[Coco] Glenside website (new & old)

[Lothan]

From: Arthur Flexser

> I always wondered why the CoCo is referred to as an 8-bit machine,
> whereas the original IBM PC, which also had an 8-bit bus and 16-bit
> registers, was consistently referred to as a 16-bit machine.
>
> Art

As I recall, the only difference between the 8088 and the 8086 is that the 
8088 had an 8-bit external data bus whereas the 8086 had a 16-bit external 
data bus. Internally, the data bus is 16 bits. The 20-bit address and 8- or 
16-bit data bus used the same pins so memory access was a lot slower than on 
other processors. The only advantage to this approach is that Intel could 
squeeze it into a 40-pin DIP.

Overall, the 8088/8086 had four 16-bit accumulators (or eight 8-bit 
accumulators), two 16-bit index registers, two 16-bit stack pointers, four 
16-bit segment registers, and a 16-bit instruction pointer. The only thing 
here that wasn't already in the 6809 are three extra accumulators and the 
segment registers.

Looking at it from this perspective makes me ask the same question. Both the 
6809 and 8088 had an 8-bit external data bus and both were essentially 
16-bit internally.

This does raise a question, though. The only real advantage to the 8088 is 
that it had segment registers that were used to augment the 16-bit 
instruction pointer register to develop a 20-bit physical address ((CS * 16) 
+ IP). As much as I despise the 8088's segmented architecture, it makes me 
wonder what might have happened if Motorola or Hitachi had bolted on a 
couple of segment registers to the 6309 to give it an effectively flat 1MB 
address space.

I remember back in the day the 80x86 architecture did not support 
position-independent code (and still doesn't to this day as far as I'm 
aware) and Windows didn't support hardware task switching, both of which 
were directly supported by OS-9 on the 6809 way back in the early '80s. 
Offhand, I'm thinking Windows Me still relied on the message pump for task 
switching and didn't switch to a hardware timer until Windows 2000 on the 
Pentium processor.