Understanding System Memory and CPU speeds

Introduction

Shopping for a new processor and motherboard can be confusing. Some of the most important terms and concepts regarding system performance are also the hardest to understand. Terms like: System Clock, Quad Pumping, Double Pumping, DDR, FSB, SDRAM, Dual Channel, and QDR make many new builders cringe. In this article I will walk you through some of these important concepts so that you can make a more informed decision when upgrading your current system or building a new one.


Part One: What's a bus

To get anything done with a computer you have to get the information you oinput to the CPU and then to any attached devices such as cards, displays, and other output devices. Inside the computer itself, this information travels in the form of signals over what is known as a bus. You can think of a bus as a road and the signals as cars. A wide road (bus) can support more cars (signals), and a smaller road (bus) supports less. The cars (signals) on the road (bus) have a speed limit (the bus speed). Although a speed limit can be broken (an overclocked bus) doing so can have adverse effects on the cars (signals).

Going along with this analogy: A computer is like a small city. You do not have just one road, but instead you have several different roads with different names and speeds.

There are three main buses in most computers:

)1 PCI Bus- The PCI bus connects your expansion cards and drives to your processor and other sub systems. On most systems the bus speed of the PCI bus is 33MHz. If you go higher than that, then cards, drives, and other devices can have problems. The exception to this is found in servers. In some servers you have a special 64-bit (extra wide) 66MHz PCI slots that can accept special high-speed cards. Think of this as a double sized passing lane on a major road that allows higher cars to go through. For information about PCI Express please see the PCI Express Guide.

2) AGP Bus- The AGP bus connects your video card directly to your memory and processor. It is very high speed compared to standard PCI and has a standard speed of 66MHz. Only one device can be hooked to the AGP bus as it only supports one video card so the speed is better compared to the PCI bus, which has many devices on it at once. </IMG>

3) Front Side Bus (FSB) - The Front Side Bus is the most important bus to consider when you are talking about the performance of a computer. The FSB connects the processor (CPU) in your computer to the system memory. The faster the FSB is, the faster you can get data to your processor. The faster you get data to the processor, the faster your processor can do work on it. The speed of the front side bus depends on the processor and motherboard chipset you are using as well as the system clock. Read on for more information about the Front Side Bus later in this article.