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Model A1311 / Mid 2011 / 2.5 & 2.7 GHz Core i5 or 2.8 GHz Core i7 Processor

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Upgrading 2011 iMac RAM. PC3-10600 vs. PC3-10666--are they the same?

I have a mid-2011 21.5" iMac with the 2.8GHz Quad-Core i7.

All sources say that my iMac is compatible with DDR3 1333MHz PC3-10600. I've been shopping around for a 16GB set of 4x4GB and I'm seeing very few PC3-10600 1333 DDR3 units around.

I do see a lot of PC3-10666 units, though. I've read some sources that say that there's no real difference between PC3-10600 and PC3-10666.

Is PC3-10666 compatible with my iMac?

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I have a mid-2011 27" iMac with the 3.1GHz Quad-Core i5. With 8 GB 1333 MHz DDR3 and would like to upgrade, please can someone tell how much more I can upgrade to?


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two of those would do you just fine!

and they are from an american company as well, so win win.

no need to try the other kind of ram, but i would assume it is not compatible.

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The "official" name for DDR memory is based on its bandwidth rather than clock speed. The easy method to convert data rate to bandwidth is to multiply by eight. Thus, DDR-400 is called PC-3200; DDR2-800 is called PC2-6400 and DDR3-1600 is called PC2-12800.

The math behind this conversion factor is simple: PC memory modules based on SDRAM technology use a 64-bit connection; there are eight bits in a byte and 64 bits equal eight bytes. For example, DDR2-800 transfers 800 megabits per pathway per second; its 64 pathways provide one eight-byte transfer per cycle and 800 times eight is 6400.

The problem comes with "rounding" and was first noticed with DDR-266 (PC-2100). The data rate of 266 MHz is actually 266.6 (continuously repeating decimal) megahertz, so the true transfer rate was 2133 MHz.

Today's DDR3-1333 has a peak bandwidth of 10666 MHz, which can be improperly rounded down and called PC3-10600, rounded up to be called PC3-10700 or stated without rounding as PC3-10666 depending on the manufacturer's desires.

Buyers will find that searching some venders for multiple DDR3-1333 brands will require them to check all three "ratings" to view modules of the same actual speed, but most brands label their DDR3-1333 products as either PC3-10600 or PC3-10666.

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A friend of mine was using an old iMac mid 2011 and she stated it was constantly overheating and freezing or shutting down. I offered to look at it but she had it in her mind the fight was a lost cause and surrendered.

So, earlier this year she went to the Apple store in her son’s town and ordered a newer refurbished model. Just a few months ago she asked me where she could recycle the 2011. I said, “Well drop it off at my house!” She asked why, what would I do with it and so on. I said, “I will play with it until it dies!” I have always been a Windows user at home and had experience on the very first models so this would be a good learning experience for me.

Well, a few months ago she brought it to me and I cleaned it up and it’s been running great ever since!

The only thing I don’t like is that I wish it was the 27” model and it only had 2 sticks of the 2GB x 10600 1333 DDR3 RAM. Not much for multi-tasking and such but it’s not been giving me much trouble at all.

Tonight I was cleaning out a shoebox of odds and ends and was completely blown away to see I had some packaged 4 sticks of 4GB 10666 1333 DDR3 RAM CL-9.

I double checked the installed RAM to realize it was only 10600. But I decided I was going to give this a try anyway.

I pulled out the 2 - 2GB sticks and put all 4 of the 10666 in here, plugged everything back in and started it up. I was cringing and sort of looking out of 1 eye. LOL It started right up, I went to the system info section and they are all correctly posted and showing status: OK

I only came searching to see what people say about doing this and instead of finding answers, I am only finding a lot of questions from people…I signed up on this site just to reply to this, even though it is about 10 years old.

So YES, the cheaper 10666 is working just as well as the 10600.

P.S. This mid 2011 is a real champ for 2021!!!

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Enriko Menzies sera éternellement reconnaissant.
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