Intel Debuts Prestonia Pentium 4 Xeons, Plumas Chipset

by Timothy Prickett Morgan

The Prestonia chips are the second generation of server processors designed by Intel that use the Pentium 4 processor core, also referred to as the P7 core. This 32-bit core differs from the Pentium III or P6 core in a number of ways, but most of these changes have been made so the processors' clock speed could be increased and it could handle the larger memory bandwidths that faster clock speeds require for efficient data processing. Most of the original Pentium II and Pentium III Xeon processors--Xeon being the Intel designation for a high-end workstation of server processor with larger L2 cache memories than are available on non-Xeon versions of Intel's chips--had external L2 caches. Advances in chip fabrication technologies have allows Intel (and other chip makers) to cram these memory circuits onto the processor chip, and thereby increase the integration of these components, which in turn allows processor clock speeds to be increased.

Intel announced the "Foster" Pentium 4 Xeon processors last May for dual-processor workstations, and it was actually shipping them by the summer in limited quantities. The Fosters were aimed at dual processor workstations and servers and used Intel's i860 chipset, which only support Rambus memory rather than the SDRAM memory that is more commonly used in the workstation and server businesses. The Foster chips ran at 1.4 GHz, 1.5 GHz, and 1.7 GHz and included 256 KB of L2 cache memory integrated on the die. They supported a 400 MHz system bus and two Rambus memory channels that could handle up to 4 GB of memory using the i860 chipset. The chips were available in 1000-unit quantities at $268 for the 1.4 GHz version, $309 at the 1.5 GHz speed, and $406 at the 1.7 GHz speed.

The Prestonia chips are a follow-on to the Fosters, and their associated E7500 chipset supports 266 MHz Double Data Rate (DDR) SDRAM memory rather than Rambus memory, which means that server vendors and customers who are rightly skeptical about Rambus memory are going to be much happier about the Prestonia/Plumas combo than they were with the Foster/i860 combo. The Prestonia chips will also be popular among server vendors because they have high clock speeds for servers--1.8 GHz, 2 GHz, and 2.2 GHz, making them the fastest server processors in the world in terms of clock speed. (Remember that Pentium III Xeon server chips maxxed out at 900 MHz, and that the only reliable and affordable Pentium II Xeon chip was the 700 MHz version. The Prestonia chips are a lot faster, and presumably a lot more powerful when running applications.) These high clock speeds are possible because Intel has manufactured the Prestonias using a 0.13-micron chip making process, which allows for smaller circuits than the 0.18-micron process used to make the Fosters and the "Merced" Itanium processors. (This 0.13-micron process is also used to make the "Tualatin" low-power Pentium III chips used in high-density rack-mounted Wintel and Lintel servers.) Because of the smaller circuitry that the 0.13-micron process allows, Intel was able to increase the on-chip L2 cache memory with the Prestonia chips to 512 MB, twice that of the Fosters.

Another big change with the Prestonia chips compared to the Fosters is that the Prestonia chips are the first to support a technology that Intel calls Hyper-Threading. Simply put, Hyper Threading virtualizes the instruction pipelines in the Pentium 4 Xeon processor and allows Intel to re-jigger them so a single processor chip looks like two processors at least as far as the operating system is concerned. Hyper-Threading is based on a long-existing technology called Simultaneous Multi-Threading, which was invented for supercomputers in the 1960s and which has not yet caught on in commercial processors. SMT can make a processor do more work than it would otherwise do--not as much as two actual, distinct processors, of course--and exactly how much more will depend to a large extent on how Windows, Linux, and their applications were written to take advantage of multithreading in the first place. Intel has made no secret of its intentions of delivering Hyper-Threading on its processors--at least not to its software partners. Intel says that four-way servers using the future "Gallatin" Pentium 4 Xeon processors (due later this year running at 1.6 GHz and with Hyper-Threading) can do about 65 percent more commercial computing work than a four-way server using 900 MHz Pentium III Xeons. Clock for clock within the same Pentium 4 Xeon architecture, about 15 percent to 30 percent of the performance gains that customers will see out there in the real world will come from Hyper-Threading.

The Prestonia chips are very inexpensive compared to other alternatives out there in the server market--something you expect from the company that accounts for over 90 percent of the shipments in the uniprocessor and dual-processor server markets. In 1,000-unit quantities, the 1.8 GHz Prestonia costs $251, the 2 GHz costs $417, and the 2.2 GHz costs $615. The E7500 chipset comes in a base configuration that costs $92 in 1,000-unit quantities, with a beefed-up version with integrated support for PCI-X storage controllers and Gigabit Ethernet links costing $132 in 1,000-unit quantities. The E7500 chipset, which supports 200 MHz DDR SDRAM memory chips, provides twice the memory and I/O bandwidth of the prior generation SDRAM chipsets from Intel, the 440BX, and provides the same 3.2 GB/sec memory bandwidth of the Rambus memory subsystem used in the i860 chipset for two-way Foster workstations. The E7500 chipset has a 400 MHz system bus, just like the i860, and it supports 16 GB of main memory, four times the amount supported on the i860 chipset.