[Coco] Glenside website (new & old)

[Luis Antoniosi (CoCoDemus)]

You forgot the full 16-bit ULA. The x86 can perform a 16-bit bitwise AND,
OR, NOT while the 6809 can't.



On Thu, Apr 18, 2013 at 11:30 PM, Lothan <lothan at newsguy.com> wrote:

> 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.
>
>
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>



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