Yeah mega transfers. 1 transfer is 8 bytes. the DD in DDRX is double data so it can send 2 transfers per channel per clock. CPUs pretty much always use 2 channels, so the formula is just GBps = 32 * MT/s. My PC has 6000MT/s DDR5 in a dual channel config so thatd be 192GBps.
Idk how apple is getting above 300GBps, maybe theyre counting the integrated GPU as part of the total. GPUs often have 4 or 6 or 8 channels so thatd make sense...