I'm pretty sure the mobile CPUs support at least 64GB of DDR3. So the memory subsystem would be desktop class but they could use the same mobile CPUs. Seems to me that might have been an option if they didn't also shrink the battery.
Actually, they don't. Per the Intel data sheet [0], the Skylake mobile processors don't even support DDR3, they support DDR3L (lower power variant of DDR3), LPDDR3 (what the MacBook Pro uses), and DDR4. Here's the max system memory per memory type:
DDR3L: 16gb (page 20)
DDR4: 32gb (page 21)
LPDDR3: 16gb (page 21)
So the only way Apple could've supported more than 16gb RAM would've been to support DDR4. [1]
I am far from an expert, but I believe DDR4 is only available in an SO-DIMM package [3]. Sure, we would all LOVE Apple to support upgradeable memory again, but that's very likely not going to happen. Just think how much thicker (teh horror!) the laptop would have to be to support that! [2]
I also suspect that Apple is using the Y-processor line which only supports LPDDR3 memory (per page 19), so that further negates the ability to use DDR4 memory. Again, this part is unconfirmed, but would make sense.
[1] I'm still curious how Intel claims the processor supports up to 64gb RAM on the short form of the processor specs. I could not find a configuration in the detailed data sheets that allowed 64gb of RAM.
[2] (sarcasm intended there, obviously it could be easily thicker and most people wouldn't mind)
Edit:
[3] Seems I likely am wrong. DDR4 is supported in a "Memory Down" configuration as well. This would've allowed Apple to use DDR4 memory if they used a U-processor line and also used DDR4 memory. From what I am reading online (no official sources, so not linking to more speculation), this would've had a battery impact of up to 20%, thus very likely why Apple didn't do it. More info on "Memory Down" here: http://www.intel.com/content/dam/www/public/us/en/documents/...
jsjohnst|9 years ago
DDR3L: 16gb (page 20)
DDR4: 32gb (page 21)
LPDDR3: 16gb (page 21)
So the only way Apple could've supported more than 16gb RAM would've been to support DDR4. [1]
I am far from an expert, but I believe DDR4 is only available in an SO-DIMM package [3]. Sure, we would all LOVE Apple to support upgradeable memory again, but that's very likely not going to happen. Just think how much thicker (teh horror!) the laptop would have to be to support that! [2]
I also suspect that Apple is using the Y-processor line which only supports LPDDR3 memory (per page 19), so that further negates the ability to use DDR4 memory. Again, this part is unconfirmed, but would make sense.
[0] http://www.intel.com/content/dam/www/public/us/en/documents/...
[1] I'm still curious how Intel claims the processor supports up to 64gb RAM on the short form of the processor specs. I could not find a configuration in the detailed data sheets that allowed 64gb of RAM.
[2] (sarcasm intended there, obviously it could be easily thicker and most people wouldn't mind)
Edit:
[3] Seems I likely am wrong. DDR4 is supported in a "Memory Down" configuration as well. This would've allowed Apple to use DDR4 memory if they used a U-processor line and also used DDR4 memory. From what I am reading online (no official sources, so not linking to more speculation), this would've had a battery impact of up to 20%, thus very likely why Apple didn't do it. More info on "Memory Down" here: http://www.intel.com/content/dam/www/public/us/en/documents/...