Re: 32bit vs 64bit Linux

>     Hi,

>     Even though I have 64bit hardware I always install the 32bit
>     version of Linux.  I do so because of the past discussions on this
>     list that made me believe the 32bit OS was better because 64bit
>     caching is actually slower due to the requirement that the cache
>     be filled to a certain point before it is moved.  I think I recall
>     something about the amount of RAM having some effect here also.

>     Allows individual processes to address more than 4 GB of RAM each
>     (in practice, most but not all 32-bit OSes also limit the total
>     usable system RAM to less than 4 GB, not just the per-application
>     maximum). While a PAE kernel also does this; it is significantly
>     slower!

>     All pointers take 8 bytes instead of 4 bytes. The effect on RAM
>     usage is minimal (because you're not likely to have an application
>     filled with gigabytes of pointers), but in the worst theoretical
>     case, this can make the CPU cache be able to hold 1/2 as many
>     pointers (making it be effectively 1/2 the size). For most
>     applications, this is not a huge deall.

>     There are many more general-purpose CPU registers in 64-bit mode.
>     Registers are the fastest memory in your entire system. There are
>     only 8 in 32-bit mode and 16 general purpose registers in 64-bit
>     mode. In scientific computing applications I've written, I've seen
>     up to a 30% performance boost by recompiling in 64-bit mode (my
>     application could really use the extra registers).

>     Most 32-bit OSes really only let individual applications use 2 GB
>     of RAM, even if you have 4 GB installed. This is because the other
>     2 GB of address space is reserved for sharing data between
>     applications, with the OS, and for communicating with drivers.
>     Windows and Linux will let you adjust this tradeoff to be 3 GB for
>     applications and 1 GB shared, but this can cause problems for some
>     applications that don't expect the change. I'm also guessing it
>     might cripple a graphics card that has 1 GB of RAM (but I'm not
>     sure). A 64-bit OS can give individual 32-bit applications closer
>     to the full 4 GB to play with.

>     Application speed is usually faster for a 64-bit application in a
>     64-bit OS compared to the 32-bit version of the application on a
>     32-bit OS, but most users won't see this speed-up. Most
>     applications for normal users don't really take advantage of the
>     extra registers or the benefits are balanced out by bigger
>     pointers filling up the cache.

>     If you have any memory hog applications (like photo editors, video
>     processing, scientific computing, etc.), if you have (or can buy)
>     more than 3 GB of RAM, and you can get a 64-bit version of the
>     application, the choice is easy: use the 64-bit OS.

>     Some hardware doesn't have 64-bit drivers. Check your motherboard,
>     all plug-in cards, and all USB devices before making the switch.
>     Note that in the early days of Windows Vista, there were lots of
>     problems with drivers. These days things are generally better.
>      nVidia for instance is one of the drivers optimized for 64bit
>     which is extremely faster.

>     If you run so many applications at a time that you're running out
>     of RAM (usually you can tell this because your computer starts
>     getting really slow and you hear the hard disk drive crunching -
>     indicating your caching), then you'll want a 64-bit OS (and
>     sufficient RAM).

>     You can run 32-bit applications (but not drivers) in 64-bit land
>     with no problems. The worst slowdown I've measured for a 32-bit
>     application in 64-bit Windows is about 5% (meaning that if it took
>     60 seconds to do something in 32-bit, it took at most 60/0.95 = 63
>     seconds with the same 32-bit application in 64-bit).

>     All in all, personally, Keith, I would install 64bit CentOs 6
>     unless you have a better reason not to?

>     Using a 32bit version over a 64bit version seems counter
>     intuitive, however that is what I have taken away from these
>     conversations about 32bit vs 64bit Linux.

>     I'm using CentOS 6.x on a LAMP server that gets a low amount of
>     traffic.   However I may make the jump to Linux on my desktop this
>     summer. (this will be my 3rd attempt to become M$ free except one
>     VM so I can use IE for testing) I think all of my hardware is 64bit.

>     So that begs the question, is 32bit better than 64bit or do I not
>     understand the issue?

>     Thank you for your feedback.

>     Keith

>     ------------------------
>     Keith Smith

>     ---------------------------------------------------
>     PLUG-discuss mailing list - PLUG-discuss@lists.phxlinux.org
>     <mailto:PLUG-discuss@lists.phxlinux.org>
>     To subscribe, unsubscribe, or to change your mail settings:
>     http://lists.phxlinux.org/mailman/listinfo/plug-discuss