What Exactly Is a Bottleneck?


The term bottleneck doesn't refer in any way to the physique of the typical computer geek. Rather, computer geeks coined the phrase when they discovered that the tapered shape of a bottle of Jolt cola limited the rate at which they could consume the beverage. "Hey," a computer geek said one day, "the gently tapered narrowness of this bottle's neck imposes a distinct limiting effect upon the rate at which I can consume the tasty caffeine-laden beverage contained within. This observation draws to mind a hitherto undiscovered yet obvious analogy to the limiting effect that a single slow component of a computer system can have upon the performance of the system as a whole."

"Fascinating," replied all the other computer geeks, who were fortunate enough to be present at that historic moment.

The term stuck and is used to this day to draw attention to the simple fact that a computer system is only as fast as its slowest component. It's the computer equivalent of the old truism that a chain is only as strong as its weakest link.

For a simple demonstration of this concept, consider what happens when you print a word-processing document on a slow printer. Your word-processing program reads the data from disk and sends it to the printer. Then you sit and wait while the printer prints the document.

Would buying a faster CPU or adding more memory make the document print faster? No. The CPU is already much faster than the printer, and your computer already has more than enough memory to print the document. The printer itself is the bottleneck, so the only way to print the document faster is to replace the slow printer with a faster one.

Here are some other, random thoughts about bottlenecks:

  • A computer system always has a bottleneck. Suppose that you decide that the bottleneck on your file server is a slow SATA hard drive, so you replace it with the fastest SCSI drive money can buy. Now the hard drive is no longer the bottleneck: The drive can process information faster than the controller card to which the disk is connected. You didn't really eliminate the bottleneck-you just moved it from the hard drive to the disk controller. No matter what you do, the computer will always have a component that limits the overall performance of the system.

  • One way to limit the effect of a bottleneck is to avoid waiting for the bottleneck. For example, print spooling lets you avoid waiting for a slow printer. Although spooling doesn't speed up the printer, it frees you to do other work while the printer chugs along. Similarly, disk caching lets you avoid waiting for a slow hard drive.

One reason that computer geeks switched from Jolt cola to Snapple is that Snapple bottles have wider necks.




Networking For Dummies
Networking For Dummies
ISBN: 0470534052
EAN: 2147483647
Year: 2004
Pages: 254
Authors: Doug Lowe

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