SQT: Megabytes and Megabits

There’s a big difference between megabits and megabytes and again between those and megabps, so watch out when you’re buying memory, storage or bandwidth.

From first principles, a bit, is a binary digit, a single 1 or a 0 in binary code. A byte is a word composed of 8 bits, so a byte is 8 times as big as a bit. A megabit is “approximately” a million bits, whereas a megabyte is a million bytes, or eight megabits; that’s storage space. Megabps in turn is a million bits per second; that’s transfer rate.

So, if you’ve got an 8Mbps (Megabits per second) connection then you’re going to be able to download one megabyte of information per second at full speed, although that rarely happens. A 4 minute song is usually compressed as an mp3 to 5 megabytes, so you’d expect that to take about 5 seconds to download, at fullspeed. A whole album of ten tracks at around 5 megabytes each should therefore take less than a minute to download at that rate.

When you move on to movie downloads you’re usually talking 700 to 1000 megabytes, which is around one gigabyte (giga meaning million), you can do the calculations yourself on download times. For more on the many other size prefixes check out the sciencebase post on zepto, yotta, and yocto.

Of course, ADSL and cable broadband speeds varying depending on load, time of day, distance from your exchange and whether you’re connection is capped or throttled.