ARM Chips Designed For 480-Core Servers 132
angry tapir writes "Calxeda revealed initial details about its first ARM-based server chip, designed to let companies build low-power servers with up to 480 cores. The Calxeda chip is built on a quad-core ARM processor, and low-power servers could have 120 ARM processing nodes in a 2U box. The chips will be based on ARM's Cortex-A9 processor architecture."
Re:And it's useless. No 64-bit support. (Score:5, Informative)
How about a link to this rant, if you want us to read it? And, if you've got a problem with PAE-like extensions, then I presume you're aware that both Intel's and AMD's virtualisation extensions use PAE-like addressing?
All that PAE and LPAE do is decouple the size of the physical and virtual address spaces. This is a fairly trivial extension to existing virtual memory schemes. On any modern system, there is some mechanism for mapping from virtual to physical pages, so each application sees a 4GB private address space (on a 32-bit system) and the pages that it uses are mapped to some from physical memory. With PAE / LPAE, the only difference is that this mapping now lets you map to a larger physical address space - for example, 32-bit virtual to 36-bit physical. You see exactly the opposite of this on almost all 64-bit platforms, where you have a 64-bit virtual address space but only a 40- or 48-bit physical address space.
The big problem with PAE was that most machines that supported it came with 32-bit peripherals and no IOMMU. This meant that the peripherals could do DMA transfers to and from the low 4GB, but not anywhere else in memory. This dramatically complicated the work that the kernel had to do, because it needed to either remap memory pages from the low 4GB and copy their contents or use bounce buffers, neither of which was good for performance (which, generally, is something that people who need more than 4GB of RAM care about).
The advantage is that you can add more physical memory without changing the ABI. Pointers remain 32 bits, and applications are each limited to 4GB of virtual address space, but you can have multiple applications all using 4GB without needing to swap. Oh, and you also get better cache usage than with a pure 64-bit ABI, because you're not using 8 bytes to store a pointer into an address space that's much smaller than 4GB.
By the way, I just did a quick check on a few 64-bit machines that I have accounts on. Out of about 700 processes running on these systems (one laptop, two servers, one compute node), none were using more than 4GB of virtual address space.