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Such a buildup usually guarantees an
anti-climax, but with Windows 2003 Server x64 Editions and AMD Opteron
CPUs, get ready for the thrill that keeps on thrilling. The 64-bit
extended address space and x86 instruction set and register enhancements
are just the beginning. But let's get beyond watching the horizon. Right
here, right now: Windows x64 and Opteron.
Microsoft's 64-bit pitch to date, adapted
from Intel's, has been utterly uninspiring: Big databases will go faster
because they'll have access to more memory. That draws a big shrug even
from me. So let's flesh out what they're trying to tell us. Few IT shops
are fretting over memory-bound database apps. Besides, it's already
possible to stuff 16GB of RAM into a 32-bit PC server, right? Wrong. You
never actually have more than 4GB of directly usable RAM in a Xeon server.
Intel's PAE (Physical Address Extension) is a hack that lets you map pages
of RAM into and out of 32-bit Xeon's limited address space. PAE is virtual
memory done with RAM, which sounds great until you consider the enormous
overhead imposed as the CPU rewrites its memory map, potentially thousands
of times per second.
When running Windows x64, EM64T (Extended
Memory 64 Technology) Xeon and Opteron do away with PAE, giving your
applications unpaged, direct access to as much RAM as your motherboard
will hold. Both give you a virtual address space that, for the next 10
years or so, is effectively infinite. Windows loves virtual memory and
manages it well, a fact that Windows enterprise apps use to great
advantage. The 64-bit version of Windows should give you the ability to
raise virtual-to-physical memory ratios. A 32-bit Windows server with 4GB
of physical memory can usually use virtual memory to mimic a system with
6GB of memory. Yes, this type of virtual memory is slower than PAE, but
it's easy to tune, requires no hardware upgrades, and it adapts to the
execution patterns of your applications.
PAE is evil, an egregious flaw in the PC
architecture that forces organizations to overspend on servers and
software licenses. But the shortcomings of Xeon's memory handling are just
one link in the chain that binds PC server users to high costs and low
expectations. It takes more than some extra pins and fresh microcode to
create a true 64-bit enterprise architecture that's wholly compatible with
32-bit software. AMD figured that taking the PC to the datacenter required
reworking the entire system architecture. They're right. Intel figured
that it could skate by selling the market on a whole system architecture
that has more in common with an 80386 system than with any other 64-bit
servers on the market.
I may be overstating the case when I say
that Opteron's total system architecture has more in common with a
mainframe or big-iron Unix box than it does with a 32-bit PC. I'm probably
overstating the case when I refer to EM64T as an Opteron simulator -- but
not by much.
Windows x64 is designed for Opteron. I'll
back that up with facts, but I won't rush it. Nobody's going to run out to
buy 64-bit hardware the second they get their hands on Windows x64 CDs.
I'll take my time, but by the time I'm done, if you opt for EM64T Xeon
over Opteron, you're a lost cause.
