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#21
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"CBFalconer" wrote in message
... Because it is an unnecessary expense. While there may be uses for addressing over 4GB to conveniently handle large databases etc., there is virtually no real need for that much actual memory. Well, maybe. Personally I want to run multiple virtual PC machines on a 64-bit OS. I reckon the extra RAM will bring real benefits, as I want to give each virtual PC 1GB RAM. Of course what you say is true for everyday apps. On the other hand, I'm irritated because Intel, in this particular case, give you no warning in the assembly manual that the 4th GB will be wasted and that you should not install more than 3GB. This information is in the technical spec (PDF on the CD) but should be highlighted in the printed guide IMO. Tim |
#22
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"CBFalconer" wrote in message
... If you don't install memory in a physical area it isn't wasted. Virtual memory systems involve remapping memory anyhow, so the software doesn't see any gaps. There is no real problem. The "real problem" is a bunch of motherboards that are advertised as 4GB, accept 4GB, but only make 3GB available (could be more than that, but in my case a full 1GB is lost). Tim |
#23
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"Michael Brown" wrote in message
... With a larger virtual address space (and the larger physical address space for PCIe), most of these problems are removed. That's what I figured. With PCIe and AMD64 extensions (and a 64-bit OS) I was surprised to run into this problem. Tim |
#24
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Tim Anderson wrote:
The cheaper motherboards (ie. most of them) for P4 or Athlon 64 support a maximum of 4GB RAM, even if the motherboards and processors support the AMD64 extensions that can address sqillions of GB. On the other hand, more upmarket boards support more RAM - up to 24GB or maybe more - for Xeon and Opteron. If you buy one of these 4GB boards and install 4GB RAM, you don't get the use of all of it. The top of the 4GB address space gets shadowed by system functions such as PCI Express addressing. This is not just a small detail - typically you lose 1GB of your 4GB. See: http://www.itwriting.com/blog/?postid=152 I can't at the moment find a clear explanation of this. I understand about the shadowing, but the question of course is why a modern board can't use a higher range of addresses to make the full 4GB available to the OS. The manufacturers mutter about "PC Architecture", but then again they also make boards that *do* overcome this limit. With PAE, PC processors have been able to address more than 4GB for years. So why are we still running into this limit? Tim If you need more than 4 GB of RAM then you need a specialized motherboard and operating system to be able to take advantage of it. Windows XP was not really designed for a high-end environment, it was designed for big business and the consumer market. Maybe a 64 bit operating system can do a lot better. The OS plays an integral part of the total package. Even if you can address more RAM on the hardware side, your OS has to be able to use it. There are a lot of processes that are running in the background for an OS to operate properly. All of these take RAM. If you throw 2 processors into the mix and are using the porper type of OS to take advantage of the situation it will take more memory and cache space to manage the extra processor. Then you may want to look at things like Massive Parallel Processing MPP, Symmetrical Multi-Processing SMP, and non-standard memory allocation between the processors NUMAQ. This is why the software licensing on a mainframe is around $100,000 annualy. |
#25
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In article ,
Tim Anderson wrote: "CBFalconer" wrote in message ... Because it is an unnecessary expense. While there may be uses for addressing over 4GB to conveniently handle large databases etc., there is virtually no real need for that much actual memory. Well, maybe. Personally I want to run multiple virtual PC machines on a 64-bit OS. I reckon the extra RAM will bring real benefits, as I want to give each virtual PC 1GB RAM. Of course what you say is true for everyday apps. On the other hand, I'm irritated because Intel, in this particular case, give you no warning in the assembly manual that the 4th GB will be wasted and that you should not install more than 3GB. This information is in the technical spec (PDF on the CD) but should be highlighted in the printed guide IMO. Tim The decision to limit user's physical memory is a cost and marketing decision on the part of the mobo manufacturer. There may be an AMD64 mobo that allows more than 4GB memory but I doubt it. The number of home users that need this much memory noy is about zero, and business users can be hit up for a more expensive mobo. If you get an dual-Opteron Mobo you can stuff 8GB into it and I'm pretty sure that a single CPU system will access all 8GB and you'll have the option of adding a second CPU later. (The second memory bank will be slightly slower than the one closest to the CPU.) -- a d y k e s @ p a n i x . c o m Don't blame me. I voted for Gore. |
#26
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"Al Dykes" wrote in message
... The decision to limit user's physical memory is a cost and marketing decision on the part of the mobo manufacturer. I have no problem with that. I do have an issue with marketing a board as "4GB" when it is in effect 3GB. Tim |
#27
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"Last Boy Scout" wrote in message
... If you need more than 4 GB of RAM Actually is was just the 4GB I wanted, not "more than". Windows XP was not really designed for a high-end environment, it was designed for big business and the consumer market. Maybe a 64 bit operating system can do a lot better. As I also mentioned, this is not an OS issue; and in any case I'm using 64-bit operating systems. Tim |
#28
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Tim Anderson wrote:
"Al Dykes" wrote in message ... The decision to limit user's physical memory is a cost and marketing decision on the part of the mobo manufacturer. I have no problem with that. I do have an issue with marketing a board as "4GB" when it is in effect 3GB. Tim Unless there's something odd about the motherboard it *is* 4GB. What happens is the BIOS should remap the top 1G above the I/O area so you end up with 3GB RAM - 1GB I/O - 1GB RAM. XP/2000 Pro won't see it, however, because they're limited to a 4 gig space and remapping the top 1G above 4 puts it 'out of range'. Win2k Advanced Server and the Win2k3 variants can use it, though, as they support 8 and 16GB address spaces (with PAE switch). With Linux you have to make sure the kernel (2.4.x or higher) is compiled with the PAE option enabled or else you have the same 4GB situation as XP. |
#29
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In article ,
David Maynard wrote: Tim Anderson wrote: "Al Dykes" wrote in message ... The decision to limit user's physical memory is a cost and marketing decision on the part of the mobo manufacturer. I have no problem with that. I do have an issue with marketing a board as "4GB" when it is in effect 3GB. Tim Unless there's something odd about the motherboard it *is* 4GB. What happens is the BIOS should remap the top 1G above the I/O area so you end up with 3GB RAM - 1GB I/O - 1GB RAM. XP/2000 Pro won't see it, however, because they're limited to a 4 gig space and remapping the top 1G above 4 puts it 'out of range'. Win2k Advanced Server and the Win2k3 variants can use it, though, as they support 8 and 16GB address spaces (with PAE switch). With Linux you have to make sure the kernel (2.4.x or higher) is compiled with the PAE option enabled or else you have the same 4GB situation as XP. This sounds like a 32 bit system. I assume that PAE doesn't exist in a 64 bit system (or for backward compatibility the OS simply maps PSE segemnts into normal chucks of 64 bit address space. ) PAE is slow becasue of the context switches. A package like Oracle can make efficient use of it but it's no replacemnt for a flat 64 bit address space. -- a d y k e s @ p a n i x . c o m Don't blame me. I voted for Gore. |
#30
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"David Maynard" wrote in message ... Unless there's something odd about the motherboard it *is* 4GB. What happens is the BIOS should remap the top 1G above the I/O area so you end up with 3GB RAM - 1GB I/O - 1GB RAM. This it is *not* doing. I tend to agree with you though. XP/2000 Pro won't see it, however, because they're limited to a 4 gig space and remapping the top 1G above 4 puts it 'out of range'. I'm running 64-bit Operating systems (Windows x64 and Linux) that have no problem addressing this range. Tim |
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