On 2025-02-18, Philip Webb <purs...@ca.inter.net> wrote: > 250218 Frank Steinmetzger wrote: >> I recommend an external USB case with an NVMe SSD inside. >> This may not be as compact and not as cheap, >> but they are much much much faster and probably longer-lasting >> than any USB stick, because their flash controllers are more sophisticated >> and the parts of higher fidelity. A not-too-cheap NVMe will do fine, >> as long as it’s TLC, not QLC flash. > > Can you explain this -- TLC/QLC -- in more detail ?
Tri-Level Cells, Quad-Level Cells. SLC (single-level cells) Each "cell" consists of a capacitor (constructed as a FET with an isolated-gate). In the old days, the capacitor was either chared or not: two levels. One bit per cell. Easy to make and reliable. If you want more bits, layout more cells. That means larger dies, which means more money. MLC (two-level cells) OK, let's also do four different charge levels! You get _two_ bits per cell with the same area of silicon. Harder to do and not quite as reliable, so we'll add a few extra blocks of cells and make software deal with blocks that don't work. TLC (tri-level cells) Hey, what if we do 8 different charge levels! Now you get 4 bits per cell. Even harder to do, even less reliable... QLC (quad-level cells) [I think you see where this is going]
