Re: The "Good" Old Days - Complete Specs for DX-10 Operating System

In article <vdjt71$3a56o$1@dont-email.me>, Rich  <rich@example.invalid> wrote:

In comp.os.linux.misc 186282@ud0s4.net <186283@ud0s4.net> wrote:

The 990 series used the TMS-9900 chip and near variants.  This was an
odd chip - kept the CPU registers out in ordinary RAM and could
switch quickly between different sets of registers.  At that time,
the external RAM and CPU kinda ran at the same speed so little was
lost putting the registers in RAM.

>
The 6502 did something similar.  It wasn't as far down the path as the
TI chip, but page zero (first 256 bytes of ram) acted a lot like an
'extended register file'.  There were even addressing modes that used
two consecutive bytes of "page zero" as a 16bit pointer into the rest
of the RAM one's system had installed,

 
...and the 65816 (the 16-bit successor to the 6502 that was used in the
Apple IIGS) let you move what was now called the "direct page" anywhere in
the first 64K of memory.  A new register for the purpose was added, along
with another one that allowed the stack to also be put anywhere in the first
64K (vs. having it locked to page 1).