Article View: comp.arch
Article #21917Re: LoadAll?
From: rob
Date: Tue, 02 Jan 1990 15:50
Date: Tue, 02 Jan 1990 15:50
19 lines
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1495 bytes
Another use for LOADALL is in DOS software that accesses extended
memory. The more standard method of switching to protected mode and then
resetting the CPU to re-enter real mode is too slow for some purposes.
LOADALL, though hardly elegant, allows access to memory above the 1Mb line
without having to switch modes. Microsoft's ramdisk and disk-caching
programs use LOADALL for accessing extended memory on a 286. As has been
noted, the 386 and 486 can switch much more easily between real and
protected modes, making LOADALL less useful.
In protected mode, LOADALL could theoretically be used to get around
the CPU protection, since it allows you to directly set the 'shadow'
segment registers. In practice, the problem of setting up a table at
an absolute address under protected mode, plus the fact that LOADALL is
supposedly a priviledged instruction, would make this difficult.
Intel is pretty adamant about avoiding LOADALL, and guards information
about it closely. I've never seen any 'official' documentation of it,
though such documentation undoubtedly exists.
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Path: arc1-ca.pugleaf.net!utzoo!utgpu!jarvis.csri.toronto.edu!rutgers!usc!snorkelwacker!bu.edu!bu-cs!mirror!prism!rob From: rob@prism.TMC.COM Newsgroups: comp.arch Subject: Re: LoadAll? Message-ID: <208300003@prism> Date: 2 Jan 90 15:50:00 GMT References: <597@unmvax.unm.edu> Lines: 19 Nf-ID: #R:unmvax.unm.edu:-59700:prism:208300003:000:1088 Nf-From: prism.TMC.COM!rob Jan 2 10:50:00 1990