Another Guide to Overclocking - Memory, Motherboard & CPU

Like it says – Ralph Nelson

Preface – Why Write Another Guide

A few months ago, I had no idea how to begin the process of overclocking my machine.  It was painful even trying to figure out what questions to ask.  This write-up is aimed at those just starting the process. It tries to provide you with the particular steps needed to undertake, investigate further, and produce some level of overclocking.

You should understand that there are various degrees of overclocking;
however, the initial steps associated with running a faster Front-Side Bus (FSB) that will produce the greatest gains. You can continue to tweak almost forever for small gains that are of little value in terms of observable performance, and you may undertake those just because it is fun for you. Nothing wrong with either perspective.

I am most familiar with AMD-based machines and while I’ve
owned and currently use Intel-based machines, I’ve not overclocked them. If you find inconsistencies in regards Intel (PIV) machines, please let me know so others aren’t mislead. And if you feel so moved, please provide verbiage to correct the situation – I’ll acknowledge you as a contributor.

Introduction

To understand overclocking, you need to realize that for the majority of mobos (motherboards), there is a single clock which controls all operations made by the computer.  The various operations (for example graphics) are slaved to the clock. 

The clock measures time in what is typically called a tick, cycle, period or the clock refresh rate, and reflects a discrete measure (small-fixed unit) of time.  The cycle is also commonly converted to an operational frequency, (frequency = 1.0 / period) in many discussions.  For example, a clock cycle of 7.5 nanoseconds converts to a 133 Mhz clock speed. (The clock cycle can be viewed as a square wave for those familiar with such representations. The cycle is thus made of a positive half and a negative half.)

A Simple Perspective of Overclocking – The Balance
of Various Component Demands

Because the various computer operations are often slaved
to the single clock, a balance of the various device speeds must be achieved so that each device is stable.

The clock controls the Front-Side Bus (FSB) and the different components use that bus speed to determine their own speed.  With a single speed available from the FSB, this creates the need for “multipliers”, a term you often hear. 

Some multipliers increase the FSB reference speed for use by their component, for example the CPU multiplier is typically greater than one; for example, an AMD XP 2100+ is set at 13 when the CPU is locked. Others slow it down; the PCI bus, for example, typically uses a multiplier of ¼ on many of today’s motherboards. 

If the multiplier slows the speed down, it may also be called a divider.  For this discussion multipliers and dividers are viewed as performing the same operation, ie changing the FSB clock speed for use by their particular devices.

One definition of overclocking is the process of balancing the various component speed needs to produce stable operation at different FSB speeds.

When you have the freedom to select the multipliers for the various devices (hard drive, video, memory, etc.), this balance is easier to obtain. That statement may not be obvious to you now but hopefully will be better understood later as we deal with the combination of memory and CPU. Ultimately, what we would really like to do is work with each device independently. Motherboards are available that allow this separation are becoming more widely available.

A Simple Overview of Memory

There are far too many characteristics associated with memory and its operation to include in this simple guide.  Thus, I will try (with the help of other contributors) to provide a brief perspective that will hopefully help you better understand memory itself.  This perspective will look at major Dynamic Random Access Memory (DRAM) types in use today and a few of their characteristics that directly influence our initial efforts in overclocking.
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Ralph Nelson

Predominant RAM Types

A reference discussing much more completely the various memory types can be found at pctechguide.com.  Here I will provide some detail related to the three main types of memory in use today – SDRAM, DDR SDRAM and RDRAM.

SDRAM – Synchronous DRAM
(SDRAM)
employs the fact that most PC memory accesses are sequential, ie the information need has been stored sequentially. Thus, all the bits can be retrieved in a burst.  The SDRAM uses a memory controller to determine the location and size of the block of memory required and then supplies the bits as fast as the CPU can take them, using a clock to synchronize the timing of the memory chip to the CPU’s system clock. 

This feature of SDRAM allows it to deliver data at burst rates of up to 100 Mhz while using a FSB of 66 Mhz.

PC133 SDRAM is an advancement of SDRAM allowing a doubling of the burst data rate and is compatible with a 133 Mhz FSB.

(This information related to SDRAM was taken from pctechguide.com.)

DDR SDRAM – Often just called DDR (Double Date Rate).  DDR works on both "sides" of the clock cycle (positive portion and negative portion), so its data transfer rate (frequently noted as bandwidth) is doubled, hence the name.

DDR memory is the most common, cost effective, and arguably best RAM option currently available. Also, it is the most overclockable RAM, with some high-end sticks allowing FSB speeds in the 200s. It is rated by both speed and bandwidth.  For example,

PC 1600 = DDR200 = 1.6 GB/s

PC 2100 = DDR266 = 2.1 GB/s

PC 2700 = DDR 333 = 2.7 GB/s
PC 3200 = DDR 400 = 3.2 GB/s

How these specifications, for example PC 1600, are obtained
is discussed in more detail in an O/C forum thread.

Note, however, that to achieve these ratings the memory needs to be driven at its rated speed.  If you put some PC 3200 in an Athlon stock mobo with a 266 Mhz FSB, it would just run at PC 2100.  Doesn’t hurt it, but you have wasted your money because you are not running it at its rated speed.  You would need to overclock the FSB to 200 Mhz to fully use the PC 3200 at its rated capacity.

RDRAM – A slightly more expensive, yet top performing memory, exclusive to the Intel P4.  RDRAM uses a clock generator of its own to run at fast speeds, which achieves the high rate (bandwidth). However, it can get quite hot, and is not a good OR easy overclocker. If the RDRAM multiplier is lowered, decent FSB speeds might be reached. For example, stock PC800 is 100 * 4, but that’s equivalent to 133 * 3. Speed is given in Mhz * 2, since it is on a dual-channel architecture.

PC800 = 4*100 = 3*133 = 3.2 GB/s