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Index > Heap > 64-bit OS in less than 4 GB ram environment

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sleepsleep



Joined: 05 Oct 2006
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sleepsleep
what are your views regarding running a 64-bit OS in an environment that has less than 4 GB memory?
Post 09 Apr 2009, 13:18
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revolution
When all else fails, read the source


Joined: 24 Aug 2004
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revolution
It depends upon your application. Do you need faster arithmetic for your task? 64x64 multiplies can be a large performance boost for some applications. So the answer is, as usual with computers, "it depends". Everything has it's place where it is useful and where it is not.
Post 09 Apr 2009, 13:22
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Madis731



Joined: 25 Sep 2003
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Madis731
I feel that the marketing stuff has gotten to someone's head.
You NEED to have a 64-bit system IF you have 4GB+,
but you DON'T NEED 4GB+ memory IF you have a 64-bit system.

That should sum it up. The rest is about to do with applications as revolution already nicely put.
Post 09 Apr 2009, 15:37
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bitRAKE



Joined: 21 Jul 2003
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bitRAKE
The primary benefit of 64-bit is the virtual address space - not the memory capacity. Congestion in the address space requires complex solutions to simple problems.
Post 09 Apr 2009, 15:41
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Borsuc



Joined: 29 Dec 2005
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Borsuc
I hate 64-bit for the same reason I hate all architecture changes Razz (since I've grown used to 32-bit apps)

bitRAKE wrote:
Congestion in the address space requires complex solutions to simple problems.
What's so hard to use ReadFile or similar functions? Confused

also doesn't 64-bit code take up more space?

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Post 09 Apr 2009, 17:13
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sleepsleep



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sleepsleep
could i conclude that, x64 is better (in term of performance) compare to x86 even in an environment less than 4GB memory?

Quote:

You NEED to have a 64-bit system IF you have 4GB+,

yeah, isn't it?

Quote:

you DON'T NEED 4GB+ memory IF you have a 64-bit system

not true??
Post 09 Apr 2009, 17:47
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Borsuc



Joined: 29 Dec 2005
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Borsuc
Madis731 wrote:
You NEED to have a 64-bit system IF you have 4GB+,
32-bit Linux can access 64GB of RAM, or so I heard.

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Post 09 Apr 2009, 21:01
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LocoDelAssembly
Your code has a bug


Joined: 06 May 2005
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LocoDelAssembly
Yes, with PAE, Windows too, but you can't have 36-bit pointers since the architecture is still 32-bit it makes not so easy to access all the physical memory. In Windows you need to use Address Windowing Extensions. Don't know how it is done in Linux but it must use something similar since again, the architecture is not enabled to access the entire 64 GB of memory without remappings in between.
Post 09 Apr 2009, 21:15
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revolution
When all else fails, read the source


Joined: 24 Aug 2004
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revolution
sleepsleep wrote:
could i conclude that, x64 is better (in term of performance) compare to x86 even in an environment less than 4GB memory?
No, like I said above "it depends". Some apps may see a performance boost with 64bit code, and the opposite is also true, some apps may see a performance drop in 64bit code. You cannot simply assume that 64bit is faster for everything.
Post 09 Apr 2009, 23:27
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bitRAKE



Joined: 21 Jul 2003
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bitRAKE
Borsuc wrote:
bitRAKE wrote:
Congestion in the address space requires complex solutions to simple problems.
What's so hard to use ReadFile or similar functions? Confused

also doesn't 64-bit code take up more space?
There is no doubt in my mind that you could work with a 50GB database in 32-bit assembly. I'm saying it is easier (fewer abstraction layers) in 64-bit.

64-bit code in general will be larger - almost all 64-bit accesses require an additional byte prefix. Very few programs actually need 64-bit accesses, and are virtually the same size. Of course, the Win64 ABI requires the use of R8 and R9 -- all new registers require the REX prefix.

(I would be lying if I said the transition to 64-bit was easy. It was the additional XMM# registers that sealed the deal for me. I haven't spent much time understanding the benefits of AVX, but it might sway me in a couple years.)

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Post 10 Apr 2009, 01:56
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tom tobias



Joined: 09 Sep 2003
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tom tobias
Here is a description of some of the changes which Intel has introduced, with regard to AVX.
Post 10 Apr 2009, 09:21
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edfed



Joined: 20 Feb 2006
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Location: 2018
edfed
why does they make a new mode?
why?
it would be simpler to implement 64 bits like they implemented MMX or SSE and IA32-EMT
Post 10 Apr 2009, 17:02
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Madis731



Joined: 25 Sep 2003
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Madis731
When your CPU is in 64-bit mode and your programs and drivers are in 64-bit mode there are some guarantees that don't exist on 32-bit platform. For extensions you need to check if they exists, but when you're already in a "mode", you can be sure that any goodies will apply.

Another benefit is that native 64-bit applications are sometimes smaller, especially if you need access to more than 2GB of application memory and/or your calculations go beyond 4 billion (with integer math). There are 8 more general purpose + 8 more XMM registers and with 32-bit mode, you would have surely needed some kind of a prefix to use them, plus the overhead of code to check if they exist.
Post 11 Apr 2009, 09:38
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Xorpd!



Joined: 21 Dec 2006
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Xorpd!
I don't think anyone has caught up to my x64 Mandelbrot code yet, although Kümmel has made some excellent progress with 32-bit code. When I first got an x64 machine you could go to the store and the clerks there would tell you that their machines were 64-bit machines even though they all had 32-bit Windows installed on them. Now it's really common to find machines with 64-bit Vista installed at the store. If you want to develop code for such machines you need to have 64-bit Windows installed yourself.
I often read that 64-bit code is bigger than 32-bit code, but given that you are using assembly language anyhow you could use 32-bit pointers for stuff that fits in 32 bits, only using 64-bit pointers when necessary. 32-bit code that does whatever is necessary when 64-bit pointers are required (whatever that is) or when twice as many registers are required isn't going to be smaller than 64-bit code that does the same.
Also 64-bit MSIE may be a little safer than the 32-bit version because most software isn't ready for it.
Post 12 Apr 2009, 17:31
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