G4 processor question

[leftbanke7]

I jumped onto the Freescale website because I was curious about what the differences were between the different versions of the G4 chip. Anyway, I got to looking and Freescale has its MPC7447A chip listed as its fastest in the line at a top speed of 1.42. A couple of questions then popped into my mind:

1. So everything Mac has that is over 1.42 and isn't a G5 is just an "overclock" or is Freescale's webpage woefully outdated? Some of the online stores have the 7447A listed as a 1.6 or 1.7 which is then overclocked.
2. I understand that the processors from the same die will act differently. Some can go faster, some are big ol' POS's. That makes sense. But due to my lack of knowledge on the subject, I'd like to know is this just some random thing that nobody can predict (ie. one batch will have a 12% rate of chips that can run stable at a higher than designed speed, another batch will have 73%) or are there tolerances that are added during the design phase that make this a much less random event?
3. Assuming that the top "natural" speed of the 7447A is indeed 1.42 as listed, how long could, for example, the PowerLogix 2.0Ghz G4 upgrade be expected to last before it gives up the ghost? You would think that a 33+% overclock would cause it to be highly unstable.

OK, I await for your wisdom, oh mighty gurus on this site. Please educate me.

 

[Lord Blackadder]

I won't even pretend to be a Freescale semiconductor encyclopedia, but I am pretty sure that Apple's 1.5 and 1.67 PowerBooks use a G4 that is rated at those speeds - not an overclock, which would be a bad idea for a laptop. However Apple currently uses the 7447B, not the 7447A. Not sure of the difference, power consumption maybe?

I checked at Other World Computing's website, and it seems that Powerlogix uses 7447A's in their top-line products. The 2.0GHz upgrade uses a 1.7GHz rated CPU, while the 1.8GHz upgrade uses a 1.6GHz rated CPU. So the 7447A does indeed appear to scale past 1.42GHz.

Sonnet used to sell a 1.7 GHz upgrade based on the 1.42GHz 7447A - I don't know if they still use that chip or if they switched to a faster one.

Bottom line is that just about every G4 upgrade available uses an overclocked chip.

 

[patrick0brien]

1. So everything Mac has that is over 1.42 and isn't a G5 is just an "overclock" or is Freescale's webpage woefully outdated?

-leftbanke7

I'll say it before someon else jumps on it, but please know that the G5 is nothing to do with the G4. It isn't even made by the same company.

The G5's architecture is basically PPC in instruction set only. The actual design is completely different. 64-bit at the least.

 

[simie]

Designed as pin-compatible replacements for Freescale's MPC7447 products, these new processors have been shown to reach speeds of 1.5 GHz. MPC7447A processors benefit from Freescale's silicon-on-insulator (SOI) process technology, engineered to help deliver significant power savings without sacrificing speed. Low-power versions of the MPC7447A are available.

extract from here

 

[leftbanke7]

-leftbanke7

I'll say it before someon else jumps on it, but please know that the G5 is nothing to do with the G4. It isn't even made by the same company.

The G5's architecture is basically PPC in instruction set only. The actual design is completely different. 64-bit at the least.

Yes, of course. I just added "and isn't a G5" to refer that I was only talking about Freescale chips. There is no question in my mind about the differences btw G4s and G5s. I supposed I should have used "Freescale" and "IBM" as opposed to "G4" and "G5" in that sentence.

 

[Mord]

freescale sells g4's rated up to 1.67GHz it's just they sell all of them to apple, every last one, it was the same situation with the 7455, apple bought every one above 1GHz, they cant advertise what is not available.

 

[simie]

After searching further on Freescale's website, I can't find any reference to a processor called MPC7447b, but what there is, is the MPC7448, which is a pin for pin compatible processor with the MPC7447A and MPC7445 and MPC7441

The MPC7448 operates up to 1.7Ghz, I think that Apple may be using this.

for further info read this

 

[IJ Reilly]

freescale sells g4's rated up to 1.67GHz it's just they sell all of them to apple, every last one, it was the same situation with the 7455, apple bought every one above 1GHz, they cant advertise what is not available.

Maybe key word here is "rated?" I just installed a Sonnet 1.7 7447A G4 in my Cube. They're currently also selling one at 1.8. Overclocked? I don't know, but it's working fine so far for me and everybody else who's bought them. Perhaps the difference in the rated speeds between the ones Apple and the third-parties sell is a function of the bus speed multiple constraints.

Other variants in current/recent production are the 7455 and the 7557, both with level 3 backsided cache, which the 7447 lacks. But they're having trouble pushing them beyond 1.3 Ghz, if the available products are any indication. Still, a 1.3 7457 will perform nearly the same as a 1.7 7447, according to the people who test such things.

 

[simie]

http://www.appleinsider.com/article.php?id=1229

According to Appleinsider the next Powerbook upgrade will use the MPC7448 Processor. So either the Powerbooks are using an updated version of the MPC7447a and Freescale have not updated the documents on their website or the processors are overclocked.

 

[Mord]

that 1.7GHz sonnet is a 1.42GHz rated moto chip.

the current powerbooks and the mac mini currently use the 7447b, i hate it when people look at white papers and think their is some kind of conspiracy going on, could it be that the papers are out of date, or motorola does not provide data on some chips they sell to apple seeing as apple is the sole customer?

the 7448 has a 1MB l2 cache if apple used it we would know, also apple does not overlcock their cpu's unless it's a small increase because of bus ratio's (1.42GHz g4's are marked out as 1.4Ghz chips), only third party upgrade companies overclock the chips as they are for tower upgrades and can have the cooling required, motorola rates the cpu's for use in 1u routers and embedded devices so when used in a tower with a normal sized cooler they can clock quite high, what matters is what speed it is warranted for, the 1.7 sonnet is warranted to 1.4GHz by motorola and 1.7GHz by sonnet due to their own testing.

people get their knickers in a twist too much over this topic and it has been beat to death too many times.

 

[zen.state]

the mac mini also uses the 7447.

 

[IJ Reilly]

people get their knickers in a twist too much over this topic and it has been beat to death too many times.

I find it difficult to beat anything much beyond unconsciousness with my knickers twisted.

But that's just me.

 

[simie]

Here is the MC7447b cpu, but no reference anywhere on Freescale's website that we can access at least and no mention of it in here. This cpu is used in the Mac mini, Hector is correct. So is it custom version of the MPC7447A CPU?