Frobozz said:
x86 cores have very different considerations than PowerPC cores do. There are logistical differences in their architectures which lend the PowerPC to work better in multi-core environments. At least, this is what the consensus of rumor, opinion, and briefly leaked documentation suggests.
Consensus? This theory is new. At least to me. Let's talk about Opteron, the P4 has reached it's end of life. These are the differences between G5/PPC970 and Opteron Multicpu systems:
Opteron:
- 8 CPU configuartions available
- Existing system CPUs can easily replaced with dual core CPUs
- NUMA architecture
- Each CPU equipped with three 1000Mhz Hypertransport links and a 800Mhz local memory interface, so one Opteron can communicate with it's environment with 32.4 GB/s
- Direct Hypertransport links between CPUs
- On-die crossbar
- Direct Hypertransport link to I/O
- Ultra low latancy On-die memory controller
G5:
- 2 CPU only configuartions available
- classical northbridge design
- Each CPU equipped 1/2 * #Ghz bus, so one PPC970@2.3 Ghz can communicate with it's environment with 9.2 GB/s when both directions are fully utilized, in one direction only with 4.6 GB/s
- Both CPUs connected to the northbridge (G5's "system controller"). No direct connection between CPUs possible
- Routing of all traffic takes place in the northbridge (CPU<>CPU, CPU<>MEM, AGP<>MEM, CPU<>IO). A northbridge was and still is a bottleneck.
- I/O connected via crippled 800MHz Hypertransport to the northbridge
- AGP connected to the northbridge
- Memory connected to the northbridge
- Shared high latency northbridge memory controller for both CPUs
Think I don't need to explain which one is the superior topology. Opteron systems live in the same spheres as Power4/5 and Itanium systems whilst PPC970 setups do not.
Kaborka