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From: vo@micomvax.UUCP (Vladimir Orlt)
Newsgroups: comp.os.minix
Subject: Re: PC Minix/64KB limit
Message-ID: <1684@micomvax.UUCP>
Date: 22 Feb 89 21:47:07 GMT
References: <415@lzaz.ATT.COM> <2485@sun.soe.clarkson.edu> <417@lzaz.ATT.COM>
Reply-To: vo@micomvax.UUCP (Vladimir Orlt)
Organization: Philips Electronics Ltd. (TDS - Montreal) St. Laurent QC, Canada
Lines: 32

In article <417@lzaz.ATT.COM> hcj@lzaz.ATT.COM (HC Johnson) writes:

>1. the 8088, 8086,80186, 80286 totally lack the ability to address beyond 64KB
-the 8088,8086,80186 address 1Mbyte
-the 80286 addresses 1Mbyte in 'real' mode, 16Mbyte in 'protected' mode
-the 80386 addresses 1Mbyte(plus 64K) in 'real' mode, 4 Gigabytes in
'protected'mode, 16Mbyte(plus 64K) in '286-protected mode'

all of the above addressing is performed by combining segment and offset
registers; only the offset is restricted to 64K.  Any machine cycle to
memory performs the segment+offset combination to generate
a physical address on the CPU's address lines; in 'real' mode, the combination
is straightforward; in 'protected' mode, it can be complicated.
	The ability to modify segment registers is obviously an integral part
of the CPUs' instruction set; compilers use it, but you can write assembly
code (or machine code) to do it as well.

>3. Extened (or is it expanded) memory uses a window in the address space of
>   the machine to access more memory.  This is the only scheme on the
>   8088/8086. 
'Expanded' memory is the correct term.  Such scientists, those PC people...

>4. the 80286 supports expanded(or is is extended) memory that addressable
>   when running in protected mode.  This paging mode...
'Extended' memory is the correct term.  In the 80286, this is not a paging mode
but a fancy segmentation mode.  Only the 80386 supports true paging, in 
addition to 80286 features.

					Vlad the re-mailer
					...philabs!micomvax!vo

"IBM is a concept by which we measure our pain" (apologies to J.Lennon)