memory upgrade

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Q re upgrading new 27" iMac. Ordered with 8Gb ram, I have 2 spare 4gb chips from my old machine, these are DDR3 1333Mz chips, the new machine has 2 x 4Gb DDR3 1600Mz chips, can i put the old chips into the new machine to get 16Gb RAM or do the different memory speeds make the old ones incompatible?

Am I better off running 2 x 4gb 1600Mhz RAM or 16gb of mixed 1333 and 1600Mz?
 
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chscag

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You can not mix memory modules. Don't do it. Just buy the correct modules and insert them in the empty slots and you'll be good to go. The new 27" iMacs are the easiest machines yet for adding memory. I have 4 x 4 GB modules in my 27" iMac for a total of 16 GB. The maximum amount of memory you can use is 32 GB.
 
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If you did as you suggested, the iMac may also be flat! It is a beautiful machine so don't cripple it with slow, old memory.
 
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chas_m

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Even if they fit, it would just likely crash continuously until you put in the correct RAM.
 
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I've since come across a lot more posts on tech forums about mixing different speed DDR3 RAM, and no-one is reporting disastrous results, they are just saying the memory will run at the speed of the slower units. If you get a performance improvement from having 16Gb ram available then I'm interested to see how that would compare with having half the memory running a little bit quicker?
 

chscag

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It's your machine, run whatever memory you want. But as inexpensive as the correct modules are, why not use the type and speed of memory that's recommended by Apple?
 
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I've since come across a lot more posts on tech forums about mixing different speed DDR3 RAM, and no-one is reporting disastrous results, they are just saying the memory will run at the speed of the slower units. If you get a performance improvement from having 16Gb ram available then I'm interested to see how that would compare with having half the memory running a little bit quicker?


You might want to check the date and the Mac models and the OS X version those posts are talking about, and remember that the later Macs and OS X versions are much fussier than they were a few years ago in their RAM tolerence. But your choice…
 

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