The Motherboard, Processor, and Memory - Frequency, Megahertz and Athlon Product Marking
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CPUs are measured in speed—or, to be more accurate, frequency, in megahertz or gigahertz. One hertz is one cycle per second. Were you to, say, tap your knee once every second, your knee-tapping frequency would be one hertz. One megahertz is one million cycles per second, and a gigahertz is one billion cycles per second. You probably can’t tap your knee that fast, at least not without some serious bruising, but current processors run at speeds well over one gigahertz.
Speed is tied closely to the price of the processor. Usually, when a higher speed processor is released to market, lower speed processors drop in price. Sometimes you can get a real bargain by getting a processor that’s been available for a few months and surpassed in speed, rather than demanding the absolute cutting edge. However, keep in mind that the processor speed makes the biggest difference in overall system performance.
The frequency rating indicates the core clock speed of the processor, and it affects only calculations that are going on inside the processor. The size of the internal registers determine how much information the processor can work on at the same time. Most current processors have 32-bit registers. That means they’re capable of dealing with 32-bit wads of data, whereas a 16-bit processor, like the 286, can not.
Pentium-class processors use a 64-bit data I/O bus. This is the processor’s external data bus that shovels data into and out of the processor. Pentium introduced superscalar architecture, which means it has two 32-bit pipelines in which to process data. The dual pipelines, at 32 bits each, match perfectly with the 64-bit data I/O bus.
Yet another bus, the address bus, is used to describe to the processor the memory locations of the data it needs to receive. Current generation processors use 36-bit address buses, also referred to as 36 address lines.
All of these processor buses are described by their width in bits. The wider the bus, the better. Think of it this way: a single 1-inch garden hose can carry a certain amount of water. If you add another 1-inch hose, they can carry twice as much water as a 1-inch hose by itself can. Use two more hoses, and you’ve doubled the water capacity again. The more hoses you add, the more water you can siphon at the same time.
Note that the data bus, the register size, and the address bus, while all vitally important, don’t directly affect the core frequency of the processor. A faster processor will always outmode a slower one.
Megahertz and Athlon Product Marking Until recently, all processors were sold with a rating in megahertz or gigahertz. For example, Pentium 4s come in 2.4GHz, 2.53GHz, 2.8GHz, 3.06GHz, and so on. AMD’s Athlons, however, are no longer marked with their true clock frequencies. Instead, AMD has adopted a marking scheme that supposedly describes the Pentium-equivalent speed. This description is called a P-rating.
For example, an Athlon XP 1500+ actually runs at 1333MHz, but according to AMD it compares in performance to a Pentium 4 1500MHz. Whether this is actually the case is the subject of heated debate in the hardware community; some benchmarks back up AMD’s theory and some don’t. For comparison, check out the Athlon P-ratings and actual megahertz speeds in Table 2-1.
Note that Table 2-1 indicates the speeds of processors based on AMD’s current Thoroughbred core. The latest Athlons, from the 2700+ and upward, support a 333MHz FSB, while earlier ones support a 266MHz core. All support 333MHz and 400MHz DDR memory.
| Athlon XP P-Rating | Actual Speed in MHz |
|---|
| 1700+ | 1467 |
|---|
| 1800+ | 1533 |
|---|
| 1900+ | 1600 |
|---|
| 2000+ | 1667 |
|---|
| 2100+ | 1733 |
|---|
| 2200+ | 1800 |
|---|
| 2400+ | 2000 |
|---|
| 2600+ | 2130 |
|---|
| 2700+ | 2170 |
|---|
| 2800+ | 2250 |
|---|
Table 2-1 Athlon XP P-Ratings and Actual Clock Speeds
 This chapter is from Build Your Own High Performance Gamers' Mod PC, by Chen and Durham (McGraw-Hill/Osborne, 2004, ISBN: 0072229012). Check it out at your favorite bookstore today. Buy this book now. |
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