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
Final Words
If you’re looking for nothing more than a purchasing decision let’s put it simply: if you’re not an overclocker, do not buy any Prescott where there is an equivalently clocked Northwood available. This means that the 2.80E, 3.00E, 3.20E are all off-limits, you will end up with a CPU that is no faster than a Northwood and in most cases slower. If you are buying a Pentium 4 today, take advantage of the fact that vendors will want to get rid of their Northwood based parts and grab one of them.
Overclockers may want to pick up a Prescott to experiment with ~4GHz overclocks – it will be easier on Prescott than it is on Northwood. And once you get beyond currently available Northwood speeds you will have a CPU that is just as fast if not faster, depending on how high you go.
When you include AMD in the picture, the recommendation hasn’t changed since the Athlon 64 was introduced. If you find yourself using Microsoft Office for most of your tasks and if you’re a gamer the decision is clear: the Athlon 64 is for you. The Pentium 4 continues to hold advantages in content creation applications, 3D rendering and media encoding; if we just described how you use your computer then the Pentium 4 is for you, but the stipulation about Northwood vs. Prescott from above still applies.
The Pentium 4 Extreme Edition at 3.4GHz does provide an impressive show, but at a street price of over $1100 it is tough recommending it to anyone other than Gates himself.
With the recommendations out of the way, now let’s look at Prescott from a purely microarchitectural perspective.
Given that we’re at the very beginning of the 90nm ramp and we are already within reach of 4GHz, it isn’t too far fetched that Prescott will reach 5GHz if necessary next year. From an architecture perspective, it is impressive that Prescott remains in the same performance league as Northwood despite the fact that it has a 55% longer pipeline.
What we have seen here today does not bode well for the forthcoming Prescott based Celerons. With a 31 stage pipeline and 1/4 the cache size of the P4 Prescott, it doesn’t look like Intel will be able to improve Celeron performance anytime soon. We will keep a close eye on the value segment as it is an area where AMD could stand to take serious control of the market.
The performance of Prescott today is nothing to write home about, and given the extensive lengthening of the pipeline it’s honestly a surprise that we’re not castrating Intel for performance at this point. Prescott is however a promise of performance to come; much like the Willamette and even Northwood cores were relatively unimpressive at first, they blossomed into much sought-after CPUs like the Pentium 4 2.4C. The move to 90nm and a longer pipeline will undoubtedly mean more fun for the overclocking community, especially once production ramps up on Prescott.
Just as was the case with the very first Pentium 4s, Prescott needs higher clock speeds to spread its wings - our data on the previous page begins to confirm this. To put it bluntly: Prescott becomes interesting after 3.6GHz; in other words, after it has completely left Northwood’s clock speeds behind.
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Jeff7181 - Thursday, March 11, 2004 - link
#98Yes, increasing the drive current means increasing the current that's flowing through the transistors, which does explain the heat increase.
watts = current x voltage
If we do the math, we can figure out how many amps the current Prescott runs on...
The 3.2 and 3.4 Ghz models have a spec of 103 watts, and the voltage is 1.385, so divide 103 by 1.385 and you get about 74.3 amps.
The 3.4 Ghz Northwood has a spec of 89 watts, and the voltage is 1.550, that's 57.4 amps.
That's a 30% increase in current, with only a 20% reduction in voltage. There's your extra heat. 103 watts vs. 89 watts... about a 16% increase in heat. We can take this a little further and say...
The Prescott at 3.4 Ghz produces 103 watts of heat, max. The Prescott at 3.0 Ghz produces 89 watts of heat, max. That means a 3.4 GHz Prescott runs on 74.3 amps, and the 3.0 GHz Prescott runs on 64.3 amps. So increasing the speed by 400 Mhz requires 10 more amps.
So a 3.6 GHz Prescott would run on 79.3 amps, which would create 109.8 watts...
and a 3.8 GHz Prescott would run on 84.3 amps, which would create 116.8 watts...
and a 4.0 GHz Prescott would run on 79.3 amps, which would create 123.7 watts...
and a 5.0 GHz Prescott would run on 104.3 amps, which would create 144.5 watts.
This is of course assuming they don't make core changes that require less current, and that they don't make core changes that require less voltage. It will be VERY interesting to see how they deal with this increased thermal output... considering it looks like the 2.8 Ghz Prescotts are maxing out at 50 degrees C with the retail heatsinks... and the thermal output of a 5 Ghz Prescott is about twice that, so, with the same heatsink as the 2.8... a 5 Ghz Prescott should run at about 100 degrees C, lol. 5 Ghz is a ways away though, 4 is much closer, but still, that's about a 75% increase in heat over the 2.8... so you're gonna be looking at full load temps around 80 degrees C unless Intel pulls something out of their hat.
On a side note...
Strained Silicon is supposed to reduce current leakage, and it does. But what I think Intel maybe didn't foresee is the 30% increase in current… or maybe they thought they could run on 1.0 – 1.2 volts.
See, voltage is electrical pressure, current is electrical volume. If you increase the volume of electricity moving through, but decrease the pressure, not as much current will leak. Think of it like a water hose. If you need a certain amount of water in a certain amount of time, you can increase the water pressure, and it will move faster so you'll have more water, but you might spring a leak in the hose... or you can just get a bigger hose and use less water pressure, which is basically what Intel did with Strained Silicon.
AMD’s approach with using SOI has been, dare I say, more successful. When you look at the specifications, the 3400+, 2.2 GHz has a maximum of 89 watts at 1.5 volts. When the PowerNow feature is used, it drops down to 2.0 GHz, and 1.4 volts, the wattage drops down to a cool 69 watts. When it drops down again to 1.8 GHz and 1.3 volts, the wattage drops to 50 watts. And finally when it drops down to 1.0 GHz and 1.1 volts, the wattage is a frigid 22 watts. Normally you would think that means for every 200 MHz increase, your wattage increases by 10 watts. However… the FX-53 runs at 2.4 GHz and it’s maximum wattage is also 89 watts. So it seems as though AMD may be estimating very high with these early processors if a 2.4 GHz chip has the same maximum heat dissipation of a 2.0 GHz chip. The only explanation I can come up with is that as they get more experience at manufacturing these chips, current leakage just gets better and better. We can only hope to see the same from Intel with the Prescott as they refine their Strained Silicon and 90nm process.
slashbinslashbash - Sunday, February 29, 2004 - link
Oh, and I think that the conspicuous silence by AT and everybody else on this subject only confirms that Intel indeed has something up its sleeve. They all say "Prescott has higher energy consumption" and "a larger transistor count" without even speculating as to what could create the wild disparity that we see with the transistor math.slashbinslashbash - Sunday, February 29, 2004 - link
#96: I'm no CPU designer, but it seems to me that the "add transistors to dissapate heat more evenly" argument doesn't make sense. Why not just have empty silicon if you need to spread things out? Adding actual transistors will also increase the amount of heat output, so the density of heat would stay the same.Lots of good speculation on Prescott/Yamhill here: http://www.chip-architect.com/
Regs - Tuesday, February 17, 2004 - link
Ah god, I'm sorry. This is suppose to be about the Prescott, and I just completely made a "fan boy" remark.Regs - Tuesday, February 17, 2004 - link
So it's pricey, runs hot, shows little improvement over the earlier northwoods, and did I mention pricey? The 3.4c is 415 dollars at newegg let alone what a 3.2 o 3.4E would cost.To us tech-gurus it comes down to common sense, but everybody knows marketing will always get the better of AMD. Intel well shovel "you're paying for the best performer", which is sadly true by a small margin if that for a huge price difference. And how people ignore the A64 completely just because 64-bit is not needed as of right now is just frustrating.
AMD made a remarkable achievement for making affordable technology while satisfying the need for higher performance.
TrogdorJW - Wednesday, February 4, 2004 - link
What does it mean to increase the transistor drive current by 10-20%? Does that mean that they need to run, say, 1.1 to 1.2 Amps instead of 1.0 Amps? (I know that's not what the processors use; I'm just using those numbers because they're easy to work with.) If that's correct, then it would certainly account for some of the heat increase.Initially, I read about strained silicon and thought that the idea was that it would take less power to run the chips at the same speed. The atoms are further apart, electrons flow more easily... doesn't that mean that strained silicon should make things run cooler? (I'll be honest - the electromagnetic physics course I had to take in college was *NOT* my favorite course. Talk about a HARD class....)
PrinceGaz - Wednesday, February 4, 2004 - link
I think Intel's heat problems are in part down to the Strained-Silicon technology they've introduced with the 90nm process as much as anything else. If as it says it increases the transistor drive-current by 10-20% then thats 10-20% more power and therefore heat being generated by each transistor for a given voltage.AMD however has opted to go for SOI now and that reduces leakage-current (waste) from the transistors, which means less heat is generated by them.
Intel is expected to introduce SOI with their 65nm process in 2005 and that should help reduce their heat problem a bit, and AMD will no doubt adopt Strained-Silicon around about the same time which will raise the amount of heat in their chips making them both about even again.
The difference now is that Intel implemented the heat-increasing performance improvement first, while AMD implemented the heat-decreasing one first.
TrogdorJW - Wednesday, February 4, 2004 - link
Aceshardware has some information on the transistors as well, on the bottom of page one of their review: http://www.aceshardware.com/read.jsp?id=60000315Of course, they also end up concluding the same things as me: the changes that Intel has really told us about don't seem like they should really be using up the 45 million added transistors. (A Northwood with 1 MB of L2 would be an 80 million transistor CPU.)
Intel did make numerous small changes to the processor, so I guess that it is possible that they could have used up all of the extra transistors. Who knows?
One other thing that isn't really being talked about anywhere is transistor density. In the past, shrinking the transistor size always ended up making chips run cooler. It appears that this may not be the case with 90nm processes and beyond. If Intel had stuck with a straight Northwood core and simply moved to 90nm, then the CPU die size would be something like half of what it currently is. So instead of 112 mm2, it would be 60 mm2 or something.
With all of the heat being generated in such a small area, maybe they had to add transistors and size just to spread out the heat dissipation? It's a weird argument, but it *could* be true. When AMD releases 90nm chips and we see how hot they get, we'll probably gain more insight into this. If AMD's chips run slightly hotter, then 90nm will have marked a transition to a new set of problems in processor die shrinks.
Pumpkinierre - Wednesday, February 4, 2004 - link
The only other explanation is that prescott is dual core. Really if the stages get smaller as the pipeline gets deeper then the transistor count should stay the same. So a dual core with double the cache should be 2xNorthwood= 110 million transistors- still 15 million unaccounted for and available for other things. Other people are saying that the 31 stage pipeline cant be right as the processor's power would be much weaker than the observed performance cf. equivalent (20 stage pipe) Northwood, despite the tweaks. It seems to perform well on the hyperthreaded enabled software and dual cpu may explain the slowness of the cache like duallies where one cpu has to keep tabs on the other. It also explains the heat for which a size reduction on a single core should augur less heat in contrast to Prescott's > 100 Watts.Pumpkinierre - Tuesday, February 3, 2004 - link
That's it. Prescott is already 64bit enabled. They have'nt bothered to switch them off as no intel mobo BIOS detects the 64bit extensions anyway. That's where the extra heat is coming from. I mean Northwood is ~130MM2 (55million transistors) and Prescott is close in size 112mm2 but 125million transistors - so approximately the same size but far greater transistor density so more heat. Even with the extra cache it should have been around 80 million and thus heat would have been at Northwood levels. The extra transistors still seem excessive for x86-64. So it might even be IA-64. Sckt 478 might not be pinned enough but 775 should do it. Here's my prediction then: ** 64bit WILL be available when Sckt LBGA 775 Prescott cpus come out in April with the new Grantsdale and Alderwood mobos **. And thats what is going on display in coupla of weeks time. How to check it, maybe write some assembler using X86-64 or IA-64 commands and see if they work.