In the original technical specifications, Valve noted that the 16GB of LPDDR5 memory was running in dual-channel, with an expected bandwidth of 5,500 MT/s. The latter figure is still correct, but Valve has updated the official product page to reflect that the memory is, in fact, quad-channel, not dual, offering up a lot more bandwidth to the APU powering the device.

Source: N4G PC Valve's Steam Deck Has Much Better Memory Than Initially Suggested