Juan Murillo Consulting

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2 - Know What You're Buying

I recently saw an advertisement for a computer motherboard and processor with the following configuration: “P4 2.4 GHz/512 KB L2 Cache, 533 MHz FSB”. As I read this I thought to myself, “What percentage of the population understands what the heck any of that means?” If you are like most PC consumers today, you are doing well to have a vague recollection of seeing some of those terms before, but really have no idea of their significance. Well, have no fear, when we are done you’ll not only know exactly what all that means, you’ll be able to use your new found knowledge when selecting your next computer to ensure you’re getting the most for every dollar you spend… and, as promised in the last edition, you won’t need a degree in computer science.

When describing how computers work, I find it very helpful to use analogies with which we are all familiar. One of my favorites is the trucking industry as we are all accustomed to seeing trucks carry various items to and fro. Whether it’s a pickup truck going back and forth to the home improvement store or a semi on the highway delivering goods to a warehouse, they all have the common purpose of getting “stuff” from one place to another. Computers are very much the same; except the “stuff” is called “data”, the trucks are called “packets”, highways are called “busses” and the stores and warehouses are called “memory” and “hard drives” respectively. In fact you can even use this analogy to relate output devices (e.g. monitors and printers) to retail stores – the purpose of both is to deliver to you the consumer, the stuff or information you want.

We’ll use this analogy to explain each of the acronyms in the preceding computer ad so that you understand what you’re buying next time you shop for a PC.

Let’s start with “P4 2.4 GHz/512 KB L2 Cache”. This little bit of jargon refers to the CPU (Central Processing Unit) or Processor. This is the headquarters of our trucking company. It makes all the decisions as to what to do and where to go. If we were going to rate the effectiveness of our company’s headquarters we would want to know how many decisions they are making and how long is it taking to make those decisions. The same can be said about rating a computer’s processor. P4 is short for Pentium 4, which is Intel’s latest version of their 32-bit “Pentium” processor series. In the last Computer Corner we learned that 32 bits would be equivalent to 4 characters of text and that “G” stands for “giga” – a prefix representing a multiplier of 1,000,000,000. “Hz” is the abbreviation for “Hertz” meaning cycles per second. If we equate our headquarters’ decisions to the characters of text this CPU can process per second, we would find that our company is capable of making 4 decisions (32-Bits) 2,400,000,000 times per second (2.4 GHz) or 9.6 billion decisions per second. Now that’s quick thinking! Similarly, this particular CPU is capable of processing 9.6 billion characters of text per second.

As we all know there’s a big difference between the time it takes to make a decision and the time involved in carrying it out. The same is true with computers. Using our trucking analogy again lets imagine that in order to make good decisions our CEO needs to meet regularly with the CFO regarding the company’s financial status. This being the case, it wouldn’t make much sense for the CFO to work in New York when the CEO works in Morgan Hill. It would waste valuable time for one to fly coast-to-coast for each meeting. This same logic is applied to computers and is the basis for the second part of the CPU description – “512 KB L2 Cache”. L2 cache is a special type of super fast computer memory that is built into the CPU. It is used to store information that the CPU accesses regularly. The larger the cache the lesser the time wasted in retrieving information used over and over again. In this case the CPU is capable of holding 512,000 bytes or characters of text in its cache.

Now that we have headquarters figured out, let’s find out just how much stuff our trucks can get to the stores in a given amount of time. This will allow us understand the meaning and purpose of a “533 MHz FSB”. Remember that the trucks represent “packets” of information, the stores are equivalent to the computer’s memory or “RAM” and the highway is called a “bus”. “FSB” stands for “Front Side Bus” and it is literally the path that connects the CPU (or headquarters) to the computer’s memory banks (or stores). Just as highways restrict the size of trucks that can travel on them, the computer’s bus restricts the size of the packets that pass through them. Pentium class motherboards have front side busses that can handle 64 bits of data per cycle. Since we know there are 8 bits in every byte (or character of text), this means that our trucks can carry 8 characters of text per trip. That may not seem like a big payload, but what the trucks lack in capacity, they make up for in speed – the trucks in this example make 533,000,000 trips from headquarters the store and back every second. So in one second our trucks can move 4,264,000,000 (8 x 533 million) characters of text from headquarters to the store and back. Likewise the computer advertised above is capable of transferring 4.264 billion characters of text between the CPU and RAM per second. Note this is less than half the rate at which the CPU can process the information.

The main lesson to take from this edition is that although the CPU or processor speed is a major factor in determining a computer’s overall performance, it is not the only consideration when purchasing a new computer. You must not only evaluate how all the components work together, you must also be realistic about how much you are paying for the latest technology. For example, you will pay nearly twice as much for a 3.06 GHz/512 KB L2 Cache processor as opposed to a 2.66 GHz/512 KB L2 processor. However, if both are placed on a motherboard with a 533 MHz FSB, you will not get twice the performance from the 3.06 GHz. In fact, you will not even get the full advantage of the 400 MHz difference between the two as the overall performance will be limited by the speed of the FSB.

In the next edition we’ll discuss how other components such as RAM and hard drives contribute to you computer’s performance and how to choose the right configuration to maximize your technology investments.

In closing I would just like to encourage you to contact me if you have any questions about what you’ve learned so far and please feel free to send me suggestions for topics you would like to see in future editions.

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