Didn’t HyperThreading suck with Pentium 4? Why bring it back?

First, you should know that a CPU core can execute only one instruction thread at a time. Since that thread will touch on only some portions of the CPU, resources that are not used sit idle. To address that, Intel introduced consumers to Hyper-Threading beginning with its 3.06GHz Pentium 4 chip. Hyper-Threading, more accurately called simultaneous multi-threading, partitions a CPU’s resources so that multiple threads can be executed at the same time.

In essence, a single-core Pentium 4 appears as two CPUs to the OS. But since it is actually just one core dividing its resources, you don’t get the same performance boost you would receive from adding a second core. Hyper-Threading does, however, generally smooth out multitasking; and in applications that are optimized for multi-threading, you will see a modest performance advantage. The problem is that not all applications were coded for Hyper-Threading when it was released and performance could actually be hindered. Hyper-Threading went away with the Core 2 series of CPUs, but Intel has dusted off the concept for the new Core i7 series because the transistor cost is minimal and the performance benefits stand to be far better than what the Pentium 4 could ever achieve.

Intel toyed with the idea of redubbing the feature Hyper-Threading 2 but decided against it, as the essential technology is unchanged. So why should we expect Hyper-Threading to be more successful this go around? Intel says it’s due to Core’s huge advantage over the Pentium 4 in bandwidth, parallelism, cache sizes, and performance. Depending on the application, the company says you can expect from 10 to 30 percent more performance with Hyper-Threading enabled. Still, Intel doesn’t force it down your throat because it knows many people still have mixed feelings about the feature. The company recommends that you give it a spin with your apps. If you don’t like it, you can just switch it off in the BIOS. Intel’s pretty confident, however, that you’ll leave it on.

Our own tests of HyperThreading on a Core i7 show that it’s definitely worth it – if you run multi-threaded applications that can exploit it.

How significant is it that Intel is killing the front side bus?

As you know, Intel currently uses a front-side-bus technology to tie its multiprocessor machines together. As you might imagine, problems arise when a single front-side bus is sharing two quad-core CPUs. With so many cores churning so much data, the front-side bus can become gridlocked. Intel “fixed” this issue by building chipsets with two front-side buses. But what happens when you have a machine with four or eight CPUs? Since Intel couldn’t keep adding front-side buses, it took another page from AMD’s playbook by building in direct point-to-point connections over what it calls a Quick Path Interconnect. Server versions of the Core i7 feature two QPI connections (desktop versions get just one), which can each talk at about 25GB/s or double what a 1,600MHz front-side bus can achieve.

For Intel, the move to QPI is long overdue as the front-side bus in multi-processor configurations was considered a serious handicap. It’s unlikely to impact people with machines with just one CPU today; but for servers, it means the world.

Tell me about Turbo Mode? It sounds like it’s from Knight Rider.

Intel designed Core i7 to be very aggressive in power management. With the previous Core 2, power to the CPU could be lowered only so far before the chip would crash. That’s because while you can cut power to large sections of the execution core, the cache can tolerate only so much power reduction before it blows up. With  the Core i7, Intel separates the power circuit, so the cache can be run independently. This lets Intel cut power consumption and thermal output even further than before. Furthermore, while the Core 2 CPUs require that all the cores be idle before reducing voltage, individual Core i7 cores can be turned off if they’re not in use.

Turbo Mode exploits the power savings by letting an individual core run at increased frequencies if needed. This again follows Intel’s mantra of improving performance on today’s applications. Since a majority of today’s applications are not threaded to take full advantage of a quad core with Hyper-Threading, Turbo Mode’s “overclocking” will make these applications run faster. In our tests, it worked well for speeding up single-threaded applications, but you will need additional cooling to exploit it to its fullest extent.

So Core i7 will work with my brand-new Socket LGA775 board right?

Silly rabbit, remember Ung’s Law: If you just bought a $500 motherboard, the new chip won’t work with it. And it doesn’t. Core i7 requires a new LGA1366 motherboard. This isn’t done just to piss you off. The on-die memory controller and tri-channel DDR3 support alone required a new board. Of course, your heat sink won’t work either (at least not without a new bracket) as the new socket is wider than the older by just a smidge, so toss it in the recycle bin too.

Just how fast is it?

Fast. We compared the top-end $999, 3.2GHz Core i7-965 Extreme Edition against the $1,399, 3.2GHz Core 2 Extreme QX9770 and AMD’s $175, 2.6GHz Phenom X4 9950 Black Edition and the Core i7 whopped ‘em both. First, AMD fanboys, please zip it. We know the Phenom is far cheaper but it’s also the absolute fastest CPU that AMD can muster right now. It’s not exactly Core i7’s fault that AMD won’t be able to kick it up a notch until the end of this year.

Second, we tested all the machines using matched components and drivers; but there’s one element that we biased in favor of the older chips: RAM. The Phenom X4 used 4GB of DDR2/800, the Core 2 Extreme QX9770 used 4GB of DDR3/1333.

Since the Core i7-965 features a tri-channel controller that requires that memory be matched in triads instead of pairs. The chip can run faster than DDR3/1066, but Intel officially rates it at DDR3/1066 so we ran it that way.

Even with the disadvantage, it cleaned both the Phenom X4’s and Core 2 Extreme’s clocks. Versus Phenom X4, we saw the Core i7 encoding, crunching, and generally running everywhere from 98 percent to 80 percent faster. Sure, there were some tests where the Phenom X4 got within striking distance (if you consider 30 percent striking distance) but for the most part, the Phenom X4 got handed its hat, soiled undies, and umbrella at the door.

The Core i7’s sibling did better, but even the mighty (and expensive) QX9770 got beat bloody by the Core i7 with many tests running from 25 percent to 45 percent faster. The only test that saw the Core i7 loose by any serious margin was in our FEAR test, but that was more than likely due to the presence of a bug in the benchmark (which is showing its age).

The upshot is that the Core i7 is a fast CPU. It instantly dispels any fears that Intel would phone it in this generation. Even with AMD on the ropes, and selling off pints of blood to make ends, Intel is clearly intent on keeping up the pressure.

Read our complete Core i7 review here!

AMD’s Phenom X3

When Four Cores are too Many and Two are Not Enough

If the gods give you lemons, make lemonade. And if the fabs give you bunk quad-core procs, you make tri cores. At least AMD does.

The company’s 2.4GHz Phenom X3 8750, 2.3GHz Phenom X3 8650, and 2.1GHz Phenom X3 8450 tri-core chips all feature the same cache size as the quad-core Phenoms, but one fewer  core. They’re targeted mainly targeted at consumers on a dual-core budget who want a little more bang for their buck. The 8750 is street priced at $180, the 8650 goes for $150, and the 8450 fetches $100.

AMD’s main problem is that its fastest CPU, the quad 2.6GHz Phenom X4 9950, costs just $185. Intel is also a factor, having lowered the price of its older quad cores to compete against AMD. For example, Intel’s 2.4GHz Core 2 Quad Q6600, which outperforms any Phenom, is now selling for just $190. Fortunately, all three of AMD’s tri cores are free of the TLB bug that hurt performance in the original quad-core Phenom chips. 

Click here for our full Phenom II overview, analysis, and benchmarks!

KIA: K10 In Action

What tales do the benchmarks tell about AMD’s Phenom?

Our comparison is based on an unlocked engineering-sample Phenom that we ran at 2.6GHz and 2.3GHz in Asus’s 790FX-based M3A32-MVP Deluxe board. We compared AMD’s CPU to the original Intel 2.66GHz Core 2 Extreme QX6700 CPU that we received from Intel more than a year ago. While it carries the Extreme tag, the QX6700 is identical to the Core 2 Quad Q6700 except that it’s unlocked. That let us run the chip at both 2.66GHz and 2.4GHz to simulate the performance of a Core 2 Quad Q6600. The board used for the Core 2 chip was EVGA’s 680i SLI. Both machines featured DDR2 RAM clocked at 1,066MHz. Memory timing was manually set on both platforms, and both machines used 150GB Western Digital Raptor hard drives and identically clocked GeForce 8800 GTX cards, as well as the same drivers.

Once we were finished with the Phenom testing, we dropped in an Athlon 64 X2 6400+ for comparison. All of these tests were done with the TLB bug disabled so no performance penalty was paid. Since AMD’s new 2.6GHz Phenom X4 9950 Black Edition is essentially the same chip as the Phenom 9900 without the TLB bug, the performance is identical. The newer Phenom X4 9950 BE, however, should offer better overclocking results.

With the speed of the 9900 topping out at 2.6GHz, we didn’t feel the need to break out Intel’s 3.2GH Core 2 Extreme QX9770. In fact, we didn’t even bother to break out a new 45nm part for our comparison, just Intel’s ancient Core 2 Quad Q6700. And what about the Intel’s new $300 2.66GHz  Core i7-920? Safely tucked into bed asleep. There was simply no reason to wake it.

The Final Verdict

AMD tried to do too much with too little. While Intel kept it safe and built its first 65nm “quad cores” by gluing two dual-cores together, AMD thought it could build a native 65nm quad core. The result was chips with low yields and an inability to push clock speeds to the point of being even remotely competitive with Intel.

The sad part is that Phenom is really not a bad CPU. It’ll whip an Athlon 64 in most tasks (gaming may favor the A64, as few games are optimized for quad-core) and it is somewhat competitive with Intel’s Core 2 Quad Q6700 part. But again, The Q6700 is more than a year old. Newer 45nm parts that have largely replaced it are from 10 to 30 percent faster.

So, after all the trash talk of “true quad core” computing, AMD is left with a consumer CPU line that it has had to deeply discount to even make them attractive.

At the end of this year, Phenom may get a shot in the arm when AMD pushes out a 45nm version but; for now, we can see only one reason to build on Phenom: you already have an AM2 board that supports the chip. Otherwise, all the performance action is on the other side of the fence.

How we tested: For the Core i7, we used an Intel DX58SO board based on the new X58 chipset with 3GB of DDR3/1066, a single Western Digital Raptor 150, Windows Vista 64-bit with SP1 installed and a GeForce 8800GTX. For the Core 2 Extreme we used a Gigabyte X48T-DQ6, 4GB of DDR3/1333, a Western Digital Raptor 150, Windows 64-bit with SP1 installed and a GeForce 8800GTX. For the Phonom X4, we used an MSI K9A2 Platinum board using the ATI 790FX chipset, 4GB of DDR2/800,  a Western Digital Raptor 150, Windows 64-bit with SP1 installed, and a GeForce 8800GTX.