How critical are "dual channel kits" for dual channel?

[Coup27]

A customer of mine has two laptops both with 2 memory slots both with 1 populated with a single 4GB DIMM. He wants me to upgrade both to 8GB. The options I have are:

1. Buy 2x 2x4GB dual channel kit. This is the most expensive option but will guarantee stability.

2. Buy 1x 2x4GB dual channel kit. Put this into one of the laptops and use the DIMM I just removed and place it into the other laptop.

Both laptops are exactly the same model, a Fujitsu Lifebook E781 and were ordered at the same time and from the same place so there is a 99.99% chance the DIMMs that came in them are the same.

These are business laptops so I cannot risk instability, but I think I'll be OK with option 2?

 

[Compman55]

Nobody can answer this for you. You will need to try option 2 and run memory tests. A system configuration of (x) hardware may work 100% rock solid that way, whereas a configuration of (y) hardware may have some minor errors.

Most cases, yes, but as you say it needs to be reliable.

 

[Charlie98]

Without opening the cases, maybe have him run CPUz and see if the two modules are the same, first. If they are, I would do option 2, if not, option 1 (stability being paramount.)

 

[BonzaiDuck]

I've mixed two dual-channel kits of the same make but differing specs together in another system precisely because they had the same spec latency settings at an identical speed -- never had a problem with that: a pair of G.SKILL DDR2-1000's and a pair of G.SKILL DDR2-900 "PI" sticks.

Somehow there is always mild encouragement suggesting that dual-channel kits are somehow "matched," but I just can't believe there would be a problem if you bought single sticks separately if they were the same model and spec.

 

[VirtualLarry]

Is it your money? Go for stability.



(Then send the spare 4GB SO-DIMMs to me, I could use them for "projects".)

 

[mikeymikec]

You're risking instability by changing the memory modules in the laptops full stop. Nothing you can buy will guarantee anything. For all you know, one of the existing modules could have a slight fault, or one of the new modules could.

While it's not a guarantee of memory-okness, I just run memtest86+ for a single pass after an upgrade.

I've mixed and matched modules and got dual channel problem free plenty of times. I can't remember the last time I had problems with it (out of probably 200 memory upgrades, maybe more). I *think* the last time I had a problem with getting dual channel was back in the days of DDR1, when some boards fussed over whether the modules were single or double sided.

I'd personally go for the cheaper option with a decent brand of memory (I go for Kingston or Crucial, I can't remember the last time I had a compatibility issue with either, and you can use their compatibility checking systems as well). Or go for the more expensive option with the idea of keeping a memory module spare for future use.

 

[ashetos]

I've done this dozens of times on laptops and desktops. My experience with DDR2 and DDR3 is that it always works whatever the memory modules are. I've never had any problem with mismatched modules.

 

[flatty]

I've done this dozens of times on laptops and desktops. My experience with DDR2 and DDR3 is that it always works whatever the memory modules are. I've never had any problem with mismatched modules.

In DDR2 case yes, in DDR3 cases, many times appear conflicts even between apropiate sticks (but not identical, sometimes even between assumed identical). Just think why quqd channel sets are sold 4x..., not for the price (almost identical with twice sets 2 channel) but for the deep same "behavior" of the sticks

 

[BonzaiDuck]

In DDR2 case yes, in DDR3 cases, many times appear conflicts even between apropiate sticks (but not identical, sometimes even between assumed identical). Just think why quqd channel sets are sold 4x..., not for the price (almost identical with twice sets 2 channel) but for the deep same "behavior" of the sticks

Even if the modules still match, if you have two sets, same color, same heatspreader, same speed and voltage spec -- and same model name -- I've found different JEDEC specs in the different pairs. Just makes you wonder. But in that case, I was able to overclock them as if they were a 4x kit. For those two kits, though, I'm hoping to use them in a quad-channel configuration next year after they release the "E" processor. Probably should save up some extra ducats to buy a complete 4x kit, just in case there are problems with these.

 

[Coup27]

Thanks for the replies. I've decided to give option 1 a try. It'll be a while until the second laptop comes my way for me to put the two original sticks in but I'll give it a pass with Memtest first before I send it out. I'll update this thread later on whether it was successful or not.