Richard:
The historically interesting thing about the ALTAIR has how insanely
primitive it was when it became the
sensation that sparked the PC revolution.
Putting a disk on an ALTAIR is kind of cool, but it misses the point of how
primitive they really were.
Yes, parallel logic is much more consistent with the Altair era.
My keyboard is 8-bit parallel, my paper tape reader is 8-bit parallel.
The only common serial devices were Teletype machines (because of their
evolution from the telegraph).
Teletypes were the most common "terminal" in use back then.
Not for me, though, I have a surplus, converted Friden Flexowriter, (or
boat anchor), that we modified to be parallel.
Do you even know what paper tape is ?
I think that every ALTAIR had to deal with paper tape at some point.
Magnetic media were too unreliable.
I have a cute little optical paper tape reader that has a row of 9 LEDs and
a corresponding row of photodiodes.
It sends data as eight bits in parallel.
There is a row of little holes in the third position that is normally
intended to tractor the paper tape through a teletype machine.
The optical paper tape reader uses this hole as a clock signal for software
handshaking with the ALTAIR through a parallel port.
To load BASIC, you entered a tiny loader program through the front panel
switches.
This program just looked for the tape reader's clock bit, delayed a little,
then read the rest of the byte and stored it in memory.
When you loaded Bill Gate's BASIC, the first data loaded was a more robust
checksum loader.
This loader quickly took control and if everything summed correctly after
then rest of the tape was read, BASIC was running when you were done.
By the way, in the beginning, ALTAIR BASIC WAS the "Operating System".
Through PEEKs and POKEs executed from your BASIC programs, you could
control all of your hardware.
I also have a "VDM-1" video display card. We converted an old TV work
with this.
After BASIC was loaded, we add a "patch" for this through the front panel
switches.
That was another interesting thing about the ALTAIR, you could always take
control of your computer through the front panel switches.
There was no "reset" button to hit when your system crashed, your just went
in and looked at what happened.
Usually, you went to location 0 and hit "run" to get out of a crash.
A "nasty" crash was when an loop overwrote your memory.
This happened fairly often too.
It was always kind of interesting to look at the patterns that appeared in
the memory when these crashes occurred.
I have always thought that if I wanted to be able to easily "boot" my
ALTAIR to show it off, I would construct
a box that would let me load and save my programs to a modern PC through
this parallel port.
Maybe just a BASIC stamp chip.
I never kept up with disk controller technology
I don't really know what a WD1002 is.
Are your Altairs original or "B" models ?
I hate to think that as an "original" Altair owner, I am, myself, a museum
piece :-)
I am only 39 years old.
When I listen to the war stories of 80 year olds, I might think of THEM as
museum pieces.
-Rob
-----Original Message-----
From: Richard Erlacher [SMTP:edick_at_idcomm.com]
Sent: Wednesday, January 03, 2001 6:16 PM
To: classiccmp_at_classiccmp.org
Subject: Re: Altair Owners ...
Yeah ... I've got a copy of that MITS DISK BASIC lying about somewhere,
though there's no documentation on hand.
The deal is that (1) with one of my scrap S-100 PCB's hacked into a WD1K
channel, the Altair can then talk to a WD1002-05 HD/FD Controller, as I'm
putting in the MITS HDC box, and use that to operate the mix of 5-1/4" hard
and floppy disks in the second box. It requires no S-100 FDC of any sort.
Since BIOS code abounds for the WD controllers, I'd say it's not only a
cool
set of hardware, but a slick way to get the OS running if it's not already,
and I do have HD drives in the form of a "back-end" driver, for the WD1K
series, that can be autoloaded on boot if CP/M is already running.
However, using a parallel port board would be more consisitent with what
was
done with the original Altair system: the one with the small desk built on
the table-high rack with a desk extending to one side. It used a parallel
port sort of thingie to talk to the SMD interface in the HDC box, and that,
in turn, talked to the CDC HAWK drive in the top portion of the rack
pedestal onto which the desktop was fitted.
I could put in some sort of parallel port thingie, and 8255, or perhaps a
pair of input ports and a pair of output ports, to provide the bits
necessary to do the job. The channel interface is a lot slicker and
faster,
though, and TTL will drive the cable a lot better than an 8255.
Either one will work, but I've no "feel" for what would be preferred by the
typical Altair owner. Of course I'm particularly interested in placing
this
stuff with someone to whom an Altair isn't an Altair if any of the hardware
doesn't say MITS on it, though only the boxes in this set are original
MITS.
Dick
----- Original Message -----
From: "ajp166" <ajp166_at_bellatlantic.net>
To: <classiccmp_at_classiccmp.org>
Sent: Wednesday, January 03, 2001 4:52 PM
Subject: Re: Altair Owners ...
> From: Rob Kapteyn <kapteynr_at_cboe.com>
>
>
> >Hey wait a minute ...
> >A BIOS on an Altair ?
> >
> >Sure there were add-ons (years later) that did this, but if you really
> want authenticity this is what we did --
> >
> >I always had to "boot" my Altair with a simple paper tape loader program
> entered from the switches on
> >front panel. I did this so many times, I had the 30 octal codes
> memorized.
>
>
> Often several times until it read the cassette correctly! Saving stuff
> was easy though bets were
> off if you could read it later.
>
> First homebrew board 8223 (x2 for 64 bytes plus 2 7489s for 16bytes of
> scratch ram) prom boot!
>
> >Once I had Altair BASIC loaded, I generally kept the machine powered up
> as long as possible.
>
>
> Or until it crashed!
>
> >I never knew anyone who actually had a actual floppy for their Altair.
> >I seem to remember that they cost more than the computer itself, and the
> computer was quite >expensive --($2,000 1974 dollars).
>
>
> I built and debugged two of them for others.
>
> Allison
>
>
Received on Thu Jan 04 2001 - 15:42:32 GMT