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Old 06-04-2010, 09:41 PM
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"Server" memory vs. "desktop" memory?!?! AND - how to tell ECC v Non

Question 1:

I am trying to buy

PC5300
DDR2
667
240 pin
ECC

Ram for my Mac Pro.

I have found it, many times.

But the least expensive versions of it are listed as "Servers only!" without the slightest indication of what that means! If the specs on a stick are exactly the specs I'm looking for, what is the difference? Why can't I buy the "server" memory? Maybe I can and this is some kind of PC thing? Isn't a server just a freakin' computer set up as a server??

Question 2:

According to the experts, I CAN use non-ecc memory in my first generation Mac Pro desktop, BUT... I shoudn't mix it with ECC, it should all be one or the other.

(I have no idea what ECC means, of course, I just do what I'm told)

So is there a way to determine the ECC-ness or lack thereof via some kind of software, AND/OR, if I actually shut down and open this puppy up, is every stick guaranteed to spell it out one way or another in black and white, or is there some more subtle and mysterious way of knowing what kind of memory it is?

And finally, if you know, what is the effect of mixing ECC with non-ECC?


My single biggest complaint in life is the spinning ball of death. It is my mission to eventually max this sucker out at 32 (unofficially - Apple only admits to 16) gigs of RAM in the hopes that the spinning ball will go away forever.
Thanks for your help!
Old 06-05-2010, 02:48 AM
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ECC is Error Checking and Correction. Don't mix the two: your computer will not like it.

Go to Crucial's Mac site and run their scanner. That will tell you exactly what you have and what you can buy.

16 GB ECC from Crucial here.
Old 06-05-2010, 09:39 AM
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ECC mandatory for servers

Servers usually have a ton more memory than your desktop. They also run 24/7. Any error that is not immediately corrected will eventually compound and crash the system. So they need the added control checking. Non-ECC is supposedly a bit faster so use non-ECC if you can. The Crucial memory site as already posted is wonderful for finding what you can use.
Old 06-05-2010, 12:16 PM
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Speaking of Crucial:
Quote:
When adding new memory, you should match what is already in your system. Adding non-ECC memory to an ECC system will disable the error-checking and correcting ability of your memory modules. While your system may still operate, the enhanced features of the ECC modules will no longer be active in your computer.

You can determine if your system has ECC by simply counting the number of black memory chips on each module. ECC (and parity) memory modules have a chip count divisible by three or five. This extra chip detects if the data was correctly read or written by the memory module. If the data wasn't properly written, the extra chip will correct it in many cases (depending on the type of error). Non-ECC (also called non-parity) modules do not have this error-detecting feature. Any chip count not divisible by three or five indicates a non-parity memory module.

Using ECC decreases your computer's performance by about 2 percent. Current technology DRAM is very stable, and memory errors are rare, so unless you have a need for ECC, you are better served with non-parity (non-ECC) memory.
Old 06-05-2010, 05:50 PM
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Is it possible to deliberately shut off ECC? If so, it would seem that "server-only" is misleading. It would seem that the server is the one getting extra features, rather than the home market.
Old 06-05-2010, 07:11 PM
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Servers can actually run just fine with non-ecc ram, its just not reccomended for a variety of reasons.

You can load a server operating system onto a $400 Walmart special and will often have a perfectly usable server. Not a very powerful one, but one good enough to drive many small offices adequately for a couple years.

Usually you use better components and more power to make a server that is going to last and does not require constant tinkering.

Last edited by drachillix; 06-05-2010 at 07:12 PM.
Old 06-06-2010, 04:21 AM
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Quote:
Originally Posted by drachillix View Post
Servers can actually run just fine with non-ecc ram, its just not reccomended for a variety of reasons.
To expand on this a bit - your average desktop board has 4 (or maybe 6) sockets for memory. Pretty much all that's needed for a memory module is to stick some memory chips on a circuit board and add the "SPD" chip that tells the system what sort of memory it is.

Servers tend to have far more memory sockets - here's one with 32 sockets. Simply putting a bunch of desktop modules in (if they would fit) will cause too much of a load (signal degradation) on the signals that are connected to all of the sockets. So the memory modules have additional chips which buffer the signals entering / leaving the module. This is generally called registered memory.

As that article points out, you can have registered without ECC or ECC without registered.

ECC allows the system to correct single-bit memory errors and detect the majority of multi-bit errors. It is an evolution of parity memory, which used a single extra memory chip to store a value indicating whether the number of 1's in that part of main memory was odd or even. That would allow a single-bit error (a 1 flipping to 0 or vice versa) to be detected, but not corrected. As memory modules got "wider" (more bits read/written at a time, although the modules did physically get longer too), desktop motherboards stopped offering parity or ECC.

ECC can slow down a system, as the calculations needed to verify that the data is uncorrupted take longer than simply reading data from memory. Some motherboards allowed ECC to be enabled or disabled for a slight speed increase. Of course, if any of the installed memory was not ECC-capable, ECC would be turned off automatically (otherwise any reads from non-ECC modules would be reported as errors).

When you see a module described as "x-something", that's the number of bits in the module. If it is a power of 2 (8/32/64) then it is non-parity/non-ECC. If x is somewhat larger than that (9, 36, 72) then it has (hopefully - see below) extra storage for the parity or ECC data.

Back when memory was much more expensive and memory modules were 8 bits wide, some memory manufacturers created modules that they called "logic parity", though a better term would be "fake parity". Those modules eliminated the parity memory chip and substituted a circuit that would always return the correct value, to fool motherboards that required parity memory. Of course, an error in one of those modules would silently return incorrect data.
Old 06-06-2010, 12:20 PM
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Why would the apparently more complex and reduced-market-size server modules cost less for given specs?
Old 06-06-2010, 02:00 PM
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A lot of motherboards can use ECC or non-ECC.
There's a bios setting that tells it to check ECC or not.

If I built a pc and installed ECC, then I'd set the bios to check it.

Quote:
Originally Posted by BigT View Post
Is it possible to deliberately shut off ECC? If so, it would seem that "server-only" is misleading. It would seem that the server is the one getting extra features, rather than the home market.
Old 06-06-2010, 03:42 PM
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Quote:
Originally Posted by jnglmassiv View Post
Why would the apparently more complex and reduced-market-size server modules cost less for given specs?
I can't say for sure without seeing the actual items, but once a particular type of server memory is no longer in demand, the price drops so the sellers can move them and not get stuck with something completely worthless later on*. If the part can be used somewhere else where there is still demand, the price won't drop as much.

* Note: prices for memory and most computer components get rather strange after they're discontinued. When a part is newly released, the price starts high and then drops (possibly after a brief spike if the part is in high demand with low availability). The price continues to drop slowly until the part is discontinued, at which point the drop accelerates. Some time after the part has been discontinued, the price will jump back up, possibly above the price when it was new. This is because there are vendors that specialize in selling obsolete parts to customers who need them to fix their something-or-other, which can only use this obsolete part. Of course, if you try to sell a part to the vendor, they'll tell you it is worthless and they can't offer you very much for it. But if you called them and wanted to buy the part, it is "rare", "hard-to-obtain", and "very expensive". If you find yourself in that situation, it is a good idea to find out the price they'd pay you for one first, and start bargaining up from there.
Old 06-06-2010, 04:42 PM
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Quote:
Originally Posted by Stoid View Post
Ram for my Mac Pro.

But the least expensive versions of it are listed as "Servers only!" without the slightest indication of what that means!
Mac Pros (note: not MacBook Pros, but the large 30+ pound pro tower Macs) are build on server motherboards (so they can support more than one physical CPU), and as such require ECC server RAM. This is the correct thing to get for your system, and the Mac Pro will not run without ECC RAM. There's also a couple of other timing standards that Apple system RAM needs to conform to, but most of it does.

If you want to be extra cautious, you can get "Apple Approved" RAM that's guaranteed to meet the specs from some places (it costs the same, they've just verified it with Apple). datamem.com is where I always buy my RAM from for high-end machines, for example; they've got the Apple Approved stuff.
Old 06-06-2010, 06:32 PM
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Quote:
Originally Posted by TimeWinder View Post
Mac Pros (note: not MacBook Pros, but the large 30+ pound pro tower Macs) are build on server motherboards (so they can support more than one physical CPU), and as such require ECC server RAM. This is the correct thing to get for your system, and the Mac Pro will not run without ECC RAM. There's also a couple of other timing standards that Apple system RAM needs to conform to, but most of it does.

If you want to be extra cautious, you can get "Apple Approved" RAM that's guaranteed to meet the specs from some places (it costs the same, they've just verified it with Apple). datamem.com is where I always buy my RAM from for high-end machines, for example; they've got the Apple Approved stuff.
Thanks for confirming that... because that's what all my research has led me to: the mac pro takes "server" ram!

Now... "dual rank" does NOT mean "dual Channel" does it, because my Mac is first generation and does NOT take dual CHANNEL. and...

the buffered/unbuffered thing...some research suggests that this means the same as registered unregistered, other not - but is this critical? I now know that my memory is fully buffered = fb-dimm, but I would like to buy cheaper memory that is "registered ecc" but not specifically listed as "fully buffered". Is that ok?
Old 06-06-2010, 09:20 PM
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Sorry, wasn't paying attention. Unfortunately, yes, you need the "Fully Buffered" stuff -- Apple plays the timings very, very tight on the Mac Pros. You also get a performance boost on the pre-Nehalem Pros if you put in the memory in units of four chips at a time: so if you're going to buy 4GB, say, get 4 one gig chips rather than 1 four-gig chip (unless you're plannning to further expand it later, in which case having the extra slots might be worth more to you than the slight speed increase. But one of the other benefits of the server motherboard is lots of memory slots (8 of them, on two independent slide-out risers: it'll be the easiest upgrade you've ever done except for maybe putting a hard drive in the same machine).
Old 04-04-2013, 11:28 AM
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Quote:
Originally Posted by Terry Kennedy View Post
I can't say for sure without seeing the actual items, but once a particular type of server memory is no longer in demand, the price drops so the sellers can move them and not get stuck with something completely worthless later on*. If the part can be used somewhere else where there is still demand, the price won't drop as much.

* Note: prices for memory and most computer components get rather strange after they're discontinued. When a part is newly released, the price starts high and then drops (possibly after a brief spike if the part is in high demand with low availability). The price continues to drop slowly until the part is discontinued, at which point the drop accelerates. Some time after the part has been discontinued, the price will jump back up, possibly above the price when it was new. This is because there are vendors that specialize in selling obsolete parts to customers who need them to fix their something-or-other, which can only use this obsolete part. Of course, if you try to sell a part to the vendor, they'll tell you it is worthless and they can't offer you very much for it. But if you called them and wanted to buy the part, it is "rare", "hard-to-obtain", and "very expensive". If you find yourself in that situation, it is a good idea to find out the price they'd pay you for one first, and start bargaining up from there.
Very well put. There's money to be made selling old ram on eBay, albeit for a limited time!
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