Four?! Why not more?

[teenix]

Don't forget the extra ROM requirements to implement the larger stack. This would have required 1 extra ROM chip to be installed on all of the early models as they were all full up.

cheers

Tony

(06-14-2021 06:56 PM)Matt Agajanian Wrote:  

(06-14-2021 01:21 AM)Steve Simpkin Wrote:  <Large Snip>

This last factor (and tradition) probably kept HP's later calculator models at 4-levels. The addition of a Last X register starting with the HP-45 also helped.

<End Snip>

Well, since including a Last X register began with the 45 in the Classic series, the tech was already there. So,
why not include the Last X register beginning with the 21?