Odd "endianness" [was Re: RE: Base 64 posts to the list]
phil at ultimate.com
Fri Dec 9 20:36:49 CST 2016
> Both One-Word and Two-Word Global Byte Pointers were added at the same
> time as extended addressing, according to the HRM. Simple "Global Byte
> Pointer" would have been inherently ambiguous.
OWG's were added to the KL ucode later:
;251 ADD CODE FOR ONE WORD GLOBAL BYTE POINTERS.
; TOOK OUT EDITS 243 AND 250 TO GET ENOUGH SPACE IN CRAM
; FOR THIS EDIT. OWGBP WITH EXTEND INSTRUCTIONS WILL NOT
; RETURN A OWGBP. THEY WILL RETURN A TWO WORD GLOBAL BP.
I can't tell off hand if there was a TOPS-20 release that supported
extended addressing earlier than UCODE version 251.
Hey! here's a ref to TWG's in the UCODE history:
;336 9 Aug 83--Back off 330 for a bit, since TOPS-10 7.02 must be tested
; and OWGs in section 0 fail for string instructions (they get converted
; to TWGs, which are illegal in section 0). For now, we will maintain
; both sources.
Maybe I'm conflating things with the legalization of OWGs in section zero
(the low 256KW of address space that behaved like a non-extended machine)
> The KI-10 processor added
> a 22-bit pager and a concept of sections to the hardware.
Are you sure? KI (aka TOPS-10) paging may have extended the physical
address space, but not the virtual address space (still limited to 18 bits).
In the end TOPS-10 used "KL" paging: DECnet had to live in a non-zero
section in the monitor (in 7.02?), and user-mode extended address was
finally added later.
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