Odd "endianness" [was Re: RE: Base 64 posts to the list]

Rich Alderson RichA at livingcomputers.org
Tue Dec 13 18:00:46 CST 2016

From: Eric Smith
Sent: Saturday, December 10, 2016 6:38 PM

> On Fri, Dec 9, 2016 at 12:47 PM, Rich Alderson <RichA at livingcomputers.org>
> wrote:

>> [1] For non-PDP10 programmers:  The original architecture of the PDP-6
>>     and PDP-10 used an 18-bit (256KW) address space.  The KI-10
>>     processor added a 22-bit pager and a concept of sections to the
>>     hardware.

> As you say, the KI10 had 22-bit physical memory addressing, almost
> identical to the "KI paging" of the later Model A KL10.  There were two
> PTEs per 36-bit word in the page table, with the five of the 18 bits
> being the APWSX properties, and the remaining 13 being a physical page
> number.  The 13-bit physical page number was concatenated with the
> offset into the 512-word page (low 9 bits of the virtual address) to
> get the 22-bit physical address.

> However, the KI10 did not have any "sections". Sections were introduced
> with the Extended ("Model B", "KL paging") KL10.

I knew that was wrong just as soon as I had hit "Send", but I also knew
that I could count on one of the PDP-10 subgroup to fix that.



Rich Alderson
Vintage Computing Sr. Systems Engineer
Living Computer Museum
2245 1st Avenue S
Seattle, WA 98134

mailto:RichA at LivingComputerMuseum.org


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