Here are the model identifiers we have in Geekbench so far and how much RAM each one has:
iPad8,1: Unknown
iPad8,2: 6GB
iPad8,3: 4GB
iPad8,4: 6GB
iPad8,5: Unknown
iPad8,6: 6GB
iPad8,7: Unknown
iPad8,8: 6GB
Source:
https://browser.geekbench.com/v4/cpu/search?page=1&q=iPad8,1&utf8=✓
The 6GB models seem to have an "x" before the last two AP digits in their logic board identifier.
The reason there are four 6GB models is because they seem to be segmented like this:
11" 1TB
11" 1TB LTE
12.9" 1TB
12.9" 1TB LTE
The other numbers seem to be like this:
11" 64-512GB
11" 64-512GB LTE
12.9" 64-512GB
12.9" 64-512GB LTE
Apple seems to list their identifiers by board changes. So the extra RAM is a board change. Adding LTE is a board change.
Now, it's important to note that it's impossible to know for sure that, say, 512GB isn't included in the 6GB group since Apple doesn't seem to segment based on drop in storage configurations. There are only two 4GB devices in the Geekbench browser at this moment, and they are both iPad 8,3. Every review that I've seen has been iPad 1TB models in 11" and 12.9" sizes. If someone can find a review that has less than 1TB AND has posted RAM information then we can know for sure. At least one of them seems to exist out there in the wild unless those two tests came from someone at Apple.
As I've spoken with other forum members on this topic, some of us have come to the conclusion that larger capacity SSDs need additional addressable RAM to for file system management. The additional amount needed for 1TB seems to be about 512MB extra over 512GB models (1GB total) when looking at other manufacturers of SSDs. Seeing as how you can't buy RAM in 4.5GB or 5GB capacities, this is why Apple put 6GB in there. So 1TB users should be getting around 1.5GB of extra RAM. But this should also mean that 512GB users have usage of 512MB of RAM total, 256GB uses 256MB total, and 64GB uses 64MB total. So, for instance, 512GB users should have 256MB less usable RAM than 256GB users. I'm not sure if that's completely the case or if Apple included some special memory somewhere else on the board for managing SSDs for 512GB and prior and for this time it was just easier to add system RAM to help on 1TB models, but if that's the case, I doubt it would split managing between some special RAM and system RAM so the 1TB might only really be 1GB of RAM better.
Anyway, this is mostly me trying to figure out logically what is going on with limited knowledge of SSD controller and logic board design, so if someone else knows better feel free to explain it so that we can all understand it. But for now this is what I think the reasoning behind the 1TB model having more RAM is. Perhaps in the future Apple could make this process better by not using system RAM but RAM attached to the flash memory itself (or maybe they already do on the lower models?) but I think they didn't want people who buy the 1TB model to be penalized with lower addressable RAM and maybe it wasn't possible for them to have another solution right now. I hope for the next model (~18 months away probably) they start at 256GB storage and include 8GB of RAM across all models.
