10 Dec
2016
10 Dec
'16
2:36 a.m.
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.