AMD64 VS EM64T
I am currently faced with choosing one of them as our forthcoming 64 bit
platform. So far I read a couple of reviews, most of which seems favor
AMD64 a little bit. I also did some initial testings on an opteron box
with Debian pure64 unstale. So far it looks good.
The price differrence is not a big issue. The most important are
performance, reliability and compatibility, esp on Linux, most likely
Debian. We will use them to run server side java applicaitons.
Redhat mentioned this in their realease statement:
“Software IOTLB — Intel EM64T does not support an IOMMU in hardware
while AMD64 processors do. This means that physical addresses above 4GB
(32 bits) cannot reliably be the source or destination of DMA
operations. Therefore, the Red Hat Enterprise Linux 3 Update 2 kernel
"bounces" all DMA operations to or from physical addresses above 4GB to
buffers that the kernel pre-allocated below 4GB at boot time. This is
likely to result in lower performance for IO-intensive workloads for
Intel EM64T as compared to AMD64 processors.”
This issue may affect database usage, but probably not a java
applicaiton server. There might be other unkown issues as well. I am
eager to know what are the Debian team and users' point on these two
platforms, esp those who already used them.