[RealMac]

While I know you can have a dual core cpu design in a SMP configuration, such seems a bit outside the consumer hardware scope right now.

I'm wondering what the advantages are from moving from one core to two. Does usually mean that each core is running at a reduced speed for traditional cpu trade-offs (heat dissipation, power usage, etc).

If this is where the G5/G6 is headed, can anyone shed some light on the advantages of such a system?

[djohnson]

More then likely, such a system will be built upon 65nm technology. This will greatly reduce the amount of heat generated and should allow the W used, and thus heat created, to be comparable to the 130nm designs of today. Of course just because it is about half the size does not equate to half the heat. Instead, it could be 4 times less due to the square of the difference.

Advantage: Dual cpus in a single chip. OS is built to handle multiple processors. You could have a dual core PowerBook! Quad systems become a reality, dual 2-cored cpus. Tack on SMT... and then we really have a killer system!

I imagine this might not make much sense but it is a rough idea of what should happen.

[power142]

At first glance (and without thinking too deeply) there are advantages and disadvantages to a multi-core design, in comparison with plain old single processor systems and conventional SMP systems (1 core per chip).

Advantages:

1) potentially pin compatible with existing sockets (although this is probably less important for us Mac users since Apple uses processor cards)
2) the two cores can have a very high speed connection between them giving enhanced performance in multi-threaded applications - although this may not be noticeable when compared with HyperTransport designs (like the G5)

Disadvantages:

1) will require aggressive cooling - after all, die space consuming power and performing work will generate heat! (true for any processor)
2) potential bottleneck if both cores have to share memory and or I/O channels, in comparison with current G5 architecture
3) applications have to be written to take advantage of extra processors - however, much software on Mac is multi-processor aware, much Unix software also

There are undoubtedly others for both lists, but few of us would likely complain if Apple released a dual core (or even SMP) G4 Powerbook that could keep cool

[Catfish_Man]

Originally posted by djohnson:
More then likely, such a system will be built upon 65nm technology. This will greatly reduce the amount of heat generated and should allow the W used, and thus heat created, to be comparable to the 130nm designs of today. Of course just because it is about half the size does not equate to half the heat. Instead, it could be 4 times less due to the square of the difference.

Advantage: Dual cpus in a single chip. OS is built to handle multiple processors. You could have a dual core PowerBook! Quad systems become a reality, dual 2-cored cpus. Tack on SMT... and then we really have a killer system!

I imagine this might not make much sense but it is a rough idea of what should happen.

Actually, a dual core 90 nm G5 would be about 120-130mm^2, quite reasonable. Single core it's 66mm^2, and you save some space by losing one of the FSB interfaces. I wouldn't be surprised to see quad core chips at 65 nm (although I can imagine it getting a bit crowded on the FSB with four cores sharing it), if heat issues allow that. One obvious way of dealing with the heat issues is to use a lower clock frequency for each core. The Pentium M uses about 1/5 the power of the Pentium 4 EE to provide about 2/3 the performance, iirc. In an app that uses dual processors well, a dual core Pentium M could be faster than the P4 for less power. I imagine similar things apply to the G5. The problem with this approach is that apps that don't take advantage of dual processors lose performance. I'm not sure how much of a problem that would be, but I think it's something that developers are going to have to deal with in the near future.

[gururafiki]

What about a dual core machine vs a single core multiprocessor machine. Is there going to be a performance difference, or is it basically the same thing besides that one machine has two chips, and the other machine has one?

[McFarmer]

gururafiki,

In the case of the G5 with a Front Side Bus speed of 1/2 the speed of the CPU and Dual Core CPUs with only one Front Side Bus (one for both cores) it comes down to this:

2 CPUs talking at 2 x 1/2 CPU speed to RAM and at 1/2 CPU speed to each other
vs.
2 Cores talking at 1/2 CPU speed to RAM and 1/1 CPU speed to each other

It would seem that applications with a massive data throughput from/to RAM would fare better on a Dual CPU setup, while apps with more computational requirements would fare better on a Dual Core setup.

An example for the former would be realtime transition effects in Final Cut Pro, and an example for the latter perhaps 3D rendering in Maya or solving equations in Mathematica.

With the G4's poor FSB speed many applications were optimized to not use the FSB if it could be avoided, i.e. calculate as much as possible internally. Those applications would again seem to do better in Dual Core machines.