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Chapter 3. Bandwidth and Processing Power

For example, consider a SCSI adapter that is connected to a PCI bus. If there are performance problems

with SCSI disk I/O, it might be the result of a poorly performing SCSI adapter, even though the SCSI

and PCI buses themselves are nowhere near their bandwidth capabilities.

3.2. Processing Power

Often known as CPU power, CPU cycles, and various other names, processing power is the ability

of a computer to manipulate data. Processing power varies with the architecture (and clock speed) of

the CPU   usually CPUs with higher clock speeds and those supporting larger word sizes have more

processing power than slower CPUs supporting smaller word sizes.

3.2.1. Facts About Processing Power

Here are the two main facts about processing power that you should keep in mind:

Processing power is fixed

Processing power cannot be stored

Processing power is fixed, in that the CPU can only go so fast. For example, if you need to add

two numbers together (an operation that takes only one machine instruction on most architectures), a

particular CPU can do it at one speed, and one speed only. With few exceptions, it is not even possible

to slow the rate at which a CPU processes instructions.

Processing power is also fixed in another way: it is finite. That is, there are limits to the CPU perfor 

mance you can put into any given computer. Some systems are capable of supporting a wide range of

CPU speeds, while others may not be upgradeable at all

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Processing power cannot be stored for later use. In other words, if a CPU can process 100 million

instructions in one second, one second of idle time equals 100 million instructions that have been

wasted.

If we take these facts and look at them from a slightly different perspective, a CPU "produces" a

stream of executed instructions at a fixed rate. And if the CPU "produces" executed instructions, that

means that something else must "consume" them. The next section describes what these consumers

are.

3.2.2. Consumers of Processing Power

There are two main consumers of processing power:

Applications

The operating system itself

3.2.2.1. Applications

The most obvious consumers of processing power are the applications and programs you want the

computer to run for you. From a spreadsheet to a database, these are the reasons you have a computer.

A single CPU system can only do one thing at any given time. Therefore, if your application is run 

ning, everything else on the system is not. And the opposite is, of course, true   if something other

than your application is running, then your application is doing nothing.

2. This situation leads to what is humorously termed as a forklift upgrade, which means a complete replacement

of a computer.