[Novalug] 64bit vs 32bit
John Franklin
franklin at elfie.org
Sun Apr 13 22:28:40 EDT 2008
Required? No. Useful? Yes.
In terms of raw processor performance, 64-bit over 32-bit gives a
modest speed-up as there are a couple more registers and each
instruction can now chew on 64-bits of data at a time instead of 32-
bits. There are also 64-bit pointers now, which take more space and
more time on the memory bus, thus tempering the advances. In general,
a 64-bit app will be slightly faster than a 32-bit app, unless it
works mostly in pointers, and not in actual data. Think: apps that
massage huge indexes of pointers.
PAE is like bank switching. Anytime the system needs to switch
extended address bits, the memory manager in the kernel has to do a
fair bit of processing and blows all the caches. IIRC, this happens
with every system call. I've seen it used at $employer, and it came
with a 15% performance hit off the top just running the kernel that
way. Period. PAE was a stop-gap until proper 64-bit processors could
come out.
32-bit apps can run happily in an otherwise 64-bit system. Yes, it
means you'll need to install all the 32-bit support libraries, so
you'll have two copies of glibc and libnss and the like. Where 32-bit
apps see benefit (if you have more than 4GB of RAM) is in the kernel
processing. The kernel can see all 64-bits of memory space, and will
set up larger disk caches. Even as a 32-bit app, you'll have access
to (potentially) more than 4GB of cache space.
jf
On Apr 13, 2008, at 9:27 PM, James Ewing Cottrell 3rd wrote:
> None of my computers will hold more than 2G anyway. I have 2 slots
> using DDR memory.
>
> Now (some) 32-bit processors and Linux have the PAE extension, which
> IIRC is intended for managing more than 4G.
>
> So I'm not sure that 64 bits are required. Anyone else want to
> comment?
>
> JIM
>
> Ken Kauffman wrote:
>> This isn't 100% true. If you do a tremendous amount of
>> multitasking, you may need more RAM than 4Gb. So you'll need 64
>> bit to take advantage of all the memory above 3.5 Gb. For
>> instance, I run 8Gb on my desktop for multitasking reasons.
>>
>> Also, keep in mind that Linux will leave applications in memory
>> even after they are closed -- unless -- it's "released" and another
>> process needs to claim that space. So you'll get a "virtual" speed
>> up of frequently used programs if you open/close a lot but do not
>> multitask as much.
>>
>> Ken
>>
>> On Sun, Apr 13, 2008 at 2:28 PM, James Ewing Cottrell 3rd <JECottrell3 at comcast.net
>> <mailto:JECottrell3 at comcast.net>> wrote:
>>
>> I have six computers in my home. One is a 64 bit, and I think my
>> daughter's may be too.
>>
>> Any computer I buy from now on will be 64 bit.
>>
>> But unless you are running processes that need large address
>> spaces (some gene mapping applications really NEED 64 bit virtual
>> address spaces, I don't really see the need. I did download and
>> install a few 64 bit Linuxi, but for simplicity I will probably
>> just run 32 distros unless I want to mirror the 64 bit environment
>> I have at work.
>>
>> At some point 64 bits will be more common than not and I will use
>> 64 bits whenever I can, but for now, the complexity (there are
>> both 32 bit and 64 libraries) isn't worth it other than getting
>> experience in the 64 bit environment.
>>
>> To give you an example, some of the plugins for FireFox only work
>> in 32 bit mode. The solution is to remove the 64 bit version and
>> install the 32 bit version. Other applications may also need to be
>> downgraded in this way.
>>
>> In other words, I'll do what is easiest.
>>
>> JIM
>>
>> Ivan wrote:
>>
>> Ivan Makfinsky wrote:
>>
>> novalug-request at calypso.tux.org
>> <mailto:novalug-request at calypso.tux.org> wrote:
>>
>> Message: 1
>> Date: Fri, 04 Apr 2008 12:03:28 -0400
>> From: William Warren
>> <hescominsoon at emmanuelcomputerconsulting.com
>> <mailto:hescominsoon at emmanuelcomputerconsulting.com>>
>> Subject: Re: [Novalug] 64bit vs 32bit (was FOSE
>> wrapup)
>> To: novalug at calypso.tux.org
>> <mailto:novalug at calypso.tux.org>
>> Message-ID:
>> <47F65150.7010208 at emmanuelcomputerconsulting.com
>> <mailto:47F65150.7010208 at emmanuelcomputerconsulting.com
>> >>
>> Content-Type: text/plain; charset=ISO-8859-1;
>> format=flowed
>>
>> That's not a 64-bit issue..that's a VT issue which is
>> different from 64 bit.
>>
>> Richard Rognlie wrote:
>>
>> On Fri, Apr 04, 2008 at 09:24:24AM -0400, Pete
>> Nuwayser wrote:
>>
>> I agree with Greg: a 64-bit OS will not run
>> on 32-bit architecture,
>> but 32-bit OS will run on 64-bit architecture.
>>
>> And to further complicate matters, there are times
>> when a 64bit CPU can
>> not accept a 64bit OS.
>>
>> I ran into this with VMware. Dell 1850
>> server. 64bit CPU. 64bit OS on the box.
>>
>> But I am unable to install a 64bit "guest" OS on
>> the box due to the
>> CPU lacking the "VT" (virtualization technology)
>> flag.
>>
>> Had to get a 1950 to get the CPU upgrade...
>>
>>
>>
>>
>> In order to determine whether or not you can run a 64bit OS on
>> a certain CPU, look for the following:
>>
>> $ cat /proc/cpuinfo | grep flags
>> flags : fpu vme de pse tsc msr pae mce cx8 apic sep
>> mtrr pge mca cmov pat pse36 clflush mmx fxsr sse sse2 syscall
>> nx mmxext ~~~~lm~~~~~ 3dnowext 3dnow rep_good
>> flags : fpu vme de pse tsc msr pae mce cx8 apic sep
>> mtrr pge mca cmov pat pse36 clflush mmx fxsr sse sse2 syscall
>> nx mmxext ~~~~lm~~~~~ 3dnowext 3dnow rep_good
>>
>> "lm" - Long mode, indicates the CPU is 64 bit capable.
>>
>> - Ivan
>>
>>
>> _______________________________________________
>> Novalug mailing list
>> Novalug at calypso.tux.org <mailto:Novalug at calypso.tux.org>
>> http://calypso.tux.org/cgi-bin/mailman/listinfo/novalug
>>
>>
>>
>> _______________________________________________
>> Novalug mailing list
>> Novalug at calypso.tux.org <mailto:Novalug at calypso.tux.org>
>> http://calypso.tux.org/cgi-bin/mailman/listinfo/novalug
>>
>>
>> ------------------------------------------------------------------------
>>
>> _______________________________________________
>> Novalug mailing list
>> Novalug at calypso.tux.org
>> http://calypso.tux.org/cgi-bin/mailman/listinfo/novalug
>>
>> ------------------------------------------------------------------------
>>
>> No virus found in this incoming message.
>> Checked by AVG. Version: 7.5.519 / Virus Database: 269.22.13/1375 -
>> Release Date: 4/12/2008 11:32 AM
>>
>
> _______________________________________________
> Novalug mailing list
> Novalug at calypso.tux.org
> http://calypso.tux.org/cgi-bin/mailman/listinfo/novalug
More information about the Novalug
mailing list