Best RAM Setup for iMac

[AppleDev879]

I have a Late 2009 iMac (4 RAM slots, 2 with 2GB each). I'd like to upgrade to 8 GB. Is it ok to just put one 4 GB module in one of the two remaining slots, leaving the last slot empty? I've heard this reduces performance slightly, but I'd like the last slot open in case I want to install more memory later. Would this really reduce the performance of the memory?

I've been looking at purchasing the memory from Crucial (see below):
http://www.crucial.com/store/mpartspecs.aspx?mtbpoid=E16129C3A5CA7304

Any help greatly appreciated. Thanks.

 

[GGJstudios]

You'll get somewhat better performance by using matched pairs of RAM, but it's not critical.

MR Guide to Matched RAM on Intel Macs

 

[alust2013]

That would work fine. The performance hit is so incredibly small that it is unnoticeable, and more memory would be better than faster anyhow. Given that it's so cheap, you could easily go for 12GB by getting 2x4GB to add if you like.

 

[iSayuSay]

I'd go with 2x4GB to fill up iMac RAM slot. I know what your plan is. You want to leave an empty slot to upgrade further when higher capacity RAM (i.e 8GB) comes in one piece, right?

Well that future is not really nearby. Maybe you have to wait a year from now before 8GB chips become cheap and common. And by the time that come, you already have money to buy another 2x8GB RAM, or even replace your iMac.

So... why not enjoying full capacity of RAM now? And upgrades the whole RAM later?

 

[JonasDK]

I'd go with 2x4GB to fill up iMac RAM slot.

So... why not enjoying full capacity of RAM now? And upgrades the whole RAM later?

+1. RAM is so cheap anyway, there is really no reason not to just fill up those RAM slots.