MacBook with 4Gb Ram question

Neoraven

macrumors member
Original poster
Nov 18, 2006
72
0
Anyone know exactly how much is reserved for APIC and PCI Express? i.e if only .5 Gb are reserved, we can still use 3.5GB of Memory making the 4GB sticks worth it. Useful excerpts?



The enhanced PCI Express configuration access mechanism utilizes a flat memory-
mapped address space to access device configuration registers. This address space is
reported by the system firmware to the operating system. PCIEXBAR defines the base
address for a 64-, 128-, or 256-MB block of addresses below the top of addressable
memory (currently 4 GB) for the configuration space associated with all devices and
functions that are potentially a part of the PCI Express root complex hierarchy. The PCI
Express Configuration Transaction Header includes an additional 4 bits (Extended
Register Address[3:0]) between the function number and register address fields to
provide indexing into the 4 KB of configuration space allocated to each potential device.
For PCI Compatible Configuration Requests, the Extended Register Address field must
be all 0’s.
 

Igantius

macrumors 65816
Apr 29, 2007
1,240
1
The max. RAM a C2D MB can access is 3.3GB - there're a few threads about this already if you're interested - plus, there was a more technical one over at Ars Technica.
 

minisamus

macrumors newbie
Jul 24, 2007
3
0
Anyone know exactly how much is reserved for APIC and PCI Express? i.e if only .5 Gb are reserved, we can still use 3.5GB of Memory making the 4GB sticks worth it. Useful excerpts?
I'm going to assume you're dealing with a MacBook Pro SR which can actually accept 2GB SODIMMs.

This problem stems from a 32bit system. In short, 32bits of addressing space is 4GB, and if you're using memory mapped IO you can only address up to 4GB - IO space. These systems are 64bit however, and I believe 10.4.x is 64 bit 'enough' to address more than 4GB.

So, it should work. But if you're trying to decide, you might want to find someone who has it working... :rolleyes:
 

Neoraven

macrumors member
Original poster
Nov 18, 2006
72
0
I'm going to assume you're dealing with a MacBook Pro SR which can actually accept 2GB SODIMMs.

This problem stems from a 32bit system. In short, 32bits of addressing space is 4GB, and if you're using memory mapped IO you can only address up to 4GB - IO space. These systems are 64bit however, and I believe 10.4.x is 64 bit 'enough' to address more than 4GB.

So, it should work. But if you're trying to decide, you might want to find someone who has it working... :rolleyes:
I'm actually on a C2D MB, I knew that only 3.3GB was addressable and I knew that APIC and PCI Express had allocated memory in the higher ends of the 3-4GB range, but I was curious as to just how much and where/what that excess memory does/goes
 

CanadaRAM

macrumors G5
I'm going to assume you're dealing with a MacBook Pro SR which can actually accept 2GB SODIMMs.

This problem stems from a 32bit system. In short, 32bits of addressing space is 4GB, and if you're using memory mapped IO you can only address up to 4GB - IO space. These systems are 64bit however, and I believe 10.4.x is 64 bit 'enough' to address more than 4GB.

So, it should work. But if you're trying to decide, you might want to find someone who has it working... :rolleyes:
No, that's pretty much wrong. It has nothing to do with the OS. OS 10.3 can address 16 Gb in a G5. Nor is the issue the intel CPU. The issue is the hardware memory controller on the intel logic boards' chipsets.

CoreDuo machines cannot recognize 2 Gb modules

Core2Duos (including the MacBook C2D that the OP has) can recognize 2 Gb modules. If you install 4 Gb of memory, due to the requirements the chipset has for hardware resource address space under the 4 Gb ceiling, only 3.3 is available for the OS to use (this is the same with Windows laptops that use the same chipsets)

The SantaRosa chipset (currently only inthe MacBook Pro) allows access to the full 4 Gb.
 

Neoraven

macrumors member
Original poster
Nov 18, 2006
72
0
No, that's pretty much wrong. It has nothing to do with the OS. OS 10.3 can address 16 Gb in a G5. Nor is the issue the intel CPU. The issue is the hardware memory controller on the intel logic boards' chipsets.

CoreDuo machines cannot recognize 2 Gb modules

Core2Duos (including the MacBook C2D that the OP has) can recognize 2 Gb modules. If you install 4 Gb of memory, due to the requirements the chipset has for hardware resource address space under the 4 Gb ceiling, only 3.3 is available for the OS to use (this is the same with Windows laptops that use the same chipsets)

The SantaRosa chipset (currently only inthe MacBook Pro) allows access to the full 4 Gb.
Thank you, I was just looking for a definite answer on this. I'm going to go ahead and purchase two 2 gig sticks, to utilize the full 3.3gb of usable memory. I'm tired of Parallels + OS X lag