Crystal

[cr250]

Myself and some friends were sitting around and someone brought up a question of a crystal on the motheboard for timeing ir something. Anyone know about this? Any info would be appreciated.

[Wiz]

if i remember correctly, the crystal is what makes the cpu go. It shakes and every shake is a hertz, therefore, the fast it shakes, the faster the cpu goes. am i right, guys?

[OuTpaTienT]

Yeah, you're sort of right. But the crystal doesn't "shake" faster or slower. The whole reason a crystal is used is because it shakes at a given & constant no matter what. Thus making it perfect to base the timing architecture on.

Exact same reason they use quatz in watches. Quatz, and many other types of crystals as well, vibrate at a known and constant frequency with a givien electrical charge put to 'em. The CPU mhz and the various buses all have their speed based on that crystal. Of course they're multiples of the actual crystal frequency, but they're still based directly off of it.

So why can't we just use some kind of man made advanced timing chip or device of some kind. Because we don't really have anything as precise as the constant frequency of a quatz crystal. Well, nothing feasible anyways. They are ways of using the half-life of certain short lived (nano seconds) sub atomic particles for very precise timing. But I'm not ready for nuclear fusion on my desktop just yet.

BTW, we DO have more feasible technology for replacing the crystal, but that technology is only just now starting to be practicle, and still isn't quite as reliable. I'm sure in the next 4-5 years (probably less) we'll do away with the crystal.

[This message has been edited by OuTpaTienT (edited 12-17-1999).]

[cr250]

Thanks for the answers. I have a few more questions though. Where does the crystal reside? Does the frequency relate to the processor speed? Faster cpu faster crystal? Thanks again.

[OuTpaTienT]

The actual crystal is usually in a silver colored tin looking little "canister" somewhere on the motherboard. Could be any shape, but is often kinda flat yet oval when viewed from above.

Faster CPU, faster crystal? NO. Like I tried to explain above, the crystal only resonates at 1 specific frequency. It's not even very high. I believe it's something like 14.31mhz for the typical quatz crystal. The key is that mhz will NOT vary. It will stay rock stable at 14.31mhz (or whatever it is). It's the stability of the frequency that is used. CPU speed and bus speeds and the like, use the crystal as a reference point. By constantly double checking with a SET value (the crystal) the high speed buses can insure that their timing does not vary, and helps all the various buses and signal stay in sync.

[scotter]

well actualy some of the old 386 and 486 boards you had to replace the crystal to overclock them so yes there was a time when the speed was set directly buy the crystal but that day has come and gone thank god http://www.sysopt.com/forum/smile.gif

[EVGTech]

Well if you did replace the crystal with a faster one you would raise the timing of the reference point and as such raise all the bus speeds. You would raise all of them and mess with timing of the system a great deal. still i belive the ISA, PCI and AGP bus speeds are all derived from the CPU bus. the CPU bus speed should be derived from the crystal. On some 486 and older boards, even some pentium boards there is no divisor or multiplier for the crystal so the crystal speed determines the cpu bus speed. in order to increase the cpu bus speed you had to remove the crystal and replace it with a faster one.

we used to advise people with 486 boards and removeable crystals to get 44 mhz crystals and run our CPU at 3x. 44x3=132. chances are that the AMDX5 would run ok at X4 also giving 44X4=172 mhz. pretty quick for a 486 board.

[scotter]

LOL http://www.sysopt.com/forum/smile.gif the more I think I know the dumber I am LOL http://www.sysopt.com/forum/smile.gif

[XT]

I hotrodded a XT to 8mhz before, Pulled the Crystal and replaced it with one from radio shack. Did this about 1987, hehe

[Prospero]

I just couldn't resist posting this.
www.icmfg.com (http://www.icmfg.com)

my family's company
You can get a feel for what else crystals are used for and what it takes to figure out freq and such.

[This message has been edited by Prospero (edited 12-18-1999).]

[reddog4629]

Hey Prospreo-check your mail. I knew Mr.Freeland way back when.