22 Jun
1997
22 Jun
'97
4:03 p.m.
Yes, but it
some cases the 'kludges' led to problems later on - 'trivial'
problems like a total incompatability between the Disk II and just about
any other machine in the world
For the most part, 5.25" disks are incompatible between any
two machines. There never was a standard format, unlike the 8"
world where IBM 3740 dominated (though that didn't mean that
everyone was compatible with it.) a PSU that was beyond the design limit when
running a system
board, language card and 1 drive
No, it isn't. I just measured the system current drain (II+, 1 Disk ][
drive, third-party language-card equivalent) and verified
this isn't true. It is true that every 10 years or so a power supply
will fail, but you can blame Astec for that. that _crazy_ slot addressing scheme
That scheme is actually pretty clever. I can put a disk controller
in slot 5, type "CATALOG,S5" and look at a drive connected to it.
No DIPswitches to set, no BIOS to modify. I can put a printer card in slot 4, type
"PR#4", and now all redirected
to the printer. I can put a serial card in slot 1,
type "IN#1", and now a keyboard hooked to a terminal on the serial
OS-9, one of my favourite micro OS's has a very nice way of handling this.
Suppose you want to add a serial card based on the 6551. You can have a
_generic_ 6551 driver that has no idea of the address of your card, and
then a device descriptor that contains the address and the paramter table
(baud rate, whether you want a LF after a CR, a pause at the end of a
screen,etc). Although most hackers used the standard assembler to make
descriptors, it would be trivial to make a 'user friendly' installation
tool.
IMHO that's a much nicer way to do it than the Apple method which means
you have to know which slot each card is in (and, in a lot of cases there
are 'standard' slots for particular cards that you'd better stick to. What
do you do if you want _2_ 80 column displays in the same machine? One in
slot 3, what about the other one).
and the saving
on chips/PSU consumption by switching the power line to
the I/O card ROM
Which I/O card is this? I've never seen anything quite like this on
any of my peripherals (or if I have, I haven't noticed over the past
20 years.) Saving components is only 'good' when it
doesn't affect performance. I am
not convinced that this is the case with the Apple ][
Oh - you'd have preferred Wozniak to use single-density FM, getting
only 90kbytes per 5.25" floppy, over the GCR which lets you get 140K? Or you'd rather lose some CPU cycles in
order to refresh the
RAM, because your preferred memory-mapped screen layout wouldn't
allow the video circuitry to do it?
Oh come on. You can scramble the address lines to the _RAM_ so that all
cells get refreshed in a sufficiently short time and still have a linear
address map as seen by the processor if you add a few more TTL chips. I've
seen it done on countless other micros.
Tim. (shoppa(a)triumf.ca)
--
-tony
ard12(a)eng.cam.ac.uk
The gates in my computer are AND,OR and NOT, not Bill