some parity questions

[pjungwirth]

The simple question first: when a memory module says it's "PC133," what does the PC stand for? It *isn't* Parity Checking, I've discovered. (I'm glad I checked before I bought anything!) So does it stand for Personal Computer? I found this on Crucial's web site:

> PC133 SDRAM meets Intel's requirements for use with 133MHz motherboards,
> and it is used in many Pentium III B, AMD Athlon, and Power Mac G4
> systems.

So if PC133 works on Macs, it seems unlikely to me that PC=Personal Computer, unless it's being used in the more generic sense. But if not Personal Computer, what does it stand for?

(Boy, and that was the simple question.)

My other question regards getting a parity-checking motherboard. I was looking on Intel's site, and they've got this big chart. Their 850, 820E, and 820 chipsets have a "yes" in the Parity column. Their 815E, 815, 815EP, and 815P chipsets have an "N/A"--not a "no," but an "N/A." What does N/A mean? Is this just marketing smoke, or is it something else? They don't mind using "no" elsewhere in this chart (though it's nowhere on the parity row). I was wondering if there's something special that would make the parity question an N/A for these chipsets. Thanks!

--Paul
~{:-)

[AwARe]

Hello pjungwirth,

In keeping with the idea I hate to see "any" question go without at least some answer.....(This is not really my strong point, dont have much experience with ECC Ram)

You will probably find some helpful information here on the forum http://www.pcguide.com/ref/ram/

I have no idea what PC stands for but I do believe that most PC133 ram is Non-Parity and Parity RAM should be designated with ECC. If it doesnt say ECC its most likely Non_Parity.

To your question about what N/A means......it means "Not Aplicable".
I would imagine this means that on the boards that say "Yes" you can use either Parity Or Non-Parity RAM, and On the boards that say N/A you would most likely not have the option for ECC Parity RAM.

On both boards you "should" be able to use both types of RAM but you wont have the option of turning on ECC on the boards that specify N/A, and the ECC function would not be utilized.

Hope you find this helpful.

Im sure someone around here knows alot more about this then I do........

EDIT: well after a little bit of reading it seems that ECC is actually not "exactly" the same as Parity........at any rate hopefully this will at least point you in the right direction.....and hopefully someone else can chime in and help answer this a little better

Extra Note: If all you're doing is building a PIII or P4 PC for your own use at home etc........standard Non-Parity PC133 is really all you need, unless you have lots of money to throw around...........anything else is gonna cost you alot more.

[This message has been edited by AwARe (edited 06-10-2001).]

[tjaymadison]

Click here (http://www.kingston.com/tools/umg/default.asp) for Kingston's Ultimate Memory Guide.


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"I am not able to rightly apprehend the kind of confusion of ideas that could provoke such a question."
-- Charles Babbage, mathematician, computer pioneer, analytical engine designer (1791-1871)
-- (Question: 'Pray, Mr. Babbage, if you put into the machine wrong figures, will the right answers come out?')

"Just because I don't care, doesn't mean I don't understand."
-- Homer Simpson

[yawningdog]

I don't know what PC means

I do know that RAM which is asynchronized (PC133) does not require parity checking, something to do with read and write being checked against each other as an error correction/detection mechanism. This would explain the N/A in the parity column. What confuses me a little, is why 850,820, and 820E listed parity checking as a yes. I figure these must be old chipsets.

ECC works in addition to regular parity checking to corect some of the errors detected by the parity check.

AwARe is mistaken about one thing. You cannot build a P4 system with PC133 memory. You must use PC800 RDRAM, which is sold with the chip.

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Make everything as simple as possible, but no simpler.

[AwARe]

yeah well ok im mistaken dog http://www.PCGuide.com/ubb/wink.gif
Like I said this not my area, but somebody had to try http://www.PCGuide.com/ubb/smile.gif
I haven't built a P4 system "yet", perhaps I asumed too much about a P4.
About as far as I got with P4's was to the point I desided I dont want one heh
Thanks for clearin that up (hope youre right cause I didnt check)

EDIT: As far as the confusion about those boards having a Yes for ECC support. Like I said not really my area, but Im pretty sure you can get ECC Parity Ram to be installed in a newer machine. Its not old by any means, at least not "that" old......Not up to a P4 aparently or whatever but Ive read a few things about people suggesting or recommending that in fact you "do" and "should" use it with a PIII system for example. Its also "ALOT" more expensive then plain old PC133.(Its not a matter of a requirement, its a matter of normal non-parity PC133 doesnt utilize Error correction) The ECC ram sticks have more chips on them then normal PC133 does, and in some way it is used to error check the data as it passes through the ram. It's supposed to be much more reliable memory and also supposed to reduce system crashes etc (Highly recommended for use on servers etc where crashing can be alot more painful then just on a plain old PC) I never had the extra money to blow or cared enough to really read all that much about it. I think its 72bit instead of 64bit? having 8 bits for error correction, honestly I have no idea but this is not old stuff this is expensive stuff lmao

Where I got confused as far as the ECC Ram goes, is that I think all ECC Ram is Parity Ram, but not all Parity Ram is ECC if that makes any sense......

The error checking is actually done on the MoBo not on the ram stick which is why you "need" a MoBo that supports it to utilize this kind of Ram......

You can pop an ECC stick in most boards , supported or not by the board, but the Error Checking Correcting wont be used unless the board has the support for it.......

Im betting the "C" in PC stands for "Clock" but Im just guessing http://www.PCGuide.com/ubb/biggrin.gif

[This message has been edited by AwARe (edited 06-10-2001).]

[pjungwirth]

Thanks for the info, everyone. I already had a pretty good sense of what non-parity, parity, and ECC were, but this was *very* interesting:

> I do know that RAM which is asynchronized (PC133) does not require
> parity checking, something to do with read and write being checked
> against each other as an error correction/detection mechanism. This
> would explain the N/A in the parity column. What confuses me a little,
> is why 850,820, and 820E listed parity checking as a yes. I figure these
> must be old chipsets.

This makes sense! It would certainly explain the N/A. The 850 chipset is for the Pentium 4 and uses 600-800 RDRAM. The 820 and 820E are for P3 and P2 chips, but they also use 600-800 RDRAM, so they wouldn't include the built-in parity checking you describe. Where can I find out more information on this automatic error-checking? I noticed that Crucial still sells PC133 ECC chips. In this case, is the ECC only adding error *correction*, then?

In the PCGuide, non-parity, parity, and ECC are three distinct options, but I can't find anywhere that sells parity memory, just non-parity and ECC. Maybe no one bothers to make simple parity anymore?

I'm building a computer to run Linux and serve personal web pages. (Well, more just to run Linux, but I ought to do something with it, right?) So it's a server, but data integrity isn't exactly imperative. Nonetheless, I might as well check out my options and learn as much from the process as I can, right?

That automatic error checking is really interesting. . . .

Paul
~{:-)

[AwARe]

Heya pjumgwirth,

Thats kinda what I was saying about being confused that all Parity Ram is "Not" ECC, but the answer to that is - *All ECC IS Parity*

As far as what it all means...........
While trying to answer your post I have learned that.........
Parity RAM is what provides the Error "Checking"
ECC adds "Correcting", and also has improved on the Checking feature of normal Parity Ram

So therefore, ECC - "Error Checking Correcting" is Parity RAM

I dont know if they make plain old Parity RAM with the intention of being used in a PIII sys, but Id suspect that you could think of ECC as a newer updated type of Parity RAM. I dont see any reason why they would make Parity Ram that wasn't also ECC at this point, if ya get what Im saying..

[This message has been edited by AwARe (edited 06-10-2001).]

[yawningdog]

At the risk of a lashing from Paleo Pete for answering a "homework" question, I'll try to put this in a nutshell.

A data byte is 8 bits long, all of which is either a 1 or a 0. The parity bit is added to the end. In even parity checking, the parity bit makes the number of ones in the byte plus the parity bit an even number. This way, if the parity bit is a one, but the total number of bits is odd, the memory controller knows the data in that byte is corrupted and therefore bad. Yes, there is also odd parity checking.

ECC (stands for error correction code) is just a way to fix or replace the bad byte and keep on truckin', as opposed to just giving an error message and offering options to continue and forget it, or stop, save, and re-boot.

So as that goes, AwARe is correct. ECC has nothing to do without parity checking http://www.PCGuide.com/ubb/wink.gif

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Make everything as simple as possible, but no simpler.

[AwARe]

A homework question? hehe

I dunno what that means exactly but at any rate thanks for the info dog http://www.PCGuide.com/ubb/smile.gif
I read "some" of this stuff on a few web sites, which is where I came up with error checking correcting <- somebody else called it that heh
I was reading something about the parity bit and then it goes on to say there are 7 aditional bits "making a complete 8 bits" in ECC memory, 7 bits used for the Correcting Code. Which makes 64 bits into 72 bits. Im still "a little" confused about the whole thing really, but I think I know enough to get through my life lmao.............

Its kind of hard trying to post "correct" info while you are learning it yourself, but I dont like to see a post go unanswered. Thanks for helping me answer it http://www.PCGuide.com/ubb/smile.gif

[rond36]

PC133 is the name of the standard set by intel and microsoft it is memory conforming to the minimum meeds of a 133mhz processor

[Paleo Pete]

lol...If I thought this was a homework question I would have been here sounding off long ago...I can generally tell... http://www.PCGuide.com/ubb/biggrin.gif

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Computer Information Links (http://www.geocities.com/paleopete/)

[rond36]

all SDRAM is synchronized not asyncronized the s in SDRAM is for syncronious
Synchronious Discharge Random Access Memory
I cant find any SDRAM with parity only non parity and ecc

[pjungwirth]

Hey guys! You are just full of information! Thanks for all your help. Here is what I've gathered about parity and ECC RAM:

First off, in either case the parity bit is the 9th bit, not the 8th. See http://www.pcguide.com/ref/ram/err.htm . It isn't actually stored in memory with a flip-flop or anything; it's just an extra connector that always sends a 1 or 0 (depending on whether you have odd or even parity). (Actually, for ECC the signal probably varies, but I don't know for sure.)

Parity only detects one-bit-off errors; it doesn't correct anything. ECC RAM detects and corrects one-bit-off errors, and it also detects (but doesn't correct) 2-bit-off, 3-bit-off, etc. errors. So the ECC functionality is a superset of the parity functionality.

*But*--while simple parity RAM modules can be used for ECC (since the ECC functions happen on the motherboard), ECC RAM modules cannot be used for simple parity. This is a wiring thing: in parity, each parity bit is individual, while in ECC, the parity bits are arranged in groups of 8. (I'm not sure what this means myself, exactly, but that's the story.) So parity *modules'* functionality is a superset of ECC modules'!

Also, running parity-checking won't slow you down, since the 9th bit is sent at the same time as the other bits. ECC RAM, however, slows down your system 2-3% (according to the PC Guide).

So, since parity RAM modules are more flexible than ECC modules, and since using ECC entails a slight slowdown (and with some gamers *any* slowdown is too much), I was surprised not to find any parity RAM on the market.

Most (if not all) of this info comes from right here on the PC Guide. It looks like a pretty old section, though, so maybe that's why it discusses parity RAM. I'd be curious to know how and when that disappeared from the marketplace. Also, the PC Guide pages on this are too old to mention that PC133 memory includes its own parity-checking. (I'm still curious about the details of how that's done.)

So that's what I've managed to figure out about non-parity/parity/ECC RAM. Does anyone have the story on why it's just non-parity/ECC today?

--Paul
~{:-)

[AwARe]

well my understanding of the reasoning is that parity ram, since it cant correct any errors all it can do is report them, most people find that nothing more then annoying, and not of much use...........

Id suspect this was the reason for the developement of ECC memory, and like I said before it seems to be a "Replacement" for simple parity ram, and I really "wouldn't" expect you to find any "non ECC" Parity Ram, or for that matter why would you want it? id be confused on that issue.........

If youre are going to bother to get parity ram you should get ECC, just be aware that yes it will slow the system slightly, but it should provide a more stable environment.........

[This message has been edited by AwARe (edited 06-11-2001).]

[yawningdog]

Have to respectfully disagree, rond36.

A is the correct prefix for converting the ajective "synchronous" to the adverb "asynchronized".

"Synchronous" is not spelled with an i.

SDRAM= Synchronous Dynamic Random Access Memory

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Make everything as simple as possible, but no simpler.

[rond36]

So I can't spell