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Although it is implied that all the content in memory is written to the hard drive under forced hibernation (using pmset), I'm still unsure whether it is safe to upgrade my macbook's memory during that state or not. I don't want to shut it off completely as it's too much of a bother to re-open all the programs I'm working with ; has anyone tried this before ?

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Upgrading as in: increasing the RAM size? – Arjan Feb 21 '11 at 19:51
I would recommend against doing any kind of non hot-pluggable hardware changes while the OS is hibernated or the computer is on. – trip0d199 Feb 21 '11 at 19:52
Really? Is it more of a bother to have a broken computer? As infrequently as you upgrade RAM, why not take the time to turn the thing off? I mean seriously, if I were doing this, I'd be careful about static electricity. No way would I have actual electricity running through my $1,000 machine. – Nathan Long Feb 21 '11 at 20:19
@trip0d199: excellent advice for second part (while computer is on). Even changing hot-pluggable hardware to hibernated computer is problematic for OS, but not for hardware in any way. – Olli Feb 21 '11 at 21:23
Why are people upvoting @trip0d199 and @Nathan Long? They don't seem to know what hibernation is. Hibernation, at least on Macs, is when your memory contents are completely written out to disk and your computer is COMPLETELY off. The only difference between a hibernation and a normal shutdown is the contents of the disk (and perhaps a few bits in NVRAM). – Spiff Feb 22 '11 at 6:16

I wouldn't try plugging new RAM while the machine is on or hibernated (or replacing one)... Anyways, even if it works and the machine doesn't freeze or have some electrical problem, you'll probably have to reboot to be able to use the new RAM.

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That cannot work. It will crash for sure.

And if by any divine intervention it would, the machine would probably not be able to see the extra RAM until you would reboot.

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Can't say for certain but I once added some more RAM to a hibernated laptop running Windows XP and the machine freaked out big time when it started up!

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Changing hard disk to another one or to SSD during hibernate freaks Mac OS X and Windows 7 completely (fail and automatic reboot). Mac OS X can't handle changing memory. It as well as other operating systems rely on memory layout, which changes then.

If you hibernate your computer, it's not hot-plugging. Static electricity is your only problem.

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