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High-Performance RAM Discover how ATI varies a winning formula to create a family of graphics cards

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High-Performance RAM
Discover how ATI varies a winning formula to create a family of graphics cards

Introduction

As I have discussed at length in various editions of my book Upgrading and Repairing PCs, the speed of RAM memory is one of the most critical factors in determining the performance of a given system. As processor speeds increase, its necessary for memory speeds to increase as well to minimize performance bottlenecks. In this article you will learn about how todays memory module designers are tweaking the designs of memory and memory modules to produce the fastest, most reliable memory yet.

Measuring Memory Performance

There are three ways that memory performance is measured:

  • throughput
  • bus speed
  • latency

I have discussed these factors in detail in Upgrading and Repairing PCs, 15th Anniversary Edition, Chapter 7, but a brief review is in order here.

The first method, throughput, measures how fast memory transfers data to and from the memory controller in MBps (megabytes per second). The second method, bus speed, measures the speed of the memory in millions of cycles per second. Although most users find throughput values more useful, most memory vendors provide both throughput and bus speed values for the memory chips in their memory modules. The bus speed is a multiple of the actual clock speed of the memory chips in a module. For example, a single-data-rate SDRAM module with a clock speed of 133MHz also has a bus speed of 133MHz (133*1=133). However, todays most common memory type, DDR (double-data-rate) SDRAM performs two memory accesses per clock cycle. Thus, a DDR SDRAM module with a clock speed of 133MHz actually has a bus speed of 266MHz (133*2=266).

Higher throughput and clock speed numbers indicate faster memory. The fastest DDR SDRAM memory modules on the market today are the PC4000 modules made by various suppliers. These have a throughput of 4,000MBps (4GBps) and a bus speed of 500MHz. Even faster PC4300 (533MHz) memory modules are expected shortly, and some current PC4000 modules are designed to tolerate overclocking to 533MHz and even faster bus speeds.

Throughput and clock speed values are useful for measuring how quickly memory chips transfer data, but dont indicate how quickly memory chips can switch to a different range of addresses. The number of clock cycles needed to switch to a new range of addresses is known as CAS latency (column-address-strobe) and is often abbreviated CL. Unlike throughput and clock speed numbers, where larger is generally better, a lower CL value is generally better for performance.

Keep in mind that the CL value is just one factor in memory timing. The SPD (serial presence detect) chip on a memory module configures the BIOS with the vendors default values for the memory module. However, if you want to vary these timings, you can disable the SPD setting in the system BIOS. This enables you to adjust the memory frequency (bus speed), the CAS latency (CL), and the settings for RAS (row-address-strobe). Overclocking-oriented websites abound in advice and test results for various combinations of memory module speed settings, processors and motherboards. Because different brands of memory modules use different memory chips, you should not assume that overclocking settings provided for one brand and model of memory module will work correctly with another brand.

Keeping Up with the Processors and the Chipsets

The fastest Pentium 4 processors from Intel run at speeds exceeding 3GHz (3.2GHz and climbing) and the fastest AMD Athlon XP runs at speeds over 2GHz (3200+ runs at 2.2GHz). The latest chipsets that these processors use provide high-speed memory buses which need fast memory to enable high system performance. For example, the 865 and 875 chipsets from Intel are designed to handle up to PC3200 (DDR400 400MHz) memory modules, while the nVidia nForce2 is designed to handle the same memory speeds-the integrated graphics version is designed to handle up to PC2700 (DDR333 333MHz) memory. Other vendors high-performance Pentium 4 and Athlon XP chipsets also handle PC3200/DDR400 memory.

Although the memory speeds that these chipsets support are quite high compared to those available just a year or so ago, they fall short of the fastest memory now on the market.

Features of High-Performance Memory

Although I dont encourage overclocking your hardware (running it faster than the rated speed) if you are performing mission-critical work, it cant be denied that the popularity of overclocking is pushing memory vendors to develop memory with much higher performance than that needed by todays most advanced chipsets and processors.

In this article, I define high-performance memory modules as DDR memory modules with speeds exceeding PC3200 (400MHz). Most of these memory modules feature special designs intended to make them more tolerant of overclocking. If you plan to overclock your system, or if you just want to have memory which exceeds the minimums by a wide margin, you should consider these products.

There are several features, which different brands of high-performance memory modules have in common. These include:

  • module design features which reduce memory module overheating
  • support for non-standard voltages
  • testing and packaging of electronically-matched modules for use in dual-channel systems

Lets look in more detail at these features and some of the vendors which use them.

Reducing Heat Buildup for Better Performance and Reliability

Excessive heat is one of memorys biggest enemies. Overheating can corrupt the contents of memory and cause the system to shut down unexpectedly, which causes the loss of all data in memory which hasnt been saved to disk. As memory chips run faster, they typically put out more heat (measured in watts). To reduce heat buildup and help prevent overheating, high-performance memory modules typically feature heat spreaders.

Heat spreaders are aluminum or copper plates which snap over the memory chips on a module. Some vendors prefer copper because of its superior thermal properties, but because some of these vendors put a decorative metal plating over the heat spreader surface to color-code different lines of memory, dont go by the color of the heat spreader alone to determine what type of metal it is. Check the vendors memory specifications sheet for the module in which youre interested.

One vendor which uses a different approach to reducing heat buildup is GeIL. Its Golden Dragon Premium line of high-speed memory is directly mounted on the modules PCB without soldering. This method, which GeIL calls Wafer Level Chip Scale Package, reduces both heat buildup and electromagnetic interference. Golden Dragon memory currently runs at a top speed of 466MHz (PC3700), which is just short of the fastest speeds available with heat-spreader construction (which GeIL also uses in its other high-speed memory lines).

Another variation on the classic heat spreader is Corsair Memorys XMS ProSeries modules. Corsair Memory was one of the first vendors to use heat spreaders on its high-speed memory, and the XMS ProSeries takes the idea a step further by using a finned aluminum heatsink to provide double the surface area of a flat heat spreader plate. The fins enable better cooling of the memory chips for greater reliability.

Fighting heat buildup is especially important for reliability because high-performance memory is always non-parity (and few chipsets sold for high-performance and overclocking support parity or ECC error correction anyway).

Extra Voltage for Extra Stability

Standard DDR memory modules are designed to use 2.5V. However, overclockers have discovered that running memory and processors at slightly higher voltages helps improve stability (assuming that the additional heat can be dealt with). Consequently, most high-performance DDR memory modules are designed to run at voltages beyond 2.5V. Some types of high-performance modules are designed to run at voltages ranging from 2.6V to as high as 3.1V to allow plenty of tolerance for the additional voltage which might be needed for stable operation. The range of available voltages depends upon your motherboard and BIOS.

Before you adjust the DDR memory voltage setting, check the data sheet for your modules to determine what the acceptable voltage range is. You should use the lowest voltage that also provides stable results at the performance you want.

Matching Modules for Better Dual-Channel Performance

With more and more systems today using dual-channel chipsets such as Intels 865 and 875, nVidias nForce2, SiSs 655FX, and others, vendors of high-performance memory are now testing pairs of memory modules on specific systems to qualify them for sale as a matched pair. Because matched-pair memory is tested on real-world dual-channel systems as well as with high-end memory testers, these two-module bundles are the best way to assure reliable performance with a system which supports dual-channel memory.

The Price of High Performance

Its not surprising to find out that the additional features and testing used to produce high-performance memory adds to the cost of that memory. How much more can you expect to pay? Typically, high-performance memory can cost anywhere from about 20% to as much as 40% more than standard memory of a given speed when both types are available. Keep in mind that if you want memory running at speeds faster than 400MHz that you almost certainly will need to choose some type of high-performance memory.

Conclusion

Because everything you create or analyze with your PC resides in memory before you save it to disk, the quality and performance of memory is a critical issue. If you want memory which is designed to perform reliably at higher speeds than normal, high-performance memory should be on your must-have list.

For Further Research

High-Performance Memory Vendors

GeIL USAs website is located at
http://www.geilusa.com

Kingstons HyperX website is located at
http://www.kingston.com/hyperx/default.asp

Corsair Memory produces the XMS and XMS Pro Series memory modules. Its website is located at www.corsairmemory.com

OCZ Technology produces the Dual Channel Gold and Platinum memory modules as well as the Enhanced Latency series. Its website is located at www.ocztechnology.com

BIOS Adjustments and Performance Tests

Toms Hardware discusses how to put high-performance memory to best use with its How to Speed Up Your RAM article at http://www4.tomshardware.com/howto/20030701/index.html

Anandtech puts various models of 500MHz memory through their paces in its Searching for the Memory Holy Grail, Part 2 article at http://www.anandtech.com/memory/showdoc.html?i=1849&p=1

Copyright©2003 Pearson Education. All rights reserved.

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