pgman@candle.pha.pa.us (Bruce Momjian) wrote:
> William Yu wrote:
>> > Well, that would give you the most benefit, but the memory
>> > bandwidth is still greater than on a Xeon. There's really no
>> > issue with 64 bit if you're using open source software; it all
>> > compiles for 64 bits and you're good to
>> > go. http://stats.distributed.net runs on a dual opteron box
>> > running FreeBSD and I've had no issues.
>>
>> 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?
From what I can see, the resulting "copy of AMD64" amounts to little
more than rushing together a project to glue a bag on the side of a
Xeon chip with some 64 bit parts in it.
I see no reason to expect what is only billed as an "extension
technology" <http://www.eweek.com/article2/0,1759,1545734,00.asp> to
alleviate the deeply rooted memory bandwidth problems seen on Xeon.
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