Why the M1 chip memory limit is set to 16GB,it is mentioned here that it is based on 64 bit ARM architecture, shouldn't it share the same memory limit which is 16 Exabytes? According to the linked answer, it should have 34 address lines, has that number been made official?
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1Intel Core i5-5300U is limited to 16 GB. i5-460M's limit is even lower, 8 GB. i5-1035G7's is 64 GB. Xeon E5-2680 v3 - 768 GB. Ryzens cap at 64 GB. All of these are 64-bit CPUs.– gronostajCommented Dec 22, 2020 at 15:37
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Great input, how are these limits calculated?– user10191234Commented Dec 22, 2020 at 15:38
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1@user10191234 The amount of addressable memory depends on the number of address lines. For example, if there are 4 lines, there are 2^4=16 address locations. More address lines=more cost.– Andrew MortonCommented Dec 22, 2020 at 15:41
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I'm not sure this does qualify as a true dupe, for the very reason stated in the answer. We don't know yet if M1 chips will be released with identical architecture but more RAM, as the RAM is essentially a part of the chip. The limit may not be yet have been reached.– TetsujinCommented Dec 22, 2020 at 16:16
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It still boils down to whether or not the chip/motherboard/stick/widget/gizmo was designed to support it and that comes down to the exact same decision of "is it worth it for this thing" and very little more. Most x86-64 processors don't come close to supporting 16 exabytes either and have limits based on what is reasonable at the time and depending on cost with many limited to 64GB for consumer chips and far more for server class chips. It's the same problem and the same reasons.– Mokubai ♦Commented Dec 22, 2020 at 16:31
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1 Answer
In the M1 the memory is a part of the M1 architecture itself. There’s no memory slot or slots on the motherboard of an M1 Mac, nor is there an area for a memory chip to be soldered on. The memory is integrated into the same package that contains the M1 itself.
This means that once you buy an M1-based Mac and choose a memory configuration, that’s it and no more. The memory here is basically part of the package itself.
Furthermore, the Unified Memory Architecture of the M1 means that these 16GB are shared between the CPU and graphics. Graphics resources such as textures, images and geometry data, are this way shared between the CPU and GPU efficiently and with no overhead, as data isn't copied across a PCIe bus.
This architecture makes for speed, but not for extensibility.
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