PC Hacks 100 Industrial-Strength Tips and Tools

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Hack 23 Determine Your CPU Speed

Benchmarking programs can tell your present system speed and if you've made any improvements.

If you expect 2.4 GHz performance from your 2.4 GHz CPU, you should find out if you're getting it. If not, find out what's holding your system back with the Benchmarking Modules in a utility such as SiSoft Sandra, which allows you to identify and compare performance of your CPU, memory, disk drive, and video adapter.

Once you've run a benchmark test on your system, you have a reference to compare with when you check the results of your CPU hacks. Figure 3-8 shows the CPU performance results from an AMD Athlon XP 2600+ Barton series before overclocking. You may also wish to note the temperature before and after CPU hacking because excessive heat is the enemy of the delicate structure inside the CPU chip.

Figure 3-8. CPU performance measurements for a stock AMD Athlon XP Barton 2600+

Overclocking the CPU, as well as trying a handful of RAM speed tweaks covered in Chapter 4, is considered risky business by any standards. Certainly CPU-intensive work like graphics rendering, spreadsheets, and database sorting that involve a lot of math will benefit from a boost in just the CPU speed. Figure 3-9 shows the performance increase of this particular test system after increasing the CPU clock speed a mere 11.4%, from 1.91 GHz to 2.13 GHz. Raw CPU performance measured in millions of instructions per second (MIPS) and million-floating-point-(math)-operations-per-second (MFLOPS) reveals a proportional 11.4% increase.

Figure 3-9. Performance measurements for the AMD XP 2600+ overclocked 11.4% to 2.13 GHz

Your total system performance is also affected by the speed, design, and operation of the chipset on the system board that binds all of the components together, the memory used, disk drive specifications, and disk drive interface cabling. Once you run benchmark tests against the system's state before overclocking, you will also learn what the Front Side Bus (FSB) speed is.

Within the realm of the CPU-chipset-memory combination, several different clock speeds are involved. The FSB is the interface between CPU and memory. The FSB is typically either 100 or 133 MHz in systems one to two years old, increasing to 200, 266, 333, 400, 533 MHz (and beyond) in newer systems. It is important that the speed of the RAM installed on the system be compatible with the FSB speed—unless your system board provides separate clocking for FSB and memory—or the system will be unstable because the slower RAM will not be able to reliably transfer data.

The FSB speed is typically the base speed of the CPU clock. The true CPU clock speed is a product of the FSB speed and an internal CPU clock-multiplier value; for example, 100 MHz (FSB) 12 (CPU multiplier) makes a 1.2 GHz system. This tells us that we'd also like to be able to change the multiplier value to increase CPU performance.

The processor's PCI and AGP I/O ports connect to the CPU's FSB through what is known as the Northbridge portion of the system's chipset. Data moves between the Northbridge and FSB at FSB speeds. The PCI bus on the outside of the Northbridge usually communicates at only 33 MHz, and the AGP bus at 66MHz (AGP is clocked by separate multipliers to achieve 2-8X speeds). Slower speed I/O devices—ISA, USB, and IDE devices—connect to the CPU through the Northbridge PCI bus through a portion of the chipset known as the Southbridge.

In most cases, the FSB or base speed also affects the speed of the PCI, AGP, Level 2 cache, and Southbridge interfaces unless the chipset provides separate multiplier value control for these interfaces. This is important to note as overclocking FSB speed can cause failure or erratic behavior of the PCI and AGP buses.

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