Originally posted by: Lord Evermore
If a CPU combines two cores in one, then the yield isn't going to be lower based on that. It would be lower based on the simple existence of twice as many transistors and circuits (probably more than twice due to interconnecting). A single core with 500 million transistors would have pretty much the same yield as a 2-core CPU with 250 million transistors per core. Obviously if you have a 2-core die with 500M transistors, it's going to have lower yields than a single core die with only 250M transistors. The Athlon64 doesn't contain two cores though, just a LOT of transistors, obviously making the yield lower just like Intel raising the transistor count makes their yield lower for awhile.
The processor is NOT a 64-bit processor. It's not doing the same thing that the Itanium does, where it has to process 32-bit code differently from 64-bit code. The CPU is still a 32-bit processor, it just has 64-bit extensions that allow it to address higher amounts of memory, and give it more registers and some other things. It's still just a 32-bit processor using the 32-bit x86 ISA. So the resources in the chip aren't "dedicated" to any particular type of processing.
It uses all the resources it can presumably, whether in 32 or 64 bit mode. The OS won't be able to make use of some things I presume if it's only 32-bit, because it can't address 64-bit memory space, but the CPU should be able to make use of the new registers just like a Pentium3 or Athlon makes use of more than the 8 registers of the basic x86 ISA by register renaming.
The onboard memory controller would have been awesome if they'd gotten the part out on time originally. Now it's just falling behind the times compared to everything else. However I was under the impression that it may be possible, either immediately or with the next version, for a chipset maker to integrate a memory controller that takes over and shuts down the A64's controller, so you get the better memory types and speeds, but at the loss of the low-latency from the integrated controller.
Incidentally, whether the A64 needs dual-channel memory or not is entirely dependent on how the internal memory to core bus is designed. I don't know yet whether it is capable of throughput between the memory controller and the core that's essentially limited only by the core speed, or if there's a "bus" that will limit it.
Of course, to AMD they're not "limiting" it at all. They're making the Athlon64 with a single channel because they are focusing it on one market segment, and have another product line that they've put dual-channel into.
So is the Athlon XP not a 32bit processor since it is basically a 16bit chip with 32bit extensions?