TRS-80 Model I

Ethan Dicks ethan.dicks at
Sun Feb 4 11:30:14 CST 2007

On 2/4/07, Pete Turnbull <pete at> wrote:
> Neither did I, for much the same reasons.  And I had to repair quite a
> few that went out of alignment, and some that had released the magic
> smoke when someone plugged the drives in "off by one" after they
> disconnected them to move the machine.

That was a problem I also saw with the drives.  Several of my friends
had Apple IIs (I had a 32K PET 2001-N), and ISTR more than one person
did that.  Not cheap.  My memory is that at the time, the bare drives
were $600 new, so even if one just replaces boards, it's not
inexpensive in that environment.

> > I didn't like the Apple ][ I/O system. Memory space was tight, but they
> > wasted lots of space with those 'soft switches' and single-bit inputs. It
> > could all have been packed into a few bytes. I am pretty sure the 6821 if
> > not the 6522 was available when the Apple ][ was designed.
> The 6820 (and 6520) and 6522 existed then.

The 6520 == 6821 FWIW.  I don't recall how much those were, but new
6522 VIAs were $8 quantity 1 in the early 1980s, so I think Woz may
have just shied away from them on the basis of cost alone.  I did
enjoy learning how to twiddle the PET user port on a 4K PET.  More
complicated than the Apple scheme (data direction registers,
interrupts, etc.), but vastly more powerful.


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