Linked by Thom Holwerda on Wed 5th Jan 2011 22:09 UTC
Windows And this is part two of the story: Microsoft has just confirmed the next version of Windows NT (referring to it as NT for clarity's sake) will be available for ARM - or more specifically, SoCs from NVIDIA, Qualcomm, and Texas Instruments. Also announced today at CES is Microsoft Office for ARM. Both Windows NT and Microsoft Office were shown running on ARM during a press conference for the fact at CES in Las Vegas.
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RE[3]: enough bits?
by phoenix on Thu 6th Jan 2011 23:39 UTC in reply to "RE[2]: enough bits?"
phoenix
Member since:
2005-07-11

Also important note the 4GB limit on 32 bit OS on a lot of x86 chips is garbage as well. PAE mode. 64gb to 128gb. 32 bit mode.

So 32 bit being limited to 4GB is mostly a market bending nothing more by Microsoft.


PAE allows the *kernel* to access more than 4 GB of RAM. However, *processes* can only see 4 GB of RAM, period. Each process can be given it's own 4 GB chunk of memory, though. But they are still limited to 4 GB.

And the kernel has to do a lot of thunking and bounce buffers and hoop jumping and whatnot to manage PAE accesses. And all your drivers need to be coded to support PAE. And all your low-level apps need to be coded to support PAE. And on and on.

PAE is a mess, and should be avoided like the plague unless there's absolutely no way to run a 64-bit OS/apps.

The only way for an app/process to access more than 4 GB of RAM (on x86) is to use a 64-bit CPU with a 64-bit kernel.

Reply Parent Score: 2

RE[4]: enough bits?
by Panajev on Fri 7th Jan 2011 09:27 in reply to "RE[3]: enough bits?"
Panajev Member since:
2008-01-09

64 bit kernel is not necessary, see OS X. X86-64 CPU's can switch between two modes of operations at run-time allowing 64 bits processes as well as a 32 bit kernel and drivers.

Reply Parent Score: 2

RE[5]: enough bits?
by Neolander on Fri 7th Jan 2011 11:08 in reply to "RE[4]: enough bits?"
Neolander Member since:
2010-03-08

Maybe you could, but once you get enough 64-bit support in the kernel to be able to run 64-bit processes, it's just weird to keep the rest of the kernel 32-bit.

Moreover, drivers and kernel could only write in the first 4GB of RAM without being PAE-aware, which could be problematic for things like DMA.

Reply Parent Score: 1

RE[5]: enough bits?
by phoenix on Fri 7th Jan 2011 17:04 in reply to "RE[4]: enough bits?"
phoenix Member since:
2005-07-11

Yeah, I know about the hybrid mode that AMD CPUs can work in.

But, I thought it was only the other way around. You could run 32-bit userland on a 64-bit kernel. Not that you could run a 64-bit userland on a 32-bit kernel.

Reply Parent Score: 2

RE[4]: enough bits?
by oiaohm on Fri 7th Jan 2011 12:10 in reply to "RE[3]: enough bits?"
oiaohm Member since:
2009-05-30

"Also important note the 4GB limit on 32 bit OS on a lot of x86 chips is garbage as well. PAE mode. 64gb to 128gb. 32 bit mode.

So 32 bit being limited to 4GB is mostly a market bending nothing more by Microsoft.


PAE allows the *kernel* to access more than 4 GB of RAM. However, *processes* can only see 4 GB of RAM, period. Each process can be given it's own 4 GB chunk of memory, though. But they are still limited to 4 GB.

And the kernel has to do a lot of thunking and bounce buffers and hoop jumping and whatnot to manage PAE accesses. And all your drivers need to be coded to support PAE. And all your low-level apps need to be coded to support PAE. And on and on.
"
Really name a Linux program that has to be changed between PAE mode and non PAE mode. Answer zero.

PAE does not have to have anything todo with userspace.

PAE thunking is way lighter than swapspace.

What stunts do 32 bit programs that need to use more than 4gb of space use. Memory mapping to file. PAE Provides more access to storage space so can reduce number of disk operations on a memory mapped file.

So don't quote trash. 64 bit system is not the only way to exceed the 4 GB limit.

Yes a program running on a Non PAE 32 bit machine can be using methods already to have more space than the 4 gb limit at the cost of performance. PAE enables you to reduce the cost of those stunts.

Shock horror is just using PAE for swap, disk cache and assisting mapped files to reduce disk accesses don't require you to be running all PAE compatible drivers. Since most drivers should not be messing with this stuff.

Here is the best bit of all PAE used this way is not even new. Its basically using same style as Expanded memory. Yes breaking the 4 gb limit goes back to 1984.

The limit is 4 gb of memory at 1 time on x86 32 bit. Yes memory mapping and other methods means a program could be many times large than that in reality with or without PAE active.

Difference is PAE can remove the speed hits from the methods used by programs to exceed the 4gb limit.

That is the big mistake here. You are presuming that programs will not be using more than 4gb of memory. That presume is based on the idea that the OS did not provide programmers with a way around that problem. What is incorrect.

Reply Parent Score: 1