A bit is a 0 or a 1, yes. However... A byte is 8 bits A nibble is 4 bits 64 bit machines primarily has to do with bus width (I'm simplifying a bit, but close enough). This determines, among other things, total addressable memory. A 32-bit OS running on a 32-bit machine can address 4 GB of memory. A 64 bit OS running on a 64 bit machine can address 16 Exabytes of memory. With overhead, the actual usable RAM is somewhat lower, but the theoretical limits are as stated. In both cases, a byte is still 8 bits. In summary, a byte is always 8 bits. It doesn't matter what the underlying bus width of the machine is, a byte is still 8 bits. Additional trivia: a lower-case b means bits, and an uppercase B means bytes. So, network speeds of 100 Mbps means 100 mega bits per second. This works out to 100/8=12.5 MBps, or 12.5 mega bytes per second.