[Coco] Glenside website (new & old)

[L. Curtis Boyle]

Do you mean like ANDD #$5555, as an example?

L. Curtis Boyle
curtisboyle at sasktel.net



On Apr 19, 2013, at 11:03 AM, Luis Antoniosi (CoCoDemus) wrote:

> 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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