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A comment on Intel mulls cutting 16 and 32-bit support, booting straight into 64-bit mode. Parent comment

Re:Intel mulls cutting 16 and 32-bit support, booting straig... by ithkuil on Thursday May 25, 2023 @02:09PM (#36074020)
It's even worse than that. If it was just the CPU...

It also simulate an old keyboard controller for the purpose of enabling the A20 gate which enables an address line.

https://en.m.wikipedia.org/wiki/A20_line

[ Parent | on HN ]
Re:Intel mulls cutting 16 and 32-bit support, booting straig... by deaddodo on Thursday May 25, 2023 @02:15PM (#36074086)
The A20 gate was deprecated (and made software-based) in Nehalem, then was removed completely in Haswell. It's never been a feature of the Zen µarch(s).
[ Parent | on HN ]
Re:Intel mulls cutting 16 and 32-bit support, booting straig... by armada651 on Thursday May 25, 2023 @02:13PM (#36074063)
Support for the A20 gate was actually already dropped as per the article you linked:

> Intel no longer supports the A20 gate, starting with Haswell.

[ Parent | on HN ]
Re:Intel mulls cutting 16 and 32-bit support, booting straig... by jylam on Thursday May 25, 2023 @02:35PM (#36074361)
It was not needed anymore in Haswell, but the support was still there. It isn't supported at all anymore.
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Re:Intel mulls cutting 16 and 32-bit support, booting straig... by bonzini on Thursday May 25, 2023 @03:11PM (#36074775)
Emulation of the keyboard controller is done by the firmware. The processor's support for A20 was tied to port 92h.
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Re:Intel mulls cutting 16 and 32-bit support, booting straig... by Dwedit on Thursday May 25, 2023 @05:40PM (#36076618)
The A20 line was famously used to hack the original XBox. By clearing A20, you prevent the XBox from booting from the hidden ROM, and it boots from regular flash ROM instead.

Some great videos about that on YouTube if you want to look.

[ Parent | on HN ]