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   
      
   4 bytes of ROM or 5 bytes? My understanding   
   from Wolfgang is that 5 bytes are required.   
      
   --- SoupGate-Win32 v1.05   
    * Origin: you cannot sedate... all the things you hate (1:229/2)