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From: Michael S <already5chosen@yahoo.com>
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Subject: Re: 80286 protected mode
Date: Fri, 18 Oct 2024 12:47:53 +0300
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On Mon, 14 Oct 2024 19:39:41 GMT
scott@slp53.sl.home (Scott Lurndal) wrote:

> mitchalsup@aol.com (MitchAlsup1) writes:
> >On Mon, 14 Oct 2024 15:04:28 +0000, David Brown wrote:
> >  
> >> On 13/10/2024 17:45, Anton Ertl wrote:  
> >  
> >> I do think it would be convenient if there were a fully standard
> >> way to compare independent pointers (other than just for
> >> equality).  Rarely needing something does not mean /never/ needing
> >> it.  
> >
> >OK, take a segmented memory model with 16-bit pointers and a 24-bit
> >virtual address space. How do you actually compare to segmented
> >pointers ??  
> 
> Depends.  On the Burroughs mainframe there could be eight
> active segments and the segment number was part of the pointer.
> 
> Pointers were 32-bits (actually 8 BCD digits)
> 
>   S s OOOOOO
> 
> Where 'S' was a sign digit (C or D), 's' was the
> segment number (0-7) and OOOOOO was the six digit
> offset within the segment (500kB/1000kD each).
> 
> A particular task (process) could have up to
> one million "environments", each environment
> could have up to 100 "memory areas (up to 1000kD)
> of which the first eight were loaded into the
> processor base/limit registers.   Index registers
> were 8 digits and were loaded with a pointer as
> described above.   Operands could optionally select
> one of the index registers and the operand address
> was treated as an offset to the index register;
> there were 7 index registers.
> 
> Access to memory areas 8-99 use string instructions
> where the pointer was 16 BCD digits:
> 
>    EEEEEEMM SsOOOOOO
> 
> Where EEEEEE was the evironment number (0-999999);
> environments starting with D00000 were reserved for
> the MCP (Operating System).    MM was the memory area
> number and the remaining eight digits described the
> data within the memory area.  A subroutine call could
> call within a memory area or switch to a new environment.
> 
> Memory area 1 was the code region for the segment,
> Memory area 0 held the stack and some global variables
> and was typically shared by all environments.
> Memory areas 2-7 were application dependent and could
> be configured to be shared between environments at
> link time.

What was the size of phiscal address space ?
I would suppose, more than 1,000,000 words?