Comment 4 for bug 1557839

In other words, I think we should follow the robustness principle here: be liberal about the units we accept (millibyte and picobyte should be fine to recognize as megabyte and petabyte, respectively) and be conservative about what we display (correct units only).

Which leaves what to do with a capital K as a toss-up. It seems weird to have just one unit that behaves differently if it's capitalized.

If we really want to eliminate ambiguity, maybe we should optionally allow people to specify units with explicit exponents:

    5*10^6 # 5 MB
    5*2^20 # 5 MiB