At Thu, 21 May 2009 23:30:44 +0300 CentOS mailing list <centos at centos.org> wrote: > > Hi! > > I ran the following test on 3 different setups: > > #!/usr/bin/php > <? > $n=1024*256; > > $usage1=memory_get_usage(); > $rusage1=memory_get_usage(true); > $a=array(); > for($i=0;$i<$n;$i++) > $a[]=0; > $usage2=memory_get_usage(); > $rusage2=memory_get_usage(true); > echo ($usage2-$usage1).'/'.($rusage2-$rusage1); > ?> > > ...and I got the following results: > > 32bit kernel & 32bit php - 18875368/19136512 > 64bit kernel & 64bit php - 35654376/35913728 > 64bit kernel & 32bit php - 18875368/19136512 > > Some client has a 64bit xen-based VPS with 512MB RAM user for > webhosting and I'm wondering if I can free some memory installing > httpd&php i386 modules. > > I understand that 64bit programs use more memory because the pointers, > integers, etc. are now 64bit instead of 32bit, but running a 32bit > program on a 64bit architecture is the same as running that program on > a 32bit architecture (just concerning the memory used)? At least, > that's my conclusion after running the above test. Am I wrong? No, you are not wrong. All x86 flavered 64-bit processors will run as 32-bit (i686) processors and when running in 32-bit mode are effectively just a i686 as far as any 32-bit program can tell. There is no reason NOT to just install a straight 32-bit OS on such a machine if there is less than 4gig of virtual memory and non-of the programms being run has any reason to use the 64-bit address space. Web hosting is a good example of this. > > Thank you! > > PS: No, the client's service provider does not offer a 32bit vps > platform and the client won't change the provider or pay for > additional memory. > -- Robert Heller -- 978-544-6933 Deepwoods Software -- Download the Model Railroad System http://www.deepsoft.com/ -- Binaries for Linux and MS-Windows heller at deepsoft.com -- http://www.deepsoft.com/ModelRailroadSystem/