Why does 64-bit version require 2x Memory?


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I was wondering if anyone knew why the 64-bit version has double the requirements in memory for Windows 7? Are they just using the 32-bit apps and tacking on extra data so that 64-bit processors can take advantage? Does this indicate that Microsoft isn't that serious about 64-bit after all this time?

Just because the processor in theory uses 2x the amount of bits per instruction, doesn't mean applications have to be 2x as large to fill that gap.... that's just inefficient.

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Ive been told this, and can confirm it as well that if you run 64 bit its recommended that you have 4gb of ram or greater to make a difference. I don't know the specifics, I have 3gb in my Dell right now and 32 bit Vista runs a lot quicker than 64 bit Vista did

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dont quote me, but i believe because the code itself is more advanced and complicated, which in general means more data is necessary to achieve the task, thus more memory is needed.

the memory requirement for x64 vs. 32 is simply a baseline, doesnt necessarily mean that it will absolutely use twice the memory

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@Evolution: 64 bit doesn't require 2x the RAM. SOME DATATYPES DO. For instance, integers will double in size but will also allow you to represent numbers that are way larger (that's why you can address more memory). A byte is still a byte.

A JPEG image will be the same size in 32 and in 64 bits when loaded in memory.

Saying 64 bits requires twice the memory is just ignorant. It's almost the same as saying it'll double your speed. 64 bits is all about allowing you to access more data at once. Sometimes that makes you require more RAM and sometimes it'll increase your speed.

@gamestargrinder: It's not like you need twice the RAM to make a difference. It's more like you'll only notice a difference if you NEED and USE more RAM than 32 bits allows. If you have 3GB on 32 bits and 6 on 64 bits and you only use 1GB, then you're unlikely to experience any difference whatsoever.

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Mainly people go for 64-bit only if they got 4GB or more memory ANYWAYS! I used to use 32-bit but i got 6gb memory now so i switched to 64-bit to make use of memory :)

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Actually, a 64bit OS has no more requirement for memory than a 32bit OS. The primary difference, at least in terms of memory, is that a 64bit OS can address a considerably greater amount of memory than a 32bit OS.

If I remember correctly:

32bit windows can address up to 4Gb - 2x2 (OS/APPS)

64bit windows can address up to 16Tb - 8x8 (OS/APPS)

The main problem is the lack of true 64bit apps for the 64bit OS...

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Actually, a 64bit OS has no more requirement for memory than a 32bit OS. The primary difference, at least in terms of memory, is that a 64bit OS can address a considerably greater amount of memory than a 32bit OS.

How sure are you that there aren't different requirements? Its nonsensical of MS to but it on the requirements otherwise.

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64 bit doesn't require 2x the RAM. SOME DATATYPES DO. For instance, integers will double in size but will also allow you to represent numbers that are way larger (that's why you can address more memory). A byte is still a byte.

Integer stay at 32bit. However, Pointers will become 64bit long, and large programs use many pointers.

Back to the OP's question: x86-64 operating systems are usually larger than 32bit ones, as they ship both 64 AND 32bit versions of all their libraries for compatibiliy. Without the 32bit ones, you could only run 64bit applications, which are only a few so far. Of course, when you ship them, they will get loaded into memory at one point, which is the second reason why x64-OS need more memory than 32bit ones.

It's the same for Linux, Windows and Mac OS X.

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The starter is referring to the MS requirements they have published. Not the trend/desires/requirements of people installing more RAM on 64bit machines.

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The starter is referring to the MS requirements they have published. Not the trend/desires/requirements of people installing more RAM on 64bit machines.

I don't know why anyone would install the OS on the baseline config with either spec, anyway. Cheaper or not, thats just no way to go.

But as to the original question, I think it's more an acknowledgement that though 640 or 768 megs is more in line with what you'd need to get the same amt of memory available for apps, almost noone is going to have that especially on a 64 bit system.

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How sure are you that there aren't different requirements? Its nonsensical of MS to but it on the requirements otherwise.

I'm not really sure what 'requirements' you are referring to, but more often than not MS will overstate a case. As of now I run Win7 (7127) on my main PC with 8Gb RAM and my wife runs win7 (7127) on her notebook with 1Gb RAM. In terms of general day to day stuff she is as happy as I am.

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How sure are you that there aren't different requirements? Its nonsensical of MS to but it on the requirements otherwise.

well i am running windows 7 ultimate 64bit just fine on 2gb of ram with no slow downs

the image below even tho i am 100% CPU usage the system is still darn responsive for about anything i do.

post-74594-1243434584_thumb.jpg

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Actually, a 64bit OS has no more requirement for memory than a 32bit OS. The primary difference, at least in terms of memory, is that a 64bit OS can address a considerably greater amount of memory than a 32bit OS.

If I remember correctly:

32bit windows can address up to 4Gb - 2x2 (OS/APPS)

64bit windows can address up to 16Tb - 8x8 (OS/APPS)

The main problem is the lack of true 64bit apps for the 64bit OS...

That's the right idea!

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Actually, a 64bit OS has no more requirement for memory than a 32bit OS. The primary difference, at least in terms of memory, is that a 64bit OS can address a considerably greater amount of memory than a 32bit OS.

That's untrue. A combination of things posted above are what is correct.

You have longer pointers, making datastructures such as lists and any dynamic memory stuff larger. Any x64-native programs will be using longer datatypes, because they have wider processor registers, which means that they will occupy more memory. You also have the WOW64 system, which is going to be loading 32-bit copies of libraries into memory as well as the 64-bit copies for native stuff.

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I'm glad that they have set the memory requirements so high, even though the 64-bit version doesn't actually use twice as much. Ideally the overall requirements should have been set even higher, because Windows is a resource-hungry monster. That way OEMs couldn't get away with selling underpowered systems that give a, well, less than ideal experience.

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x86-64 has larger pointer types. Some instructions are also longer. But 2x as large is a huge stretch; in my experience, it's more like 25% more, give or take 10% for most code. But a lot of programs contain much more than just code, like graphics, UI text, etc., and those things will remain the same.

You also have to consider is the fact that you have a duplicate copy of most system libraries and DLLs loaded (one copy for 64-bit programs, one copy for 32-bit programs). Depending on your usage pattern, how many apps you have open, etc., it may very well be the case that this extra overhead for 32-bit compatibility will overshadow the rest...

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this happens when you're using too many 32bit applications. A x64 Windows uses the WOW64 technique to run 32bit applications. So the 32bit dlls also must be loaded into the memory. That's why a x64 windows uses more memory.

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