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Apple Notebooks Apple's notebook computers including MacBook Pro, MacBook, MacBook Air, PowerBook, and iBook.

Has the new PowerBook increased memory speed?


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AlexN
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The new PowerBook uses DDR2 memory running at 333MHz. I'm wondering what was the speed in the previous generation? I know for a fact that the iBook runs at 266MHz, not sure about the PowerBook.
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ldjalal

 
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Quote:
Originally Posted by AlexN
The new PowerBook uses DDR2 memory running at 333MHz. I'm wondering what was the speed in the previous generation? I know for a fact that the iBook runs at 266MHz, not sure about the PowerBook.
I dont know if this is 100% right, but from what i've heard, the new DDR2 ram is only used to lower the power consumption, and therefore to increase the battery's life. Because of the G4's front bus, the DDR2 wont be used to its advantages and therefore will not increase performance. As I said, im not sure about this, but thats what i've read...
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Avalon

 
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Quote:
Originally Posted by ldjalal
I dont know if this is 100% right, but from what i've heard, the new DDR2 ram is only used to lower the power consumption, and therefore to increase the battery's life. Because of the G4's front bus, the DDR2 wont be used to its advantages and therefore will not increase performance. As I said, im not sure about this, but thats what i've read...
This is correct, and also that DDR2 RAM will become cheaper than DDR in the near future, as it's becoming a standard.

The G4 can't even handle a DDR bus, thus the fastest bus speed (and obviously memory transfer speed) is 167MHz SDR. That's why there's no speed benifit between DDR and DDR2, there wasn't even a speed benefit when they moved from SDR to DDR, due to that lack of the G4 CPU to support a DDR bus.
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AlexN
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What about the previous gen PowerBook? Did it run at 333MHz?
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Quote:
Originally Posted by AlexN
What about the previous gen PowerBook? Did it run at 333MHz?
Yes, it did. My 17" PowerBook G4 uses DDR PC2700 SDRAM. It has a speed of 333 MHz.
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The old powerbooks used
DDR PC2700 2.7 GB/sec

The new powerbooks use
DDR2 PC2-4200 4.2GB/sec

Don't forget to use the new User Reputation System
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Quote:
Originally Posted by AlexN
What about the previous gen PowerBook? Did it run at 333MHz?
Because of the G4s limitation, the frontside bus was (and still is) 167MHz SDR (single data rate).
The speed of the frontside bus is what determines the speed of the memory access.
So even with the Double Data Rate memory, it can't acces the memory at the speed of 333MHz, as the CPU can not run in DDR mode.

DDR uses the same clockspeed than SDR (167MHz for PC2700) but due to the DDR technology, it accesses it twice as fast, which is why it's also said to run at 333MHz. And it is twice as fast, presuming that the CPU has a DDR-bus, which the G4 has not.
This is the biggest drawback of the G4 CPU, and shows why it is simply outdated.

The reason why Apple used DDR and now uses DDR2 memory is simply cost (SDR memory gets rare and therefore expensive) and marketing (it always looks better to have the "newest" technology, eventhough there's no technical benefit).
But all this is only true for Macs with G4 CPUs. The G5 CPU handles DDR and DDR2 at their full speed.
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AlexN
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Quote:
Originally Posted by trpnmonkey41
The old powerbooks used
DDR PC2700 2.7 GB/sec

The new powerbooks use
DDR2 PC2-4200 4.2GB/sec
Since they run at the same speed, 333MHz, it really dosen't make sense that the bandwidth is different, does it?
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AlexN
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Quote:
Originally Posted by Avalon
Because of the G4s limitation, the frontside bus was (and still is) 167MHz SDR (single data rate).

So even with the Double Data Rate memory, it can't acces the memory at the speed of 333MHz, as the CPU can not run in DDR mode.
So the front side bus of the 1.67GHz PowerBook is 167MHz?
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Quote:
Originally Posted by AlexN
So the front side bus of the 1.67GHz PowerBook is 167MHz?
Every PowerBook G4 since the 1.25Ghz has 167MHz FSB. Or maybe since the 1GHz, not sure about which one exactly introduced the 167MHz FSB.

By the way, the iBook G4 has an 133MHz FSB (except the new 14" 1.42GHz, which has an odd 142MHz FSB).
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Quote:
Originally Posted by AlexN
Since they run at the same speed, 333MHz, it really dosen't make sense that the bandwidth is different, does it?
I'm not very familiar with the DDR2 specs...
Concerning real clock cycles, both SDR and DDR run at 167MHz. SDR handles one information per cycle, while DDR handles 2 per cycle, which is why it is referred as 333MHz, because it is twice as fast. Though the raw clock speed of the memory is still 167MHz.
It is pretty difficult to exactly explain why that is so, as it requires some good knowledge of digital electronics...maybe through searching on Google you'll find a good explanation, and perhaps also one that tells the difference between DDR and DDR2.
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lil
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Hiya,

I went into this a little here:

Apple holding Press Event October 19th

AFAIK, SDR still wouldn't match the 167MHz bus, as SDR only went to 133MHz, so it does need DDR to reach that FSB speed. Different case on the 133MHz bus iBooks and such like.

But hopefully that above post clarifies the situation.

However it is entirely correct that the CPU would need a 200/266/333/400/533 etc. FSB to take the full advantage of DDR.

Vicky
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Quote:
Originally Posted by lil
Hiya,

I went into this a little here:

Apple holding Press Event October 19th

AFAIK, SDR still wouldn't match the 167MHz bus, as SDR only went to 133MHz, so it does need DDR to reach that FSB speed. Different case on the 133MHz bus iBooks and such like.

But hopefully that above post clarifies the situation.

However it is entirely correct that the CPU would need a 200/266/333/400/533 etc. FSB to take the full advantage of DDR.

Vicky
Wow! Had missed that one! Pretty good explanation. Thanks Vicky! :cool:

SDR simply means Single Data Rate, which simple means that with every single clock cycle one infomation is transmitted, unlike DDR, which transmits two information units per clock cycle. DDR 333 (or PC 2700) runs at 167MHz, but data flow is as if it were running at 333MHz, that's why it's always referred to that speed. But it's not the real physical clock speed of DDR.
SDR bus speed exist up to 167MHz, on the Mac as well as in the PC world (which is where most standards come from).
SDR memory on the other hand never went past 133MHz, which is why Apple had to use DDR-memory in the first Macs with a 167MHz bus. Nevertheless, as I already stated, the G4 can't use a DDR bus speed, so there's no speed benefit at all from putting DDR or even DDR2 memory in a G4-based computer.
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