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.
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