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What would you do?

  • Keep the 16GB of 5300 and throw another 16GB of 5300 on top of it.

    Votes: 2 33.3%
  • Keep the 16GB of 5300 and throw another 16GB of 6400 on top of it.

    Votes: 1 16.7%
  • Ditch the 5300 and get 32GB of 6400.

    Votes: 3 50.0%
  • Are you mad? Apple says use 6400! Get that 5300 out immediately!

    Votes: 0 0.0%

  • Total voters
  • Poll closed .

h4lp m3

macrumors 6502
Original poster
Jun 29, 2011
New Orleans
My 1st gen dual core (MacPro1,1) with 16GB (4x4gb) has served me well for the last 5 years but it's now time to retire it. I just bought a used quad-core (MacPro3,1) for a really great price but the previous owner kept all of his RAM, so I installed the 16GB kit from my old Mac Pro.

I didn't realize that Apple specifications call for PC2-6400f in the MacPro3,1 and I've been running it with 5300 for the last 3 days without any problems.
Is this bad? Am I bottle-necking my machine?

I want to max it out with 32GB, but my dilemma is dollars. I would prefer to keep my existing RAM and just buy the other 16GB but not if it's going to slow the computer down.
Last edited:


macrumors regular
Sep 6, 2011
Thanks, but I still have one unanswered question: Can I mix the ram? Would it be better to have 16GB 5300/16GB 6400 or 16GB 5300/16GB 5300?

If you can avoid mixing ram you should. Very old school equipment had to have all memory matching or it wouldn't run at all. Newer equipment often handles it well. Sometimes you get into a non tested bug area if you don't have all the same memory.

You should match up with the specs for your machine. If you cannot find the exact specks for your machine, try Crucial's memory tool in their store. In a few clicks you get what should work on the first try.

Slow memory will make your machine slower. If it turns on it should handle it ok. Just slower. You'll notice it when you do tasks that utilize the memory excessively.


macrumors 6502a
Jun 13, 2004
Read on this forum or with a web search:
1. Will all 8 banks of memory be treated as the slower 5300 if you mix with the 6400?
2. Will having 32GB of 5300 compensate for any speed loss?
3. The price of FB6400 is expensive!
4. With 16GB of 5300 you are half way there!:)
5. Will the 16GB of 5300 go to waste if you decide to go 32GB of 6400?
6. The price alone of 32GB 6400 will give you the answer!:eek:
Last edited:


macrumors 6502
Apr 28, 2003
You ...

... are not doing high end critical database managment, so there really is no point in securing the fastest RAM speed possible.

The RAM speed is measurable in benchmarks, of course, but it it has no measurable impact for 99.9% of your work tasks.

My advice: keep your 16GB and add the other 16GB when you feel comfortable money wise.
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