
Why is there no CR1, and why are control registers such a mess anyway? (2010) - JoshTriplett
http://www.pagetable.com/?p=364
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ars
Context:
[https://news.ycombinator.com/item?id=13126858](https://news.ycombinator.com/item?id=13126858)

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ethbro
You have to love comments that spawn links. "Why _is_ that a thing?"

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falsedan
The tl;dr:

    
    
      > The i486 added a few more control bits, and some of them
      > went into CR0. But instead of overflowing the new bits
      > into CR1, Intel decided to skip it and open up CR4
      > instead – for unknown reasons.
    

a.k.a. :shrug:

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Gracana
Spaces in front of your >s make your quote a raw formatted block that's really
hard to read on a mobile device. :/

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ams6110
Instead of email-style quotes, just add an asterisk before and after the
quoted text. _That puts it in italics_ and makes it obvious that it's quoted
material but it will wrap properly on various screen widths.

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scrollaway
I wish HN would simply support quoting with `>`. It's a recurring pain. That
way it could be made to look good on mobile too...

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caf
My suspicion is that some application in the 286 - OS/2 days was found to
expect an 'invalid opcode' fault from CR1, so that's why it had to stay
reserved.

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yuhong
This reminds me of how INT 0Fh had to stay reserved because of a Pentium Pro
errata.

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yuhong
The original 486 did not have CR4. It was added when Intel backported VME and
later PSE to later 486 processors.

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madgar
For those working closer to the metal than I: are these special instructions
dispatched to dedicated circuitry, or are they actually microcoded?

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jburgess777
> This entry was posted in archeology, trivia, whines on July 2, 2010 by
> Michael Steil.

So I guess (2010) is appropriate for the title.

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DiabloD3
It was already old in 2010, nothing has retroactively changed in the text.

