64 bit and RAM

Birdseye · Post by **Birdseye** » Mon Aug 03, 2009 6:16 pm

I always thought 64 bit meant we could address up to 128GB of ram in windows.

However, I just installed 64bit XP and System still has me at 3.12 GB just like XP. WTF?

anyone gots a clue? I wanted to bump to 8gb but what would be the point if i cant see all 4 now?

amazing you guys are still here, no idea who else i could ask

Warlock · Post by **Warlock** » Mon Aug 03, 2009 6:32 pm

thats odd im running XP64 here and it sees all 4gb.

how is your mem setup 4 1gb sticks or 2 2gb sticks?

U did a fresh install cause i know u cant upgrade from 32 to 64

AceCombat · Post by **AceCombat** » Mon Aug 03, 2009 6:54 pm

im assuming you have 64-bit hardware?

Admiral LSD · Post by **Admiral LSD** » Mon Aug 03, 2009 8:11 pm

What's your motherboard chipset? The Intel 945 (used in plenty of late model P4/early Core 2 desktops as well as an entire generation of Centrino laptops), in particular, has a fixed 4GB address space with no option to remap the MMIO space above the system RAM space meaning that, 64-bit OS or otherwise, you still wind up with the \"4GB issue\".

Zantor · Post by **Zantor** » Tue Aug 04, 2009 12:13 am

A 64-bit OS and CPU can address up to 8GB of memory; 32-bit can address up to 4GB. Often support for those amounts aren't put in by motherboards, BIOS, or OSes because of the effort needed to support such an amount.

For example, this is why most 32-bit boards/chipsets supported up to 2GB of RAM most of the time. Also, until additions and modifications to memory paging and instruction sets were added, adding the 4th gigabyte took one gigabyte just to have the paging or addressing table to address the 4th gigabyte, so you end up with 3GB effectively. Improvements in memory paging and some instruction set modifications removed the need for that huge table.

64-bit can do effectively double what 32-bit can but more optimized, so in the maximum, 64-bit can support up to 8GB of RAM. Again, it depends on if the motherboard/chipset, BIOS, AND OS are programmed/configured to support that amount of memory. It is very likely that Win XP 64-bit does not support more than 4GB of RAM because of how it was programmed.

Sirius · Post by **Sirius** » Tue Aug 04, 2009 12:54 am

I have a 64-bit OS and CPU with 12 GB of memory.

(The theoretical maximum addressable memory space for a 64-bit computer is 16 exabytes, but in practice most configurations support much less than this; the highest-end desktop versions of Windows 7 will support 192 GB, for instance.)

Krom · Post by **Krom** » Tue Aug 04, 2009 8:57 am

Zantor wrote:A 64-bit OS and CPU can address up to 8GB of memory; 32-bit can address up to 4GB. Often support for those amounts aren't put in by motherboards, BIOS, or OSes because of the effort needed to support such an amount.

For example, this is why most 32-bit boards/chipsets supported up to 2GB of RAM most of the time. Also, until additions and modifications to memory paging and instruction sets were added, adding the 4th gigabyte took one gigabyte just to have the paging or addressing table to address the 4th gigabyte, so you end up with 3GB effectively. Improvements in memory paging and some instruction set modifications removed the need for that huge table.

64-bit can do effectively double what 32-bit can but more optimized, so in the maximum, 64-bit can support up to 8GB of RAM. Again, it depends on if the motherboard/chipset, BIOS, AND OS are programmed/configured to support that amount of memory. It is very likely that Win XP 64-bit does not support more than 4GB of RAM because of how it was programmed.

ROFL, I'm sorry Zanator but that is hilariously wrong. You don't seem to understand at all.

32 bits supports a maximum of 4 GB of address space. 33 bits would support 8 GB of address space, 34 bits would support 16 GB... see the pattern here? Each additional bit doubles the supported address space. So while 32 bit is limited to 2^32 (-1) address space (4,294,967,295 bytes) 64 bit is able to address 2^64 (-1) or 18,446,744,073,709,551,615 bytes or 16 exabytes. In case you don't get the scale of what 16 exabytes is, it is over 17 billion gigabytes.

Zantor · Post by **Zantor** » Tue Aug 04, 2009 9:13 am

I am familiar with data measure scale up to yottabytes and zetabytes. Krom, you certainly do have a better understanding of how numbers relate with computing than I do, so thank you for the corrective insight.

If windows won't see more than 4GB, it wasn't programmed to support more than that. That's the only explanation I can come up with.

Sirius · Post by **Sirius** » Tue Aug 04, 2009 10:25 am

The numbers I found for WinXP 64-bit said 128 GB or something around there. 4 GB is of course an inherent limitation of 32-bit, but it should really support more in the 64-bit version.

Grendel · Post by **Grendel** » Tue Aug 04, 2009 11:02 am

Enable \"Memory remapping for 64bit OS\" in the BIOS. Or, if that option isn't available, set \"PnP aware OS\" to \"Yes\". If that doesn't help, your hardware is too old.

BUBBALOU · Post by **BUBBALOU** » Tue Aug 04, 2009 11:13 am

Your totally restricted by the motherboards support for that amount of RAM and Addressing. Basically that is it in a Nutshell

Warlock · Post by **Warlock** » Tue Aug 04, 2009 2:08 pm

Most MB that support 64bit can run up to 16gb unless its for a server then its much much higher

My MB is 2yrs old almost 3 and its supports a max of 32gb like I'm ganna need that much lol

To me if he has 4 1gb sticks he could have a bad stick even the cmos sees all 4gb iv had it where the OS didn't. Run a mem tester just in case never hurts to try

Darktalyn1 · Post by **Darktalyn1** » Tue Aug 04, 2009 11:04 pm

You can definitely run up to 16gb on a 64bit machine because we have several computers at work with that much.

When I dual booted my home computer, the xp32 sees 3gb and vista64 sees 4gb. Not sure why yours isn't registering

Canuck · Post by **Canuck** » Tue Aug 04, 2009 11:10 pm

Sirius wrote:The numbers I found for WinXP 64-bit said 128 GB or something around there. 4 GB is of course an inherent limitation of 32-bit, but it should really support more in the 64-bit version.

X 2 Ram = 128 GB XP64, also depends on MoBoard... mine can do 16 GB max. Others do more or less.

Admiral LSD · Post by **Admiral LSD** » Tue Aug 04, 2009 11:56 pm

/me points to his earlier comment about the 945

I think we need a practical demonstration...

On the left it says the machine has 4GB RAM installed but if you add the numbers in the Activity Monitor window up, they come to 3GB. Before you say \"LOL, Mac fail!\" let me elaborate. The 945, in both mobile and desktop trim, has a fixed 2^32 address space. It also doesn't support the 64 bit remapping feature meaning, in either 32 bit or 64 bit modes, you're still limited to 4GB of address space.

The reason Apple set the ceiling bang on 3GB is, I believe, so the non-Pros with integrated graphics wouldn't have more memory available than the Pros with dedicated graphics. A 128 or later, a 256MB dedicated GPU would push the usable memory ceiling down further than the Intel intregrated (which only use about 8MB or so at boot up).

It's not just Apple that fudge the numbers like this, either. While Vista32 originally showed the usable RAM, MS changed it somewhere along the line (SP1 I think) so it instead showed the installed amount with the actual usable amount kept largely hidden (It's listed in the sysinfo app but beyoond that, I don't know). 7, I believe, lists both the installed and usable amounts on the Computer properties sheet but puts the installed amount first. This may have been backported to Vista as well, I'm not sure.

Krom · Post by **Krom** » Wed Aug 05, 2009 8:46 am

On a side note, 64 bit CPUs and the like don't actually support 64 bits of memory address space, the limit on the Athlon 64's x86-64 implementation is actually 48 bits (256 TB).

Jeff250 · Post by **Jeff250** » Wed Aug 05, 2009 12:46 pm

It's actually even more complicated than that.

On a typical Athlon 64 box:

Code: Select all

$ cat /proc/cpuinfo | grep 'address size'
address sizes	: 40 bits physical, 48 bits virtual

So even though each process has a 48 bit virtual address space, the kernel can only use 40 bits to address the physical memory. So no process can hope to fill its address space with unique pages to physical memory.

Compare this to PAE enabled 32-bit operating systems where your address sizes are 36 bits physical, 32 bits virtual, which is the opposite case of the above.

Hostile · Post by **Hostile** » Wed Aug 05, 2009 2:20 pm

I like yogurt!

AceCombat · Post by **AceCombat** » Wed Aug 05, 2009 5:12 pm

Birdseye · Post by **Birdseye** » Thu Aug 06, 2009 12:50 am

haha

its amazing this drew so many replies i feel like this board should be dead. i no longer have a way to play to descent, i think now that i'm in 64 bit.

I have one instance of XP and tonight I installed VISTA 64 bit ultimate (its great). The Vista is reporting all 4GB, but the XP lists 3.2 still. Dunno, my 'pro' external sound card only has a 64 bit vista driver, so I am going to use vista and have the XP64 as a backup (has a few programs installed).

system-
q6600 overclocked (312) to 2.81 ghz w/ zalman fan on silent mode

4gb patriot memory ddr2
Asus P5W DH Deluxe

Birdseye · Post by **Birdseye** » Thu Aug 06, 2009 12:53 am

Next question:

I have the 4GB going, what if I added 2 4GB DIMMs in the primary slots and moved my 2 2gb DIMMs to the secondary slots? This would give me 12GB, I just want to be sue that will run well. Would going all the way with 4 4GB really be that much more faster or stable? Going with two 4gb is only like $250 and then I'd really be taking advantage of the RAM advantage in 64 bit at low cost.

Admiral LSD · Post by **Admiral LSD** » Thu Aug 06, 2009 1:53 am

That board is based on the 975X chipset which shouldn't have the 4GB shenanigans the 945 does. It only supports 8GB RAM though so you're only option if you want more RAM is another pair of 2GB DIMMs. If you're running BIOS 1506 or later check under Advanced -> Chip Configuration to see if the Memory Remap Feature is enabled.

Sirius · Post by **Sirius** » Thu Aug 06, 2009 3:11 am

Might be difficult to run the original Descent binaries, but XL and Rebirth still run on 64-bit (speaking from experience, in fact).

Krom · Post by **Krom** » Thu Aug 06, 2009 8:03 am

Yeah, Rebirth even runs in Windows 7 RC 64 bit. As far as I know Descent 3 works too.

Foil · Post by **Foil** » Thu Aug 06, 2009 8:32 am

Yep, Descent3, DxX-Rebirth, and D2X-XL all work fine on my Vista x64 machine.

AlphaDoG · Post by **AlphaDoG** » Thu Aug 06, 2009 9:42 am

Zxerol in Prepare for Descent thread on Penny Arcade wrote:Although Descent 3 is not open-source, it works as-is all the way up to mother****ing Windows 7 x64. Yeah, I just ran it ten minutes ago. It works and I'm awesome and you all can suck it. Game was so ahead of its time it runs on operating systems FROM THE FUTURE.

BUBBALOU · Post by **BUBBALOU** » Thu Aug 06, 2009 10:15 am

AlphaDoG wrote:
Zxerol in Prepare for Descent thread on Penny Arcade wrote:Although Descent 3 is not open-source, it works as-is all the way up to mother****ing Windows 7 x64. Yeah, I just ran it ten minutes ago. It works and I'm awesome and you all can suck it. Game was so ahead of its time it runs on operating systems FROM THE FUTURE.

Great intro an review..

Krom · Post by **Krom** » Thu Aug 06, 2009 10:59 am

Windows program works in Windows... A shocking revelation!

Birdseye · Post by **Birdseye** » Thu Aug 06, 2009 11:23 am

I think the main problem is I can't run the mouse at 200Hz, i don't know if that is totally true.

Krom · Post by **Krom** » Thu Aug 06, 2009 11:35 am

Modern USB mice can sample at up to 1000 Hz, although it would be different from what you are used to no doubt.

64 bit and RAM

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