# 16GB of memory, PAE, and custom FreeBSD 8.1 Kernel



## badaei (Jan 9, 2011)

Hello, I am running FreeBSD 8.1. I have a machine with 16GB RAM on it. The system says that 16GB are available with the standard Generic Kernel. I looked into the GENERIC configuration file and did not find "option PAE" set, but it recognizes 16GB anyway? I'm making a custom Kernel right now, do I need this option if the GENERIC kernel doesn't have it and it appears that 16GB are available? Is this only for large memory support for older machines? I have the Intel Xeon x3440 chip.

Thank for any guidance I greatly appreciate it.


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## DutchDaemon (Jan 10, 2011)

That's a 64-bit chip, so you're probably running amd64? What says [cmd=]uname -a[/cmd]
?


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## badaei (Jan 10, 2011)

DutchDaemon said:
			
		

> That's a 64-bit chip, so you're probably running amd64? What says [cmd=]uname -a[/cmd]
> ?




```
# uname -a

8.1-RELEASE FreeBSD 8.1-RELEASE #0: Mon Jul 19 02:36:49 UTC 2010     [email]root@mason.cse.buffalo.edu[/email]:/usr/obj/usr/src/sys/GENERIC  amd64
```

Now I'm really confused. So I want to compile the kernel at 

/usr/src/sys/amd64/conf

not

/usr/src/sys/i386/conf

right?

And does PAE not apply? I realize the confusion I am throwing out there. 

Thanks for your input.


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## gordon@ (Jan 10, 2011)

You are running a 64-bit kernel which does not need PAE to address memory larger than 4GB.


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## DutchDaemon (Jan 10, 2011)

Exactly. That's why I asked for your uname output. An i386 (32-bit) installation would need PAE to address more than ~4GB of RAM. No such limitation exists on amd64 (64-bit), so you're all set. And yes, your kernel config lives under /usr/src/sys/amd64/conf/. Again: no need to change anything to address your 16GB of RAM.


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## badaei (Jan 10, 2011)

DutchDaemon said:
			
		

> Exactly. That's why I asked for your uname output. An i386 (32-bit) installation would need PAE to address more than ~4GB of RAM. No such limitation exists on amd64 (64-bit), so you're all set. And yes, your kernel config lives under /usr/src/sys/amd64/conf/. Again: no need to change anything to address your 16GB of RAM.



Thanks! Not sure how to give thanks so that it appears on my profile. It says I've given zero thanks but I'm really grateful for your help.


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## badaei (Jan 10, 2011)

OK, I figured out how to give thanks through the forum button. I didn't see it there before. Thanks again!


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