based PCs.

When IBM came out with their PC, they simply called it the IBM PC, and people began using PC to mean IBM PC. So "PC Compatible" was commonly used to mean IBM PC Compatible, as if IBM invented the personal computer, rather than just "legitimizing" it. I personally think your professor is either being unclear and unfair, or completely wrong (or both).

This was a Unix PC: AT&T Unix PC, and ran genuine AT&T Unix.

That said, I wouldn't really call Unix a PC operating system today; even though it can be, it's pretty rare.

Edit: There is also the possibility - which can only be deduced after his comments - that he meant ones that are designed only for a PC, such as MS-DOS, DR-DOS, PC-DOS, and the original Mac OS (and possibly OSX).


The "About Solaris: there was one PC-compatible version" statement is incorrect. From 1992 to 2011, there has been ten Solaris versions supporting x86 hardware (2.1, 2.4, 2.5, 2.5.1, 2.6, 7, 8, 9, 10 and 11), not to mention the various OpenSolaris/illumos based ones.

In any case, since its early design stage, Unix has been developed with portability in mind so is not, unlike most if not all competing OSes of that time, tied to a specific architecture.

  • My coworker is currently running a stock release of Windows on a Sun box that shipped with Solaris installed. The only quirks have been related to locating compatible device drivers for a couple of the server-grade peripherals made from obscure chip sets. But even those quirks were resolved by drivers made available by Sun themselves. Windows was a supported configuration of the box.
    – RBerteig
    Mar 29, 2012 at 18:12

First of all, I would not waste my time on people who think that "name three PC operating systems" is an interesting homework exercise. Or even something to talk about.

Your prof moves his definitions around to try to make perfectly rational, right thinking people around him appear to be wrong.

Oh, I meant "operating systems that exclusively have run on PC hardware".

PC compatible? No, no! I meant IBM PC! Not HP, not Compaq, not ACER, not your ASUS motherboard from Taiwan in a no-name brand case.

Did I say PC/AT? No, I mean PC! You know, 4.77 Mhz, 512 K memory, floppy drives only. No Not the XT with its 10 meg hard drive, not the AT, and not the PCjr. No 80x86 where x is not blank, and the 86 isn't 88.

Acceptable answers might be: PC-DOS, MS-DOS 2.0, CP/M 86 and MS-DOS 3.3.



Mac OS X is Unix and the Leopard version is the first and only BSD variant to achieve Unix Certification, and that's certainly considered a PC operating system.

The various BSD variants are notable in that they are in fact descendants of UNIX, developed by the University of California at Berkeley with UNIX source code from Bell Labs. However, the BSD code base has evolved since then, replacing all of the AT&T code. Since the BSD variants are not certified as compliant with the Single UNIX Specification (except for Mac OS X 10.5 Leopard and Mac OS X 10.6 Snow Leopard), they are referred to as "UNIX-like".

So if your professor means UNIX as in the certified, branded version, that narrows the group considerably. If he means UNIX-like, that is a completely different semantic and opens the doors for way more things that run on PC hardware.

  • 2
    Why? Macs are not PCs. Even Apple says that.
    – slhck
    Mar 29, 2012 at 8:13
  • 14
    @slhck, Macs aren't derived from the IBM PC™ product line, but they're personal computers. They're not mainframes, they're not servers (at least not the ones we're talking about), they're not embedded systems (though iPhones are). When you buy a Mac you take it home and put it on your desk. It's a computer for your personal use.
    – Wyzard
    Mar 29, 2012 at 8:23
  • 1
    That was more of a tongue-in-cheek comment. Of course they're personal computers. But clearly, Apple doesn't want to sell "PCs".
    – slhck
    Mar 29, 2012 at 8:53
  • 1
    I actually detest Apple with their "we're not a PC" high horse
    – rickyduck
    Mar 29, 2012 at 10:49
  • 6
    It's a reasonably reaction to the PC == Windows mindshare. If I go into a games shop, the products have XBox, PS3, PC and Mac on the boxes. If Apple started claiming to make PCs then they'll just get unhappy customers who can't run the software labeled as "PC".
    – Quentin
    Mar 29, 2012 at 11:22

Let's take an average definition of "PC" being what the professor thinks it is -- an Intel desktop.

So he's trying to point out that Unix is a whole class of operating systems, many do not run on PCs... This is correct.

However, Windows is also a class of operating systems, and wow... many don't run on PCs!! Windows CE is a version of Windows, as are Windows Embedded and Windows Phone (with multiple versions).

Many versions of Linux don't run on PCs.

So the only "correct" way to answer his question would be to list instances--something along the lines of "Windows XP, Windows NT, Windows 7 and Windows 8" which is lame and he probably would have said something about these all being the same OS.

Linux is also a problematic answer, not all Linux builds are meant for PCs, although you could easily list 20 versions of Ubuntu made for PCs.

Mostly, the question should be, why do you have such a pointless and ambiguous question on your tests?


Is Unix a PC Operating system?

There were certainly (commercial) ports of Unix before Linux ever arrived on the PC scene, such as Interactive Unix and Santa Cruz Operations (aka SCO) Unix, that first ran on i386 and i486 PCs.


First, I quote two lines from Wikipedia about Unix. This will make it clear the differences between Unix and UNIX.

Unix (officially trademarked as UNIX, sometimes also written as Unix) is a multitasking, multi-user computer operating system originally developed in 1969 by a group of AT&T employees at Bell Labs, including Ken Thompson, Dennis Ritchie, Brian Kernighan, Douglas McIlroy, and Joe Ossanna.

The term Unix (capital U) is often used informally to denote any operating system that closely resembles the trademarked system.

Your professor is not wrong. When UNIX was created computers were so expensive that no one had a personal version. People usually used to share a Unix system which was running on a mainframe or minicomputer. Before UNIX became cheap, the IBM PC was released and many people could afford to buy it. And the term PC (personal computer) was broadened. After that UNIX or Unix became cheap and people could use them in PC (this PC is a common noun, IBM-PC is a proper noun).

  • The professor continues discussing "Unix variants", so the original UNIX is probably not what he meant.
    – Legolas
    Mar 29, 2012 at 10:47
  • 3
    Microsoft licensed UNIX from AT&T in 1979, and sold it under the name Xenix ported to various platforms for years. SCO created the Xenix port to the IBM-PC hardware platform, and sold Microsoft Xenix on that platform. I had an IBM-PC XT box in 1986 that ran Xenix 2.x, which was a fairly clean port of UNIX System V, and really did support several timesharing users on a single 80286 CPU.
    – RBerteig
    Mar 29, 2012 at 18:21
  • And in the page you are refering, it also says: "Among all variants of Unix, the most widely used are Linux" Mar 29, 2012 at 22:23

Maybe it is not a technical question but a political one.

Microsoft want us to believe that all other operating systems are old/slow/command-line only/hard to use/not used by anyone/…. I think that Microsoft has got to your professor.

This answer was sent from my Unix PC (Debian Gnu/Linux). Linux was originally an x86-only operating system. According to the owners of UNIX™ GNU/Linux is a Unix, but not a UNIX™.


Frage: Nennen Sie 3 PC-Betriebssysteme.

i'd guess PC in German is Einzelplatzrechner thus a single seat computer maybe

you might focus that computer cannot provide two seats but one - most MIDs with some embedded OS would be fine for today. Even windows is too functional in this regard.

or you want to thin PC is an IBM Personal Computer or similar.

Then you can name any system imaginable. OSX. Windows 95, FreeDOS (yes -apple systems can run windows also in place of OSX, just a bit costly)

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