Originally Posted by bsmit007
4GB can be addressed by a 32-bit processor you don't need to have a 64-bit processor for that.
This is true, but you're forgetting a few important details. The maximum addressable memory area in a 32bit addressing system is indeed 4GB. But this address space has to take into account all memory addressed devices within the system in addition to the main RAM. There's video memory, BIOS, firmware and I/O locations for devices installed in the system, etc... In a typical PC or Mac system with 256MB video memory and the usual fare of standard components, there's about 3.6GB of address space left for the RAM. Installing 4GB into such a system is just installing extra RAM that can't be used and in many situations (in OSX, Xindows and Linux too) the full 4GB can often cause undesired conflicts and instabilities. There are 32bit solutions to such RAM limitations such as system BIOS/ROM/Firmware that can isolate RAM into various chunks or "pages" and special software for the operating system to help cope with this. But most of these solutions come with a performance hit and increased risk of problems or incompatibilities. To further complicate the whole memory addressing issue on 32bit systems, for various technical reasons that would take pages to try and explain with any meaning, there are other limitations. And this applies to the PowerPC and x86 architectures as well as some others... Memory addressing windows in which there's typically 2 of them, are usually split right down the middle of your RAM by the OS. But with Windows and Linux (and I believe OSX allows it as well), there's the optional ability to split 1GB or so for the OS itself and reserve the rest for the applications. Additionally, on these 32bit platforms, there's a maximum of 2GB addressable per CPU process. So in most situations any single application or process on your system can't address more than 2GB.
Moving to a 64bit system increases the addressable space by a huge margin. But also be aware that current G5 CPUs, the new Intel 64bit chips and AMD's AMD64 chips all use a 40bit memory addressing scheme rather than a full 64bit. With a 40bit address range, we have the capability to have 1TB of addressable RAM and device memory within a system. Window aperture sizes, process limitations, etc.. still apply, but they are greatly enlarged from the 32bit schemes.
As for these new iMac systems, I'm not sure why Apple isn't offering a 4GB configuration. Unless they're intentionally restricting the system to 3GB or just don't feel that people will buy the full 4GB. I'd love to put 4GB into a new 24" iMac and see what it will do... I bet it works just great and we'll see people trying it in the real near future.
|First of all tiger is not a pure 64-bit OS like Win XP x64 although Leopard should be if Apple marketing s to be believed.
Correct... Hopefully Apple comes through though.