Maximum Theoretical RAM for Yonah

[neocell]

I've tried searching this site, as well as the net for some info on how much RAM a 32-bit CPU can address. Basically all I got was 2GB from apple's site, but is that apple induced? I know they made a bit of noise about the 64-bit G5 being theoretically able to address 4TB of RAM, but I can't find the theoretical limit for a 32-bit processor. Just wondering, 'cause if it's only 2GB won't this hamper the pro-line of laptops. If you need more RAM will you have to wait for Memron or can a 32-bit do more than 2GB? Thanks for the answer. If there's already a thready addressing this, please indicate

 

[CanadaRAM]

It;s not the CPU, it's the memory controller that counts *literally*. So the choice of memory capacity is independent of the CPU.

(except on some Athlons, where the memory controller is on the CPU die)

 

[neocell]

So why all the noise from apple about 64-bit enabling 4TB worth of RAM. Maybe I just read it wrong, but it seemed that they were trying to indicate that it was the change from 32 to 64 that enabled this (not just a change in the memory controller). So I guess we can expect greater than 2GB max RAM in the new intel PB?

64-Bit Memory Addressing
The dual-core PowerPC G5 joins forces with Mac OS X v10.4 Tiger to enable 64-bit computation. With 42 bits of physical address space, the PowerPC G5 supports a colossal 4 terabytes (4TB) of system memory. Although it’s not currently feasible to purchase 4TB of RAM, the advanced architecture of the PowerPC G5 allows for plenty of growth in the future.

 

[generik]

It is a 32 bit processor, so it is still 4GB.

Nevermind the fact that it will probably have 2 DIMM slots and the price of the memory modules can easily afford you a quad.

 

[dubbz]

The physical size of the RAM slots, RAM prices and things like that will likely be a bigger issue than the theoretical maximum RAM of the x86-32 arch, which is 4GB... though this can be worked around. Afaik, Windows support up to 32GB on 32-bit systems.

And... even if Apple had released a Powerbook G5, there's no way they could fit 4TB on it (unless they secretly have access to 2TB DIMMS).

Edit: (generik kinda said the same, but with less words than me )

 

[semaja2]

the reason about the 64bit processor is that the 64bit technology allows more over the 32bit

 

[Sun Baked]

Apple has a 2GB physical limit with the 32-bit addressing because the OS uses the other space for VM.

In reality the PPC is a 36-bit processor, but Apple really never took advantage of the capability.

Though some servers in the PC world have made use of this feature on the Pentiums to get around their 4GB limit.

 

[jhu]

Apple has a 2GB physical limit with the 32-bit addressing because the OS uses the other space for VM.

In reality the PPC is a 36-bit processor, but Apple really never took advantage of the capability.

Though some servers in the PC world have made use of this feature on the Pentiums to get around their 4GB limit.

the 36-bit memory addressing began with the pentium pro allowing the processor to address up to 64gb of memory in 4gb segments. according to this site, 36-bit addressing was available for the ppc 7450, not all ppc chips.

 

[jaw04005]

Off topic, but if decided to add 2GB more to my PowerMac G5 (making it 4GB), I would not see a performance increase?

 

[generik]

Off topic, but if decided to add 2GB more to my PowerMac G5 (making it 4GB), I would not see a performance increase?

It really depends on your needs.

 

[gekko513]

Even if a 32 bit system is able to handle more than 2 or 4 GB of physical memory, the applications that run in 32 bit mode will only be able to deal with 2GB of memory because the pointers are 32 bit and half of the 4GB that can be adresses by this is set aside as kernel mode memory. To utilise more than 2GB of memory for one single purpose on a 32 bit system you need to go through all kinds of hoops.

 

[neocell]

Thanks everyone for the quick replies. So it basically comes down to what dubbz said about actual DIMM space. Probably only 2 so 4GB max. I guess that's okay for a couple of years. I would have been worried if it was only 2GB.

**EDIT**

Just read gekko513's post. Maybe I spoke too soon

 

[neocell]

Even if a 32 bit system is able to handle more than 2 or 4 GB of physical memory, the applications that run in 32 bit mode will only be able to deal with 2GB of memory because the pointers are 32 bit and half of the 4GB that can be adresses by this is set aside as kernel mode memory. To utilise more than 2GB of memory for one single purpose on a 32 bit system you need to go through all kinds of hoops.

So does this mean this mean that only half of the 1.25 GB I have in my 12" PB is used by applications, or does this issue only come up in 32-bit systems with more than 2GB of RAM. God I'm ignorant

 

[jhu]

Even if a 32 bit system is able to handle more than 2 or 4 GB of physical memory, the applications that run in 32 bit mode will only be able to deal with 2GB of memory because the pointers are 32 bit and half of the 4GB that can be adresses by this is set aside as kernel mode memory. To utilise more than 2GB of memory for one single purpose on a 32 bit system you need to go through all kinds of hoops.

that actually depends on what os you're using. on linux you can set the memory usage to 3gb for user applications and 1gb for kernel usage.

 

[gekko513]

So does this mean this mean that only half of the 1.25 GB I have in my 12" PB is used by applications, or does this issue only come up in 32-bit systems with more than 2GB of RAM. God I'm ignorant

A 32-bit application can allocate and use 2GB of user mode RAM and an additional 2GB of kernel mode RAM as long as the system has enough room in physical RAM and swap space on the hard drive.

From the application's standpoint it won't care if the memory is in physical RAM or on the hard drive. It will just work slower if not everything can fit in physical RAM. The OS takes care of shuffling data between physical RAM and the hard drive.

So even if you have only 1.25 GB of RAM, each and every application can pretend that is has 2 GB available, and the OS will make a best effort of keeping the data that is most often used in physical memory.

 

[gekko513]

that actually depends on what os you're using. on linux you can set the memory usage to 3gb for user applications and 1gb for kernel usage.

Yes, and you can do that on other OS'es, too, I think, but it is one of the hoops that you need to go through.

 

[jhu]

So does this mean this mean that only half of the 1.25 GB I have in my 12" PB is used by applications, or does this issue only come up in 32-bit systems with more than 2GB of RAM. God I'm ignorant

no, this is all virtual.

 

[neocell]

A 32-bit application can allocate and use 2GB of user mode RAM and an additional 2GB of kernel mode RAM as long as the system has enough room in physical RAM and swap space on the hard drive.

From the application's standpoint it won't care if the memory is in physical RAM or on the hard drive. It will just work slower if not everything can fit in physical RAM. The OS takes care of shuffling data between physical RAM and the hard drive.

So even if you have only 1.25 GB of RAM, each and every application can pretend that is has 2 GB available, and the OS will make a best effort of keeping the data that is most often used in physical memory.

Thanks. I'm a bit more edumicated now