A computer components & hardware forum. HardwareBanter

If this is your first visit, be sure to check out the FAQ by clicking the link above. You may have to register before you can post: click the register link above to proceed. To start viewing messages, select the forum that you want to visit from the selection below.

Go Back   Home » HardwareBanter forum » General Hardware & Peripherals » General
Site Map Home Register Authors List Search Today's Posts Mark Forums Read Web Partners

PC 4GB RAM limit



 
 
Thread Tools Display Modes
  #21  
Old May 14th 05, 07:39 AM
Tim Anderson
external usenet poster
 
Posts: n/a
Default

"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  
Old May 14th 05, 07:42 AM
Tim Anderson
external usenet poster
 
Posts: n/a
Default

"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  
Old May 14th 05, 07:45 AM
Tim Anderson
external usenet poster
 
Posts: n/a
Default

"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  
Old May 14th 05, 01:30 PM
Last Boy Scout
external usenet poster
 
Posts: n/a
Default

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  
Old May 14th 05, 02:12 PM
Al Dykes
external usenet poster
 
Posts: n/a
Default

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  
Old May 14th 05, 03:15 PM
Tim Anderson
external usenet poster
 
Posts: n/a
Default

"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  
Old May 14th 05, 03:22 PM
Tim Anderson
external usenet poster
 
Posts: n/a
Default

"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  
Old May 14th 05, 04:26 PM
David Maynard
external usenet poster
 
Posts: n/a
Default

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  
Old May 14th 05, 04:36 PM
Al Dykes
external usenet poster
 
Posts: n/a
Default

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  
Old May 14th 05, 05:10 PM
Tim Anderson
external usenet poster
 
Posts: n/a
Default


"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


 




Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

vB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Forum Jump

Similar Threads
Thread Thread Starter Forum Replies Last Post
overcoming the 300 gigabyte limit || Homebuilt PC's 2 February 2nd 05 04:30 AM
Controller that allows drives over 137gb limit?? John Barrington General 4 June 22nd 04 11:10 AM
Somewhat off-topic...Customizing the TIF limit for Internet Explorer MovieFan3093 Dell Computers 2 October 23rd 03 03:22 AM
Temporary Internet Files limit HistoryFan Dell Computers 3 October 16th 03 03:32 PM
Limit to processor speed? ZITBoy Homebuilt PC's 31 September 17th 03 12:46 AM


All times are GMT +1. The time now is 08:35 PM.


Powered by vBulletin® Version 3.6.4
Copyright ©2000 - 2024, Jelsoft Enterprises Ltd.
Copyright ©2004-2024 HardwareBanter.
The comments are property of their posters.