Dude, where's my 4GB?

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Re: Dude, where's my 4GB?

Postposted on Wed Aug 19, 2009 8:37 am

aff_tim wrote:sounds like an investment priority of faster GPU instead of more video card ram would be prudent for system ram optimization.


Or you could get an x64 OS and not have to deal with half of this madness. :wink:
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Re: Dude, where's my 4GB?

Postposted on Wed Aug 19, 2009 2:17 pm

aff_tim wrote:sounds like the available memory is actually a moving target with the % of on board video ram being utilized at any given instant to be a factor involved in the available system memory issue.
No, that's not how it works. A given video card has a set of registers that specify how much space it wants in the system memory map for DMA operations. This may or may not correspond to how much RAM is on the card, but it's set in stone by the firmware on the card. At boot, your system's BIOS reads these registers and sets aside that area. When Windows boots, that chunk of the physical memory map is already unavailable. It does not change over time; the only way it would change is if you flashed a different firmware on the card (and perhaps not even then).

But we're already at the point where more on-card video memory is giving limited returns; mostly it's useful for people running at high resolutions (and/or high AA levels). Doubling the video memory from 512MB to 1GB may give you 3 or 4 FPS in something like Far Cry, and next to nothing in other games. Of course, that may change in the future, but given that games these days seem to be optimized for consoles with their much lower resources, i wouldn't count on it. (There are some wrinkles in DX10/11 that may make that memory more useful, but the ability to do demand paging from system memory mitigates that somewhat since games can also be more efficient in how they use on-board memory.)
but as I now understand it, on-board video chips using system ram is not the resource hog I perceived the on-board chip to be.
& the new side port video memory is actually of less benefit than would appear at 1st (well marketed) glance.
There's still contention on the bus for that system memory, so it's still much slower than dedicated memory. Sideport memory or on-card memory belongs to the GPU alone, and that makes a difference. Dedicated cards also tend to use fast memory optimized for graphics ops.
SuperSpy wrote:Or you could get an x64 OS and not have to deal with half of this madness. :wink:
Yeah. But on older hardware that may not help, since (as we've discussed multiple times) there are motherboards that will accept a 64bit CPU but don't offer the option of hoisting RAM above the area set aside for DMA devices, and/or don't offer more than 32bits of physical address lines.
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Re: Dude, where's my 4GB?

Postposted on Sun Aug 23, 2009 11:45 am

I had to look up some stuff up to understand (NOT) the system RAM issues clarified (? :lol: ) by monseigneur urbergerbil.

DMA = direct memory access
DMA operation: Interaction between the main CPU and DMA device.
Many hardware systems use DMA including disk drive controllers, graphics cards, network cards and sound cards. DMA is also used for intra-chip data transfer in multi-core processors,

modern devices include their own DMA controllers on the device itself. Drivers for these devices must obtain the physical addresses to be used for data transfers and for command/status access and map them into the device registers.

Direct memory access (DMA) is a feature of modern computers and microprocessors that allows certain hardware subsystems within the computer to access system memory for reading and/or writing independently of the central processing unit.

Computers that have DMA channels can transfer data to and from devices with much less CPU overhead than computers without a DMA channel.

With DMA, the CPU would initiate the transfer, do other operations while the transfer is in progress, and receive an interrupt from the DMA controller once the operation has been done.
Without DMA, using programmed input/output (PIO) mode for communication with peripheral devices, or load/store instructions in the case of multicore chips, the CPU is typically fully occupied for the entire duration of the read or write operation, and is thus unavailable to perform other work.

:roll: :o
I just got a personal blue screen
.. quite amazing what goes on inside the box .. in addition to the fans. that I understand :oops:

http://www.eventhelix.com/RealtimeMantr ... 0%28DMA%29
http://docsrv.sco.com/HDK_concepts/ddT_dma.html
http://en.wikipedia.org/wiki/Direct_memory_access


oh,
2 to the 32nd (32 bit OS) = 4,294,967,296
& 4 gig = 4,096,000,000
WTF 8)
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Re: Dude, where's my 4GB?

Postposted on Sun Aug 23, 2009 2:59 pm

aff_tim wrote:2 to the 32nd (32 bit OS) = 4,294,967,296
& 4 gig = 4,096,000,000
WTF 8)

4 gig is 2^32, whoever quoted 4,096,000,000 is rounding :P
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Re: Dude, where's my 4GB?

Postposted on Sun Aug 23, 2009 5:53 pm

SuperSpy wrote:
aff_tim wrote:2 to the 32nd (32 bit OS) = 4,294,967,296
& 4 gig = 4,096,000,000
WTF 8)

4 gig is 2^32, whoever quoted 4,096,000,000 is rounding :P

Severely so.

4 GiB = 4,096 MiB = 4,194,304 KiB = 4,294,967,296 Bytes

The memory system addresses 8 bit blocks.
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Re: Dude, where's my 4GB?

Postposted on Sun Aug 23, 2009 5:57 pm

That'd be 4 kiMB. Kibimegabytes, because you're mixing measurement methods.

Not that that hasn't been done before, of course.

Floppy disks aren't 1.44 MiB or 1.44 MB. They're 1.44 kkiB.
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Re: Dude, where's my 4GB?

Postposted on Sun Aug 23, 2009 6:26 pm

ah, 4096meg ..not ..
DOH!
:oops:
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Re: Dude, where's my 4GB?

Postposted on Fri Sep 25, 2009 8:10 pm

the answer my friend is blowing in the wind...................
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Re: Dude, where's my 4GB?

Postposted on Sat May 08, 2010 11:44 am

I have a question about 4GB of RAM and "memory remapping" option in BIOS. i have recently upgraded my PC and reinstalled my 32-bit OS. When I enable this option I typically end up with a "MEMORY_MANAGEMENT" BSOD, disabling it makes my PC freeze with a high-pitched noise from my speakers.. Now I am not sure whether this BIOS option was enabled or disabled when I was installing my OS, so can anyone tell what how it may be related to new 32-bit installs, or changing it after the installation? Will reinstalling my PCI devices solve the problem, provided I leave it disabled for my 32-bit OS?

I have an X-Fi xtreme music and a TV tuner, both PCI cards..

Thanks!
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Re: Dude, where's my 4GB?

Postposted on Sat May 08, 2010 2:27 pm

Anyone?
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Re: Dude, where's my 4GB?

Postposted on Sat May 08, 2010 5:01 pm

You know, it really isn't good form to bump a post after only 3 hours.
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Re: Dude, where's my 4GB?

Postposted on Sun May 09, 2010 9:16 am

bhtooefr wrote:You know, it really isn't good form to bump a post after only 3 hours.

Well, my apologies if I sounded very demanding by doing that.
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Re: Dude, where's my 4GB?

Postposted on Sun May 09, 2010 10:55 am

If you have a spare hard drive, just do a quick from-scratch install with remapping disabled to see if it helps.
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Re: Dude, where's my 4GB?

Postposted on Sun May 09, 2010 2:25 pm

On a 32bit OS the setting of this switch shouldn't matter: if it's off, some RAM is inaccessible because it is shadowed by the PCI devices; if it is on, the RAM is inaccessible because it is remapped above the 4GB boundary.

If you are getting errors no matter which way this switch is set (even if they differ in detail) it's possible the problem has nothing to do with the switch. Are you sure your memory is all good (run a memtest on it)?

If you're not encountering a hardware problem (like bad memory) then it's possible that you're hitting some problem with the drivers. You said you upgraded your PC -- was the system running properly with the new hardware before you tried re-installing the OS? What 32bit OS are you trying to install (XP?) Have you tried installing the OS without the new hardware (it's possible Windows is detecting the new hardware and selecting drivers for it, but the default drivers that you'd have on any original Windows XP CD would be very old and might have problems with newer hardware)?

Since we're talking about a 32bit OS and possibly other hardware problems that likely has nothing to do with memory remapping or the 4GB limit (and "lost" RAM below that) you might want to open a fresh thread for this.
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Re: Dude, where's my 4GB?

Postposted on Sun May 09, 2010 3:47 pm

UberGerbil wrote:On a 32bit OS the setting of this switch shouldn't matter: if it's off, some RAM is inaccessible because it is shadowed by the PCI devices; if it is on, the RAM is inaccessible because it is remapped above the 4GB boundary.

If you are getting errors no matter which way this switch is set (even if they differ in detail) it's possible the problem has nothing to do with the switch. Are you sure your memory is all good (run a memtest on it)?

If you're not encountering a hardware problem (like bad memory) then it's possible that you're hitting some problem with the drivers. You said you upgraded your PC -- was the system running properly with the new hardware before you tried re-installing the OS? What 32bit OS are you trying to install (XP?) Have you tried installing the OS without the new hardware (it's possible Windows is detecting the new hardware and selecting drivers for it, but the default drivers that you'd have on any original Windows XP CD would be very old and might have problems with newer hardware)?

Since we're talking about a 32bit OS and possibly other hardware problems that likely has nothing to do with memory remapping or the 4GB limit (and "lost" RAM below that) you might want to open a fresh thread for this.

I figured it out, it was my RAM that was at fault.. I have bought 2x2GB of OCZ sticks that are rated for 1600MHz and both sticks fail at recommended settings and one of them causes BSODs at whatever setting is used.
How ironic, I payed an extra for premium and looks like I'll pay more to RMA it, speak of "thoroughly tested" and "premium quality"..
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Re: Dude, where's my 4GB?

Postposted on Sun May 09, 2010 5:01 pm

axeman wrote:Friends don't let friends buy OCZ.
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Re: Dude, where's my 4GB?

Postposted on Sun May 09, 2010 6:16 pm

First time buying OCZ and don't happen to have friends that can give that level of an advice..BUT it looks like I bought the sticks at a fantastic price when they first appeared on the Danish market and now they cost almost 40% more :o Gonna RMA and sell them, so the price can cover my RMA expenses+a pair of low-voltage G.Skill sticks :lol:

Just to stay within the topic, i have to mention that one shouldn't fiddle with "memory remapping" feature after an install.. Looks like changing it may affect your PCI sound card, provided you have one, or your GFX card, since my system froze when the feature got enabled and I played some flash videos that are accelerated by the GPU.
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Re: Dude, where's my 4GB?

Postposted on Fri May 21, 2010 1:24 pm

So SysInternals' new RamMap utility (mentioned in today's shortbread, which prompted me to update this thread) can give folks a graphical verification that their x64 system is indeed "hoisting" the RAM above the 4GB boundary.

Here's an x64 system with 4GB of physical RAM. Note the .75GB mapped above 4GB (aka 0x100000000).

Image

This is a fun tool if this kind of stuff interests you, though you have to have a bit of knowledge to make sense of what you're seeing. (Vista/Win7 only, and you need Admin rights.)
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Re: Dude, where's my 4GB?

Postposted on Fri May 21, 2010 2:26 pm

UberGerbil wrote:So SysInternals' new RamMap utility (mentioned in today's shortbread, which prompted me to update this thread) can give folks a graphical verification that their x64 system is indeed "hoisting" the RAM above the 4GB boundary.

Here's an x64 system with 4GB of physical RAM. Note the .75GB mapped above 4GB (aka 0x100000000).

[Link to picture]

This is a fun tool if this kind of stuff interests you, though you have to have a bit of knowledge to make sense of what you're seeing. (Vista/Win7 only, and you need Admin rights.)

I see that in memtest86+ too. It splits each test into multiple runs with their own percentages, weird at first but kind of funny now that I am used to it. Sometimes I would see like the 256K-16M range gets scanned, and then it is the 32M - 2240M, and then 3000M - 3200M. It jumps around. ;)
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Re: Dude, where's my 4GB?

Postposted on Fri May 21, 2010 2:59 pm

Flying Fox wrote:I see that in memtest86+ too. It splits each test into multiple runs with their own percentages, weird at first but kind of funny now that I am used to it. Sometimes I would see like the 256K-16M range gets scanned, and then it is the 32M - 2240M, and then 3000M - 3200M. It jumps around. ;)

Some of that might be due to something other than RAM hoisting. I'm pretty sure Memtest86+ tests the RAM occupied by its own program code by moving itself out of the way, then testing the RAM it previously occupied.
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Re: Dude, where's my 4GB?

Postposted on Thu Jan 13, 2011 8:14 am

This applies to WIndows NT x86 when you do not use PAE.

1. The OS total addressable memory space is 4GB, this includes physical ram and the device I/O table.

This applies when using PAE.

1. PCI devices must support > 32bit addressing ( a whole crapload of them do not) for best stability and performance. Creative labs anyone?

now for the fun stuff

The PC device IO map was always at the top of the memory space on the PC platorm (dos and windows) as this allows for the system to use all the physical ram. The only time you run into a situation where you canoot see all of the physical ram is when you reach the limits of the platform's memory addressing space. Go back to the 8086 days when the machine could see 1MB ram and memory above 640K was pretty much reserved for device I/O (and a few other things). Same thing with PCI device I/O map, it's always at the top of the memory space.

The reason we have remap feature instead of just contining to move the PCI I/O map to the top of the memory stac has everything to do with what is mentioned above (it would cause a lot of hardware to malfunction.
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Re: Dude, where's my 4GB?

Postposted on Mon Nov 12, 2012 9:17 pm

Most recent boards have a "Remap memory above 4GB" or some other option.
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