Carrell Loses His Baby: Say Goodbye to Sideport

Sitting at dinner with Eric Demers and Carrell Killebrew is honestly one of the best experiences I’ve ever had working with ATI. Before he got huge and subsequently left, I used to have annual dinners with Pat Gelsinger at Intel. They were amazing. To get to sit at the same table as someone as talented and passionate as a Gelsinger, Demers or Killebrew is one of the most fortunate and cherished parts of my job.

Eric was telling me about how they trimmed down 870 from over 400mm2 down to 334mm2 and how wonderful the end product was. I stopped him and asked for more detail here. I wanted an example of a feature that they had to throw out but they really wanted to keep in. Manufacturers rarely tell you what they threw out, marketing likes to focus on what’s in the chip and make everything sound like a well calculated move. Thankfully, marketing wasn’t allowed to speak at my dinner.

Eric turned to Carrell and said: “i know one feature we could talk about.”


Carrell responded, “OH MY GOD, that’s totally not fair.” (note that Carrell does not sound like a teenage girl, imagine that phrase just spoken more engineer-y).

When ATI first talked about the Radeon HD 4870 X2 they told us about a feature called Sideport. It was a port off each RV770 GPU that could be used for GPU-to-GPU communication.

Sideport as it was intended to be used

The whole point of doing CrossFire in alternate frame rendering mode (AFR) is that the chips never have to talk. The minute you have to start synchronizing them, you kill performance. Sideport was supposed to alleviate that.

Unfortunately, due to power reasons, Sideport was never used on the 4870 X2. ATI’s reference design had it disabled and all vendors followed suit.

Sideport was Carrell Killebrew’s favorite feature, and he had to give it up.

In early 2008 ATI realized they had to cut this chip down from 20 - 22mm on a side to 18mm, everyone had to give up something. Carrell was the big advocate for making 870 smaller, he couldn’t be a hypocrite and not give anything up.

A bunch of my conversation with Carrell at this point had to go off the record. Sideport would have been useful in RV870, but it’s unfortunately not there. Although he did tell me not to be surprised if I saw Sideport again at some point. Carrell doesn’t give up easily.

Adjusting Trajectory & Slipping Schedule What Made it All Ok: 4 GPUs in < 6 Months


View All Comments

  • simtex - Sunday, February 21, 2010 - link

    Excellent article ;) Insider info is always interesting, makes me a little more happy about my -50% AMD stocks, hopefully they will one go up again. Reply
  • NKnight - Wednesday, February 17, 2010 - link

    Great read. Reply
  • - Friday, February 19, 2010 - link

    you should write a (few)book(s); of course in multi eReader formats

  • - Saturday, February 20, 2010 - link

    Nvidia blames sales shortfall on TSMC">

    one dot you didnt connect in the article was AMD's foundry experience, which gives AMD a big advantage over NVIDIA; must have been an oversight?

  • truk007 - Tuesday, February 16, 2010 - link

    These articles are why I keep coming here. The other sites could learn a lesson here.

  • dstigue1 - Tuesday, February 16, 2010 - link

    I think the title says it all. But to add I also like the technical level. You can understand it with some cursory knowledge in graphics technology. Wonderfully written. Reply
  • sotoa - Tuesday, February 16, 2010 - link

    Excellent work and very insightful indeed! Reply
  • juzz86 - Tuesday, February 16, 2010 - link

    An amazing read Anand, I can wholeheartedly understand why you'd enjoy your dinners so much. One reader said that these were among the best articles on the site, and I have to agree. Inside looks into developments in the industry like this one are the real hidden gems of reviewing and analysis today. You should be very proud. Thanks again. Justin. Reply
  • talon262 - Tuesday, February 16, 2010 - link

    Hell of an article...congrats to Anand for putting it out there and to the team at ATI for executing on some hard-learned lessons. Since I have a 4850 X2, I'm most likely going to sit Evergreen out (the only current ATI card that specs higher than my 4850 X2 (other than the 4970 X2) is Hemlock/5970 and Cypress/5870 would be a lateral move, more or less); while I run Win7, DX11 compatibilty is not a huge priority for me right this moment, but I will use the mid-range Evergreen parts for any systems I'll build/refurb over the next few months.

    Northern Islands, that has got me salivating...

    (Crossposted at Rage3D)
  • Peroxyde - Monday, February 15, 2010 - link

    Thanks for the great article. Do you have any info regarding ATI's commitment to the Linux platform? I used to see in Linux forums about graphics driver issues that ATI is the brand to avoid. Is it still the case? Reply

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