Version 1.0
10/3/98
By Frank Monroe
Contents:
Introduction and Disclaimer
So you want to overclock a Celeron?
Why is the Celeron so overclockable?
What does stepping mean?
What is an S-code?
What is 'multiplier locking' and 'bus locking'?
Which type of Celeron should I buy?
Which motherboard should I use?
What kind and how much memory?
What about cooling?
How do I overclock?
What if it doesn't work?
Will it damage my CPU or other components?
Where can I learn more?
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Introduction and Disclaimer
I created this FAQ because, after reading literally thousands of posts, I
still see the same requests for basic instructions over and over in each
Newsgroup and forum. There are many web sites with similar information,
but many people either can't find these sites or they don't have web
access. Since I have never seen a FAQ like this posted in any of the
Newsgroups I read, I took it upon myself to offer this small contribution
to novice overclockers everywhere. I don't claim to have all the answers
and I can't guarantee that everyone will be able to overclock their
Celeron, but after reading this FAQ you should be well on your way to a
successful experience.
Overclocking is not recommended by any manufacture (especially Intel) and
will void your warranty. I do not advise anyone to follow these
instructions unless they are willing to assume all associated risks. I
have consolidated in this document information that I've learned while
overclocking my own system or that I have read about the experiences of
others. Overclocking can damage your system. Working inside your power
supply or wiring 110 volt fans can cause serious personal injury if done
by the inexperienced or without the proper precautions. If you're unsure
or in doubt about any of these procedures, seek professional advice. I
am providing this document for informational purposes only.
If any one out there in Net-land has suggestions, comments or
contributions for this FAQ, feel free to contact me. Frank Monroe
email: monroef...@hawaii.rr.com
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So you want to overclock a Celeron?
You've read a few posts, maybe visited a few web sites. Everyone is
reporting their success and claiming fantastic speeds from a lowly 266 or
300 mHz CPU. You're excited at the prospect of a high performance CPU
for, essentially, small change and you want to get in on the action. The
speed of a P2-400 or -450 for $90 or $150 sounds too good to be true.
But wait, they're talking about S-codes, multiplier locking, Pin B21,
CAS-2, and other esoteric terms. Names like Deschutes, Klamath and
Mendocino are bandied about while you wonder what these words have to do
with computers. Now you're confused. How hard is this going to be? Is
it worth it? Do you need to be an Electrical Engineer to overclock a
Celeron? In a word, no. With the right hardware and a little luck, it
should be a snap.
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Why is the Celeron so overclockable?
As you may know, a given chip design is used for CPU's of many different
speeds. The P2 and Celeron designs are named after Western US counties:
Deschutes, Klamath and Mendocino. More on this later.
In theory, a CPU is tested first at its maximum speed. The ones that
pass the testing process at this speed are marked as such and sold as
top-of-the-line CPU's. Those that fail at the fastest speed are tested
at successively lower and lower speeds until they run reliably. These
slower cores are then marked with the speed at which they passed the
testing process and sold as slower processors. At least, that's the
theory. No one really knows how Intel decides which cores get marked for
a given speed. Several other factors, such as customer demand and
production quality, affect how many processors of each speed are
produced.
A CPU of any given speed can usually be made to run somewhat faster if
one is willing to play around with the motherboard settings. This is the
overclocker's bread and butter. Now, through a convenient turn of
events, Intel has produced a CPU with an unusually high capacity for
overclocking.
Intel has long controlled the high-end CPU market while its competitors,
Cyrix and AMD were gaining market share in the low and mid-price range
because of the popularity of lower priced PC's. Intel finally realized
what was happening and wanted to recover the low ground while also
keeping the high end market (can you say "total market domination"?).
When Intel designed the CPU core for their newest line of processors, the
P2, they changed the way the CPU was mounted. All P2's are mounted on a
circuit board, called an SECC (Single Edge Contact Cartridge), that plugs
into a special, patented CPU slot (Slot 1) similar to a PCI slot.
[Intel calls the Celeron packaging a SEPP (Single Edge Processor Package)
but it's still compatible with the Slot 1 connector, go figure.] AMD
and Cyrix do not have a Slot 1 CPU, so if you want high-end speed, you
need to buy an Intel processor. Thus the high-end market is preserved
for Intel. Now, Intel needed a cheap Slot 1 CPU to corner the low-cost
PC market.
Enter the Celeron line. To reduce production costs, Intel left out the
expensive Level 2 cache. Also, to eliminate design costs, the original
Celerons (C266 and C300) used the same CPU core as the new 350-450 mHz
P2's (code name Deschutes). [Remember, design costs account for a huge
percentage of the total cost of a CPU. Once in production, it costs
exactly the same to manufacture a core destined for use as a 266 mHz
processor as it does to use that same core in a 450 mHz processor.] Many
media pundits immediately dubbed the Celeron a backward-stepping piece of
crap because of the lack of the L2 cache. Later, perhaps due to the poor
reviews from hardware critics, Intel released the Celeron 300A and 333
with 128 Kb of built-in cache. Again, they used basically the same core
design with some modifications to incorporate the on-die cache. The
C300A and the C333 modified Deschutes core carries the code name
Mendocino. Since Celerons use a Slot 1 motherboard, you can't upgrade to
one of Cyrix's or AMD's fast new CPU's later, when prices come down.
They don't have Slot 1 CPU's and Intel has the patent. Now Intel has
again regained a foothold in the below-$1000 PC market and insured that
the upgrade dollars also come home to Papa Intel too.
Here's where it gets interesting. The fastest P2 CPU's (350 to 450)
require a relatively new type of Slot 1 motherboard with the BX chipset.
The BX motherboard runs at a bus speed of 100 mHz. They can also run at
66 mHz bus which allows them to accept slower P2 CPU's (233, 266, 300 and
333) and Celerons. The Celerons are supposed to be used on the earlier EX
and LX generation of Slot 1 motherboards which run at 66 mHz only. Since
the Celerons have the exact same core as the new architecture P2 CPU's,
there's nothing to stop you from setting the bus to 100 mHz and running a
Celeron at 400 or 450 mHz.
People started buying BX motherboards and Celerons and overclocking the
hell out of them by setting the bus speed to 100 mHz. A chip meant to run
at 266 running at 400 mHz and more was unheard of previously. It's all
because Intel is trying to capture the low-cost CPU market without the R
& D costs of a new chip. It's really a marketing stroke of genius when
you think about it. Produce one type of CPU. Take the best ones, add
512 kb of fast, expensive cache and sell it as the top-of-the-line CPU
for $700+. Take the rejects, leave off the expensive L2 cache and sell
them as cheap Celerons. Except they're too smart for their own britches.
The production yield of 450 mHz cores is too good and the "rejects" are
too few and far between. Because they want to flood the market with $100
CPU's, they have to mark them as 266 to 333 mHz Celerons and sell them
cheap anyway. It doesn't cost them any more since both chips came off
the same production line. Because the P2-450 market is relatively small
compared to the low and mid priced market, the demand is greater for
Celerons.
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What does stepping mean?
Celerons come in four flavors. The C266 and C300 without L2 cache and
the C300A and C333 with 128 Kb L2 cache. Each type of Celeron has
several slightly different variations, called a "stepping". Stepping 0
(zero) cores are the original production run. When minor imperfections
(bugs) are found in the instruction programming (micro-code) of the core
or in other parameters of the chip, they are fixed and the next batch of
cores will incorporate the changes. This batch will be identified as
stepping 1. If another change is required later, the stepping number
will be incremented again. As each successive refinement to the chip is
made, the next higher stepping number will be assigned. For many
reasons, one stepping may be easier to overclock than another, but
usually the higher stepping cores make the best, most stable CPU's.
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What is an S-code?
An S-code (Intel actually calls it an S-Spec.) is a 5 character
designation beginning with 'S' used to identify the various different
types, stepping, voltage and packaging of Celerons and other Intel
processors. There are currently 14 (as of 27 Sep 98) different S-codes
for the Celeron family of CPU's. OEM packaging is just the SEPP in a
plastic container. There is no heatsink/fan attached, so you need to buy
your own. The warranty, if any, is usually only
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