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| Authored by: JamesK on Monday, April 15 2013 @ 02:18 PM EDT |
Yes, I am aware how he showed how MS-DOS was "borrowed" from CP/M when
he demonstrated a secret command in court. I was thinking more of from the user
perspective, where MS-DOS was in many ways a step backwards from what was
available in CP/M and elsewhere. For example, while my memory is a bit fuzzy on
this, I seem to recall CP/M-80 supported the concept of individual users with
their own area of the disk. MP/M was also available back in the 8080 days, long
before anything like it was availble from MS or even 3rd party utilities such as
Sidekick. When I first used DOS, I had been working with VAX/VMS for a while,
so I immediately saw many shortcomings in DOS. This, coupled with the hardware
deficiencies of the IBM PC (at the time I was working as a computer tech on
minicomputers and also had my own S100 bus computer) I recognized, I really
wasn't thrilled with that combination. For example, you may recall the issues
of sharing IRQs on the XT & AT computers. This is because for some reason
IBM went with active high interrupt lines, rather than the standard practice of
active low. Active low makes it much easier to share that line, because
something grounding the line generates the interrupt and then software poles the
possible devices to determine which. With active high, you could have one
device trying to provide a high level, while another was trying to hold it low.
This caused problems with the TTL logic that was commonly used then and still
does with other technology. As a result, if you had 2 serial ports, they had to
have their own interrupt lines. In contrast, on my S100 IMSAI 8080, I could
share the interrupt lines quite easily and even designed and built my own 8 port
serial I/O card, with all the ports sharing one interrupt line.
BTW, "interrupt line" refers to the hardware and "IRQ" or
interrupt request is a software instruction that may be caused by an interrupt
line going active. The term IRQ was commonly used with 8086 and later CPUs and
8080 CPUs the instruction was called "INT".
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