PowerMac DDR Clarification

arn

macrumors god
Original poster
Staff member
Apr 9, 2001
14,509
1,792
Xlr8yourmac.com provides clarification on the hot-topic of DDR in the new PowerMacs:

I'm getting lots of mails on this but as you can clearly see from the Apple PowerMac G4 specs page - they note the system bus bandwidth at 1.3GB/sec - clearly indicating that is *not* a DDR system/CPU (frontside) bus. Just like the Xserve, the new G4s use a single data rate system/cpu bus and a DDR memory bus.
 

Arcady

macrumors 6502
May 24, 2002
402
24
Lexington, KY
167 to each or both?

What I want to know is this: Does the system controller have one CPU bus at 167MHz that is shared by both G4's, or are there two 167MHz busses, each talking to a G4 at 167MHz? If there are two busses for the CPU's, then it would improve things a bit, since both CPU's would have fullspeed access to the memory at their bus speed.

Does the Xserve have two CPU busses, or just one shared bus? Anyone know the answers to these questions? The guesswork stuff isn't helpful.

Thanks :D
 

porovaara

macrumors regular
Mar 7, 2002
132
0
sf
Re: 167 to each or both?

Originally posted by Arcady
Does the Xserve have two CPU busses, or just one shared bus? Anyone know the answers to these questions? The guesswork stuff isn't helpful.

Thanks :D [/B]
Single.
 

tortus

macrumors member
Jan 29, 2002
73
0
Los Angeles
Basically...

Apple threw the DDR onto exisitng motherboards with little changes here and there in an attempt to quell our disatisfaction with the current state of PowerMacs. Sure, the Front Side Bus will be running at 167 mhz, but the CPU is still communicating with the controller at a lower speed than the DDR. All the while, there are PCs out there pushing 500 MHZ FSB. As you can see from the XServe Benchmarks, not much difference between the dual Gigs (sans shiny face plate) and the XServe in terms of performance. By the way, Via is introducing the KT400 chipset that will allow for 200 mhz memory clock speeds. With DDR, we are looking at a 400 mhz memory bus. Apple where are you?

Expect a Badass, new system architecture in spring 2003. Keep the faith brothers and sisters.
 

jadam

macrumors 6502a
Jan 23, 2002
699
1
Re: Basically...

Originally posted by tortus
Apple threw the DDR onto exisitng motherboards with little changes here and there in an attempt to quell our disatisfaction with the current state of PowerMacs. Sure, the Front Side Bus will be running at 167 mhz, but the CPU is still communicating with the controller at a lower speed than the DDR. All the while, there are PCs out there pushing 500 MHZ FSB. As you can see from the XServe Benchmarks, not much difference between the dual Gigs (sans shiny face plate) and the XServe in terms of performance. By the way, Via is introducing the KT400 chipset that will allow for 200 mhz memory clock speeds. With DDR, we are looking at a 400 mhz memory bus. Apple where are you?

Expect a Badass, new system architecture in spring 2003. Keep the faith brothers and sisters.


GRRR but the athlon can only use a 133mhz bus, the KT400 adds nooo benefit AT ALL with current Athlons!!!! look at the Nforce bencmarks, i mean seriously nforce is dual channel hence 128bit and just barely does better than single channel 266mhz motherboards.
 

Mosco

macrumors regular
May 26, 2002
240
22
Apples explanation taken from maccentral:

"What's different in our architecture from the PC architecture -- which has a higher marketing spec number for the bus -- is that they have every single thing on the system competing for that bus," said Greg Joswiak, senior director of hardware product marketing at Apple. "It has to move quickly because it has a lot of traffic and congestion on the bus. We have each part of the system with its own dedicated bus to the system controller. That means these things don't have a latency or congestion as they wait for other data to migrate through the bus."
 

tortus

macrumors member
Jan 29, 2002
73
0
Los Angeles
New Athlons coming with 166mhz, possibly 200mhz

The new Athlons will be sporting a 166 FSB with rumors of 200 fsb not too far off. The point I was trying to make concerned Apple's progress and not the FSB of the AMD systems. Apple comes out with a Memory bus at 333 and other companies are simultaneously 1-upping Apple. The systems are still wonderful and great, but they are a step behind in terms of the latest and the greatest. Hopefully, they take a big leap ahead next year.
 

ImAlwaysRight

macrumors 6502a
The railheaddesign.com explanation (link above) is the best I have seen.

Why do people keep bringing up XServe tests? The XServe uses ATA/66 and a 133MHz FSB. Folks, the new mid- and high-end PowerMacs have ATA/100 and 167MHz FSB, plus have faster DDR at 333MHz. This will be faster than the XServe taken the combination of these three upgrades, not to mention the better video card. Yes, the new dual gig will be faster than the old dual gig, plus it costs $500 less. Overall, it is a good speed improvement (not fantastic, but good).
 

deepkid

macrumors regular
Jul 22, 2002
153
0
chicago
Can you see what's on the chips?

aromac
macrumors newbie


GOT MY NEW POWERMAC!!! DUAL 1GHZ

So far everything running incredibly smooth. I ran my logic audio on it and it runs it effortlessly. Damn thing is a noise monster though. The fan kicked in out of nowhere for a few seconds and scared the **** out of me.


===

Would you mind taking a look inside at your CPU to whether or not if it says which Motorola chips were used? I'm not sure if it would specify 7455 or 7470...but would be cool if this could be cleared up (since you already own a new powermac). Would system profiler give this detail, as well?

Thanks much!
 

firewire2001

macrumors 6502a
Apr 2, 2002
718
0
Hong Kong
Re: Can you see what's on the chips?

Originally posted by deepkid
aromac
macrumors newbie


GOT MY NEW POWERMAC!!! DUAL 1GHZ

So far everything running incredibly smooth. I ran my logic audio on it and it runs it effortlessly. Damn thing is a noise monster though. The fan kicked in out of nowhere for a few seconds and scared the **** out of me.


===

Would you mind taking a look inside at your CPU to whether or not if it says which Motorola chips were used? I'm not sure if it would specify 7455 or 7470...but would be cool if this could be cleared up (since you already own a new powermac). Would system profiler give this detail, as well?

Thanks much!
::sigh:: i remember being a newbie.. sorta..

hey, you prolly meant to use the quote function.. you click on the quote button up above and type what you want, or if yer using ie you type [quote!] [\quote!] (without the "!"'s)..

who the heck posted that quote anyways.. "So far everything running incredibly smooth. I ran my logic audio on it and it runs it effortlessly. Damn thing is a noise monster though. The fan kicked in out of nowhere for a few seconds and scared the **** out of me."?
 

deepkid

macrumors regular
Jul 22, 2002
153
0
chicago
Re: Re: Can you see what's on the chips?

Originally posted by firewire2001


::sigh:: i remember being a newbie.. sorta..

hey, you prolly meant to use the quote function.. you click on the quote button up above and type what you want, or if yer using ie you type [quote!] [\quote!] (without the "!"'s)..

who the heck posted that quote anyways.. "So far everything running incredibly smooth. I ran my logic audio on it and it runs it effortlessly. Damn thing is a noise monster though. The fan kicked in out of nowhere for a few seconds and scared the **** out of me."?

aaaaAAAh!! Well I belong to too many different boards and code too much crap each day! :) Thanks for the tip, however.

Actually I snatched that from the incredibly long Powermac introduction thread..figured it would be easier for Aromac to see his post replied to in this new thread.

Some people were saying that the chips are 7470 (one guy said he friend's father is a higher-up at Mot in TX and verified, etc)..just wanted someone with a machine to take a peek.

Been a pretty interesting discussion, thus far.
 

jadam

macrumors 6502a
Jan 23, 2002
699
1
Originally posted by Sun Baked
This is interesting.

Scroll down to the picture and read the post.

http://arstechnica.infopop.net/OpenTopic/page?a=tpc&s=50009562&f=8300945231&m=5110932035
HRRRMMRMRMRMMMMM

Originally posted by jadam
errrr.... one thing. The low end powermac is a sweet deal.

Now why have DDR if it doesnt increase bandwith to the FSB? well lets see. If you were using an old Powermac and lets say you were using the video card and 2 PCI cards and FireWire and USB and such, now you have to u se some of your bandwith for those proccess dont you? sure you do, and guess what, the 2 processors dont get 1.1gb/sec of bandwith but instead get much less.

now with DDR you have more memory to go around, you have a dedicated 1.3gb/sec for the processors and another 1.3gb/sec for say the hard drives and the AGP video card and the PCI cards and Gigabit Ethernet and FireWire and USB and such.

there are reasons for things :p

anyways, the low end is sweeeeeeeeeeeeeeeeeeeeeeeeeeetttttttt, just wish i could afford it :(


http://forums.macrumors.com/showthread.php?s=&threadid=9405&perpage=25&pagenumber=8


WHAT DID I SAY?????????

no but NO ONE LISTENS TO ME! only when its on Arstechnica do they listen to someone else....... LISTEN TOOOO MEEEE
 

DavidRavenMoon

macrumors regular
May 11, 2002
136
2
Staten Island, NY
Re: Basically...

Originally posted by tortus
Sure, the Front Side Bus will be running at 167 mhz, but the CPU is still communicating with the controller at a lower speed than the DDR. All the while, there are PCs out there pushing 500 MHZ FSB.
This is a common misconception. Actually the RAM is also being clocked at 167 MHz...DDR RAM is not faster than SDR RAM! However DDR offers twice the memory bandwidth SDR RAM does at the same clock speed.

DDR effectively doubles the bandwidth available by sending data on the falling edge of the clock cycle as well as on the rising edge.

What Apple didn't do was to have two busses, one for each CPU. One explanation I have heard is the G4's need to be on the same bus for SMP.
 

barkmonster

macrumors 68020
Dec 3, 2001
2,123
12
Lancashire
The XServe uses ATA/100 and a 133MHz FSB.

The thing puzzles me is the explaination of RDRAM (or at least the 400Mhz bus) on the intel site :

P4 1.4 - 2.0Ghz info

The 400 MHz system bus is a quad-pumped bus running off a 100 MHz system clock making 3.2 GB/sec data transfer rates possible.
That's the old version of the P4 with the 256K L2, the new one's running off the same 133Mhz system clock as the entry level G4 but they've quad pumped it to 533Mhz and doubled the L2 cache size.

I think seeing as we've got 2.7Gb/s of bandwidth to share with our PCI cards, AGP graphics card, ethernet, USB, firewire and airport, not to mention the hard drive controllers are both independent of cpu. We should see some improvement over the old motherboard purely because the system controller seperates the cpu's bandwidth from the components.

I'd love to see how these macs perform in Protools LE!!!

All that bandwidth for the hard drives and pci slots has got to have quite an impact on performance.
 

jadam

macrumors 6502a
Jan 23, 2002
699
1
Re: Re: Basically...

Originally posted by DavidRavenMoon


This is a common misconception. Actually the RAM is also being clocked at 167 MHz...DDR RAM is not faster than SDR RAM! However DDR offers twice the memory bandwidth SDR RAM does at the same clock speed.

DDR effectively doubles the bandwidth available by sending data on the falling edge of the clock cycle as well as on the rising edge.

What Apple didn't do was to have two busses, one for each CPU. One explanation I have heard is the G4's need to be on the same bus for SMP.
because they need to be sycnronized... err
 

deepkid

macrumors regular
Jul 22, 2002
153
0
chicago
pretty enlightening

Originally posted by Sun Baked
This is interesting.

Scroll down to the picture and read the post.

http://arstechnica.infopop.net/OpenTopic/page?a=tpc&s=50009562&f=8300945231&m=5110932035
The Natebrau system architecture explanations are pretty good applesauce for us novices! I had to reread it a few times, but it does make sense.

It does make me wonder what hurdles Apple'd have to clear in order to have an independent bus for each chip (7470s required?), how much improvement we'd see... and how much that'd cost, etc. etc.

Thanks for the reference.