Yasha Karant <[log in to unmask]> writes:

> how much additional RAM and hard drive space is required by this
> X86-64 implementation?

The memory usage going from 32 to 64bit x86 really depends on the code
you run.  My understanding is it boils down to how much of the job's
memory is made up of pointers as compared to other data types that are
invariant under this bit change.  This can vary a lot and of course it
matters what the absolute memory usage is to begin with.  If you are
concerned you should benchmark your actual code on both bit'isms.

But, I can relate a few data points.

The jobs we tend to run here are ~1-2GB to start with and I've seen ~50%
increase in memory usage for the same code complied in 32 and 64 bits.
These jobs come from relatively large C++ code bases and the code tends
to be written for functionality first and size optimization later (if
ever).  I imagine they represent a, if maybe not the, worse case.

For the various laptops and workstations I have with <4GB of RAM, I keep
them in 32 bits even if they have amd64/x86_64 CPUs as these jobs
benefit more from the added ~50% memory than the ~20% extra processing
power available in 64bits.  These are all Debian or Ubuntu so still
retain the option to stick at 32.

For more prosaic workloads, the change in pointer size is not apparently
important, at least in my experience.  For example, I have a 64bit
Debian VPS doing light web serving that runs in 512MB of RAM.  This
particular VPS happens to be somewhat cheap and crappy, but I've never
had an out-of-memory condition.


I have not noticed any practical impact on HDD space usage from going to
64bit, if there even is any.

-Brett.