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.
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INTC - Monday, February 2, 2004 - link
Ummmm yea, kinda reminds me of cooking an egg on an Athlon XP http://www.biggaybear.co.uk/Menu/Aegg/Aeggs.htmlcliffa3 - Monday, February 2, 2004 - link
something good to include on the mb compatibility article would be what boards would house the 2.8/533...i'm wondering myself if the E7205 chipset would...i have a p4g8x, and it would be a welcome upgrade with HT and all the other goodies if it oc's well.Stlr22 - Monday, February 2, 2004 - link
They didn't burn down, but the proc were running hot. Not to mention, these are the FIRST releases in the Prescott line. What's it gonna be like later on?....Just think, a P4 based computer that turns your living room into your very own Sauna!!....WHOOO-HOOO!!.....now that's what I call a bargain!
INTC - Monday, February 2, 2004 - link
The message is clear: Anandtech and all of the other review sites didn't burn down so I guess it's not a flame thrower.Prescott is not as fast as I had hoped but is definitely not the step backwards as some were rumoring it to be. I think a Prescott 2.8 @ 250 MHz FSB will be really nice to play with until I see what Intel announces at IDF in a few weeks.
Icewind - Monday, February 2, 2004 - link
The message is clear: Im buying an Athlon 64.Vanners - Sunday, February 1, 2004 - link
Did anyone catch the error in Pipelining: 101?if you halve the time for a stage in the pipeline and double the number of stages. Yes this means you can run at 2GHz instead of 1GHz but the reality is you're still taking 5ns to complete the pipe.
Look at it like a motorbike: You drop down a gear and rev harder; you make more noise but you are still doing the same speed.
The only reasons to drop down a gear are to break through your gears (i.e. slow down) or to rev significantly higher than the change in gear ratio in order to move faster (with more torque).
The trouble Intel has is that they drop down a gear then rev 6 months to a year later.
kamper - Sunday, February 1, 2004 - link
Just curious, Anand or Derek: what board did you use to get the 3.72 GHz oc? Obviously it wasn't the intel board used in the benches. I guess we'll hear all about this in the compatibility review though :)keep up the good work, that last point about smaller margins at higher clockspeeds (vs. Northwood) was cool. Let's just hope the pattern continues.
Stlr22 - Sunday, February 1, 2004 - link
Seems to me like people either got cought up in some of the hype and expected to much or some people expected to little and that history would repeat itself (Willamette vs Palomino)The fact that the Prescott fared much better in it's launch compared to the Willamette might be a hint to not underestimate it. Prescott isn't really looking bad now, and I think it will hit stride faster then the Willamette core did.
The next couple of years are gonna be really interesting.
Damn, ya just gotta love it!
ntrights - Sunday, February 1, 2004 - link
Great review!KF - Sunday, February 1, 2004 - link
I've grown to appreciate CRAMITPAL. If you read around the opinionated diatribes, he has some good stuff that people avoid saying for fear of retaliation. I suppose if I were in love with Intel, he would tick me off.But, it does look like Intel has created a CPU that should ramp up to speeds high enough to beat the A64 in 32bit mode, and that is all they needed to do.
Regardless of how much heat that is going to take, Intel must have some way in the works to handle it.
Looks like they might not charge an arm and leg for it, which is the biggest shock.