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Xeon and Itanium bring new performance to workstations and servers The New Xeon More than the Name Is Different

Xeon and Itanium bring new performance to workstations and servers
The New Xeon More than the Name Is Different

With the introduction of the newest Xeon processors, Intel has made a break in more ways than one from its previous Xeon models:

While the latest Xeon is based on the Pentium 4 and its NetBurst micro-architecture, the name of the new processor is simply "Xeon". The names of previous Xeon versions (Pentium II Xeon and Pentium III Xeon) made it very clear what desktop processor they were derived from, but now Xeon is simply called "Xeon".

The new Xeon has also abandoned the Slot 2 motherboard interface used by previous versions. This Xeon uses a new socket interface, called Socket 603. As with the Pentium III and Pentium 4, the new Xeon has integrated its L2 cache into the processor die, making the bulky and expensive cartridge design used by earlier Xeon versions no longer necessary.

The new Xeon is being marketed primarily as a dual-processor (DP) workstation chip, although it can also be used in single and multi-processor server applications. It's easy to see why the Xeon has been repurposed: it was introduced at about the same time as the new Intel Itanium. The Itanium is Intel's first 64-bit processor, and the Itanium is the processor that Intel is now marketing as its primary server product.

Major Features

The new Xeon has the same core as the Pentium 4, so that it include the following major features that the Pentium 4 introduced:

  • Hyper-pipelined technology, enabling processors to reach higher speeds than with shorter internal data pipelines. Both the new Xeon and the Pentium 4 are already available at 1.7GHz.
  • A new Advanced Transfer L2 Cache with a 256-bit pathway and the ability to transfer data on each clock cycle. This provides a maximum transfer bandwidth that is as much as 5 times faster than Pentium III or Athlon L2 data transfers.
  • Hardware Prefetch, which enables the processor to anticipate the data needed next and retrieve it in advance.
  • A quad-pumped interface to its 100MHz FSB, providing 400MHz performance for memory transfers, and support for dual RDRAM channels.
  • Support for SSE2, the successor to SSE multimedia instructions. SSE featured 70 instructions, while SSE2 adds 144 new instructions. As with SSE and its ancestor MMX, software must be SSE2-enabled to activate these new instructions.

Xeon Packaging

The Xeon's Socket 603, while it has almost 50% more pins than the Socket 423 that the Pentium 4 uses, is the same overall size. The difference is that the pins on Socket 603 are clustered tightly around the CPU die area, rather than being spread out to the edge as with the Pentium 4's Socket 423 and the Pentium III's Socket 370 (which the Celeron also uses) processors. The pins in Socket 603 are tightly spaced, but no longer use the staggered pin-grid-array (SPGA) design found on previous processors. Instead, it resembles the micro PGA connector used on recent mobile Intel processors.

The First Xeon Chipset

Intel's 860 motherboard chipset is the first chipset to support the Xeon, and it has the following standard components:

  • The 82860 Memory Controller Hub (MCH) interfaces to the processor, memory, and graphics, providing North Bridge functions to the chipset. It supports dual RDRAM memory channels (so that two identical RDRAM modules at a time must be used for memory upgrades), 1.5v AGP 4x video and two connections for 64-bit PCI controllers such as the 82806AA P64H chip described below.
  • The 82801BA I/O Controller Hub (ICH2) provides South Bridge and Super I/O functions, including 32-bit PCI, Ultra ATA100, integrated LAN controller, and dual USB ports. The ICH2 also has six-channel digital audio and AC 97 audio support.

Motherboard makers can also add the following optional components:

  • The 82806AA 64-bit PCI Controller Hub (P64H) enables 64-bit PCI slots to run at either 33 or 66MHz. One of these chips is needed for each 64-bit PCI bus. Each P64H chip provides full FSB speed (800MBps) to its 64-bit PCI bus, and thus provides more than enough bandwidth to support 64-bit PCI cards at 66MHz, which require only 533MBps.
  • The 82803AA RDRAM-based memory repeater hub (MRH) divides each memory channel into two, and enables motherboards to handle more memory.

Motherboards Supporting the New Xeon

All of these motherboards use the same Intel 860 chipset and also integrate SCSI host adapters. Tyan's Thunder i860 and Iwill's DX400-SN use a riser card which contains two 82803AA MRHs to support up to eight RIMM modules. The Super Micro SUPER P4DC6, on the other hand, uses on-board RIMM sockets only, and is a better choice for slimline rackmount servers.

Interestingly enough, Intel doesn't currently offer a motherboard for the Xeon. To make it easier for you to find motherboards that work with Xeon and other Intel processors, Intel has a search engine on its web site at http://appsr.intel.com/scripts-boards/default.asp


While the Xeon's roots in the Pentium 4 are easy to see if you go beneath the surface, the Intel Itanium is the true revolutionary: it's Intel's first 64-bit processor designed to compete with 64-bit enterprise server processors from Sun, HP, and others. The Itanium can also be used in very high-performance workstation operations.

The Itanium initially runs at speeds of 733MHz and 800MHz, which are modest by desktop standards, but when combined with 64-bit operation, make even the first Itaniums very fast. Early Intel-provided benchmarks suggest the 800MHz Itanium will outperform the Sun's UltraSPARC 750MHz processor by a substantial margin in various transaction-processing operations.

The Itanium uses a new processor technology called Explicitly Parallel Instruction Computing (EPIC), which allows the processor to perform multiple instructions at the same time. While EPIC is completely different than the CISC (Complex Instruction Set) technologies used by 32-bit processors from Intel and others, the Itanium is able to run 32-bit Intel-compatible software as well as native 64-bit software being introduced by Microsoft and others.

Parallelism All Over

As the Itanium's EPIC processor technology would suggest, parallelism is the key to Itanium's performance.

  • Two integer units
  • Two memory units
  • 2-way set-associative cache Advanced Load Address Table
  • Two pairs of floating-point math units (see "Floating Point Math Power") below

Itanium's EPIC design minimizes branching and other overhead penalties to provide better performance.

Cache Size and Cache Type

The Itanium uses a three-level cache, including an L1 cache size of 32KB, an L2 cache size of 96KB, and, depending upon the model, either 2MB or 4MB of L3 cache. While the initial versions of the Itanium use off-die L3 cache contained in the Itanium processor cartridge, the upcoming "McKinley" version of the Itanium may incorporate its L3 cache on-die.

Floating Point Math Power

Because the Itanium is designed for high-precision technical workstation tasks as well as server operations, it also features a very power math co-processor function. Each Itanium processor features two floating-point multiply-accumulate (FPMA) units that work with 82-bit data. Each FPMA can perform two FP operations per clock cycle and provide single, double, and double-extended precision for very accurate calculations. In addition, the Itanium also has two multimedia FP units that can perform two single-precision FP operations per clock cycle. This gives the Itanium a maximum of eight FP operations per clock cycle.

Memory Details

The Itanium has a 64-bit memory bus running at 266MHz. The memory bus also supports 8 ECC bits, enabling the processor to use ECC memory, which can correct single-bit memory errors in the processor's data bus as well as in the L2 and L3 memory caches. The L1 cache uses parity checking to detect memory errors. The Itanium's memory address space is 64-bits, and does not have the segmented design familiar to users of 32-bit processors.

Physical Packaging

Itanium comes in a 3 by 5-inch cartridge using a new slot called Slot M. The cartridge contains the processor and either 2MB or 4MB of cache memory, as well as a thermal sensor. The cartridge uses a built-in heat pipe lid, which allows for passive cooling. The processor and L3 cache use separate voltages.

Operating Systems and Applications Support

The Itanium is supported by 64-bit versions of popular workstation and server operating systems, including Windows XP 64-bit, Windows 64-bit Advanced Server Limited Edition 2002, HP-UX 11i v1.5, Linux, and AIX-5L. Itanium is also compatible with 32-bit Intel-compatible programs, enabling companies to move gradually from 32-bit to 64-bit software.

The Intel 460GX Chipset

The 460GX chipset supports Itanium-based servers as well as workstations. The 460GX chipset is a more complex chipset than the chipsets available for desktop processors or even the new Xeon. Its components include:

  • The 82461GX system address controller (SAC), which interfaces the address and control portions of the Itanium's system bus and memory bus with the system data controller (SDC). It connects with the graphics expansion bridge, wide PCI expansion bridge and PCI expansion bridge.
  • The 82462GX system data controller (SDC), which connects to the SAC via the memory data and control buses
  • The 82463GX memory address controller (MAC) transmits memory addresses and commands
  • The 82464GX memory data controller (MDC) transmits data to and from memory
  • The 82465GX graphics expansion bridge (GXB) connects the AGP 4x slot to the SAC via an expander bus
  • The 82466GX wide and fast PCI expansion bridge provides the interface for two 66MHz, 64-bit PCI buses and connects them to the SAC via an expander bus
  • The 82467GX PCI expansion bridge connects two 33MHz, 32-bit PCI buses to the SAC via an expander bus, and can be configured to provide a single 64-bit 33MHz PCI bus as an option
  • The 82468GX I/O and firmware bridge (IFB) provides a PCI to ISA bridge, PCI IDE, USB hub and host, SMBus, power management and firmware hub functions. It connects to the PXB.
  • The 82802AC firmware hub (FWH) stores BIOS and firmware information and security features. It connects to the IFB.
  • The NEC# UPD66566S1-016 programmable interrupt device (PID) provides IRQ steering functions and various bus interfaces.

Itanium Systems

Major vendors including HP, Compaq, IBM, Gateway, and Dell will be selling Itanium-based servers and workstations starting this summer.


Both the new Xeon and Itanium provide great improvements in the performance of workstations and servers, but you'll see Xeon in more places much sooner than Itanium, though Itanium's 64-bit operation is the future of computing.

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