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Rounding Up the Latest Pentium 4 Chipsets How the new SiS 645 and Intel 845D compare to the rest of the P4 players (compares major features such as memory bus, USB support, etc.)

Rounding Up the Latest Pentium 4 Chipsets
How the new SiS 645 and Intel 845D compare to the rest of the P4 players (compares major features such as memory bus, USB support, etc.)

When the Intel Pentium 4 was first introduced, you had just one chipset to choose from, the Intel 850, and one memory type, the expensive Rambus DRAM (RIMM). This limited your choices significantly, as well as lifting a lot of money from your wallet at initial purchase time and during memory upgrades.

With the advent of third-party solutions and a newer generation of Intel chipsets, you now have many more choices in chipset and memory performance and system/motherboard pricing. In this article, you'll learn about the latest Pentium 4 chipsets, the SiS 645, the Acer Labs ALi Aladdin P4, and the Intel 845D, and see how they compare to other chipsets such as VIA's P4X266 and Intel's original 850 and 845 chipsets.

Which Memory Types Are Best for the Pentium 4?

The short answer to that question is "the fastest", and here's the reason why. The data bandwidth of the Pentium 4 processor is 3.2GB/second, which means that the most desirable memory type for the Pentium 4, without regard to cost, is memory which is at least as fast as the data bandwidth. Here's how the maximum memory bandwidth compares for the major memory types supported by the Pentium 4 chipsets on the market:

Memory Type

Maximum Bandwidth

Used by



Intel 845 (original)



Intel 845D (new), VIA P4X266 & P4X266A,

ALi Aladdin P4,

SiS 645



ALi Aladdin P4, SiS 645


3.2GB/sec (dual-channel; 1.6GB/channel)

Intel 850

As you can see from this table, the Intel 850 is the only chipset which provides an exact match for the Pentium 4 processor's data bandwidth, although the new DDR333/PC2700 DDR memory used by some third-party chipsets is a close second.

However, pairs of identical PC800 RDRAM RIMM modules must be used to achieve this performance, making systems with the Intel 850 chipset more expensive to buy initially and more expensive to upgrade later because of the high cost of RDRAM RIMM modules and because they must be bought in pairs. DDR and SDRAM-based chipsets use single DIMM memory modules for upgrading, making them less expensive to buy and upgrade.

The PC133 memory supported by the original motherboards and systems using the Intel 845 provides only about 1/3 the memory bandwidth needed by the Pentium 4, making it an poor choice for all but the budget-minded.

Intel + DDR Memory Equals the Latest 845 Chipset

Starting late in 2001, computer and motherboard makers using the Intel 845 chipset were finally allowed to take advantage of the chipsets support for both DDR200/266MHz memory as well as the entry-level PC133 SDRAM which was the only supported memory type when the chipset was introduced in mid-2001. The chipset itself is identical to the original 845, as you can see from visiting the Intel Developer Web site; only the officially authorized memory support types are different. Since 168-pin SDRAM and 184-pin DDR SDRAM modules can't be interchanged, make sure that a system or motherboard based on the 845 chipset is designed to handle DDR SDRAM before you buy it. Although Intel doesn't officially use this designation, most refer to the DDR version of the 845 as the 845D. I will use that designation in this article as well. The 845D chipset includes the 82845 Memory Controller Hub (equivalent to the North Bridge chip) and the 82801BA I/O Controller Hub (also called the ICH2 and equivalent to the South Bridge chip).

The 845 chipset provides four USB 1.x ports (or 2.x with the newest I/O Controller Hub chip), support for AGP 4x video cards, Ultra ATA/100, AC97 audio, and support for the communications network riser (CNR) card for LAN, audio, and USB ports. The 845D chipset is also compatible with Intel's new Application Accelerator software, which is designed to speed up boot times, provide for faster disk I/O for games and graphics applications, and provide data pre-fetch support for Pentium 4 processors.

In benchmark tests, the 845D chipset teamed with DDR memory beats out the 845/PC133 SDRAM combination, but both are bested by other chipsets on the market, including the VIA P4X266A with DDR SDRAM and the pioneering Pentium 4 chipset, the Intel 850 with RDRAM. For more information on the Pentium 4/Intel 850 and 845 chipsets, read Faster AMD and Intel Processors Are Coming, Can You Upgrade? on this Web site.

The VIA P4X266A - The "A's" Have It

VIA's P4X266A is an updated version of its powerful and controversial P4X266 chipset. It differs from the original version by adding support for VIA's Performance Driven Design (faster timings and deeper instruction queues) in its new VT8753A North Bridge chip and support for Ultra ATA/133 IDE drives with its new VT8233A South Bridge. The P4X266 can also use the companion VPX-64 64-bit PCI controller chip to enable 33MHz and 66MHz 64-bit PCI cards on systems with the P4X266 chipset.

For more information on the original VIA P4X266 chipset, read VIA Strikes Back - With Its New Pentium 4 Chipset on this Web site. To learn more about the benefits of Performance Driven Design, read Improving a Classic - VIA's KT266A Chipset for AMD-Based Systems on this Web site.

Note that since the P4X266A chipset is pin-compatible with the original P4X266 chipset, motherboard manufacturers will be able to easily switch to the newer chipset. Early reviews of the P4X266A chipset suggest, as with the VIA KT266 versus KT266A chipset tests, that you will want to look for the P4X266A, instead of the original P4X266, if you want the best performance from a VIA-based solution.

SiS Joins the Big Leagues with the SiS645

Silicon Integrated Systems (SiS) has long been regarded as a low-end chipset maker. While it has pioneered extreme integration (producing several "chipsets" which use just one chip for all functions), most of its past products have offered low performance and have not been very popular with major motherboard makers in the US market.

However, the two-chip SiS 645 chipset offers high performance due to its innovative design and support for the newest type of DDR memory, DDR333.

The SiS 645 is named after its North Bridge chip, the 645, which supports up to 3GB of PC133 or DDR memory, including the industry-standard DDR266 as well as the new DDR333 variety. This is possible because the 645 chip supports memory bus speeds up to 166MHz, instead of the normal 133MHz memory bus used with DDR266 memory.

Unlike Intel's chipsets, some of which are customized to work with the original Socket 423, while others work only with the newer Socket 478 processors, the SiS 645 supports both socket flavors. It supports AGP 4x video cards, and has a 533MBps connection to the SiS961 South Bridge chip via SiS's own MuTIOL 266MHz bi-directional data bus. This is the fastest connection yet between chips in a PC chipset, doubling the speed of the 266MBps connection used by the VIA Technologies' V-Link technology in the P4X266 chipset and by Intels HubLink architecture in its Intel 8xx chipsets. MuTIOL is also a 16-bit connection, which also improves throughput compared to the 8-bit data path used by VIA and Intel.

The SiS 961 Media I/O chip serves as the South Bridge equivalent to the SiS 645 North Bridge, and is connected via the fast Multi-Threaded I/O Link (MuTIOL) interface developed by SiS. The 961 features integrated 10/100 Ethernet or HomePNA 1.0/2.0 network support, AC97 audio with 5.1 channel support for DVD playback and advanced gaming, 6 USB ports, support for Ultra ATA100, 6 PCI bus-mastering slots, and full compliance with the PC2001 design standard developed by Microsoft and Intel.

In benchmark tests performed by popular hardware Web sites Toms Hardware Guide and AnandTech, the SiS645 chipset on a reference motherboard produced by SiS matches or surpasses VIAs P4X266 when equipped with DDR266 memory. When the SiS 645 chipset is used with DDR333 memory, it is a strong second place to the Intel 850 chipset in gaming benchmarks and sometimes beats the 850 in popular business benchmarks.

If you prefer integrated video, watch for the upcoming SiS 650, which integrates the SiS 315 graphics core (a good performer in tests) with the SiS 645 in a single North Bridge chip.

The Acer Labs Aladdin-P4

Acer Labs, the chipset arm of Acer, is the latest vendor to provide a Pentium 4 chipset teamed with DDR SDRAM. Its Aladdin P4 chipset includes the new M1671 North Bridge and the new M153D+ South Bridge. The mobile version, the Aladdin P4M, replaces the M1535D+ with the M1535+ South Bridge. The M1671, like the SiS645, supports DDR333 (PC2700) memory for a peak memory bandwidth of 2.7GB/second, and the M1535D+ South Bridge supports the latest Ultra ATA/133 hard disk interface standard. The 1535D+ also provides AC97 and legacy Sound Blaster Pro and SB16 compatibility, support for S/PDIF input/output, and 6 USB ports.


The first performance reviews of the Aladdin P4 and SiS 645 chipsets involve so-called "reference" motherboards produced by the chipset vendor. The performance of actual motherboards and systems may be better or worse than a reference board because of differences in BIOS options, and in the case of these chipsets in particular, whether the system or motherboard is using DDR333/PC2700 memory or the slower DDR266/PC2100 memory that is the current industry standard for DDR SDRAM.


While the Intel 850 with RDRAM is still the best performer for gaming applications on the Pentium 4, the Aladdin P4 and SiS645 with DDR333/PC2700 DDR memory are very close in performance, and can even surpass it for some business applications. Pentium 4 systems based on industry standard DDR266/PC2100 DDR memory significantly surpass the performance of Intel's initial teaming of the 845 chipset with PC133 SDRAM and are also slightly faster in most cases when the 845 is teamed with DDR266/PC2100 DDR memory. With several chipsets available that support DDR memory, Pentium 4 users have a wide variety of high-performance, cost-effective systems to choose from.

For further reading

Intel 845

The official Intel website for the 845 chipset: http://developer.intel.com/design/chipsets/845/

SiS 645

The official SiS website for the 645 chipset: http://www.sis.com/products/chipsets/oa/pentium4/645.htm

Anandtech's review of the SiS 645:


ALi (Acer Labs) Aladdin P4

The official Acer Labs website for the P4 chipset:


The OCWorkbench preview of the Aladdin P4:



The official VIA Technologies website for the P4X266A chipset:


Comparative Reviews

Tom's Hardware pits the VIA, SiS, and Intel chipsets against each other:


VR-Zone's head-to-head matchup also includes the ALi Aladdin P4 chipset:


An early comparison of the P4X266A with its predecessor is available as part of Tbreak's review of the Shuttle AV45GTR motherboard:


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