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The Importance of Hard Disk Performance
I keep insisting that the performance of the hard disk is important. But why? Surely the hard disk's performance level can't be as important as that of the CPU, or memory, or other core system components. Or can it?
It is true that for many aspects of computing, the hard disk's performance level is not much of an issue. If you are recalculating a massive spreadsheet, or doing complex rendering of 3D objects, the amount of sheer processing power in the system is of paramount concern; the hard disk will only come into play periodically. However, these sorts of specialty operations are not indicative of how most of us use our PCs. Typical PC use involves loading programs, and loading and saving data frequently. All of these operations require access to the hard disk. And therefore, hard disk performance becomes an issue constantly as we use our machines.
The importance of hard disk performance even goes beyond this however. After all, we also use all the other main components of our system constantly, so aren't they equally important to the performance equation? Well, yes and no. The importance of the CPU, motherboard and other core components is very important. But much as the strength of a chain is equal only to that of its weakest link, in many ways the performance of a system is only equal to that of its poorest-performing component. Compared to the solid state components in a PC, hard disks have by far the worst performance. And even as hard disks improve in speed, CPUs, video cards and motherboards improve in speed even faster, widening the gap. Thus, hard disks continue to constrain the overall performance of many systems.
In the amount of time it takes to perform one random hard disk access, one of today's CPUs can execute over a million instructions! Making the CPU fast enough to process two million instructions while it waits doesn't really gain you much unless it has something to do with that time. Only improving the hard disk's speed to reduce the wait time will get you where you want to go. Any time you see your hard disk's activity light flashing, the odds are that the rest of the system is twiddling its thumbs waiting for those slow mechanical components to "do their thing".
The applications where hard disk performance issues are most important are obviously those that do a lot of reading and writing to the hard disk, instead of doing a lot of processing. Such tasks are said to be "I/O bound", where "I/O" stands for "input/output". These tasks are contrasted to those described earlier which use the CPU a great deal and are called (unsurprisingly) "CPU bound". Multimedia editing applications, especially those dealing with large audio and video files, are probably the ones most affected by the speed of the storage subsystem. Also up there are applications that process files, including compilers and many disk utilities. Initially starting your PC is also a very I/O-intensive application, as the operating system loads literally hundreds of files. Improving hard disk performance can shave time off the boot process in a very palpable way.
The need for improved performance is a major driving factor behind the rise in popularity of RAID.