4G of RAM under Windows XP; boot.ini's "/3G" switch

[hacksaw]

My brother-in-law bought 4GB for his old Windows XP laptop and asked me to install it for him (pair of 2GB modules - one was easy to install, the other was under the keyboard and was a pain in the neck to access ... hence him asking me to do it). After installation, on powerup I immediately checked the BIOS settings and noted that all 4GB were detected, and then booted from CD to run memtest86+ and there were no errors. Second boot was into Windows XP, and it was rock solid. No sign of trouble. Then I added the "/3G" switch to the relevant entry in boot.ini and restarted. Third boot was insane. The system was sluggish, applications would start up and hang, etc. A normal restart seemed to go fine, but on the fourth boot chkdsk fired up! Yikes. After that it was back to applications hanging and general system instability.

So I booted the thing up in safe mode and removed the "/3G" switch. Restart. Now the thing is rock solid again. What gives?

 

[hacksaw]

Oh, should have mentioned: this is XP Pro.

 

[blakerwry]

This site explains some of the pros and cons to the /3g switch...
http://blogs.technet.com/askperf/archive/2007/03/23/memory-management-demystifying-3gb.aspx

Perhaps you're running into one of the cons... Never used it myself, but I don't have any Windows systems with more than 2 GB of RAM.

 

[Will Rickards]

Suggestion: Install XP Pro x64 or server 2003 instead and get native 4GB support no switches or anything. Sure it will be an additional cost though.
I'm running XP x64 and have no real problems. You probably want to make sure you have drivers for all the hardware on the laptop first though.

Also you should know that with 4GB of ram, his laptop won't hibernate anymore. I didn't know this. Some crazy MS restriction.

 

[hacksaw]

Thanks for the link to that article, blakerwry. It's the first one that's done a half-way decent job on explaining how Windows handles 4GB of RAM. As for XP 64, I don't have it. Besides, it's not a 64-bit system, and I assume that's a requirement for XP 64, no?.

 

[ddrueding]

I've never used the /3G switch, so I can't help. Any system I work on with more than about 3GB of RAM runs a 64-bit OS.

 

[Will Rickards]

Well if it doesn't have a 64bit processor, XP x64 isn't for you. Not sure if the 32bit server 2003 will work better.

 

[Will Rickards]

Looks like 32bit server 2003 has the same 4GB limit http://en.wikipedia.org/wiki/Server_2003

 

[sechs]

Looks like 32bit server 2003 has the same 4GB limit http://en.wikipedia.org/wiki/Server_2003

I think that's just for lower-end versions of Server. Enterprise will address up to 64GB, as I recall.

Also, I'm pretty sure that all x86 versions of server enable PAE, which allows the operating system to use extensions to access the additional memory.

 

[Bozo]

Memory limits:

http://msdn.microsoft.com/en-us/library/aa366778.aspx

Scroll down the page.

Bozo :joker:

 

[Stereodude]

I have a XP Pro 32-bit system with 4GB of RAM. XP doesn't use all of only 3.5GB, but I don't care. Everything I read said to avoid using the /3G switch.

 

[LiamC]

You can use the /3G switch, and it is usable, *provided* all the applications that will run on the box are *aware* of the /3G switch. The software has to be compiled for it especially. If it isn't /3G aware, I suggest Ibuprofen+codeine.