You can get 64-bit Xeons also but it takes hit in the I/O department due to the lack of a hardware I/O MMU which limits DMA transfers to addresses below 4GB. This has a two-fold impact:

1) transfering data to >4GB require first a transfer to <4GB and then a copy to the final destination.

2) You must allocate real memory 2X the address space of the devices to act as bounce buffers. This is especially problematic for workstations because if you put a 512MB Nvidia card in your computer for graphics work -- you've just lost 1GB of memory. (I dunno how much the typical SCSI/NIC/etc take up.)

I thought Intel was copying AMD's 64-bit API.  Is Intel's
implementation as poor as you description?  Does Intel have any better
64-bit offering other than the Itanium/Itanic?

Unfortunately, there's no easy way for Intel to have implemented a 64-bit IOMMU under their current restrictions. The memory controller resides on the chipset and to upgrade the functionality significantly, it would probably require changing the bus protocol. It's not that they couldn't do it -- it would just require all Intel chipset/MB vendors/partners to go through the process of creating & validating totally new products. A way lengthier process than just producing 64-bit CPUs that drop into current motherboards.

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