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Intel's Pentium 4 – An Upgrader's Perspective

Intel's Pentium 4 – An Upgrader's Perspective

What's new about the Intel Pentium 4? Quite a lot, starting with its name; at least for now, Intel has abandoned roman numerals for easier-to-read Arabic numerals. But the change in nomenclature is just the beginning.

Internally, the Pentium 4 introduces a new microarchitecture called NetBurst and is the first Intel processor which is truly optimized for the high memory transfer rates available with RDRAM. This is possible because the Pentium 4 uses a very high speed 400MHz processor bus (also called front-side bus or FSB). Technically speaking the processor bus is a 100MHz quad-pumped bus that transfers 4 times per cycle (4x), for a 400MHz effective rate. Since the bus is 64-bits (8 bytes) wide, this results in a throughput rate of 3,200 MB/sec. This matches the speed of the dual channel RDRAM, which is 1,600 MB/sec per channel, or 3,200 MB/sec total. The use of dual channel RDRAM means that RIMMs must be added in matched pairs.

Currently all Pentium 4 chipsets (and therefore motherboards) require expensive Rambus DRAM (RDRAM) for memory. Intel has stated that chipsets using DDR (Double Data Rate) SDRAM are being developed, which will present a much lower cost high-performance alternative.

While early benchmarks indicate that current models of the processor are no faster than the AMD Athlon at most office tasks, games such as Quake III Arena that are memory-intensive show the processor in its best light. Avid gamers may be the among the first to want to make the change. But, moving to the Intel Pentium 4 is likely to be the most expensive upgrade you'll ever make short of buying a brand-new system. Here's why.

The Intel Pentium 4 introduces a new CPU socket, more stringent memory configuration and even new power supply and case requirements. The many changes even an RDRAM-equipped Pentium III-based system must undergo to use a Pentium 4 CPU should be carefully considered before you jump on the Pentium 4 bandwagon.

The CPU Socket

The Pentium 4 is the first Intel CPU to use the new Socket 423, which has 53 more pins than the Socket 370 that the Pentium III and late-model Celeron processors used. Therefore, you need a new motherboard for your Pentium 4; there's no way to retrofit the P4 to older Socket 370 or Slot 1 motherboards. The P4's more sophisticated memory pipeline, which uses two Rambus channels to communicate with memory, requires the extra pins.

Memory Requirements

While current Pentium 4-based motherboards use the same Rambus RDRAM RIMM modules introduced for use with some of the chipsets used in Pentium III motherboards, the dual RDRAM channels that the Pentium 4 uses require you to install pairs of identical modules (called RIMMs). If your Pentium III motherboard uses SDRAM then you'll need to get entirely new RDRAM memory for any P4 upgrade. If your Pentium III board uses RIMMs, but is not using two identical (same speed/same size) RIMM modules, you'll need to buy additional RIMMs to match the modules you're currently using to make identical pairs to use on your new Pentium 4 motherboard. What if you're using three RIMM modules on your current motherboard? If two are identical, you can use them on your new motherboard; if you want to use the third one, you must buy a matching module since you must populate your Pentium 4 motherboard with either one or two pairs of RIMMs. Both pairs of memory must be the same speed, but need not be the same size.

Power Supply Shockers

With speeds currently ranging from 1.3 to 1.5GHz, the Pentium 4 requires a lot of electrical power, and this adds another complication to the life of the upgrader. To reduce the load on the 3.3V and 5V power, most Pentium 4 motherboards include voltage regulator modules to power the CPU, which runs on 12V power instead. Because the ATX motherboard and power supply design originally allotted only one pin for 12V power (each pin is only rated for 6 amps), additional 12V lines were needed. The fix appears in the form of a third power connector, called the ATX12V connector. This new connector is used in addition to the standard 20-pin ATX power supply connector and 6-pin auxiliary (3.3/5V) connector. Fortunately, the power supply itself won't need a redesign, there is more than enough 12V power available from the drive connectors. To utilize this, PC Power and Cooling sells an inexpensive ($8.00) adapter that converts a standard Molex-type drive power connector to the ATX12V connector. Normally a 300-watt (the minimum recommended) or larger power supply would have more than adequate levels of 12V power for both the drives and the ATX12V connector.

If your power supply doesn't have enough oomph (300-watt minimum), you need to purchase a replacement; some vendors now sell an off-the-shelf ATX12V ready model, or one that uses the adapter mentioned above. Before you pick up your credit card to buy a power supply, though, take a good look at your current computer case.

Time to Buy a New Case?

Cooling requirements for CPUs have come a long way since the tiny passive heat sinks used on Intel's first-generation OverDrive upgrade CPUs for the 486DX/33. As CPUs exceed the 1GHz standard, huge active heatsinks are required. These heavy (sometimes over 1 pound) heatsinks can damage a CPU or destroy a motherboard when subjected to vibration or shock, especially during shipping. To prevent this, Intel's specifications for the Pentium 4 add four standoffs to the ATX chassis design flanking the Socket 423 to support the heatsink retention brackets. These standoffs allow the chassis to support the weight of the heatsink instead of depending upon the motherboard as with older designs.

The heatsink retention mechanism consists of two brackets that are screwed to new chassis standoffs through the motherboard, and then two clips which attach the heatsink to the brackets. The brackets and clips are to be included with the motherboard, and the standoffs with screws are to be included with the chassis. For compatibility between chassis and motherboards, Intel is recommending that all Pentium 4 motherboards use the same location for the CPU: near the right edge of the motherboard. This allows case designers to supply a single modified ATX case design for all Pentium 4 motherboards. Even so, vendors can also use other means to reinforce the CPU location without requiring a direct chassis attachment. For example, Asus' new P4T motherboard ships with a metal reinforcing plate to allow off-the-shelf ATX cases to work with the motherboard.

What's Left from Your Old System?

As you can see from the previous sections, upgrading an existing system to the Pentium 4 require more expenses than most previous CPU upgrades. While motherboard replacements are common, the additional power supply, memory, and case requirements of the Pentium 4 mean that even a RIMM-based Pentium III user may only be able to salvage some of their PC's RAM, drives and external devices when making the move to the Pentium 4.

Another consideration is that future versions of the Pentium 4 (codenamed, "Northwood") may use a different socket than the first version (one with 478 pins instead of 423). This would be similar to how Intel changed the original Pentium sockets early in their lifecycle. Because of the many additional expenses you will incur when upgrading to Pentium 4, take a good look at both your upgrade budget and at the performance you expect to gain. You may find that changing other components of your existing system, such as adding memory, installing a faster processor that will fit your existing motherboard, or switching video cards, will be a better use of your funds. In most cases moving to the Pentium 4 is best done with a completely new system purchase rather than an upgrade.

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