and the Macintosh
Many people are interested
in running alternative operating systems on their
Macintoshes. There are quite a few options available, but
UNIX support is probably the most sought. Most people
don't know that UNIX and the Mac play together quite
Brief background for UNIX:
UNIX was developed in the late 1960's by Ken Thompson and
Dennis Ritchie at AT&T Bell Labs, it was strongy
influenced by Multics, an operating system for minicomputers
of the time. It was designed from the ground up to be a
multitasking, multi user (1) operating system with
protected memory - fully buzzword-compliant even by today's
standards. Multi-threading was adapted, and incorporated
later, but fit in the architecture well. UNIX was also coded
completely in the C programming language, making it machine
independent - something of a novelty back then, when
operating systems were written in straight assembly.
(1) For multi-user
personal computer operating systems, UNIX is the only
game in town. NT is not really multi-user, it is more of
a glorified file and print server with decent
administration tools. You can log in as different users,
but only one can be logged in at a time without special
software (like Citrix's WinFrame). UNIX is true
multi-user. You can create accounts for your friends and
you can all be using the box simultaneously across the
network - with no additional software. This includes GUI
support through X-Windows. The clients can even be on
diverse platforms - the only necessary common denominator
is an X server on each client machine.
In 1975, UNIX was made available to universities at a
reduced cost, where it became extremely popular. In 1984,
the University of California, Berkeley made available an
enhanced version of UNIX called Berkeley Standard
Distribution (BSD) UNIX. AT&T sold the rights to UNIX
and the hands have changed many times since. Currently the
X/Open Company owns the AT&T source. Since then, many
BSD features have been incorporated back into the AT&T
variant, currently called System V. Most commercial Unices
are based on this version and most free Unices are based on
BSD. More recently, Linus Torvalds and programmers across
the globe have developed a UNIX clone called Linux, of which
there are multiple variants.
Unices and their clones all have a similar architecture,
and the ideas pioneered by UNIX show through in all modern
operating systems. Shared traits include kernels, file level
security privileges, piping, TCP/IP networking, file-mapped
protected virtual memory, load-balancing and all of the
others that Microsoft claims are new technology in NT. The
differences between Unices is in the details; for instance,
all Unices have similar command line utilities, but each
variant might have different options for these utilities.
All Unices consist of a kernel, a command line and command
The Mac has an interesting history with UNIX. Until very
recently, Apple was very tightlipped about their hardware.
If you wanted to write a new operating system or port an
existing one, you had to twiddle bits by hand to see what
they did and then write the OS around that. For this reason,
work was very slow to get any of the UNIX variants on Mac
hardware until recently.
Apple had their own version of UNIX called A/UX that ran
on any 030 and 040 machine with the Paged Memory Management
Unit installed. This was an AT&T variant with a bunch of
BSD extensions. Possibly the most interesting aspect of A/UX
was that you could run stock standard System 7 compliant Mac
applications on it. It wasn't until late 1992 that any
Unices besides A/UX were ported to the Mac, and all of these
UNIX ports were done without Apple help. NetBSD and
FreeBSD are two of them. Lately however, Apple has
been much more open with their hardware specs.
Prior to the acquisition of NeXT, Inc., Apple brought
briefly to market the PPC based Network Server 500 and 700.
These were Apple's brief foray into AIX, a version of UNIX
maintained by IBM for their RS6000 boxes. Apple's version of
AIX will only function on these two boxes.
PPC Mac owners have several choices, and each is
- MkLinux (mklinux.apple.com), a Linux variant,
is an Apple skunk works project. It hosts the Linux
kernel on top of the Mach microkernel (written at
Carnegie-Mellon by none other than Avie Tevanian). Mach
is an extra layer of abstraction between the kernel and
hardware. This makes diverse hardware support a little
easier at the expense of some speed.
- LinuxPPC (www.linuxppc.org), also a Linux
variant, is a project headed up by Paul Mackerras. It
builds upon the work from the MkLinux team, but utilizes
a "monolithic" kernel - meaning there is no micro kernel
abstraction layer. The kernel talks to the hardware
directly. This ensures that for every hardware feature,
bug or addition, the kernel will be modified. That's the
penalty paid for a return of some 10% additional
- MachTen (www.tenon.com) is a BSD variant
running on the Mach micro kernel. What makes this one
really different (other than the fact that it is the only
shipping UNIX for the Mac that is not free) is that it
runs as a standard Mac application. This means that to
use UNIX, you double click an application in the Finder.
Within that application's memory space (as set through
the Get Info box), lives a real UNIX. This unusual (but
powerful) approach has some unique trade-offs.
- The pluses:
- You can run Mac applications along side of
- You don't have to reboot to use UNIX. If UNIX
crashes (not likely), you can restart it with a
- All Macs are supported with very little change
since it is really an application as far as the
MacOS is concerned. It uses the MacOS hardware
drivers. That means that your NuBus cards, your PCI
cards and your accelerators will still work.
- There are two versions of MachTen -
Professional and Regular. The Professional one
allows MachTen to do all of the virtual memory and
memory management, regardless of which OS you use.
This results in more speed and stability for the
- The drawbacks:
- While the MacOS has control of the processor,
it does co-operative multitasking, and while
MachTen has the processor, it does preemptive
multitasking. There is a slider that controls the
ratio of MacOS to MachTen processor utilization.
This is a blessing and a curse because running
MachTen fast enough to be usable might limit the
usability of the MacOS side and vice-versa.
- Although MachTen uses the MacOS device drivers,
making compatibility less of an issue, these may
not be as robust or as fast as similar drivers on
the UNIX side.
- If the MacOS crashes, the UNIX side does
- Rhapsody: (devworld.apple.com/rhapsody/)
Although this is not released to the general public, it
is a UNIX variant nonetheless. Based on the BSD release
and hosted on a Mach Microkernel, Rhapsody is best
described as A/UX with a new outlook on life. Rhapsody is
made up of more than just the standard UNIX kernel,
command line, command line tools and windowing system. It
has a "blue box" for MacOS compatibility - sort of the
reverse of what MachTen does, Rhapsody's UNIX hosts a
MacOS process rather than MacOS hosting MachTen as an
application. Rhapsody uses the YellowBox API (application
programming interface) which is based on on work done by
Steve Jobs and crew at NeXT, Inc. and their
OpenStep/NeXTSTEP. YellowBox is a real Object-Orieted API
that allows programmers more freedom and productivity
than other API's. Most importantly to end users, Rhapsody
wraps all of the text-based administration inherent with
most Unices, with a very clean and powerful Mac look and
feel (all those text configuration files essentially get
controlled by graphical control panels and an easier to
X marks the spot
You may be wondering: "Why is UNIX is so great: it
doesn't even have any pictures to click!", but fortunately
you'd be jumping the gun. All UNIX variants have a windowing
system available called X-Windows. X is a windowing system
that sits on top of UNIX much in the same way that Windows95
sits on DOS, only in a much more elegant fashion, with loads
less overhead and with more configuration abilities than you
can shake Bill's head at.
The best thing about X is that by itself, it doesn't do
anything. For it to draw windows, you need a window manager.
There are several of these, and each has a separate look and
feel. There are window managers that look like Windows95 and
ones that look like MacOS. There are some that are very
plain, and others that look like alien landscapes. Each
window manager is configured via a text file. You determine
just about everything. The only thing that might be
difficult to wrap your brain around with X is that each
"client" machine requires an "X Server" if you want to
deploy applications from one machine to another via a
network. The "X Clients" are actually the applications
running, not the other machines connecting. The "server"
that holds the application binaries need not even be running
Why use Unix?
So you might be thinking, "OK, this is a fairly complete
primer for UNIX on the Mac, but why you'd want to put UNIX
on a Mac".
Here are a few reasons:
- To learn UNIX
- To prepare for Rhapsody and Mac OS X (at a geeky
administration and power-user level).
- For ease of use, MacOS rules. For scalability and
reliability, UNIX rules. I run LinuxPPC on one of my Macs
(a 7500 with a 604/120 card), and not only is it faster
than the MacOS on the same machine, it is worlds more
- UNIX is ideal for serving information, be it web,
database, file or print. There are Appletalk modules, web
servers, high-speed object oriented databases and file
and print services available for Linux - all of them
native and all of them FREE!
- If you are interested in programming, but don't want
to pay big bucks for Metrowerks Codewarrior (a very good
development environment for the MacOS), UNIX has a huge
array of programming tools and a set of learning and
troubleshooting resources online that can't be beat.
- To expand your horizons. MacOS may have the look and
feel you love, but most larger businesses (the ones with
IS departments) like to see a rounded
résumé. Besides, if you can convince anyone
to buy a Mac simply because the hardware is more reliable
and the processor is faster - even if they never plan on
using the MacOS - that helps Apple's bottom line, since
Apple makes money on hardware not software.
- You'll learn to hate DOS and Windows even more. MacOS
is elegant and integrated, but UNIX is elegant,
integrated and extremely stable.
- You'll understand why command lines are a good thing,
especially if your only previous experience with them was
- Remember, Unix is the only multi-user System
If you still have questions as to why, then Unix is
probably not the right solution for you. Unix is not for
everyone. But there are certainly many that have great
interest in Unix, and the Mac based Unices offers these
people some pretty compelling solutions.
Some of the above terms might be a little confusing to
UNIX newbies, so here's a quick rundown of some of the major
ideas in UNIX.
- The kernel acts as the arbitrator to the hardware
drivers. He's the guy that does all of the nitty-gritty
work like I/O, memory management, security and process
- Every program in UNIX is a process. The kernel
assigns each process a PID or process identification
number. A process requires a context-switch (the stack
and memory protection and so on) must all change to
protect one process from the other processes. Each
process may have multiple threads (which are "light
- Programs (processes) often have multiple threads. A
thread is a lightweight process, that does not require a
context switch, and so they are "faster" (less processor
intensive). Sometimes threads are incorrectly called
- Since UNIX was designed to be multi-user, each file
(and directory) has security privileges associated with
- Command Line:
- There are many "command line interfaces" (CLIs) for
UNIX, and they are called shells. Common shells include
C-Shell, Bash (Bourne-Again Shell) and Korn. They differ
in their functionality, but they all have built-in
utilities to look at the contents of directories and the
contents of files. These are what you type commands into.
Some are very complex, much like programming languages,
some are basically rudimentary scripting tools but all
allow you to do multi-step tasks by creating shell script
- Command Line Tools:
- A shell handles all of the user interaction with the
kernel, and the command line is each user's parent
process for any tools that they use. Tools vary from disk
utilities to word processors to compilers. These are text
based. Some use a library called "Curses" that allows
terminal style screen building.
- Piping (pipes):
- Most UNIX utilities are modular in nature. You give
them an input and they generate an output. You can string
together commands by piping them together to achieve a
desired goal. Piping is named for the ASCII "pipe"
character, what is used between the commands.