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  From: David Newall <davidn@rebel.net.au>
  To  : Mike Andrew <mikero@norfolk.nf>
  Date: Thu, 29 Jun 2000 18:04:13 +0930 (CST)

Re: More space required

> So that my comments aren't extreme, the design of the PC at the time
> was (in my opinion) excellent. Yes, it had flaws, but as a desktop
> machine it was overall better than anything else out there.  Perhaps like
> you, I had various flavours of MC6802/9/Z80 style desktops at that time, all
> were good, but the pc had less overall flaws.

Hmmm, interesting perspective.  It used a 16 bit CPU with an 8 bit data bus
(8088), and came standard with 128KB of RAM.  Options included upgrades to
512MB of RAM but no further.  It included the ubiquituous cassette
interface, and a choice of one or two floppy disk drives.  Video display
was provided by a choice of MDA (monochrome display adaptor) or CGA (colour
graphics adaptor)  System clock ran at ... goodness me, I'm scratching to
recall whether it was 5MHz or 8MHz.  Maximum address space was 1MB, of
which the top 384MB is reserved for BIOS and hardware, leaving 640KB
addressable for programs and data.

The PC included an 8 level programmable interrupt controller, of which I
think five interrupts were unassigned.  This was a good thing and a bad
thing.  Without doubt interrupt processing is simplified if you know for a
fact that only one device uses any interrupt level.  On the other hand, we
continue with the legacy of IRQ conflicts to this day.

It's competitors at the time were the Apple ][, which used a RISCish 8 bit
CPU (6502), and came (at the time) standard with 48MB RAM.  The Apple ][
was venerable even then, and also included a cassette interface.  It came
standard with colour graphics, had a choice of between zero and twelve
floppy disks, and between zero and six hard disk drives.  The Apple ][
system clock ran at 1MHz.  The Apple ][ had two interrupts: One maskable
(ie the hardware could choose to ignore it) and one non-maskable (it could
not be ignored.)  Thus the Apple ][ never did have a problem with interrupt
conflicts.  Maximum address space was 64KB, of which 12KB was preloaded
with BIOS, 4KB was reserved for general hardware, and various amounts,
depending on video mode, was reserved for the screen.  The fractured
address space was one of the ]['s biggest weaknesses.

Another competitor was the Apple ///, which initally came standard with
128MB RAM, and later 256MB.  The Apple /// could be upgraded to 512MB.  It
also had colour graphics as standard.  The Apple /// was, in fact, a
typical Apple hack, which is to say it abused the intended design in quite
clever ways.  The Apple /// system clock ran at 2MHz, and, like the IBM PC,
included a standard real time clock.  The Apple /// was an upgraded Apple
][.  It had a maximum address space of 64MB of RAM and used sophisticated
bank-switching to take advantage of the addition RAM that the machine could
accomodate.

The Apple //e was a contempory of the Apple ///.  It came standard with
128KB of RAM, and was rather like a cut-down Apple ///.

Compared with the Apple ][, //e and ///, the IBM PC was a superior machine.
It could directly address much more memroy, although the 8086's segmented
addressing mode made this almost as hard to use as the Apple ///'s
bank-switched memory.  The 8 level interrupt controller has not proven to
be a benefit, in that it's one of the major causes of hardware
configuration errors.  Apple's machines de jure were no-brainers to
configure: You pop a hardware card into an available slot and it just
worked.  Intel's IO bus has proven to be another nice idea that failed to
live up to it's promise: Having to ensure hardware IO addresses are
correctly configured is the second major source of configuration errors on
PC's, and this also continues.  (Thankfully we're getting around this by
making the hardware configure itself; but this is a work-around to an
unneccesary design deficiency.)

Around the same time as the release of the IBM PC, Apple released the Lisa.
This used a 68000, and I frankly forget how much memory it included as
standard.  I'm inclined to think it came with 1MB and went up from there.
The Lisa had no video options: You got monochrome graphics.  The Lisa came
with a choice of one or two typically Applie wierdoed floppy drives, and
with one hard disk drive.  (I don't know if you could have had more.) There
is no question that the Lisa had an operating system which was ten years
(or more) in advance of the IBM PC.  I should say that Microsoft only
caught up with the Lisa five years ago -- and the Lisa was an early 80's
machine.

Soon after the Lisa, and certainly contemporaneous with the IBM AT, came
the Macintosh.  This was rather a cutdown Lisa.  It initally came with
128KB of RAM, and a choice of one or two floppy drives.  Apple released
upgraded versions in quick succession, mostly to expand the RAM and provide
hard disk capabilities.  As with Lisa, the Macintosh had a vastly superior
operating system than the Lisa.  (Sadly the Mac is still behind Lisa in
terms of OS design.  MacOS X will finally rectify that.)

I have to say that the IBM PC was faster than the Apple ][, //e and ///,
and could make sane use of more memory, however it was not excellent.  Many
of the design choices turned out to have two edges: The choice of the 8086
was perhaps the worst, with its separate IO bus and segmented architecture.
The use of the PIC in the PC, and later a second cascaded PIC, has been of
dubious value, and it's a fact that even today trying to correctly
configure all of the installed hardware is a major source of effort and
failures.

The PC was by no means an order of magnitude better than Apple's low-end
machines, and compared to Apple's newer machine, Lisa, I think the
convincing argument is that PC was inferior.

In terms of available software, the Apple ][ held it's own for a long time.
Apple's DOS was not as good as PC-DOS, but it wasn't much worse.  Apple's
SOS (for the Apple ///) and ProDOS (for the Apple ][ and //e) was much
better than PC-DOS.

I hope you will understand that I have not included third party add-ons to
any of the machines of the time.  They do change the story, but perhaps not
the result.

I'm unconvinced that "the design of the PC at the time was excellent."

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