Ask Dan: Low voltage? Dual core? Decisions, decisions...

Date: 26 July 2007
Last modified 03-Dec-2011.


Just wondering what the difference is between equivalent CPUs that are low-voltage/not low-voltage. I notice the LV ones, like this Athlon 64 X2 4800+, are cheaper than the older versions, but that alone doesn't really tell me anything.

Are the LV ones less powerful in real terms? Do they emit less heat? More heat? No difference? How should I choose?

I've tried Googling but I get the feeling I'm not hitting the right search queries, my guess is I'm sorta meant to already know.

I am looking at building a machine where the close calls will probably go the way of quieter over raw power (thinking about an Antec Sonata II case, and so on). So if a particular CPU might potentially be the difference between needing an extra case fan or whatever, I'd love to know.

Also... I imagine that it's better to go dual core over a single-core option, even if the single-core has a slightly higher clock speed? Logic suggests the dual core will do better in the real world, but hardware regularly defies logic.

Any help much appreciated - apparently it's been just a little long since I looked at hardware.



There've been no fewer than four CPUs carrying the name Athlon 64 X2 4800+, each cheaper than the last, as you'd expect. They provide a potted history of the usual trajectory of a given model of CPU, which does indeed often involve lower power consumption in the later versions.

The first X2 4800+ was the top-of-the-line model when dual core Athlons first came out in 2005. It used the "Toledo" core, running at 2400MHz with two 1Mb level 2 caches (one for each core), a 12X multiplier, and a Thermal Design Power (TDP) of 110 watts. It was a Socket 939 chip; its three descendants are Socket AM2.

Next came the Windsor-core X2 4800+, with the same specs but an 89 watt TDP thanks to the new and improved core. Core voltage was much the same, though, so nobody was calling this a "low(er) voltage" chip.

The next X2 4800+ was another Windsor-core chip, again with the same performance specs but with a 1.2-1.25V core voltage, versus the 1.3-1.35V core for the previous two. That brought the CPU down to a TDP of only 65 watts. AMD saw fit to dub this generation of the Windsor core "Energy Efficient", though it still used about three-quarters as much power as the model that came before it.

The latest X2 4800+, released at the end of 2006, is a Brisbane-core chip, still with the Energy Efficient moniker and the same 65 watt TDP as the one before it. It's got a 2500MHz core speed (and thus a 12.5X multiplier of the same 100MHz base HyperTransport clock that all of the other chips use), but only 512k-times-two of L2 cache. Its core voltage is actually a hair higher than that of the EE Windsor core, but the smaller L2 cache and new 65nm manufacturing process keeps the power much the same.

(That's 65nm versus 90nm for the other three, though there's no standardised way of measuring manufacturing process feature size, so you shouldn't pay too much attention to it.)

As far as performance at stock speed goes, it's a wash. The first three X2 4800+s are exactly the same, and the 2.5GHz smaller-cache Brisbane version is only barely different, for desktop-computer tasks.

If you're a mad overclocker, though, you want the Brisbane chip; it's more likely to run at elevated speeds than the Windsor, which in turn was better than the old Toledo.

It's still possible to buy Windsor-core X2s, but it's easy enough to tell what you're going to get if the reseller lists the actual core speed, as Aus PC Market do. If the two-significant-figure gigahertz spec ends with an odd number, you're looking at a Brisbane, as indeed you are in the case of the AusPC item.

The Brisbane-core chips from the 3600+ to the 4800+ run at 1.9, 2.1, 2.3 and 2.5GHz, respectively, versus 2.0, 2.2, 2.2 (with more cache) and 2.4GHz for the Windsor CPUs with the same model numbers.

The Brisbane-core X2 5000+ runs at 2.6GHz, the same as the Windsor-core chip with the same name, so you can't tell them apart in the typical online store unless it tells you the core type right up front, or at least the amount of L2 cache - 2x512k for the Brisbane, 2x1024k for the Windsor (which, yes, means the Windsor's faster at stock speed for some tasks).

Overclockers shouldn't care about the 5000-and-higher chips, though (everything above 5000+ is still Windsor-core), because the high-end versions of any given CPU are unlikely to be able to run a lot faster than the cheaper lower-speed models. The current X2s don't, at least, carry the usual big price premium; the 3GHz-stock-speed X2 6000+ is still only a $AU242-delivered item, which makes it quite attractive for non-overclockers after a fast PC.

Anyway, whether they're called "Energy Efficient" or not, the current mainstream dual core AMD Athlons and Intel Core 2 Duo chips are much the same as far as power consumption goes.

Thermal Design Power is not a well defined figure. It's only supposed to represent the maximum heat output a computer case designer needs to take into account when making an enclosure for a given CPU, so there are considerable fudge figures involved. This also explains why a series of CPUs with different clock speeds can have the same TDP, when actual power scales directly with the clock speed (and roughly with the square of the core voltage).

It's also possible - though not easy in normal use - to get a CPU to consume more power (and thus emit more heat) than its TDP. TDP is still the best across-the-board rule of thumb we've got for comparisons, though.

Over the years, many "low voltage" or "low power" CPUs have been released, some of which are only low power when compared with the hundred-watt-plus monsters of the last several years, and some of which genuinely do let you substantially reduce the power a computer consumes.

Some of the low power chips are thing like Via's C-whatever and EPIA series, which let you make a great little shoebox-sized business box with little to no need for fans at all, but which are far behind current mainstream chips for games, media encoding and so on. Most of the rest of the low power chips are laptop processors, which are usually not available in a desktop-chip form factor, so you can't make a normal computer that uses one.

At the moment, probably the best of the few genuinely low power, yet speedy, desktop processors is the Core 2 Duo "T" series. They're essentially laptop chips that can be plugged into a few (Socket M) desktop boards, so they occupy the same niche that desktop Pentium M CPUs did a while ago. Which is to say, they cost you more in the first place, and use a different socket from the regular desktop chips, but give excellent performance and significantly lower power consumption (and, thus, heat).

If you're not really fanatical about saving power, though - like, if you're not trying to make a solar-powered house - then the $AU489.50 delivered price of a 2GHz 34 watt T7200 (bare chip - CPU cooler not included!) will probably not turn your crank very quickly when you compare it with the 65-watt E-series Core 2 Duo chips that use the much more popular LGA775 socket.

(Which isn't really a socket at all, since the pins stick up from the Land Grid Array "socket", waiting for a ham-fisted do-it-yourselfer to bend 'em, while the processor now has lots of little contact dots on its flat lower surface. But you get the idea.)

Just yesterday, Intel officially released their new cut-price faster-bus Core 2 Duos, which start with the E6550. That's a 2.33GHz chip, with a thousand-unit-quantity price of only $US163.

Here in Australia, Aus PC Market already have the retail-package version of the E6550 for $AU289.30 delivered (Australians who'd like to order one can click here to do so!). The new 1333MHz bus speed means you can't expect these new chips to work on every LGA775 board without at least the latest BIOS update, but once you clear that hurdle these chips are hard not to like.

And the power consumption difference between a mainstream Core Duo or Athlon X2 and an E-series laptop CPU isn't necessarily that high, in normal operation of a computer.

When a CPU doesn't have much to do, there isn't nearly so much of a difference between the "low power" chips - even the laptop versions - and the faster and/or cheaper regular versions. If a PC has a quiet enclosure with a few slow 120mm fans and a stock-speed Core 2 Duo E6550, it ought to be quiet enough for most people's home theatre applications, let alone office use, even without innovative ductwork.

This applies even if you install a high-powered video card. Every graphics card these days has variable-speed fans that may make a racket when you're playing a 3D game, but which keep quiet (and save their tiny little bearings) the rest of the time.

If you don't care about 3D games, of course, you might as well get a low-end fanless card, or just use a motherboard with built-in graphics.

Regarding your dual-versus-single-core question: Yes, it generally is a better idea to get dual core, these days.

A year and a half ago (when I wrote this), dual core chips still had a substantial price premium, so there was very little reason for most users to bother with them. Most people still don't actually do anything that benefits greatly from more than one processor core, but the price difference is now small enough that you might as well go dual, if you're building a new computer anyway.

Basic single-core chips are still good for most gamers (since there are still very few games that use more than one CPU core at all, let alone efficiently), and they remain the way to go if you're a complete penny-pincher. You can get a single-core Sempron for about $AU70 that's more than fast enough for most people's purposes, and it can even run a 64-bit OS if you want; if I were kitting out a whole office with new PCs and wanted to keep the price down, I'd seriously consider the humble Sempron.

The cheapest Core 2 Duos are getting down close to $AU200 these days, though. And there's also the Pentium Dual-Core, because we needed yet another flavour of Intel chip, didn't we?

The desktop Pentium Dual-Cores are called the E2140 and E2160, and they're entry-level chips priced below everything else Intel currently offers. Their stock speeds are 1.6 and 1.8GHz but, apparently, they often have a lot of overclocking potential, which can be expected to push their standard 65 watt TDPs up a bit.

The Pentium Dual-Cores are based on the perfectly acceptable Allendale core (as opposed to the cut-down Conroe that was previously inaccurately referred to as Allendale - not that it really matters), they're more than fast enough for all sorts of applications even if you don't overclock them, and they're a bit less than $AU150 and a bit more than $AU150, respectively. And they use the standard LGA775 socket, though once again with an asterisk or two after that and dire warnings to make sure your motherboard knows what to do with new strange CPUs.

The Athlon 64 X2 4800+ that started all of this is in the same price bracket as the Pentium Dual Cores, and significantly faster at stock speed for almost any task, but not as overclockable.

That's because pretty much nothing seems to be as overclockable as the E21x0s. People are running them at 1.8 or 1.9 times their stock speed, at which speed they actually outpace the Extreme Edition X6800, which costs ten times as much.

When you can get a proper dual core chip, AMD or Intel, for only about twice the price of a bargain basement Sempron, saving eighty bucks to get a single core sounds like false economy. And buying an LGA775 Celeron sounds downright crazy, since they cost about the same as the X2 4800+!

When you take into account the fact that an E21x0 chip that only overclocks by 50% appears to be a miserable slug, these basic chips start looking like a good option even for people who can afford a much fancier CPU.

Australian shoppers who'd like to buy a Brisbane-core Athlon 64 X2 4800+ from Aus PC Market for a lousy $AU145.20 delivered can do so here.

If the new 1333MHz-bus Core 2 Duo E6550 sounds more your speed, Aus PC Market have it for $AU289.30 delivered here.

If you'd like to try the Pentium Dual Core E21x0 overclocking lucky dip, Aus PC Market have the E2140 for $AU146.30 delivered here, and the E2160 for $AU163.90 delivered here.