iMac memory

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Level 1

8 points

iMac memory

I have a iMac (Retina 5K, 27-inch, Late 2015) with 8GB memory and wanted more memory. Apple says I can upgrade to 32GB with DDR3 PC3-14900. I bought and installed Four 8GB DDR3 PC3-14900 and started experience random resets, sometimes as often as 5 minutes apart. Ran the bootup "D" test and everything checked out. I put the original 8GB back in and everything ran fine for days. So I contacted the memory vendor and he asked if the original memory was DDR3 PC3L-14900. Why would Apple put laptop memory in an iMac - even when Apple information clearly states that this iMac comes with DDR3 PC3-14900. But I humored the vendor and took a look. Well - SURPRISE - the original memory is DDR3 PC3L-14900 "LAPTOP MEMORY".

So my questions are 1) why is laptop memory in an iMac and 2) why does none of the Apple information say anything about DDR3 PC3L-14900 memory, and 3) is the latest iMac a desktop with

iMac with Retina 5K display, macOS Sierra (10.12.1), 8GB DDR3 PC3L-4900 (laptop memory)

Posted on Nov 22, 2016 8:46 AM

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Answer 1

Nov 22, 2016 9:05 AM in response to W. Wolf

The L in PC3L does not stand for Laptop. It stands for Low Voltage. i.e that type of RAM uses less power than the normal PC3.

1. Apple uses SoDIMM or Small outline Dual In-Line Memory module which are usually found in laptops due to space considerations on all its computers. Desktop and laptop alike. Functionally there is no difference between a laptop sized module and a desktop sized one. They work the same, but the smaller ones put out less heat which helps in iMacs since there are no cooling fans, and heat dissipation is done through the aluminum casing in the case of newer iMacs.

2. Why would it mention anything about it? Apple uses the same ram modules for all its computers, laptop and desktop. There's no reason to to point out a factor that has no bearing on functionality or compatibility with other ram modules.

3. Your question got cut off apparently.

With that said, what vendor did you buy this RAM from? What brand of RAM is it? Macs are picky about RAM. Suggested brands are OWC and Crucial for best compatibility.

The difference between Low power and regular RAM modules should not cause your Mac to reset. That's more due to the RAM modules not being designed specifically for Macs.

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Answer 2

KiltedTim

Level 10

232,378 points

Nov 22, 2016 6:07 PM in response to W. Wolf

There really isn't any difference between "laptop memory" and "desktop memory" except in people's minds. "Laptop memory" tends to be a more space efficient package.

That said, Macs are notoriously picky about RAM. Most RAM you can buy just won't measure up in a Mac, regardless of what the specs on the box say.

Buy from Crucial or Other World Computer. They are both known to sell high quality RAM that works in Macs.

It's not as cheap, but as you've found, going cheap isn't always the best idea.

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Answer 3

W. Wolf Author

Level 1

8 points

Nov 22, 2016 6:18 PM in response to Phil0124

Yes, I know the L isn't for laptop, however it is for low voltage. 1.35v to be specific, without the L indicates a 1.5v memory card. The lower voltage reduces the memory's prime power need (long lasting battery) and lower thermal dissipation (runs cooler) - both design drivers in laptops. However, running 1.5v memories instead of a 1.35v probably results in an increase in the bit error rate (BER) especially when lots of the memories are being used - and she he OEM memories are non ECC. I don't know how much margin Apple built into the 1.35v power supply, but if it wasn't enough to handle 1.5v then thats probably why they ship 'L' memories. I'd bet the Apple reliability engineers made that call and didn't let the manual writers know because the Apple manual clearly does not call out the requirement for low voltage memory.

if Apple is notoriously picky on RAM, then the manual needs to be more specific wouldn't you agree?

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Answer 4

Nov 23, 2016 7:16 AM in response to W. Wolf

They are picky about quality of the RAM. The voltage requirement is not a factor that needs to be considered.

There is no limitation in the power supplied to the RAM slots. If the RAM requires 1.5v that's what it will get.

There's nothing more Apple needs to specify about the RAM.

Places like OWC and Crucial test the RAM and can guarantee the RAM they sell you will work with the Mac.

With other vendors its a gamble even when the specs match.

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