64bit question

[isus]

my friend and i were discussing the g5 and panther...

panther is a 32-bit os. the g5 is 64-bit.

can a program take FULL advantage of the 64-bit cpu even though the os itself is only 32-bit?

[rafter109]

I say no, but what the hell do I know, im just a stupid PC user. JJ :laugh:

[isus]

yes you are, rafter109 :-P

rafter109 is the friend in question here.

and just for the record:

i do believe i read somewhere (although i am too lazy to go look) that a 64-bit app would be able to use the 64-bit cpu, regardless of the fact that panther is still 32-bit.

[the evn show]

Panther and the version of Jaguar shipping on G5s have extentions that enable software to make use of the 64-bit processors (and some of the new 32-bit stuff on G5s too like the hardware sqrt() function). You are free to do 64-bit pointer addition, operation on registers holding 64-bit integers, etc.

Panther will address "lots" of gigs of ram, but any given process can only access 4gb of physical memory: you can have as many of these processes as you want (physical memory is the limitation here). This is the major limitation of panther.

Not an issue for most of us because we aren't specing G5s with >4gb of ram, but if you were building 8gb or 16gb G5s for high end photoshop or final cut work then you might run into this.

[DjmUK]

Just as the evn show says, in other words.

- Panther is primarily 32-bit, but has 64-bit extensions built into it.

- 32-bit programs can take full use of the CPU.

- 64-bit programs can take full use of the CPU.

- The CPU/OS is backwards compatible with both 32/64-bit applications.

I'm guessing that the next major update of Mac OS (10.4) will be natively 64-bit. But would that make a difference..? we don't use over 4Gb of RAM (the average user) so we won't be using the CPU(s)/OS to it's full potential. As long as we can run both 32/64-bit programs we'll be happy.

[macman87]

just a question, since the g5 is capable of running 32bit programs as well as 64bit programs, does it mean that it is not as powerful as a processor like the italium II which only does 64bit programs?

[DjmUK]

just a question, since the g5 is capable of running 32bit programs as well as 64bit programs, does it mean that it is not as powerful as a processor like the italium II which only does 64bit programs?

That's a good point. Although, just because it's 64-bit - doesn't mean it will be used to it's full capability.

For example,

1.) Say a program required 16-bits as a single stream of data. The 32 & 64-bit will calculate that stream at the same speed.

2.) Say a program required 32-bits as a single stream of data. The 32 & 64-bit will calculate that stream at the same speed.

3.) Say a program required 48-bits as a single stream of data. The 64-bit will calculate that stream at the same speed.

4.) Say a program required 64-bits as a single stream of data. The 64-bit will calculate that stream at the same speed.

x.) Say a program required 64-bits as a single stream of data (on a 32-bit CPU). The CPU would then take 2 passes (2x 32-bit streams), so it would take twice as long - in the millionth's of a second mind you ;) and the 64-bit would complete it in a single pass (1x 64-bit stream).

It's very difficult to explain, let's just say that the G5 can do both 32 & 64-bit and for the price it's a great deal. The Itanium II is extrememly expensive, and the downside of that chip is that it cannot handle the current 32-bit programs as easily as the G5 (if at all).

[helmers]

Okay, but most CPU's to date have several parts in them that allready are 64-bit. Also, a program cannot be "fully optimized" for both 32 and 64, without incurring overhead. There must be some additional code, if it is included, it is bloat, if it is not included there are two versions.

[isus]

thanks guys :) i win!

[lexor]

you loose a bit of performance (a couple of million cycles per page request in virtual memory) but otherwise apps take full advantage of the CPU. i.e. 32 bit aps fully use 32bit portion, 64bit take full advantage of all 64bits. The slight (notice slight) performace hit comes from the fact that it has to keep track of 2 different page types, which store, it's probably the same page, but it has to spend time figuring out which one it is, and which portions to use and which are garbage. not to worry you typing of the keyboard wastes more CPU cycles than page read/writes.

[kairon]

Just as the evn show says, in other words.

- Panther is primarily 32-bit, but has 64-bit extensions built into it.

- 32-bit programs can take full use of the CPU.

- 64-bit programs can take full use of the CPU.

- The CPU/OS is backwards compatible with both 32/64-bit applications.

I'm guessing that the next major update of Mac OS (10.4) will be natively 64-bit. But would that make a difference..? we don't use over 4Gb of RAM (the average user) so we won't be using the CPU(s)/OS to it's full potential. As long as we can run both 32/64-bit programs we'll be happy.

I don't think so. Cut off all your past customers when the G5 just only came out?And isn't even in all product lines yet?You might also think they could develop versions for 32-bit and 64-bit, but I just don't see them having two seperate versions. I say OS 11 before things are 64-bit only.

[rafter109]

Not so fast isus. Wasn't your question

can a program take FULL advantage of the 64-bit cpu even though the os itself is only 32-bit?

? You couldnt possibly have won yet since no one has technically answered your question. No one has addressed a pure 32-bit OS in this topic at all and the only one that even comes close is the evn show who stated that panther was a 32-bit OS with extensions for programs to utilize 64-bit features. If it were not for those extensions in panther, would the programs still be able to run as 64-bit? That is the question that needs to be answered before anyone wins this debate.

[isus]

haha

i think evn show answered just fine. who cares what would happen if the extensions existed or not? they do on the os that runs on the g5, if you are dumb enough to put a FULL 32-bit os (such as 10.2.6) on your g5, that's not my problem.

[rafter109]

That's still not answering the question that you asked. Now if you were to have asked whether panther allowed software to utilize the 64-bit instructions on the G5, you would have won. Unfortunately, you didnt ask that question and instead asked whether a 32-bit os could allow programs to utilize 64-bit instructions on a cpu. And as far as I'm concerned you have lost due to a technicality in the wording of your question.

Next time just be sure to express yourself exactly as you mean to be taken and not leave any details out.

[isus]

hmm, i lost, and you didn't win.

if you had a problem with the question, you should have stated it last night, when you first replied.

unfortunately, you stated no problem with the question, it was pointed out that panther has 64-bit extensions, and therefore, your whole argument about how apple is misleading consumer's by showing a 64-bit desktop which can't run 64-bit apps at full speed was shown to be your misinformation, not mine.

in that respect, i won.

i know how much you hate it when i win.

[rafter109]

yes you did win in the respect that panther can run 64 bit apps. but as far as the question posted in this forum, you lost due to the fact that apparently 64 bit apps cannot run on a pure 32bit os and I was correct in that respect. The place where we were both wrong was in the fact that panther has extensions for 64-bit instructions. We were both under the assumption that it was a pure 32-bit os.

There, I think it is fairly settled and it has concluded in a draw. :happy:

[isus]

finally. damn.

yes, i used bad wording... yes, i understand that a pure 32-bit os cannot use 64-bit apps. however, you were the only one that said panther was 32-bit.

i never said it, but i remember reading on appleturns that it had 64-bit extensions to do this.

i was too busy writing my research paper to find the proof though.

[frod]

is there any real point for a common program to be 64bit?

wouldn't it just slow down remedial tasks since it has to address larger memory locations and perform 64bit math instead of 32bit math?

[MrA]

For the 'common' program, no. There wouldn't be any point to it being 64 bit. All common programs today can get along just fine with 32 bit. However, if the program was 64 bit and compiled for a 64 bit processor (ie. itamiums & G5s), assuming the 64 bit instructions took the same time to execute as the 32 bit ones (as it should), the program should run at the same speed. Maybe even faster.

Why faster? I dunno, but on the pentium, a 32 but multiply is faster than a 16 or 8 bit one.

[the evn show]

Both Windows XP Home and Mac OS X 10.2.1 are 32-bit operating systems (if that's what you want to call them) but both allow you to do operations on 64-bit instructions in hardware on '32-bit chips' Altivec is allows you to deal with 32,64, or 128 bit numbers in registers that are 128bits wide without any special hacks. The x86 alphabet soup SIMD systems have similar capabilities - though not as advanced as Apple/motorolla/ibm's VMX (IIRC SSE2 re-uses the standard x86 FPU registers to do it's dirty work rather than providing it's own) they still get the job done.

At what point do you call an application 64-bit instead of 32-bit? The first time put a 64bit number in V0? R0? maybe into the segment register? Where exactly do we draw the line?

FYI the RS6000 chips used in visualization systems are 64-bit and so is the OS that ships with those machines (solaris) but it has a 32bit userland because the overhead of using 64bits outweighs the performance benifits. An instruction that operates on 64bit number specifically should be faster than a cludge of 32bit instructions that do the same thing, however a 64bit add should be roughly the same speed as a 32bit add on an otherwise identical chip.

Itanium runs 64-bit code faster than 32bit because it does it through emulation

P-pro chips were also optimized to run 32bit code, the 16bit transistors were compromized in order to get these increases.

[MrA]

Both Windows XP Home and Mac OS X 10.2.1 are 32-bit operating systems (if that's what you want to call them) but both allow you to do operations on 64-bit instructions in hardware on '32-bit chips'

Yes, but the 64-bit instructions are done by using 2 or more 32-bit instructions to 'emulate' the 64-bit one. If you had a 64-bit OS, all it's 64-bit processing would be done using single 64-bit instructions rather than multiple 32 bit ones.

BTW, SSE2 could not use the fpu registers because they are only 80 bits wide. SEE/SSE2 requires 128-bit registers to work with. MMX however does use the fpu registers since those are only 64-bits wide (but they can't do 64-bit operations). This is very screwy since you can't use the fpu and MMX at the same time.

[Southern Patriot]

You might also think they could develop versions for 32-bit and 64-bit, but I just don't see them having two seperate versions.

I don't see why Apple wouldn't have two builds of OS X 10.4 (or whatever). It's not like it would be without precedent. Previous versions of the OS (such as 8.1) supported totally different chip architectures (68K & PPC), and the installation difference was transparent to the user. Why would it be any more difficult for the installation program to check for the CPU type (32 bit or 64 bit) and install the apropriate binaries? It's not like Apple is scared of using more than one CD for the OS (and if it was put on DVD, it would make this part even easier). Not all of the programs included would need to be re-compiled for 64 bit (I mean, what would Text Edit gain??). Since OS X is already BSD based, and there are already 64 bit versions of BSD for other processors, so just how hard do you think it would be for them to compile OS X as 64 bit?