# Physical Memory Limits of Windows XP 64 Bit Operating System



## Gauravs90 (Oct 3, 2009)

Unlike the annoying memory limits of Windows XP Home Edition, Windows XP Professional x64 can address far more memory than previous versions of the operating system. Just how much RAM can be added to the 64-bit o/s?



Since the introduction of Windows 95, most computer users both in the home and in the office have used some form of 32-bit operating system. Windows 95, 98, 98SE, ME, 2000, XP Home, and XP Professional are all 32-bit operating systems.
 In the early days of 32-bit operating systems, RAM (computer memory) increased over time in the average computer from 32 megabytes (MB) to about 512 MB at the release of Windows XP in 2002. As memory use increased, reaching the memory limits of Windows XP became a real possibility.
 With the introduction of Windows XP x64 in mid-2005, memory limits looked like a thing of the past. Unfortunately, slow support by computer hardware vendors ensured that the memory limits of 32-bit operating systems would haunt computer users starting in about 2006.

*Why are There Memory Limits in Operating Systems?*

Many people ask why there even are memory limits in operating systems. Why can’t we simply add as much RAM as our motherboards will physically allow? The answer lies in the nature of addressable information.
 As many people know, computers use a binary language to calculate, store, and retrieve information. A bit of information can convey two states, on and off, signified by zeroes and ones in binary language.
 A 32-bit operating system can address only 2^32 (i.e. 2 raised to the 32nd power) bits of total memory. This amounts to 4,294,967,296 bits of information. This is why Windows XP has a 4 gigabyte (GB) memory limit. To make matters worse, the operating system can only address about 4 GB of cached memory in total. This means that the total amount of RAM recognized by Windows XP is 4 gigabytes, which includes all cached memory in the computer such as RAM, graphics memory in a video card, cached storage in a CPU, and other sources.
 This is why Windows XP only reports about 2.8 to 3.25 GB of RAM in a computer with 4 GB of RAM. The missing RAM is equal to the total cacheable memory from other sources in the computer. To make matters worse, Windows XP can only dedicate 3.25 GB of memory to any single process.

*Theoretical Limits of a 64-bit Operating System*

Using the logic discussed above, the theoretical memory limit of a 64-bit operating system is 2^64 (i.e. 2 raised to the 64th power) which equals 18,446,744,073,709,551,616 bytes (16 exabytes). To make things easier, this is about 18,446,744,073 GB.
 Of course, today no computer could possibly use that much memory. This figure simply represents the theoretical memory limit of a 64-bit operating system.

*The Memory Limits of Windows XP x64*

Windows XP 64 uses the same kernel as Windows Server 2003 (version 5.2.3790.1830). The impracticality of expecting that any computer or operating could take advantage of 16 exabytes of memory led Microsoft to cap the memory limit of Windows XP x64 to 128 GB of memory per process. This memory limit is far above the 4 GB limit of previous 32-bit operating systems and leaves enough breathing room for unforeseeable increases in memory requirements of computers and software in the near future.
 Few home computers are capable of using even 8 GB of memory. This limit is not attributable to the operating system but the limitations associated with the motherboard. It is impractical to think that any home user could take advantage of even 8 GB of memory, let alone 128 GB. Motherboard manufacturers rarely make their motherboards capable of using 8 GB of memory although some high-end gaming boards can use 16 GB of memory. Many servers can never have enough memory. They are much more capable of using and sometimes exceeding the use of 128 GB of memory.

*Conclusion*

Although home users often hit the 4 GB limit of 32-bit operating systems, it is unlikely the 128 GB memory limit of Windows XP x64 will be a problem in the near future. A 64-bit operating system can theoretically address 16 exabytes of information. Still, Microsoft capped the limit in its Windows XP x64 operating system to 128 GB, a limit that is likely to outlast the use of Windows XP x64 as a home operating system.


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## krishnandu.sarkar (Oct 3, 2009)

hm....

so how much RAM can we use for Vista(32bit and 64bit) and Win 7(32bit and 64bit)??


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## Krow (Oct 3, 2009)

^Vista and 7 x64 can use upto 128GB RAM AFAIK. 32bit OSes can't support more than 3.25 GB anyway.

@ *OP* If you have not written this tutorial, then please post the source too.


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## krishnandu.sarkar (Oct 3, 2009)

^Thnx...

Is 64bit OS's are better than 32bit OS's?? If yes how??


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## Krow (Oct 3, 2009)

They support more RAM and hence you can use resource hungry apps like video editing softwares and also video encoding/conversion softwares with ease considering the fact that more RAM is used.

Only downside is that quite a few apps don't support x64. It is not completely backward compatible with 32bit.


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## krishnandu.sarkar (Oct 3, 2009)

ohhhh ok.......Does 64bit OS's need more RAM to run??

I saw on some ReadMe's tat Minimum Req of RAM is 1GB for 32bit OS and 2GB for 64bit OS.


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## Krow (Oct 3, 2009)

Must be that way. I have not used x64 OS yet, but when I do (by about 12-13th of this month), I'll get back to you about performance. The whole point of x64 OS is that more RAM can be utilised and hence it must have higher system requirements.


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## krishnandu.sarkar (Oct 3, 2009)

okzzz.....thnx......!!


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## topgear (Oct 4, 2009)

@ Gauravs90 - it's not that 32bit OS can use only 4GB mem@ max. The OS makers only made consumer grade 32bit OS to support 4GB ram @ max. That's why XP and Vista x86 edition supports only 4GB mem @ max.

A 32 bit OS can also support 128GB mem @ max. Tha's why windows server 32 bit data center edition supports 128GB of mem and enterprise edition 64GB and their x64 consuterparts supports 2TB mem.

all 32bit windows 7, vista and Xp supports 4GB at max.
BTW, vista ultimate and xp x64 supports 128GB mem max but win 7 ultimatex64 supports 192Gb mem.

@ krishnandu.sarkar - I'm using xp x64 and vista x64 both. From my experience I can tell
you will nget some great HDD response time and data through output if you use x64 edition. But there is not any substantial difference in mem bandwidth and cpu performance. 

If you use softs like maya, 3ds max, VMware ie rendering and virtualization app s a lot with 4GB meme minimum you can benifit from x64 OS.


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## Krow (Oct 4, 2009)

That's good information *topgear*. Soon even I'll start with Win7 x64!


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## krishnandu.sarkar (Oct 4, 2009)

@topgear
thnx.....!!

@Techlomaniac
Thnx....!!

Got it....!!


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## topgear (Oct 5, 2009)

@ Techalomaniac & krishnandu.sarkar - My pleasure buddies


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