From: muta...@gmail.com   
      
   On Tuesday, September 13, 2022 at 12:24:43 AM UTC+8, anti...@math.uni.wroc.pl   
   wrote:   
   > muta...@gmail.com  wrote:   
   > > On Monday, September 12, 2022 at 4:23:43 AM UTC+8, s_dub...@yahoo.com   
   wrote:   
   > > > On Sunday, September 4, 2022 at 1:55:32 PM UTC-5, muta...@gmail.com   
   wrote:   
   > > > > On Monday, September 5, 2022 at 1:03:24 AM UTC+8, Scott Lurndal wrote:   
   > > > > > "muta...@gmail.com"  writes:   
   > > > > > >On Sunday, September 4, 2022 at 9:25:34 PM UTC+8, wolfgang kern   
   wrote:   
   > > > > > >> On 04/09/2022 06:32, muta...@gmail.com wrote:   
   > > > > >   
   > > > > > >Noone had done segmentation before and it   
   > > > > > >would take decades of science still to   
   > > > > > >work through the repercussions.   
   > > > > > Several very successful systems that predate the   
   > > > > > 8086 by a full decade used segmentation; examples include the PDP-11,   
   > > > > > the B6500 et alia.   
   > > > > They presumably didn't do 4 bit shifts or similar   
   > > > > so didn't hit the a20 issue nor the flexible shift issue.   
   > > > >   
   > > > > The a20 is probably because of cp/m PSP though,   
   > > > > not segment shift.   
   > > > They presumably didn't do 4 bit shifts or similar   
   > > > so didn't hit the a20 issue nor the flexible shift issue.   
   > > >   
   > > > The a20 is probably because of cp/m PSP though,   
   > > > not segment shift.   
   > > > ~~~   
   > > >   
   > > > Gosh, istm you have these concepts jumbled up.   
   > > >   
   > > > Sorry for the review but..   
   >    
   > >   
   > > So first we have the justification for address wrap.   
   > > So that call 5 could be implemented.   
   > >   
   > > Perhaps we need to go back to the 8080   
   > > and/or cp/m to see whether the call 5   
   > > could have been replaced with something   
   > > that could have future-proofed the   
   > > situation.   
   > No "perhaps". Call 5 was for CPM compatibility. Original   
   > CPM was for 64kB address space, so no problem _preserving_   
   > compatiblity with respect to segment manipulation/wraparound:   
   > this was new stuff. 8086 was different instruction set   
   > so if was possible to implement equivalent functionality   
   > in different way.   
   >   
   > Even if you insist on having exactly the same functionality,   
   > in PSP it is easy to do without wraparound: just put extra far   
   > jump at end of BIOS ROM and in PSP have jump to this extra jump.   
   > Cost is extra 4 bytes of ROM used by the jump and extra   
   > machine cycles to execute extra far jump per each call 5.   
   >   
   > Of course, once BIOS without this extra call was in the wild   
   > DOS had to support such BIOS-es and gate A20 was logical   
   > solution...   
   >   
   > --   
   > Waldek Hebisch   
      
   Even if gate a20 was a logical solution,   
   would it have been reasonable for msdos to   
   have an explicit bios call to enable wraparound?   
      
   Even if existing bioses don't implement that   
   call, it doesn't matter, because the 8086 is   
   going to wrap around anyway.   
      
   It's only when the 80286 arrives that the   
   bios call needs to actually work.   
      
   --- SoupGate-Win32 v1.05   
    * Origin: you cannot sedate... all the things you hate (1:229/2)