1.  petabyte(n = noun.quantity) pb - a unit of information equal to 1000 terabytes or 10^15 bytes;
is a kind of computer memory unit
is a part of eb, exabyte
has parts: tb, terabyte

2.  petabyte(n = noun.quantity) pb, pebibyte, pib - a unit of information equal to 1024 tebibytes or 2^50 bytes;
is a kind of computer memory unit
is a part of eb, eib, exabyte, exbibyte
has parts: tb, tebibyte, terabyte, tib