Usable RAM versus maximum RAM?

[ddrao1]

Has anyone heard anything about usable RAM versus the maximum expandable. I have a MBP 2.2GHz w/ 2 x 1GB RAM currently.

Someone told me recently that even if I replaced both SIMMs with 2GB cards, that the computer would only use something like 3GB total. Is this true?

 

[CanadaRAM]

Hi Welcome to MR

The Search function of the site is a useful first stop, we have covered this numerous times.

The CoreDuo machines can accept only 2 Gb RAM (2 x 1 gb SODIMMs)

The Core2Duo machines can accept 3 Gb ( 1 x 1 Gb + 1 x 2 Gb) or 4 Gb ( 2 x 2 Gb SODIMMs) but in any case cannot utilize more than 3.3 Gb RAM due to a limitation in the hardware memory controller - just like every other Windows Core2Duo laptop.

The Core2Duo Santa Rosa machines (as of today, only the MacBook Pro 2.2 and 2.4 GHz in the Apple line) can install and use 4 Gb total RAM (2 x 2 Gb) because their chipset has a newer memory controller.

 

[MarkMS]

It all depends on the machine, just like CanadaRAM said. I think if you put 2 x 2GB RAM, it would recognize it as 4GB on the 2.2GHz MBP. The person that told you otherwise might have been under the impression that you machine was not a C2D SR machine.

 

[Compupaq]

I think the OP is talking about the 32 bit barrier you hit when you install more than 3GB of ram because of the system not being able to address more memory than that. I don't know if it applies to macs, but it does on the windows end.

It's talked about more here

 

[CanadaRAM]

I think the OP is talking about the 32 bit barrier you hit when you install more than 3GB of ram because of the system not being able to address more memory than that. I don't know if it applies to macs, but it does on the windows end.

It's talked about more here

First of all, there is no 32 bit barrier in the Mac OSX (otherwise, how could Mac Pros and G5's have been addressing 8 Gb + of RAM for years?). Second, it is not an issue with the CPU having a 32 bit barrier, because the intel Core and G5 chips are 64 bit.

It is a problem with the specific chipset of the first generations of intel Core motherboards, which cannot remap addresses for system resources like PCI slots and other hardware addresses out of the 4 Gb address space. These hardware resources don't use RAM, but they do use the addresses that the RAM would need, so RAM at those addresses cannot be reached. As mentioned, the Santa Rosa chipset does map the hardware addresses out, and therefore can address 4 Gb of RAM.