anoopks

Hi,
First of all apologies if this is not the right forum.

This is a first of its kind for me. There is an existing 32 bit C application that needs to be ported to a 64 bit machine. Now apart from taking care of pointers, size of int, conversions, Endian-ness, so and so forth, there is something else that has to be answered.

Perhaps the question will be vague and ideas incoherent. So please bear with me.

I have been asked to also find out, what can be suggested by us to the end customers as a good reason to increase RAM (why the same increase would not do the trick in a 32 bit machine, but in 64 bit machine)?

So lets take a 32 bit machine with 512 MB RAM.

The virtual process address space is 2 ^32 - 1.

In a 64 bit machine it will increase to 2 ^64 - 1.

But will the increase in the RAM, not be beneficial in both the cases? I mean, and I could be wrong here, I think the question is perhaps not correct technically, since an increase in the RAM will help in either case.

Putting it more strictly, can there be a case when an increase in the RAM would only benefit a 64 bit application on a 64 bit machine, and not a 32 bit application on a 32 bit machine?

Any pointers as to how to proceed to investigate will be highly appreciated.

Thanks in advance,
Anoop.

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Brian

64 bit can have a load more ram whereas 32 bit is restricted to 4gb max. We are quickly moving towards that 4gb ceiling so it is a good idea to switch to 64 bit now.

anoopks

lol yes, that would be the physical limit and in real world perhaps not many end users would like to match that limit.

Anoop.

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Intelligence: Finding an error in a Knuth text.
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Always code as if the person who ends up maintaining your code will be a violent psychopath who knows where you live.

If Java had true Garbage collection, most programs would delete themselves upon execution.

Brian

640kb ought to be enough for anyone. - Bill Gates

Bubba

No need to go to 64-bit yet until it has been tried and tested. I'm not paying to be someone else's guinea pig.

It's just a bigger pipe anyways.

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sand_man

>>It's just a bigger pipe anyways.

You say it like it is no big deal. Maybe it isn't yet, but 64-bit is the next gen of personal computers.

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Thantos

Actually the next generation is 3 state devices or 4 state devices. Then there are of course bio-electrial devices after that.

To answer the OP's orignal question: Unless you made assumptions there is nothing you really need to do to convert. The majority of what'll change is how big certain objects are. But if you are using good methods (like sizeof(int) instead of 4) then you'll be just fine.

anonytmouse

You may be interested in this article series: Old New Thing: Summary of the recent spate of /3GB articles

>> But will the increase in the RAM, not be beneficial in both the cases? <<

Extra RAM will only be beneficial if the system or your program is using the extra memory available.

CBUK

If you’re dealing with numbers larger than 32 bits 64 bit processors are faster as they don’t need to split the number up into two parts as a work around. A larger instruction set has also been introduced to improve the efficiency of the. Fedora produce a 64 bit open source operations system.

More that 4GB of memory is quite limited unless you count the forth-coming version of windows. Other uses may include massive graphic files or video editing. Bear in mind that sticks of RAM of 2GB cost more that 5 times as much as a 1GB stick.

Benefit will depend on the type of app you have written, an office application will see no benefit whereas a maths package may well. You would be wise to wait a couple of months as dual core 64 bit processors are just around the corner hopefully.

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Jez

64 bit is a must (soon).

My bro does 3D design using Rhino, and it struggles with *only* 1.25 GB RAM with the complex models he produces. With windows having a 2GB limit per process, there's not much headroom now.

Also I'd like to write stuff with a 64 bit processor in mind for performance reasons. Remember the x86-64 architecture gives the register-starved 386 model some much needed registers, which compilers will like.

fungus_mungus

This is so true! Anyways, getting back to the main topic... Switching from 32 bit to 64 bit is good for someone who writes programs that need vast quantities of memory. Examples would be search engines or graphics based games. Being a person who writes tiny programs that could very well run on a 286 I wouldn't be able to tell you how much of a better performance you would get out of a 64 bit machine other than more memory and faster additions. If you follow the language standard well, i.e. use ints and sizeof() you should be fine. C tends to be a very portable language. You can probably compile something on a 32 bit machine from a 16 bit machine like a 286. I work on a 32 bit machine but like I said my programs probably could run on a 16 bit machine and probably even a 64 bit one although that would not do anything for me. Bottom line - think of moving up from a 32 bit machine to a 64 bit machine as moving from a 16 bit machine to a 32 bit machine. If I remember a 16 bit machine could only access 1 MB? Right? Bitmaps used to only be able to fit into 64 KB segments. Now they can take up 4 GB. So what's going to have to change is not your program but the resources that it accesses and how it does it. If you are fine with the current size of your resources then your work is done. I guarentee it!