[TUHS] Can't load split I&D files (in one PDP-11/23 PLUS)

Lyle Bickley lbickley at bickleywest.com
Fri Jun 26 08:17:10 AEST 2009

On Thursday 25 June 2009, Pete Turnbull wrote:
> On 25/06/2009 21:49, Wilko Bulte wrote:
> > Quoting SPC, who wrote on Thu, Jun 25, 2009 at 08:57:47PM +0200 ..
> >> Well, the matter is simple: I'm trying to install 2.11 BSD in one PDP-11/23
> >> PLUS with 4MB of ram, and the 'restor' and 'icheck' utilities don't load in
> >> he PDP, returning this message:
> >>
> >>   "Can't load split I&D files"
> >>
> >> I tried with the diverse distributions of Vtserver and diverse versions of
> >> 'restor'. In the case of the 2.9BSD this don't happen but the utility can't
> >> understand what is the 'vt' device.
> >>
> >> Someone has encountered and solved this problem ?
> > 
> > I could be wrong, but I think the 11/23 is not a split ID CPU?
> Correct, it isn't.  You cannot run 2.11BSD in a PDP-11/23 or similar 
> machine because a lot of things in 2.11BSD require split I&D.  It's 
> declared on the first page of the setup instructions:
>     "This distribution can be booted on a PDP-11 with 1Mb of memory or
>      more, separate I&D, and with any of the following disks:"
> You need an 11/73 or better to have split I&D.  For those who might not 
> know what that means, it refers to the processor's ability to keep 
> I(nstructions) and D(ata) in separate spaces, so in effect virtually 
> doubling the amount of memory that can be used.  That is, you can have 
> (almost) 64K of instructions *and* (almost) 64K of data at the same 
> time.  Without split I&D, you have 64K in total for both.

As Pete says, you can't run 2.11 on an 11/23.

However, I do run 2.9 BSD on my 11/34 as it does NOT require seperate I&D
as does 2.11 BSD.

Might want to try using 2.9 on your 11/23.  Here's the CPUs supported by
2.9 BSD:

11/23, 11/24, 11/34, 11/34A, 11/34C, 11/40, 11/44, 11/45, 11/55, 11/70

Min. required memory is 192K


Lyle Bickley
Bickley Consulting West Inc.
"Black holes are where God is dividing by zero"

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