IT IS A CPU LIMITATION, YOU DOLT!
Jun. 27th, 2009 02:36 pm![[personal profile]](https://www.dreamwidth.org/img/silk/identity/user.png){kind=small}
strredwolfA particular "software analyst" claims that the 4 gig RAM limitation in 32-bits is a joke, and says it's a Vista licensing scam from Microsoft. http://www.geoffchappell.com/viewer.htm?doc=notes/windows/license/memory.htm for the full article.
Let me call bull on this one.
First, and most simple reason: Some CPU's have 32 bit wide address spaces. The newest one to have this is the Intel Atom (the one geared for netbooks). If the address space is set for 32 bits, that means it can only address 2^32 (that's 2 to the 32nd power) bytes of RAM. 2^32 is 4 gig (not 4 billion bytes, that's the base 10 version). To get even more RAM address space, you must have a 64-bit processor that can address more space... and not all of them will do it. Some Core 2 Duo's are stuck in 32-bit hell, but AMD's Athlon 64's, 64 X2's, and Phenoms are all 64-bit.
Now, to get even more technical, because there's a few "gotchas".
Second: Because a 32-bit CPU can only address 4 gigs of space, and a video card (like the Nvidia Geforce cards) has up to a gig of RAM for itself, you're going to loose whatever main memory you have if you max the RAM for the CPU out to 4 gig.
Example: Nvidia Geforce 9800 on a WinXP system, having 4 gigs of RAM and a 1/2 gig on the video card. XP will report at most 3.5 gigs because the video card has to be fully seen.
You don't have that limitation in 64-bit mode.
Third: There is a way around it, but it's crude and comes from the 16-bit days of the IBM XT. Back then, it was called LIM EMS (Logitech/Intel/Microsoft Epanded Memory Specification), which swapped 64K chunks of RAM supplied on an expansion board in and out of a reserved area of the 1 Meg address space the old Intel 8088 CPU has.
Now, in 32-bit land, a similar technology is called PAE. And it's only useful for swap, because it's slower than accessing the RAM directly (in 64-bit mode) but faster than smacking it onto the disk.
Now who thought up of PAE (Physical Address Extention)? Intel, back in the Pentium Pro days. The same guys who invented LIM EMS!
Forth: Vista's a joke by itself anyway. Wait until October and get a copy of Windows 7, or go with a copy of Ubuntu 64-bit.
Let me call bull on this one.
First, and most simple reason: Some CPU's have 32 bit wide address spaces. The newest one to have this is the Intel Atom (the one geared for netbooks). If the address space is set for 32 bits, that means it can only address 2^32 (that's 2 to the 32nd power) bytes of RAM. 2^32 is 4 gig (not 4 billion bytes, that's the base 10 version). To get even more RAM address space, you must have a 64-bit processor that can address more space... and not all of them will do it. Some Core 2 Duo's are stuck in 32-bit hell, but AMD's Athlon 64's, 64 X2's, and Phenoms are all 64-bit.
Now, to get even more technical, because there's a few "gotchas".
Second: Because a 32-bit CPU can only address 4 gigs of space, and a video card (like the Nvidia Geforce cards) has up to a gig of RAM for itself, you're going to loose whatever main memory you have if you max the RAM for the CPU out to 4 gig.
Example: Nvidia Geforce 9800 on a WinXP system, having 4 gigs of RAM and a 1/2 gig on the video card. XP will report at most 3.5 gigs because the video card has to be fully seen.
You don't have that limitation in 64-bit mode.
Third: There is a way around it, but it's crude and comes from the 16-bit days of the IBM XT. Back then, it was called LIM EMS (Logitech/Intel/Microsoft Epanded Memory Specification), which swapped 64K chunks of RAM supplied on an expansion board in and out of a reserved area of the 1 Meg address space the old Intel 8088 CPU has.
Now, in 32-bit land, a similar technology is called PAE. And it's only useful for swap, because it's slower than accessing the RAM directly (in 64-bit mode) but faster than smacking it onto the disk.
Now who thought up of PAE (Physical Address Extention)? Intel, back in the Pentium Pro days. The same guys who invented LIM EMS!
Forth: Vista's a joke by itself anyway. Wait until October and get a copy of Windows 7, or go with a copy of Ubuntu 64-bit.
no subject
Date: 2009-08-18 10:29 am (UTC)The article gives a perfectly reasonable and sufficiently detailed explanation of how the PAE kernel comes to be limited to using only memory below 4GB. Remove the limitation and it uses memory above 4GB too. Whether the PAE kernel actually does use PAE (as seen by the chip) is just not the article's domain and is not necessary for anything the article claims.
Whether the PAE kernel actually does use PAE (as seen from the operating system) is not proved, I accept. It's just the obvious explanation that fits the observations, and it's the only explanation that isn't fantastic. If you need to chase the fantastic to justify having called me a "dolt" and a fraud, well, I leave you to it.
On minor points...
Finding a Pentium 3 or 4 with a chipset that takes 4GB may be easier for some. Debugging may be easier for others. Disassembling may be easier for hardly anyone, but it's what I do. How else do you think I even imagined the patch except by knowing of the memory-limiting code first?
Yes, Vista is a half-baked rush release with many irritations and outright defects. But it has been for nearing 3 years the current version of the dominant operating system. Inasmuch as anything to do with computers is worth understanding, Vista must be understood, as must the next Windows version, good or bad. As an aside, consider that theology faculties all round the western world have atheists on the staff.
As for Windows 7, I haven't seen it yet - disassembly takes enough time that I work only on released versions - but numerous websites in China and Taiwan had reproduced the patch for Windows 7 within a couple of weeks of my posting a draft of the article in January. I leave it to others to decide whether it's newsworthy. I have my work cut out finding out what Windows actually does.
Geoff Chappell.