current TiBook processors not able to fully utilise DDR RAM?

[cb911]

i was just reading in another thread about the current TiBooks not being able to fully use DDR RAM. i was just wondering how much truth there is in this?

i'm usually not a very technical person, but on this occasion if someone wants to run me through the theory of why this is not possible then feel welcome.

also, if someone knows of any websites that are about the current TiBook processors and DDR RAM then i wouldn't mind having a read...

 

[BenderBot1138]

DDR DilemaDon'tRun

That's an interesting claim... the Powerbook incorporates 32 MB of DDR RAM in its video systems. It's clearly possible.

Seems a tad ridiculous to say hey, we can't have DDR anywhere but the video card. Plus, Apples reasons for the RAM they incorporate are manyfold, but my main vote is for SPECIFICATIONS.

 

[vniow]

Well, if the Powerbook is a G4 and the G4 towers can't utilize DDR to its full potential, then it's same to say that the Powerbook can't either.

They should do it anywayz, just for marketing reasons.

 

[gambit]

Well...

thats cause of the motherboard not the G4 proccesor... there is a slight bottleneck in the design. No flaming intended. By the way I LOVE your avatar... "ITS GOT BIG TEETH!"

 

[Chryx]

Re: Well...

Originally posted by gambit
thats cause of the motherboard not the G4 proccesor... there is a slight bottleneck in the design. No flaming intended.

The exact opposite infact, the G4-7455 has a single data rate 133 (or 167) Mhz * 64bit frontside bus, which is its line to the outside world aka the system controller, to which the memory is attached.

The system controller in the new Powermacs (and the Xserve) has a 133/167Mhz DDR memory interface, but the bus to the processor (from the system controller)is limited to 133/167 SDR as the processor can't support anything higher and as such the processor can't take advantage of the bandwidth that's actually available from the memory subsystem.

There isn't anything Apple could do on the mainboard level to compensate for Motorolas lagging bus interface.

 

[Falleron]

Thats right. Its motorala thats chip cant handle DDRAM. Therefore, I think Apple is using DDRAM in the powermacs + Xserves just for marketing purposes.

 

[cb911]

so even the DDR RAM in the towers and the Xserves isn't fully used to it's full either?

and the reason that TiBooks can't fully use DDR is because of the bottleneck in the processor?

damn, i was starting to get all hyped on DDR...

 

[Falleron]

Originally posted by cb911
so even the DDR RAM in the towers and the Xserves isn't fully used to it's full either?

and the reason that TiBooks can't fully use DDR is because of the bottleneck in the processor?

damn, i was starting to get all hyped on DDR...

As far as I am aware, the current G4 cant use DDRAM well. Why do you think the old Dual Ghz using PC133 RAM is about the same speed as the DDRAM 1Ghz PowerMac? There is a bottleneck in the system. Until Motorola releases their next chip (I think in January) this problem will exist.

 

[MacBandit]

Originally posted by Falleron

As far as I am aware, the current G4 cant use DDRAM well. Why do you think the old Dual Ghz using PC133 RAM is about the same speed as the DDRAM 1Ghz PowerMac? There is a bottleneck in the system. Until Motorola releases their next chip (I think in January) this problem will exist.

It's about the same speed because the old Dual had 2MB L3 cache and the new one only has 1MB L3 cache. Even with that handicap the new dual is faster then the old in most situations. Granted it's not by much but it is slightly faster. That just goes to show the benefit that the DDR and 167MHz bus has given the new macs.

I thought everyone in the world already new the 7455 G4s could not utilize DDR Ram. The biggest advantage to the current macs with DDR is when using DMA (Direct Memmory Access). All the subsystems in all current macs are able to use DMA that means in a new G4 the hard drives are able to spool to memory at full DDR speed. It also means that the video card is able to read from memory at full DDR speed. Completely bypassing in most cases the cpu. This is what gives the new G4s a huge advantage. Especially when doing video card intensive operations. Such as games.

 

[Falleron]

Originally posted by MacBandit



It's about the same speed because the old Dual had 2MB L3 cache and the new one only has 1MB L3 cache. Even with that handicap the new dual is faster then the old in most situations. Granted it's not by much but it is slightly faster. That just goes to show the benefit that the DDR and 167MHz bus has given the new macs.

I thought everyone in the world already new the 7455 G4s could not utilize DDR Ram. The biggest advantage to the current macs with DDR is when using DMA (Direct Memmory Access). All the subsystems in all current macs are able to use DMA that means in a new G4 the hard drives are able to spool to memory at full DDR speed. It also means that the video card is able to read from memory at full DDR speed. Completely bypassing in most cases the cpu. This is what gives the new G4s a huge advantage. Especially when doing video card intensive operations. Such as games.

I know the old dual has the extra cache. I was just over simplifying the situation. I think if the G4 chip could use the full bandwidth of DDRAM then the whole system would be a lot quicker than they are today.

 

[jefhatfield]

with all that said, pro and con, let's get the ddr in the tibook...even if it only helps a tiny bit

 

[Falleron]

Originally posted by jefhatfield
with all that said, pro and con, let's get the ddr in the tibook...even if it only helps a tiny bit

Does DDRAM produce extra heat? if so, Apple may leave it out for now, especially if it does not make much difference to performance. However, if they go for the marketing position, they will include it. DDRAM sounds better.

 

[jefhatfield]

Originally posted by Falleron

Does DDRAM produce extra heat? if so, Apple may leave it out for now, especially if it does not make much difference to performance. However, if they go for the marketing position, they will include it. DDRAM sounds better.

if it negatively affects battery time, the number one issue with mobile users, then i say hold off on the ddr ram

 

[MacBandit]

Originally posted by jefhatfield


if it negatively affects battery time, the number one issue with mobile users, then i say hold off on the ddr ram

I'm under the understanding that it produces more heat and uses more power. Not a lot more but it is more in both cases.

 

[Chryx]

Originally posted by MacBandit

I'm under the understanding that it produces more heat and uses more power. Not a lot more but it is more in both cases.

DDR sdram at the same clockspeed should use LESS power and as a sideeffect generate less heat.

PC133 = 3.3v
PC2100 = 2.5v

current draw is pretty close IIRC, and (as a real world example, though not a very scientific one) the PC2700 I've got around here doesn't get as warm as the PC133 does.

 

[shadowfax]

i think the real issue is that DDR RAM costs considerably more per MB, esp at what apple charges. they would probably have to up the high end to 3400$ to go DDR, and they know a lot of people would hate them for that. i don't think they will go DDR.

 

[chmorley]

Your mileage may vary

Originally posted by Falleron
As far as I am aware, the current G4 cant use DDRAM well. Why do you think the old Dual Ghz using PC133 RAM is about the same speed as the DDRAM 1Ghz PowerMac? ...

This seems to vary depending on the benchmark(s) used. While the first results that came out indicated they were roughly equivalent in speed, the review in the latest MacWorld indicates that the new DDR Dual 1GHz Power Mac outperforms the old one by 20% on average. If the old adage that users can notice any performance difference >15%, this is significant.

So despite the smaller L3 cache, something about the design of these machines seems to make them significantly faster.

Nonetheless, it is apparent that they are not taking full advantage of the power of DDRAM.

Chris