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On 2015-03-02 04:49, Dave Angel wrote:
> On 03/01/2015 08:59 PM, MRAB wrote:
>> On 2015-03-02 01:37, Dennis Lee Bieber wrote
>>>
>>>     You'd be able to run it on a TI99/4 (in which the BASIC interpreter,
>>> itself, was run on an interpreter... nothing like taking the first
>>> "16-bit"
>>> home computer and shackling it with an interpreted language that was
>>> run on
>>> an interpreted language)
>>>
>> The "16-bit" CPU had a 16-bit address bus (64K address space). If you
>> were going to switch from an 8-bit processor to a 16-bit processor, one
>> of the pluses you'd be looking for would the ability to directly
>> address more than 64K.
>>
>
> The 16 bit address bus permitted addressing of 64k words.  On most
> processors, that was 64k bytes, though I know one Harris had no bytes,
> but every memory access was 16 bits.  It therefore had the equivalent of
> 128k bytes.  Likewise I believe some of the DEC and DG minis had 128k
> bytes of addressability.
>
I have (or had, not sure where it is!) a manual of the TMS9900
processor, and I'm sure it addresses 64k _bytes_.

Wikipedia says "65,536 bytes or 32,768 words".

> Usually, the term 8bit processor was referring to the size of the
> register(s), not the address bus.  All the 8 bit micro-processors had 16
> bit address buses.  In fact, 4 bit processors generally had 12 to 16 bit
> address buses as well.  So a 4 bit processor with a 16 bit address bus
> could address 32k bytes, a half byte (a nybble) at a time).
>
> The IBM PC's 8088 had an 8 bit data-bus and 20 address lines.  But they
> called it a 16bit processor, to try to distinguish it from 8 bit
> processors like the 8080.  Anyway, it was code compatible with the 8086,
> which really did have a 16bit data bus and 20 bit address bus.
>