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System Factors

As I probably reiterate in too many places on this site, the components in a PC system are interrelated, and affect each others performance in many ways. This makes it difficult to measure the performance of any component in isolation. Some tests are better able than others to isolate the component being tested, but it also depends on the component. Hard disks are virtually impossible to completely isolate from the rest of the system, because every access of the hard disk involves a transfer through the main processing subsystems.

The following are the main parts of the system directly influence the performance of the hard disk subsystem:

• System Processor: Every benchmark that you run on your hard disk involves instructions that are processed on the main system CPU. A faster CPU will run these benchmarks faster than a slower one, and I have found it to be quite consistent that testing the same drive on a machine with a much faster CPU, will result in higher scores. This is accentuated when using one of the transfer modes that requires intervention from the processor, such as PIO, which is what the majority of systems today use.
• System Motherboard, I/O Bus and Chipset: These are all related since they are all part of the motherboard. The system bus is the interface for the hard disk and faster buses will lead to faster theoretical external transfer rates. The system chipset is what controls the operation of the bus and its characteristics can influence hard disk performance. It also must support higher transfer rate modes for them to work, for example Ultra ATA's 33.3 MB/s high-speed rate.
• System BIOS: The BIOS influences hard disk performance in several important ways. First, it must provide explicit support for the higher transfer rates. Second, it's efficiency is a factor in performance when BIOS routines are called. Third, some BIOSes implement enhanced features such as block mode that enable improved performance, while others do not.

The bottom line of all this is that comparing drives can only be fairly done using a comparative benchmark. In my opinion, you cannot get a system-independent single score that gives a fair assessment of a hard drive's performance.

Next: Command Overhead and Multiple Device Considerations

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