🚀 go-pugleaf

In article <pkrloc$ttj$1...@Iltempo.Update.UU.SE>,
Johnny Billquist  <b...@softjar.se> wrote:
>The KL10 added 5 bits to addressing, giving you 32 sections, or 23 bit 
>addresses. The architecture itself allowed up to 30 bits for addresses, 
>giving you 12 bits for sections, or 4096 sections.
>
>Which would have been a fairly large addressing space, but starting to 
>be small by todays standards. (We're talking about roughly the same as a 
>32-bit address in 8-bit byte addressable machines.)

The 23 bit address would have been small but the 32 bits would take
you to 4GB which would have been good for at least another decade after
the -10 died in 1983.

>And the change to the basic architecture is fairly unintrusive, if I 
>remember right. In a "pointer", most of the left halfword is unused. You 
>have the indirect bit, and not much else. The architecture grabbed 12 
>bits there for the section, but said that a zero means your current 
>section. Also, all direct addressing is always referring to the current 
>section. So pretty much all existing programs would continue to run 
>without changes. However, you could easily move data or routines to 
>another section, and just call them there, and not much else needed 
>changing. Just remember to get the correct section into pointers if you 
>did start to spread out over several sections.

Well, sort of.  There's no need to guess, the reference manual is in
bitsavers.  Programs running in section 0 had 18 bit addressing.
Programs running in any other section had mixed 18 or long adddesses
depending on the instruction and in a few stack instructions, on the
contents of the high bits of the pointer.  It was a lot like near and
far addresses on a 286 which were a pain to keep track of.

There was a lot of PDP-10 code that depended on the fact that you
could store addresses in the high or low half of a word, and use
halfword instructions to manipulate them.  With longer addresses you
had to change your data structures which meant you had to change your
code, so either you did what someone suggested in a previous message,
keep your program in section 1 and treat everything else as a data
space, or you had to rewrite your code, at which point you might as
well rewrite it for the nice flat address space of a Vax.

-- 
Regards,
John Levine, jo...@iecc.com, Primary Perpetrator of "The Internet for Dummies",
Please consider the environment before reading this e-mail. https://jl.ly