Anyone have any info on the obscure MX11 PDP-11 option?

[Al Kossow]

It is in the Dick Best Options and Modules List 197503
Steve Rothman is shown as responsible engineer

On 6/24/19 1:38 PM, Noel Chiappa via cctalk wrote:
> While I asking on the TUHS list about the KS11, someone mentioned the MX11
> Memory Extension Option, described as "enabl[ing] the usage of 128 KW memory
> (18-bit addressing range) ... developed by the Digital CSS (Computer Special
> Systems)".
> 
> I'm not familiar with this