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From: torb@idt.unit.no
Newsgroups: comp.sys.intel
Subject: Segment limits on 80386
Message-ID: <1990Jan17.164046.10641@idt.unit.no>
Date: 17 Jan 90 16:40:46 GMT
Sender: torb@idt.unit.no (Tor Brekke)
Reply-To: torb@idt.unit.no ()
Organization: Div. of CS & Telematics, Norwegian Institute of Technology
Lines: 21


I am currently developing an operating system kernel for an 80386
based, 16 node hypercube, and I am having some trouble with the
documentation. Both "80386 Programmer's Reference Manual" and "80386
System Software Writer's Guide" are ambiguous in their interpretation
of the limit field in segment descriptors, so I am seeking the wisdom
of the net to help me in this matter. 

What I want to know is the maximum segment size for a *small* segment.
Both references mentioned above says both 64KB and 1MB for expand-up
segments. What's right ?? I would guess 1MB since the limit field is
20 bits long. 

For expand down segments the references agree on 64KB as maximum for a
small segment. Is this right ?? 1MB seems more logical with a 20
bit limit field.

Thanks in advance

Tor Brekke
Email: torb@idt.unit.no