800MHz RAM (PC2-6400) on Early 2008 MacBook

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Level 1

65 points

800MHz RAM (PC2-6400) on Early 2008 MacBook

Is it possible?

I'm just curious since my processor's FSB is 800MHz. I attempted to do so with some non-Apple approved RAM & it failed for either (A) not being Apple RAM or (B) it not taking 800MHz.

Just curious if anyone knows. Thanks!

4th-Gen MacBook, Custom built PC, Mac OS X (10.5.6), 2.4GHz C2D, 4GB-RAM, 320GB 7200RPM HDD, 19-inch LCD, Microsoft 5000 Bluetooth Mouse, Apple Pro keybo

Posted on Mar 29, 2009 3:31 PM

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Answer 1

Kappy

Level 10

362,007 points

Mar 29, 2009 3:44 PM in response to CIA Jones

That model requires PC2-5300 DDR2 667 MHz RAM. Even if the 800 MHz RAM worked it wouldn't operate any faster than the 667 MHz RAM.

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Answer 2

CIA Jones Author

Level 1

65 points

Mar 29, 2009 9:26 PM in response to Kappy

Well that was my primary concern. If it would work and if so would it allow for the faster speed.

Thanks again!

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Answer 3

y_p_w

Level 6

17,762 points

Mar 30, 2009 9:11 AM in response to CIA Jones

Red Drako wrote:
Well that was my primary concern. If it would work and if so would it allow for the faster speed.

It's complicated.

It seems that you can get it to work with one caveat. It just has to be mixed with at least one memory module of a supported speed - PC2-5300 (so-called "PC2-5400" probably works) or PC2-4200 for your machine. This seems to be some strange quirk to Intel's memory controller and/or the firmware settings that Apple is using.

I thought that most memories were programmed with secondary settings (SPD EEPROM has this info), but apparently the Intel chipset MacBooks don't use them. However - the chipsets are designed to use memories of mixed speeds in the two slots, and then defaults to the slower speed of the two. That's the only workaround that has been reported to work.

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Answer 4

CIA Jones Author

Level 1

65 points

Mar 30, 2009 9:21 AM in response to y_p_w

Yea, it would just down-clock to the 667MHz speed. It'd be pointless then.

I guess I'm just a little obsessive about getting my hardware to move as fast as I possibly can. Upgraded my MacBook to 7200RPM drive & put in 4GB RAM. Hehe, I guess that's just my PC tweek-aholic side.

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Answer 5

y_p_w

Level 6

17,762 points

Mar 30, 2009 12:14 PM in response to CIA Jones

Red Drako wrote:
Yea, it would just down-clock to the 667MHz speed. It'd be pointless then.

However - that's what it's supposed to do. DDR2 memory can function at a wide range of clock speeds and the programming of CAS latencies, etc is pretty standard and based on the number of clocks. The SPD information is supposed to indicate where the optimum performance would be, as well as recommended secondary settings at a slower bus speed.

Most of the experiences relayed here are of people who bought PC2-6400/DDR2 800 because they thought it should be backwards compatible and/or found it was available at a better price at one retailer or another.

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Answer 6

y_p_w

Level 6

17,762 points

Mar 30, 2009 12:20 PM in response to CIA Jones

Red Drako wrote:
Is it possible?

I'm just curious since my processor's FSB is 800MHz. I attempted to do so with some non-Apple approved RAM & it failed for either (A) not being Apple RAM or (B) it not taking 800MHz.

Front side bus? The front side bus is at 800 MHz, but the memory bus is actually at a max 333 MHz. DDR2 667 really only refers to the data being transmitted on both edges of a 333 MHz clock.

In any case, memory bus clocks don't have to be matched to FSB frequency any more. It used to be that they had to operate at the same speed or a multiple in order to properly synchronize, but it's more advanced than that now. You could run PC2-4200 (DDR2 533) where it's nowhere near being a multiple of 800 MHz. Modern systems handle non-multiple ratios pretty well.

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Answer 7

CIA Jones Author

Level 1

65 points

Mar 30, 2009 1:08 PM in response to y_p_w

y pw,

I'm aware that DDR2 will adjust speeds, and that they don't have to be the same multiples to function; that's not my concern. And I suppose it's my fault for not stating it more clearly.

I was curious if 800MHz RAM would actually run at 800MHz being that this MacBook's processor's FSB is 800MHz. Now if the motherboard/logic board doesn't support 800MHz then it obviously won't. It was more of a question of if this model MacBook would support that.

The advice & input I have received here is stating that, even if 800MHz RAM would function, it would only function at 667MHz speeds; which is all I wanted to know. It's not a question of how DDR2 RAM functions, just a matter if this model will allow for faster RAM to work at the faster speed. Based upon the general input here, this answer is "no."

Thank you again everyone, I appreciate your assistance to my question!

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