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Groups > alt.os.assembly > #20
| From | James Harris <james.harris.1@gmail.com> |
|---|---|
| Newsgroups | alt.os.assembly, alt.lang.asm, alt.os.development |
| Subject | Re: Protected mode on 64-bit CPU |
| Date | 2016-09-04 13:01 +0100 |
| Organization | A noiseless patient Spider |
| Message-ID | <nqh2e0$fal$1@dont-email.me> (permalink) |
| References | <563a8630-6a56-4480-9b76-d519ca60acbe@googlegroups.com> <20160903231714.401eef2c@_> |
Cross-posted to 3 groups.
On 04/09/2016 04:17, Rod Pemberton wrote: > On Sat, 3 Sep 2016 19:10:19 -0700 (PDT) > muskrat7@gmail.com wrote: > >> Does anyone know why 64-bit long mode does not have built-in hardware >> protection? I know many didn't use the 32-bit hardware segmentation >> but it was a nice option to have if you wanted... Did they just get >> rid of it in 64-bit mode due to the perception it wouldn't be used or >> were there other limitations that prevented this feature? Segmentation was a brilliant idea but was let down by Intel's Protected Mode implementation which distinguished between segmented and non-segmented pointers and thereby created lots of complexity. People generally just used 32-bit pointers. I gather than when AMD asked Microsoft and others what they wanted from 64-bit mode there was, because of the familiarity of the above flat 32-bit address mode, little or no demand for segmentation. AMD therefore dropped it and lots of other things for which they found little or no interest. (They did not delete these things from the CPU - which still has them in PMode - only from 64-bit Long Mode.) IMO, even with the flat pointer model, it is a pity that AMD went as far as they did. -- James Harris
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Protected mode on 64-bit CPU muskrat7@gmail.com - 2016-09-03 19:10 -0700
Re: Protected mode on 64-bit CPU Rod Pemberton <NoHaveNotOne@zxdehrnyya.cam> - 2016-09-03 23:17 -0400
Re: Protected mode on 64-bit CPU "wolfgang kern" <nowhere@never.at> - 2016-09-04 11:27 +0200
Re: Protected mode on 64-bit CPU James Harris <james.harris.1@gmail.com> - 2016-09-04 13:01 +0100
Re: Protected mode on 64-bit CPU Muskrat <muskrat7@gmail.com> - 2016-09-04 10:10 -0700
Re: Protected mode on 64-bit CPU James Harris <james.harris.1@gmail.com> - 2016-09-04 21:53 +0100
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