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From: Rich <rich@example.invalid>
Newsgroups: comp.os.linux.misc,alt.folklore.computers
Subject: Re: The "Good" Old Days - Complete Specs for DX-10 Operating System
Date: Thu, 3 Oct 2024 17:02:28 -0000 (UTC)
Organization: A noiseless patient Spider
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In comp.os.linux.misc Scott Alfter <scott@alfter.diespammersdie.us> wrote:
> 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).

Nice, I did not know that about the 65816.

I do wonder why restrict it to only first 64K?