Intel's Pentium 4 E: Prescott Arrives with Luggage
by Anand Lal Shimpi & Derek Wilson on February 1, 2004 3:06 PM EST- Posted in
- CPUs
Execution Core Improvements
Intel lengthened the pipeline on Prescott but they did not give the CPU any new execution units; so basically the chip can run faster to crunch more data, but at the same speeds there are no enhancements to work any faster.
Despite the lack of any new execution units (this is nothing to complain about, remember the Athlon 64 has the same number of execution units as the Athlon XP), Intel did make two very important changes to the Prescott core that were made possible because of the move to 90nm.
Both of these changes can positively impact integer multiply operations; with one being a bit more positive than the other. Let us explain:
The Pentium 4 has three Arithmetic and Logic Units (ALUs) that handle integer code (code that operates on integer values - the vast majority of code you run on your PC). Two of these ALUs can crank out operations twice every clock cycle, and thus Intel marketing calls them "double pumped" and says that they operate at twice the CPU's clock speed. These ALUs are used for simple instructions that are easily executed within 1/2 of a clock cycle, this helps the Pentium 4 reach very high clock speeds (the doing less work per cycle principle).
More complicated instructions are sent to a separate ALU that runs at the core frequency, so that instead of complex instructions slowing down the entire CPU, the Pentium 4 can run at its high clock speeds without being bogged down by these complex instructions.
Before Prescott, one type of operation that would run on the slow ALU was a shift/rotate. One place where shifts are used is when multiplying by 2; if you want to multiply a number in binary by 2 you can simply shift the bits of the number to the left by 1 bit - the resulting value is the original number multiplied by 2.
In Prescott, a shift/rotate block has been added to one of the fast ALUs so that simple shifts/rotates may execute quickly.
The next improvement comes with actual integer multiplies; before Prescott, all integer multiplies were actually done on the floating point multiply unit and then sent back to the ALUs. Intel finally included a dedicated integer multiplier in Prescott, thanks to the ability to cram more 90nm transistors into a die size smaller than before. The inclusion of a dedicated integer multiplier is the cause of Prescott's "reduced integer multiply" claim.
Integer multiplies are quite common in all types of code, especially where array traversal is involved.
Facebook
Twitter
RSS
104 Comments
View All Comments
Stlr22 - Sunday, February 1, 2004 - link
post*Stlr22 - Sunday, February 1, 2004 - link
KristopherKubickiEarlier you said that I should read the article.
What was your point? What was it about my first pot that you disagreed with?
KristopherKubicki - Sunday, February 1, 2004 - link
#7:I agree 100% with Anand and Derek. This processor will be a non-event until we get in the 3.6GHz range. Similar to Northwood's launch.
#10:
Check out our price engine. We have already been listing the processor a week!
http://www.anandtech.com/guides/priceguide.htm
http://www.monarchcomputer.com/Merchant2/merchant....
cliffa3 - Sunday, February 1, 2004 - link
In the table on page 14 it shows that the 90nm P4@2.8 will have a 533 MHz FSB, but is that the case? I did some quick google research and can't find anything to support that...please confirm or correct, thanks.NFactor - Sunday, February 1, 2004 - link
Yes, I must agree this is an amazing article, one of the best i have ever read. Thanks.Xentropy - Sunday, February 1, 2004 - link
VERY interesting article. Thank you Anand and Derek! One of the best I've read on Anandtech, and I consider yours the best hardware site on the net!One correction, on page 7, you say, "if you want to multiply a number in binary by 2 you can simply shift the bits of the number to the right by 1 bit," but don't you mean shift to the left one bit (and place a zero at the end)? It's much like multiplying a decimal number by ten for obvious reasons.
Anyway, it looks like the Prescott is somewhat of a non-event at this time. Just new cores that perform fundamentally the same as the current ones at current speeds. The real news will come later; Intel has just positioned itself for one hell of a speed ramp to come. Northwood was clearly at the end of the line. One analogy, I suppose, would be that Intel didn't fire any shots in the CPU war today, but they loaded their guns in preparation to fire.
The coming year will be an exciting one for us hardware geeks. I'm interested in seeing how higher clocked Prescotts play out as well as whether anything 64-bit shows up before 2005 to support AMD's stance that we need it NOW.
Again, thanks for a very thorough article!
Stlr22 - Sunday, February 1, 2004 - link
KristopherKubickiSo what's your take on these new Prescotts?
KristopherKubicki - Sunday, February 1, 2004 - link
Anand scolded me for not reading the article :( I only read the conclusion and the graphs. Turns out the decision making isnt as clearcut as it sounds.As for the thing with the inquirer. Well, lots of people had prescotts. We had one back in August I believe. The thing is they were horribly slow - 533FSB 2.8GHz. Everyone drew the conclusion that these were purposely slowed processors that were jsut for engineering purposes. While the inq benched this processor, most people didnt just becuase they were under the impression this was not to be the final production model. Hope that clears up some discrepancy about the validity.
Cheers,
Kristopher
wicktron - Sunday, February 1, 2004 - link
Hehe, I guess the Inq was right about this one. Where are all the Inq bashers and their claim of "fake" benchies? Haha, I laugh.Stlr22 - Sunday, February 1, 2004 - link
KristopherKubicki - "read the article..."lol that might be a good idea, as I only broswed it and read the conclusion. :D