Actually, when you consider how many banks of memory it would take to obtain 100GB/s, it's a bargain. Desktop DDR5-4800 tops out at 38.4 GB/s, so you would need three, desktop DDR5 memory sticks to get that - but it would not even matter because a 12th Gen desktop Intel Core i9 can't handle more than 75GB/s at once. Now, DDR5 is falling in price, but low-power laptop grade DDR5 is still quite a specialized part, let alone with such bandwidth potential.

In a nutshell, not all RAM is created equal.

For slow-ass DIMM memory, sure. But we're talking on-die integrated memory that's leagues ahead of any PC memory in performance.

It’s DDR5 on-die ram. The M1 ultra is essentially 4 M1s with an on-die messaging fabric and separate ram for each compute “node”, iirc.