Matthias Hopf wrote:
With i386 you will only be able to access 3 or 3.5GB of your memory. At
least half a megabyte will be wasted. Background: The PCI cards have to
be mapped into the available 32bit address space.
----
Has anyone actually seen this first hand with any Intel processor
with PAE? I've never seen this and it doesn't sound right. I have seen
evidence to support the contrary: from /proc/meminfo on my (i386) system:
MemTotal: 4147236 kB
MemFree: 1321928 kB
Buffers: 220 kB
Cached: 2424472 kB
SwapCached: 0 kB
Active: 967832 kB
Inactive: 1488312 kB
HighTotal: 3275304 kB
HighFree: 1117840 kB
LowTotal: 871932 kB
LowFree: 204088 kB
SwapTotal: 4200956 kB
SwapFree: 4200956 kB
Dirty: 0 kB
Writeback: 0 kB
AnonPages: 31292 kB
Mapped: 20620 kB
Slab: 350396 kB
PageTables: 788 kB
NFS_Unstable: 0 kB
Bounce: 0 kB
CommitLimit: 6274572 kB
Committed_AS: 98708 kB
VmallocTotal: 112632 kB
VmallocUsed: 14668 kB
VmallocChunk: 97292 kB
HugePages_Total: 0
HugePages_Free: 0
HugePages_Rsvd: 0
Hugepagesize: 2048 kB
--------------------------------
Perhaps its a problem on AMD based systems? I know it's a
problem on WindowsXP -- Microsoft crippled XP in SP2 to limit it to 3G.
It supported 4G in SP1 and earlier, though it still required a patch
to work properly, but MS forced XP to 3G, supposedly in the name of
"security", but more likely to create some need to upgrade XP to the
Server edition or Vista (which, I assume, they'd claim was more secure,
and could handle 4G).
64-bit programs actually execute faster than 32-bit, but need more
memory (all pointers have double size). This is counterintuitive, but
can be explained: the x86_64 architecture has more free registers
available than i586. Only programs that trash memory a lot (inlcuding
lots of pointers) might run slower due to higher memory throughput.
---
Yeah -- wondered about that -- seems "longs" and
'long double's (floats) take twice the space on 64-bit, but it only
seems to add ~10% (have seen 25 to over 40% on some 32-64 bit
comparisons for other arch's (not "ia" arch).
Performance is mixed, but under 10% in all benchmarks I've
seen, but some figures show integer performance might have a slight edge
on ia32, but floats are faster, memory moves/loads seem uniformly
faster.
You can run i586 programs on a x86_64 kernel, in fact this is very much
advised for firefox (stabiliy, plugins) and video players (due to
win32codecs). AFAIK openoffice isn't even ported to x86_64 yet. Other
ports are not really clean yet, so the i586 binaries are often more
stable.
----
I noticed the 64-bit libraries are under a different path. To
switch to x86_64, shouldn't I be able to just install an x86_64 kernel
initially then install/switch over apps at leisure?
So:
Downside for x86_64: stability, complexity (mixed architecture setup),
more memory needed
Upside for x86_64: faster, more memory available
---
Well, I don't get more memory until I buy some -- since x86_64 takes
slightly more memory, I'd have slightly less, "free", memory in the short
term..., no?
Maybe if I can install the x64 kernel and side-by-side 32/64-bit apps,
I can see where I benefit with the 64-bit compile?
thanks,
-linda
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