Originally posted by Barto
You refer to a system with a seperate memory and system controller. This is impossible. A system controller is the chip which links the CPU and Memory and to other devices in the system. Hence, it is the "system" controller.
Oh come on. The system controller is a name. It can denote anything anyone wants. I used the name because many people are familiar with the name and can understand the symbolism.
The Apple diagram, instead of refering to northbridge/southbridge renames them System Controller/IO Controller
And??? Northbridge/Southbridge is PC nomenculture, so Apple use their own. The name doesn't mysteriously change the function of the chip.
Apple has chosen to put controllers for devices which would benefit from the decreased latency and increased bandwidth in the system controller. Ethernet, FireWire and the primary ATA bus.
As has every chipset creator on the planet. Integration has been the name of the game since about 1970, in case you haven't noticed.
You're saying, in essence, "Let's have a basic system controller where everything apart from memory [and I'm assuming AGP] is in the IO controller(s)".
BUT there is simply no off-the-shelf chip for Apple's IO needs. Apple would have to use multiple PCI-based controller chips for FireWire 800, Gigabit Ethernet, USB 2, ATA, Audio, Bluetooth, serial ports etc. If you wanted a beige box, there would be fewer controllers of course. But we are talking about Power Macs, not beige boxen.
That we know about yet. How far off can it be? I just want Apple to concentrate on its strong points and use others where it makes sense. nVidia nForce 3 PRO is short Firewire 800, but is up Dolby 5.1 sound, serial ATA and built in RAID. How long until they fix that?
This normally would be a low-bandwidth, high latency solution. Your idea is to build eDRAM into the system controller. However, the individual PCI controller chips combined with the eDRAM might end up as expensive as having 5 different non-Apple PCI-based IO controllers. I don't think anyone can state that one Power Mac solution would be cheaper than the other.
I specifically mentioned using eDRAM as a possability. There are many other things you can do with the extra space, including not using it.
This leaves one question remaining: Why would you limit Apple's SMP horizons by distributing controllers in such a way? Your system would limit Apple to one or two CPUs, with the cost increasing exponentially as more are added. With seperate hypertransport-based companion chips, Apple could add however many chips they want, and not end up with more busses than CPUs (and more cost to the end user) in low end systems.
And? Where is 100% of Apple's market at the moment? If someone wants a 4 CPU system let Apple cater for it in a very high margin xServe based product. I have always been talking desktops, and have assumed that in a thread discussing desktops you would be too.
You find me a 4 CPU system that is not considerably more expensive than a similar 2 CPU system. You won't find one because greater than 2 is hard and expensive. You need significantly better infrastructure to do 4 and greater CPU systems well (i.e. not the Daystar toy). Thats why there are no white box 4 CPU systems. They are all systems from HP, Sun, IBM etc. Big systems vendors who have been creating these architectures for years and years. Yes it is simpler now, but still hard, and not a market Apple should enter lightly.