William Yu wrote:
> >>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.)

When you say "allocate real memory 2X" are you saying that if you have
16GB of RAM only 8GB is actually usable and the other 8GB is for
bounce buffers, or is it just address space being used up?

--
Bruce Momjian | http://candle.pha.pa.us
pgman@candle.pha.pa.us | (610) 359-1001
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