RAM: difference between SEC and BBC?

I am buyign some memory for my proliant server. I didn't want to buy it from hp as it's too expensive. I pulled out my existing memory and found it's actually made by samsung. and the model is M393B5673FH0-CH9Q5

I found 2 websites that are offering the model, but one is SEC and the other is BBC, whats' the difference? both of them have same M393B5673FH0-CH9Q5, btu the price is big difference.


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andyalderSaggar maker's framemakerCommented:
SEC stands for Samsung Electronics Corporation, it's not a memory spec.
No idea what BBC stands for except British Broadcasting Corporation.

It doesn't make much sense to be buying 2GB sticks these days anyway, exactly what model/generation ProLiant do you have, and what RAM is currently installed (including whether UDIMM or RDIMM, which CPU(s) and how many? What is new target amount of RAM?

From that I can give you a better spec of RAM to buy, quite likely 8GB 2rank x4 as they're well priced. Then you can get Kingston or any other equivalent from the HP part numbers.

Oh, and don't bother about the HP DDR3 memory configurator, it's OK for what it does but isn't as flexible as the CPUs/servers are so doesn't offer the best configs.
andyalderSaggar maker's framemakerCommented:
okamonAuthor Commented:
I have a proliant ml350 g6 with 1 cpu, 4 gb of memory (2gb x 2). I just want to have 8gb in total as it's for my lab. I did run the HP memory configurator and it suggest me to go for 2 gb each for best performance... is not true? or I get same performance if I put a one 4gb on top of my 2x2gb?

Will I run into any issue if I mix with Kingston memory?
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andyalderSaggar maker's framemakerCommented:
1 * 4GB is fine, you'd have 2GB on 2 channels and 4GB on one of them whether you added 2*2GB or 1*4GB. Best performance is got by having same amount on each channel, that would be 12GB, 2 new 4GB ones plus the current two shuffled to be on the same channel.

Models with 2 * 2GB are quite likely to have UDIMMs rather than RDIMMs and you really have to confirm that since you can't mix. If you boot SmartStart, maintenance, insight diagnostics you can get a report of exact part number.

No issues mixing makes, they're all covered by a JEDEC standard. They do have to have temperature sensors in them though (which ECC RAM does have) or the fans will go on full speed.
ECC (which is what you typically install in servers) is Error Correcting Code memory http://en.wikipedia.org/wiki/ECC_memory.  It handles parity errors which can be caused by random events and fixes them.

The other RAM you were looking at was RDRAM, a product of RAMBUS and not very favored these days - it is not compatible with any other kind of RAM.

As a general rule, you want to use memory in pairs, and they should be the same spec, in order to take advantage of dual channel operation which will double the bandwidth.  Mixing memory in servers is not the best approach, because you have the risk of some incompatibility.
okamonAuthor Commented:
andyalder, I agree with Callandor that I should use memory in pair.
"4GB is fine, you'd have 2GB on 2 channels and 4GB on one of them.." if I do this then I cannot double the bandwidth
andyalderSaggar maker's framemakerCommented:
Not pairs on this one Callandor, it's Xeon 5500 series with 3 memory channels per CPU. The channels work independantly so you get 3*throughput of a single channel for the lower addresses however it's mixed and only loose interleaving on the but of RAM that sticks above the rest, e.g. 2*2GB + 4GB first 6GB is  3way interleaved and the last 2GB is non-interleaved. Older CPUs liked pairs, and the E5s in the very latest Intel 2P servers like quads although they'll put up with just about any mix and still perform well.
okamonAuthor Commented:
actually my cpu is XEON E5620 2.4GHZ. Same case?
The E5620 is triple channel, but I've never heard of the split interleaving andyalder is referring to.  Andy, if you can give me a link to do further reading on this, I'd appreciate it.
okamonAuthor Commented:
Callandor, so if I put 4 x 2gb instead of 2x2gb + 1x4gb... will that degrade the performance? I know you have explained something in your previous post but I don't really get it.
andyalderSaggar maker's framemakerCommented:
Section 3.2.2 x3650M2/x3550M2/iDpx 2.0 of http://www.crc.nd.edu/~rich/Nehalem/Nehalem%20Memory%20performance.pdf where it talks about the 8/16 slot IBM server; that has two channels that take 3 Dimms but channel3 only takes two so you put a double-sized DIMM in the second rank of channel 3 to compensate and it preserves interleaving. Balancing's not as important in real life as the whitepaper makes out though since they're using a benchmark specifically designed to to test memory bandwidth.

There's a good comparison on benchmarks from Fujitsu on Page 14 (19) of http://sp.ts.fujitsu.com/dmsp/Publications/public/wp-westmere-ep-memory-performance-ww-en.pdf - STREAM is knocked down to 39% of what you could get with 3 way interleaving whereas SPECint is only knocked down to 76% of peak performance.

The Fujitsu whitepaper also mentions the mixed size interleaving still working -
"This situation, which is best for interleaving, can also exist with non-uniform DPC values when using different-sized DIMM strips."

With the old classic 2 way interleaving the channels fetched adjacent data blocks so an analog would be to retrieve a 16 bit word with one byte from each DIMM - thus the requirement to have matched DIMMS. With the new interleaving the channels act independantly so they could be reading from completely different address spaces or even from different banks. That's unless you use lock-step mode (Dell call it advanced ECC) where channels 1 and 2 act in old fashoned interleave mode that allows a whole chip to die and ECC keeps it going with x8 chips as well as x4 chips (ftp://ftp.hp.com/pub/c-products/servers/options/Memory-Config-Recommendations-for-Intel-Xeon-5500-Series-Servers-Rev1.pdf). I'm not 100% sure but I think you need matched DIMMS if you want lock-step to protect you against whole chip failure on x8 chips.

5600 is near enough the same as 5500 as far as RAM is concerned although it adds memory sparing on 3 channels with channel 1 and 2 active and 3 as spare. It's pretty rare to use anything other than independant mode since it's the highest performing one.
andyalderSaggar maker's framemakerCommented:
There is a very tiny performance benefit of having 2 * 2GB DIMMS in a single channel over having a 4GB one, that's down to precharge delay. It's so insignificant it's not worth considering in my opinion.

Much appreciated.  In your first reference, I saw "Always populate all 3 memory channels on each processor with equal memory capacity", under 4.0 Best Practices.  Is the reason you're making your recommendation because this server doesn't have triple channel slots?
andyalderSaggar maker's framemakerCommented:
It has 3 channels (9 sockets) per CPU  but it's only going to be a little bit faster with evenly populated RAM than with an unbalanced configuration because there are so many other performance considerations. Breaking "best practices" on the RAM configuration may add a nanosecond or two to some job but you have to compare that with getting something from the pagefile at 10ms.

8GB can't be balanced across the 3 channels evenly anyway and it was sold with just two DIMMs which isn't optimal.  Best practice says to use 3 * 2GB DIMMs for a 32bit / 4GB server and just not using all the RAM you bought, HP still sell the 2 * 2GB model though since price matters more than best practice does most times - it's stable with just about any memory configuration.

okamon is after the cheapest upgrade as far as I see it or they wouldn't be asking about 3rd party RAM in the first place. I'd still buy an 8GB stick rather than a 4GB one though since they'll probably want to upgrade again in a year or so and the 8GB duall ranks have only recently come out as the cheapest option so we're unlikely to see a sudden price drop for about 18 months.

There is a reason for HP's inflated price, they qualify their RAM to run with the BIOS tweak of using full clock speed with two banks populated, default is to slow down a bit  so you're paying for that, they've even started checking to see if it's HP tested RAM during POST before allowing full speed on the G8s.

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andyalderSaggar maker's framemakerCommented:
There is another option, buy a bag of 2GB DIMMs from a broker, We regularly remove the original RAM to put bigger sticks in as HP don't sell ramless servers to th general public, Must be thousands of brand new unused sticks on ebay.
Very good in-depth explanation, Andy.

Well, okamon, you've got your answer from one of the best.
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