In less than a month Intel will be introducing their 865 and 875 platforms that, among other things, will enable support for a new line of Pentium 4 processors.

As we've discussed in the past, Intel is reaching a thermal/frequency wall with the current generation 0.13-micron Northwood Pentium 4 core. It is possible to scale the Northwood core past its current 3.06GHz frequency, and in fact Intel will be doing just that with a 3.2GHz Pentium 4 in the coming months, but going much further beyond that would require more effort than is absolutely necessary given the state of the competition.

With AMD's Athlon 64 not due out for several months, it doesn't make sense for Intel to push for higher frequencies on their current manufacturing process as doing so would become fairly challenging given the thermal and power requirements of >3.2GHz clock frequencies. Instead, Intel is focusing on improving the overall performance of the Pentium 4 platform through the new chipsets we mentioned above coupled with an increase in FSB frequency.

When the first Pentium 4 was released, based on the 0.18-micron Willamette core, the NetBurst FSB ran at a 100MHz frequency and sent data 4x per clock, effectively making it a 400MHz FSB from a data rate standpoint. Shortly after Intel introduced the 0.13-micron Northwood core, the transition was made over to a 533MHz FSB; the performance boost we saw with the 533MHz FSB was more than reasonable as it, along with an increase in memory bandwidth, helped increase the Pentium 4's overall IPC by feeding more data into its pipeline.

With the 865 and 875 platforms, Intel will be enabling support for a 800MHz FSB and thus a new line of 800MHz FSB Pentium 4 CPUs also due out shortly. But what sort of performance boost should we expect out of increasing the FSB to 800MHz? That's exactly the question we're looking to answer today as we perform our first tests at 800MHz.

What's in a faster FSB?

Improving overall system performance is a game of removing bottlenecks and making paths that aren't already bottlenecked as fast as possible. When dealing with increasing the frequency of a FSB, there are two major factors that influence whether or not the faster FSB will actually improve performance.

The first factor is whether or not the transmit buffers on the FSB interface of the North Bridge (or MCH) will receive data fast enough to take advantage of the faster FSB. In order to understand this factor you have to have an understanding of how data flows from main memory into the chipset and finally to the CPU (and vice versa). When the CPU issues a read request onto the FSB, it sends the address of the data it needs in main memory onto the FSB. The address of the data needed is then forwarded on, via the FSB, to the chipset's FSB interface contained within the North Bridge, or in the case of the Pentium 4, the Memory Controller Hub (MCH). The FSB interface hands off the address to the memory controller, also contained within the North Bridge/MCH, and then the address request is sent to main memory and the North Bridge/MCH waits for the data at that address to be charged and ready to be sent from main memory. Once the data is ready, it is sent from main memory to the memory controller in the North Bridge/MCH, handed off to the FSB interface and then put on the FSB and sent to the CPU.

In the case of the Pentium 4's FSB, the actual operating frequency of the bus is 100/133MHz (for the 400 and 533MHz FSBs respectively). Addresses are sent twice per clock, which makes the FSB transfer addresses as fast as a 200/266MHz FSB would; and finally we have the quad-pumped data transfer rates, which means that data can be sent 4x per clock, effectively making the FSB transfer data as fast as a 400/533MHz FSB would. Since data, not address, transmission is what eats up the majority of FSB bandwidth, Intel gets away with calling the Pentium 4's FSB a 400/533MHz FSB. With the forthcoming 800MHz FSB, addresses will be transferred at 400MHz and data will be sent at 800MHz. What's interesting to note is that addresses will be transferred on the new FSB as fast as data was sent on the first Pentium 4 FSB introduced back in 2001.

Back to the original point however, if the North Bridge/MCH isn't able to get data from main memory as quickly as it can send it through the FSB then there's no point to increasing the FSB frequency. Think of it like this; let's say you had a highway going straight into a mall, with an identical highway going straight out of the mall. Both highways have the same number of lanes and initially they have the same 45mph speed limit. Now let's say that there's a great deal of traffic flowing in and out of the mall and in order to get more people in and out of the mall quicker, the department of transportation agrees to increase the speed limit of the highway going into the mall from 45mph to 70mph; the speed limit of the highway leaving the mall is still stuck at 45mph. While more people will be able to reach the mall quicker, there will still be a bottleneck in the parking area leaving the mall - since the increased number of people that are able to get to the mall still have to leave at the same rate. This is equivalent to increasing the FSB frequency but leaving the memory frequency/bandwidth unchanged on a chipset, you're speeding up one part of the equation while leaving the other part untouched.

In this case, the focus is more on balancing FSB and memory bandwidth rather than frequencies (although it is important to have frequencies that are in sync with one another in order to keep latencies as low as possible). The Pentium 4 features a 64-bit wide FSB interface, and we've already explained the frequencies this FSB can run at. Simple multiplication shows us that the 533MHz FSB can offer a maximum of 4.264GB/s of bandwidth. The 845PE chipset has a 64-bit DDR333 memory interface, offering a maximum of 2.664GB/s of memory bandwidth, and the 850E chipset has a 32-bit PC1066 RDRAM memory interface that provides at most 4.264GB/s of memory bandwidth. As you can see just by looking at the bandwidth numbers, the 850E chipset is perfectly balanced for the amount of bandwidth offered by the 533MHz FSB, which is why it is significantly faster than the 845PE.

The 800MHz FSB will offer no less than 6.4GB/s of bandwidth, which would require either a 32-bit PC1600 RDRAM memory interface (note that the PC1600 standard does not exist) or a 64-bit DDR800 memory interface (also a non-existant memory technology). Well, if you can't get faster memory, you widen the memory interface in order to increase bandwidth. Remember that bandwidth is the product of bus width and transfer rate, so if you can't improve the transfer rate, you increase the width of the bus. In the case of the upcoming 865 and 875 chipsets, Intel took the 64-bit DDR memory interface of the 845PE chipset and added a second 64-bit channel along with adding DDR400 support. A 128-bit memory interface (2 x 64-bit channels) with DDR400 memory now offers exactly 6.4GB/s of memory bandwidth, perfectly balanced with the 800MHz FSB, without using exotic memory technology or speeds that aren't readily available.

With an increase in both the FSB frequency and memory bandwidth, the performance will not be hindered by bottlenecks in the platform itself, but we still have to ask the question of whether or not the CPU can benefit…

Feeding the Beast with more Bandwidth

The Pentium 4 architecture allows it to execute a maximum of 6 instructions per clock, courtesy of its multiple ALUs, FPUs and dedicated load/store units. However the number of instructions per clock (IPC) that are actually executed are nowhere near this maximum, thanks to a number of annoying factors. The fact of the matter is that most x86 code can't be made to be parallel enough on an instruction level in order to take advantage of a wide array of execution units, thus a number of the execution units of the Pentium 4 go unused during normal execution (this is where Hyper-Threading comes in handy).

Then there is the issue of actually getting instructions and data into the Pentium 4's pipeline so that they may occupy those execution units. Because of the extremely slow speed of memory (compared to the high speed on-chip cache of the CPU), the CPU burns a lot of execution time just waiting around to be fed new data to work on (or waiting for data that is necessary before existing operations may be completed).

Taking this idea of making the CPU wait to get data, you can see that if you decrease the amount of time that it takes the CPU to get data then the overall efficiency of the CPU will increase (its IPC will increase). Taking our highway/mall example from the previous page, let's focus on the number of sales that the mall can handle at any given point; assuming the number of sales are limited by the number of people we can get into the mall and the number we can get out of the mall after they're done, if we increase the speed of the two highways going to and leaving the mall then in theory, the number of sales transactions would increase. The number of sales that occur are analogous to the average IPC of a CPU, so you can see how increasing the FSB frequency and memory bandwidth would lend to a faster overall system thanks to an increase in IPC.

The benefit of a faster FSB (and higher bandwidth memory subsystem) will only become more and more clear as clock speeds increase; the faster the CPU gets, the more it will depend on getting more data, quicker in order for it to keep from becoming too bottlenecked. We won't see the full benefits of a 800MHz FSB and dual channel DDR400 until Prescott ramps up (90nm Pentium 4) in clock speed in 2004, but that isn't to say that performance won't improve today.

800MHz FSB Chipsets

We've already discussed the 875 and 865 chipsets in a decent amount of detail in our IDF coverage, so here's a quick recap:

The focus of 2003 will obviously shift to the new 875 and 865 chipsets, but motherboard manufacturers also have other options to look at for 800MHz FSB support.

The 845PE chipset isn't dead yet, several motherboards makers (including a few top tier manufacturers) plan on releasing new 845PE motherboards that have been validated to support 800MHz FSB Pentium 4 processors. These 800MHz FSB 845PE motherboards will basically be a cheap way of getting 800MHz FSB support, but obviously won't perform nearly as well as the 875 and 865 solutions.

At the moment, SiS' 655 chipset has taken away Intel's 2 year plus long performance reign in the Pentium 4 market, though only while operating at the fastest memory timings and at the highest supported memory speed (dual channel DDR400 mode). Nonetheless, this is quite impressive, especially since SiS wasn't considered a real player in the CPU chipset market not too long ago.

SiS is no less competitive when it comes to supporting 800MHz FSB P4 processors. As we just mentioned, we have run extensive tests on several SiS 655 motherboards, and much to our dismay only one of them is able to reliably overclock to 800MHz FSB in dual channel DDR mode. MSI, Gigabyte and ASUS confirmed that their SiS 655 motherboards will not officially support 800MHz FSB processors at any point in time, via a BIOS update or otherwise.

But what motherboard makers plan on doing instead is releasing boards based on the SiS 655FX and SiS 648FX chipsets, which are validated for 800MHz FSB operation. The 655FX is simply an updated version of 655 that has been debugged and validated for 800MHz FSB P4 processors, just as the 648FX is an updated version of 648 that has been debugged and validated for 800MHz FSB P4 processors. Most motherboard makers expect mass production of their SiS 655FX motherboards to begin sometime in late April or early May; in other words just after Intel's 875 launch but before the 865 launch. SiS 648FX motherboards are expected to start trickling into the retail channel sometime later this month.

The Test

For this type of review we needed a dual channel DDR motherboard that was capable of memory speeds up to dual DDR400 and at 533MHz FSB. The only motherboards that offer this kind of capability are ones based on the SiS 655 chipset. After testing the few SiS 655 motherboards currently available, the Gigabyte SINXP1394 (SiS 655) motherboard was the only 655 motherboard we were able to get working at 800MHz FSB. This setup was not stable 100% of the time, but was just good enough to run our benchmarks at 800MHz FSB.

Our 800MHz FSB tests were made possible by one of Intel's mobile Pentium 4 processors, the 1.7M processor. This CPU has a default multiplier of 12 (instead of 17) when installed in a desktop motherboard like the Gigabyte SINXP1394. In general, the lower the multiplier the higher the FSB overclock, and since 12 is by far the lowest Pentium 4 multiplier in existence, the 1.7M was the perfect CPU for our 800MHz FSB overclocking tests. So as previously mentioned, we were able to run the Gigabyte SINXP1394 at 800MHz FSB, which adds up to 12 X 200MHz for a 2.4GHz core clock. We had no trouble finding a 2.4GHz Pentium 4 processor that ran at 533MHz FSB to compare to our mobile processor.

We would like to thank Technonut from our forums for loaning us the 1.7M processor for this review.

Content Creation & Office Performance

Content Creation Performance Internet Content Creation SYSMark 2002 2.4GHz Pentium 4 @ 800MHz FSB (Dual DDR333) 2.4GHz Pentium 4 @ 800MHz FSB (Dual DDR400) 2.4GHz Pentium 4 @ 533MHz FSB (Dual DDR333) 2.4GHz Pentium 4 @ 800MHz FSB (Dual DDR266) 2.4GHz Pentium 4 @ 533MHz FSB (Dual DDR400) 2.4GHz Pentium 4 @ 533MHz FSB (Dual DDR266) 330 326 318 311 305 301 | 0 | 66 | 132 | 198 | 264 | 330 | 396

There are a few interesting things to take away from this chart; for starters, dual DDR333 performance is better than dual DDR400 performance, which absolutely isn't the case you'll see with the 865/875 chipsets assuming you're using fast DDR400 memory. This should give you an idea that the SiS 655 obviously isn't optimized for dual DDR400 operation, much less 800MHz FSB operation, but again, that's why this is a preview.

General Usage Performance Office Productivity SYSMark 2002 2.4GHz Pentium 4 @ 800MHz FSB (Dual DDR333) 2.4GHz Pentium 4 @ 800MHz FSB (Dual DDR400) 2.4GHz Pentium 4 @ 533MHz FSB (Dual DDR333) 2.4GHz Pentium 4 @ 800MHz FSB (Dual DDR266) 2.4GHz Pentium 4 @ 533MHz FSB (Dual DDR400) 2.4GHz Pentium 4 @ 533MHz FSB (Dual DDR266) 193 191 188 184 182 180 | 0 | 39 | 77 | 116 | 154 | 193 | 232

As you would expect, the 800MHz FSB doesn't increase performance tremendously under office applications, mainly because we're not FSB/memory bandwidth bound in these cases.

Video Encoding Performance - DiVX/XMpeg 4.5

MPEG-4 Video Encoding Performance MPEG-2 to DiVX Conversion using XMpeg 4.5 & DiVX 5.0.2 (Frames per Second - Higher is Better) 2.4GHz Pentium 4 @ 800MHz FSB (Dual DDR400) 2.4GHz Pentium 4 @ 800MHz FSB (Dual DDR266) 2.4GHz Pentium 4 @ 800MHz FSB (Dual DDR333) 2.4GHz Pentium 4 @ 533MHz FSB (Dual DDR400) 2.4GHz Pentium 4 @ 533MHz FSB (Dual DDR266) 2.4GHz Pentium 4 @ 533MHz FSB (Dual DDR333) 54.7 52.6 52.4 51.5 50.7 50.1 | 0 | 11 | 22 | 33 | 44 | 55 | 66

Video encoding is relatively platform intensive and thus we continue to see reasonable performance gains from the 800MHz FSB.

Gaming Performance

Gaming Performance Quake III Arena - 1024x768 High Quality 2.4GHz Pentium 4 @ 800MHz FSB (Dual DDR400) 2.4GHz Pentium 4 @ 800MHz FSB (Dual DDR333) 2.4GHz Pentium 4 @ 533MHz FSB (Dual DDR400) 2.4GHz Pentium 4 @ 533MHz FSB (Dual DDR333) 2.4GHz Pentium 4 @ 800MHz FSB (Dual DDR266) 2.4GHz Pentium 4 @ 533MHz FSB (Dual DDR266) 303.6 297.0 290.8 287.1 283.7 274.9 | 0 | 61 | 121 | 182 | 243 | 304 | 36

Gaming Performance Jedi Knight 2: Outcast - 1024x768 High Quality, AF Disabled 2.4GHz Pentium 4 @ 800MHz FSB (Dual DDR400) 2.4GHz Pentium 4 @ 800MHz FSB (Dual DDR333) 2.4GHz Pentium 4 @ 533MHz FSB (Dual DDR400) 2.4GHz Pentium 4 @ 533MHz FSB (Dual DDR333) 2.4GHz Pentium 4 @ 800MHz FSB (Dual DDR266) 2.4GHz Pentium 4 @ 533MHz FSB (Dual DDR266) 122.3 119.5 116.6 114.9 113.5 109.7 | 0 | 24 | 49 | 73 | 98 | 122 | 147

Gaming Performance Unreal Tournament 2003 Demo - Flyby 1024x768 2.4GHz Pentium 4 @ 800MHz FSB (Dual DDR400) 2.4GHz Pentium 4 @ 800MHz FSB (Dual DDR333) 2.4GHz Pentium 4 @ 533MHz FSB (Dual DDR400) 2.4GHz Pentium 4 @ 533MHz FSB (Dual DDR333) 2.4GHz Pentium 4 @ 800MHz FSB (Dual DDR266) 2.4GHz Pentium 4 @ 533MHz FSB (Dual DDR266) 166.60 164.68 162.43 160.76 159.62 156.80 | 0 | 33 | 67 | 100 | 133 | 167 | 200

Gaming Performance Unreal Tournament 2003 Demo - Botmatch 1024x768 2.4GHz Pentium 4 @ 800MHz FSB (Dual DDR400) 2.4GHz Pentium 4 @ 800MHz FSB (Dual DDR333) 2.4GHz Pentium 4 @ 533MHz FSB (Dual DDR400) 2.4GHz Pentium 4 @ 533MHz FSB (Dual DDR333) 2.4GHz Pentium 4 @ 800MHz FSB (Dual DDR266) 2.4GHz Pentium 4 @ 533MHz FSB (Dual DDR266) 62.81 61.32 59.97 59.04 57.95 56.41 | 0 | 13 | 25 | 38 | 50 | 63 | 75

Professional 3D Performance

High End Workstation Performance SPEC Viewperf 7.0 - 3DSMAX-01 2.4GHz Pentium 4 @ 800MHz FSB (Dual DDR400) 2.4GHz Pentium 4 @ 800MHz FSB (Dual DDR333) 2.4GHz Pentium 4 @ 800MHz FSB (Dual DDR266) 2.4GHz Pentium 4 @ 533MHz FSB (Dual DDR400) 2.4GHz Pentium 4 @ 533MHz FSB (Dual DDR333) 2.4GHz Pentium 4 @ 533MHz FSB (Dual DDR266) 9.273 9.212 8.997 7.951 7.886 7.708 | 0 | 2 | 4 | 6 | 7 | 9 | 11

High End Workstation Performance SPEC Viewperf 7.0 - DRV-08 2.4GHz Pentium 4 @ 800MHz FSB (Dual DDR400) 2.4GHz Pentium 4 @ 533MHz FSB (Dual DDR400) 2.4GHz Pentium 4 @ 533MHz FSB (Dual DDR333) 2.4GHz Pentium 4 @ 800MHz FSB (Dual DDR333) 2.4GHz Pentium 4 @ 533MHz FSB (Dual DDR266) 2.4GHz Pentium 4 @ 800MHz FSB (Dual DDR266) 39.81 38.85 37.18 36.75 34.15 32.32 | 0 | 8 | 16 | 24 | 32 | 40 | 5

High End Workstation Performance SPEC Viewperf 7.0 - DX-07 2.4GHz Pentium 4 @ 800MHz FSB (Dual DDR400) 2.4GHz Pentium 4 @ 800MHz FSB (Dual DDR333) 2.4GHz Pentium 4 @ 800MHz FSB (Dual DDR266) 2.4GHz Pentium 4 @ 533MHz FSB (Dual DDR400) 2.4GHz Pentium 4 @ 533MHz FSB (Dual DDR333) 2.4GHz Pentium 4 @ 533MHz FSB (Dual DDR266) 30.59 30.32 29.58 25.54 25.28 24.89 | 0 | 6 | 12 | 18 | 24 | 31 | 37

Professional 3D Performance (continued)

High End Workstation Performance SPEC Viewperf 7.0 - LIGHT-05 2.4GHz Pentium 4 @ 800MHz FSB (Dual DDR400) 2.4GHz Pentium 4 @ 800MHz FSB (Dual DDR333) 2.4GHz Pentium 4 @ 800MHz FSB (Dual DDR266) 2.4GHz Pentium 4 @ 533MHz FSB (Dual DDR400) 2.4GHz Pentium 4 @ 533MHz FSB (Dual DDR333) 2.4GHz Pentium 4 @ 533MHz FSB (Dual DDR266) 9.944 9.875 9.620 9.303 9.241 9.125 | 0 | 2 | 4 | 6 | 8 | 10 | 1

High End Workstation Performance SPEC Viewperf 7.0 - ProE-01 2.4GHz Pentium 4 @ 800MHz FSB (Dual DDR400) 2.4GHz Pentium 4 @ 800MHz FSB (Dual DDR333) 2.4GHz Pentium 4 @ 533MHz FSB (Dual DDR400) 2.4GHz Pentium 4 @ 533MHz FSB (Dual DDR333) 2.4GHz Pentium 4 @ 800MHz FSB (Dual DDR266) 2.4GHz Pentium 4 @ 533MHz FSB (Dual DDR266) 7.534 6.994 6.939 6.555 6.300 6.218 | 0 | 2 | 3 | 5 | 6 | 8 | 9

High End Workstation Performance SPEC Viewperf 7.0 - UGS-01 2.4GHz Pentium 4 @ 800MHz FSB (Dual DDR400) 2.4GHz Pentium 4 @ 800MHz FSB (Dual DDR333) 2.4GHz Pentium 4 @ 533MHz FSB (Dual DDR400) 2.4GHz Pentium 4 @ 800MHz FSB (Dual DDR266) 2.4GHz Pentium 4 @ 533MHz FSB (Dual DDR333) 2.4GHz Pentium 4 @ 533MHz FSB (Dual DDR266) 3.485 3.458 3.397 3.384 3.362 3.302 | 0 | 1 | 1 | 2 | 3 | 3 | 4

Final Words

You'll notice that we kept our commentary on benchmarks to a minimum in this review, mainly because of this table below showing the performance improvement the 800MHz FSB provided in each of our benchmarks (we're comparing 2.4/800 vs 2.4/533 both using dual DDR400):