I just finished reading BeOS or
NeXT: Did Apple Make the Wrong Choice? While it is a well written
article, some points are explained poorly and some are just plain
wrong. I am writing this note to you in hope that you will publish it
and correct some of the points that Mr. Ploudre made.
Multitasking
Multitasking is the ability to run more than one program at the
exact same time. While this is impossible on a single processor system,
it is possible on a multiprocessor system. On a single processor
system, the CPU must quickly switch between programs to give the
illusion that it is running more than one program at the same time.
This leads us to the two major types of multitasking: cooperative
and preemptive. Mac OS 8 and Windows 3.1/95/98/Me use cooperative
multitasking (Windows 3.1/95/98/Me use preemptive multiprocessing to
switch between DOS sessions, but we will ignore that for now). Mac
OS X and Windows NT/2000 use preemptive multitasking. Preemptive
multitasking is better in most circumstances, but let's look at
both.
Cooperative Multitasking
Imagine that your computer is a kitchen. Instead of programs, you
have three appliances: a blender, a clock, and a lamp. You are the CPU,
and you have a single power cord that you have to switch between all of
the appliances. Now this is part is tricky, each of the appliances has
a "locking" power plug. In other words, when you plug the power into
the appliance, the appliance "holds" onto the cord until it releases
the cord, then you can move the cord to another appliance.
Everything is working well in your kitchen, and all three appliances
are working in perfect harmony. Then you decide to add a stereo. You
add the stereo, and there are problems. The clock starts showing the
wrong time, and the lamp is flickering. Remember when I wrote about
each appliance "'holding" on the cord until it lets go? Well, that is
the problem with cooperative multitasking. The CPU can not move to the
next process until the current process releases control. While this is
nice for an application that sometimes needs a little extra CPU time, a
poorly written application can hog the CPU and basically starve all of
the other applications.
Preemptive Multitasking
Preemptive multitasking works a bit differently. Imagine instead of
plugging the power cord directly into the appliance, each appliance has
an extension cord attached that runs to you. So instead of plugging
directly into each appliance, you plug into the appliance's extension
cord. So now you don't need to wait until the appliance releases the
cord, you can switch cords whenever you like. That is preemptive
multitasking. The CPU switches between the applications when it wants
and each application thinks that it has full control of the CPU. With
preemptive multitasking no one application can hog the entire
system.
Multithreading
If multitasking is running multiple applications at the same time,
multithreading is running multiple parts of an application at the same
time. An example would be a word processor. Remember when you had to
type the document and then run the spellchecker? And remember how you
had to wait for it to send your document to the printer? With
multithreading, the spellchecker can run at the same time as you type.
That way you see all of those little red lines immediately. And you can
start typing immediately after you tell the file to print. When you
tell the program to print the file, it spawns the process (creates a
new process and executes it), and the CPU can send that process to the
background so you can keep typing.
Journaling File System
A journaling file system is always a good thing. However, a
journaling file system will not prevent file system corruption, nor
does it add any extra security. A journaling system will corrupt as
easily as any other file system if a power outage occurs in the midst
of a disk write. The benefit is on the restart.
A journaling file system keeps a log of all the file system writes.
On a non-journaling file system, a disk repair program must check the
entire file system for errors. On today's large hard drives this can
take some time.
On a journaling file system, the disk repair program, which must
still be executed, can read the journal entries of all of the open
files. This way, the entire disk need not be scanned, only the
previously open files.
Disk fragmentation will always occur. Here is a visual
example of fragmentation. For simplicity sake, each file is represented
by a number and each character equals one meg.
You have a clean disk and you save a 10 meg file. Your disk looks
like this.
- 1111111111
You then save a 5 meg file.
- 111111111122222
You then save a 3 meg file.
- 111111111122222333
You then add 2 megs to the '2' file.
- 11111111112222233322
You add 1 meg to the '1' file.
- 111111111122222333221
You delete the '2' file. See the 'open' spaces between the
files?
- 1111111111 333 1
You save a 4 meg file.
- 11111111114444 333 1
You save a 6 meg file.
- 111111111144445333551555
You add 2 more megs to the '1' file.
- 1111111111444453335155511
As you can see, the file system has become fragmented. Fragmented
just means that all of the files are not contiguous. You notice how the
'5' file is located in three different parts of the disk. Rather than
the hard drive reading the file at one time, it has to read parts of it
from three different areas. This takes time. And when a file is
scattered in thousands of places across a hard drive, you can
understand how this can really slow down a system. BTW, if we ran a
disk defragmenter on the above hard drive the result might look like
this.
- 11111111111114444333555555
BeOS
I can speak well of Be. I was one that looked anxiously for the Be
beta that was distributed with Mac Tech magazine. I was an original
beta1 and beta2 tester. I bought the first release when it was
available on the Intel platform. I was amazed at the spinning teapot
demo. And that was the problem.
That is all the OS could do. It could spin a teapot and play several
movies without dropping frames. A nice technological demo, but hardly a
career choice. In other words, there were (and are) no apps for
the wonderful little OS. Sure, Be designed it on a clean sheet of paper
- the same paper they could use to list every application ever written
for Be and still have room to doodle.
- There is an old joke that goes like this. How was God able to
create the world in 6 days? No backwards compatibility needed.
When Apple decided to go with NeXT over Be, Be couldn't even print.
Be, while blazingly fast, was blazing fast for a reason. Nothing was
running on it. Apple chose to go with the OS that was stable, proven,
and gorgeous. Apple also got NeXT's unbelievably fast development
environment, the leading application server software WebObjects, and
the Mac's father and Apple's savior, Steve Jobs. (Personal note: I
still remember leaving work late for Christmas vacation ecstatic after
reading that Steve Jobs was back at Apple.)
Speaking of NeXT's fast development environment, Steve Jobs used to
demo it in a unique way. When Steve was giving a demo or seminar of
NeXT, he would have a programmer onstage with him. The programmer would
start writing an application at the start of the seminar. Steve would
close the seminar by demonstrating the app that had just been
written!
As for Apple choosing NeXT or Be, I think the choice was quite
clear. So the next time you think that Mac OS X or OS 9 is
holding your system back, you should thank Apple. Thank Apple that
there are device drivers for hardware, extensions, and thousands of
applications that "slow down" that wonderful computer with its gorgeous
and elegant GUI.
Links
Share your perspective on the Mac by emailing with "My Turn" as your subject.
