Macbook Pros: 64bit?

[nonarKitten]

Each OS deals with memory differently. Under Windows, the only advantage of moving to 64-bit was to increase headroom of both applications and the kernel to more than 2GB each. A TLB flush only occurred between context switches, which is why "threads" are preferred to processes.

With OS-X its quite different - each application has a full 4GB of virtual address space along with the kernel. This means the CPU has to perform a TLB flush not only when switching processes, but also when a process makes an OS call. Since 64-bit eliminates the need for TLB flushing, there will be a noticeable performance increase.

...What performance boost? There is nothing intricately faster about 64-bit. Sure you get a few extra registers on the CPU but that's not going to make a huge difference. Unless the process can use more than 4Gb of address space it gains very little by being 64-bit...

 

[Aranince]

Performance will also dramatically increase when editing large files or pictures.

 

[raymondu999]

Well? Is there a definitive answer yet?

 

[nonarKitten]

Well? Is there a definitive answer yet?

Let's look at one (and pretty much the only) fact - the MacBook Pro can address a full 4GB right now. This indicates that the 9400M can address more than 32 bits. Why? Because the 256MB/512MB of graphics memory isn't being deducted from that space, which is the case for ALL 32 bit chipsets. The simple fact that this address space can be moved beyond the 4GB barrier seems to indicate that the chipset registers are greater than 32 bit.

This answers the chipset registers question, but doesn't answer how much RAM you can wire to it. I would suspect that there are only 32 address pins, that with dual channel allows for a maximum of 8GB of RAM, but with no public disclosure, we won't know until someone takes the gamble and buys two $600 4GB DDR3 SODIMMs.

That being said, that's only a limitation of the physical address bus and has nothing to do with the CPU's address space or other benefit of moving to a 64 bit operating system which is eliminating the mandatory cache flush on a context switch -- a fact that hurts performance more than most people think.

 

[alphaod]

There is a difference between the chipset and the CPU. The CPU is 64-bit. It seems the chipset is 32-bit. The means that you can only have 4Gb of RAM, but you can run 64-bit software.

CPU is 64-bit like you mentioned, but I think the chipset is supports 36-bit memory addressing, so I really don't think 4GB is the limit.

 

[nonarKitten]

CPU is 64-bit like you mentioned, but I think the chipset is supports 36-bit memory addressing, so I really don't think 4GB is the limit.

That's probably very likely. Note 36-bit = 64GB which is more than any workstation has today, let alone any laptop.

DDR3 spec calls for a maximum module size of 16GB. We're probably a few years away from having anything of that density, but it's in the spec. Building a chipset that supports DDR3 but doesn't support the spec would be very short sighted.

 

[Sharangad]

Let's look at one (and pretty much the only) fact - the MacBook Pro can address a full 4GB right now. This indicates that the 9400M can address more than 32 bits. Why? Because the 256MB/512MB of graphics memory isn't being deducted from that space, which is the case for ALL 32 bit chipsets. The simple fact that this address space can be moved beyond the 4GB barrier seems to indicate that the chipset registers are greater than 32 bit.

The dekstop 9300 version has 4 DIMM slots and can take 4 GB sticks:

http://www.cclonline.com/product-info.asp?product_id=27203&category_id=251#

"Up to 16GB of DDR2 memory"

 

[raymondu999]

Hallelujah! Is this the answer we have been looking for? at least we know it's 33-bit, in the very least.

http://www.9to5mac.com/8GB-MacBook-NVIDIA

 

[nonarKitten]

Hallelujah! Is this the answer we have been looking for? at least we know it's 33-bit, in the very least.

http://www.9to5mac.com/8GB-MacBook-NVIDIA

Absolutely. It looks like the chipset can easily support 8GB and probably 16GB. The real limitation is the maximum size of DIMMs and with PCs, whether or not the BIOS will initialize all the RAM. EFI doesn't have that problem, the system will see as much RAM as the chipset can see.

It's funny reading the posts that so many people still do not have a clear understanding of what "bits" refer to, and how that meaning is different whether you're referring to CPU registers, chipset/device registers or the physical wires connecting them together.

I would imagine that AMD, nVidia and Intel have all wired 1:1 the DDR3 specification to their chipset - that is, there aren't any disconnected pins on the [SO-]DIMM sockets. The JDEC spec calls for a maximum size of 16GB per DIMM, so I would assume that the maximum memory the MacBook Pro [late 2008] can accommodate is 32GB. I would also assume that the chipset registers themselves are either 48 or 64-bit and can throw their address spaces well outside of normally addressable RAM.

However, there are still issues with drivers - if Apple "officially" only supports 4GB then they can put IO into the 4GB-to-8GB region. It would be really "silly" of them to do so, yet they have on many occasions in the past. It might be possible in theory to install more RAM, but until Apple officially endorses it, it would be, at best, an experimental function. That is, I wouldn't do that on a machine I need to run 24/7.

 

[alphaod]

Hallelujah! Is this the answer we have been looking for? at least we know it's 33-bit, in the very least.

http://www.9to5mac.com/8GB-MacBook-NVIDIA

There is a difference between 8GB work and 8GB actually being usable. I tried 8GB on my MBP and it slow down to an usable state. However 6GB works amazingly.

 

[raymondu999]

Yeah. We don't know what'll happen if we put 8GB in a new Late 08 MBP. And we don't know if Apple has artificially limited it, from software, to not accept 8GB.

 

[akm3]

This picture here is kind of scarry : http://static4.ifixit.com/igi/ibNAinnlQ5XKQXpH.large

It looks like the new MBP is MUCH larger that the early 2008 model

This picture shows the difference more accurately.
http://static4.ifixit.com/igi/NeXvgJho4i5yYpVp.large

 

[Tex-Twil]

This picture shows the difference more accurately.
http://static4.ifixit.com/igi/NeXvgJho4i5yYpVp.large

Thanks.
On this photo we can also see that the difference is not that big:

http://www.slashgear.com/wp-content/uploads/2008/10/mbp4_slashgear.jpg

Tex

 

[bolen]

I'll run my soon to arrive MBP with 4GB for a while and then probably upgrade to a big SSD and 8GB when getting bored.

 

[Baffles]

Let's look at one (and pretty much the only) fact - the MacBook Pro can address a full 4GB right now. This indicates that the 9400M can address more than 32 bits. Why? Because the 256MB/512MB of graphics memory isn't being deducted from that space, which is the case for ALL 32 bit chipsets. The simple fact that this address space can be moved beyond the 4GB barrier seems to indicate that the chipset registers are greater than 32 bit.

This answers the chipset registers question, but doesn't answer how much RAM you can wire to it. I would suspect that there are only 32 address pins, that with dual channel allows for a maximum of 8GB of RAM, but with no public disclosure, we won't know until someone takes the gamble and buys two $600 4GB DDR3 SODIMMs.

That being said, that's only a limitation of the physical address bus and has nothing to do with the CPU's address space or other benefit of moving to a 64 bit operating system which is eliminating the mandatory cache flush on a context switch -- a fact that hurts performance more than most people think.

That means nothing because even if the memory bus were 32 bit, that would only affect system RAM, not the graphics card and such (because the memory bus doesn't apply to those, they have their own controllers). The 32/64 bit difference in the sense you're talking about is the OS, not the memory controller.

 

[alphaod]

…then probably upgrade to a big SSD and 8GB when getting bored.

You mean when you feel like burning some $$$

 

[nonarKitten]

That means nothing because even if the memory bus were 32 bit, that would only affect system RAM, not the graphics card and such (because the memory bus doesn't apply to those, they have their own controllers). The 32/64 bit difference in the sense you're talking about is the OS, not the memory controller.

Regardless of the address bus of the graphics card itself. the CPU has to be able to address all the RAM. That's why 32bit chipsets would deduct IO space from the top of 4GB and leave users with as little as 2.5GB of RAM.

Significant chunks of address space below 4GB (the highest address accessible via 32-bit) get reserved for use by system hardware:

• BIOS – including ACPI and legacy video support

• PCI bus including bridges etc.

• PCI Express support will reserve at least 256MB, up to 768MB depending on graphics card installed memory

What this means is a typical system may see between ~256MB and 1GB of address space below 4GB reserved for hardware use that the OS cannot access. Intel chipset specs are pretty good at explaining what address ranges gets reserved by default and in some cases call out that 1.5GB is always reserved and thus inaccessible to Windows.

By the way, according to Gizmodo, nVidia has officially confirmed that the chipset can address a full 8GB and fully supports Hybrid SLI. http://gizmodo.com/5067433/confirme...l-gpu-and-on+the+fly-switching-in-macbook-pro