TRS-80 Model I
frustum at pacbell.net
Sun Feb 4 02:17:31 CST 2007
Chuck Guzis wrote:
> On 3 Feb 2007 at 22:56, Jim Battle wrote:
>> Let's look at contemporaries (1977 micros). The Sol-20 had 64x16
>> text, and unless you polled the hblank signal and limited yourself to
>> poking one character per 50 uS, you'd get snow on the screen. There
>> were others that had the snow problem as well (eg, exidy sorcerer).
>> The TRS-80 didn't have the snow problem, but it too had a 64x16 text
>> display. The PET (which I never used) also had character graphics of
>> the most pathetic sort.
> The DIsk II didn't come out until 78. The 1977 Apple had only a
> casette interface. Remember that OSI (from around the same time)
> used a 6850 UART for the same purpose, yet OSI didn't get any acclaim
> for the "genius" of the controller. Instead, it got slammed for the
> incompatibility of the floppies.
> A major part of Apple lore, it seems to me, is the mystique.
The Compucolor II (1977) also used a serial chip (TMS5501) for streaming
bits to/from the disk. Furthermore, they used an undocumented test mode
of the chip to make it operate at the bit rate they needed (otherwise it
tops out at 9600 baud). The disk format is single sided, and gets about
50 KB per disk.
I'd say using the serial controller chip in a floppy application is
clever as well. The Compucolor design doesn't use DMA either and the
CPU is very busy keeping the chip fed. Compucolor/OSI didn't have
nearly the success of the Apple II, so accolades are harder to come by.
Over the past few years I've had a couple OSI machines go through my
hands before I traded them for other things I cared about more. The
industrial design of the C1P was on par with that of a hobby project.
Most of the OSI machines, including the ones with disk drives, were
introduced in 1979.
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