Why is there no CR1, and why are control registers such a mess anyway? (2010)

[JoshTriplett]

http://www.pagetable.com/?p=364

[ars]

Context: https://news.ycombinator.com/item?id=13126858

[ethbro]

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

[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:

[Gracana → falsedan]

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

[ams6110 → Gracana]

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.

[scrollaway → ams6110]

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...

[Dylan16807 → Gracana]

Strange. It's only 60 characters wide, so it should work fine. But the site fits it into a scrollable box only half the width of the screen.

[falsedan → Dylan16807]

Yeah, I couldn't believe it when I saw it!

[falsedan → Gracana]

I'm posting from a mobile device and it looks unreadable, I hoped it was just for me because I know it looks fine on desktop…

[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.

[yuhong → caf]

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

[yuhong]

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

[madgar]

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

[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.

[DiabloD3 → jburgess777]

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