Measuring bandwidth

An issue that comes up for me at work time and time again is customers misunderstanding how bandwidth is measured.

Data is traditionally measured in Bytes. A CD contains 650MBytes of data. Bandwidth is measured in bits however, and this is what most customers misunderstand. A CD measured in terms of bandwidth, is 5,200Mbits (there are 8 bits per byte). Note that in writing, you use a capital ‘B’ to denote Bytes, and a lower-case ‘b’ to denote bits.

The issue is that bandwidth is traditionally measured in bits, not bytes. A 1Mbit circuit lets you download at 100KBytes/second. A lot of people make the mistake of thinking that a 1Mbit circuit is the same as downloading at 1MBytes/second.

This becomes a problem when a customer – as has happened today – complains of a slow speed problem. The systems (which I built and maintain) show this customer as downloading up to 32Gbits per day. They dispute this via the phone, proclaiming that they only downloaded “4 gig” (in a 5 hour window, I’ll add). If you do the math: 4*8 = 32. 32Gbits. On a standard ADSL line, that’s a crazy amount of usage – averaging around 1.8Mbit/s for that 5 hour window. During peak hours, an ADSL Max line (due to contention) may only be able to achieve 2Mb/s. It’s a classic case of someone mistaking Bytes for bits… of course, explaining that to them is another matter.

Leave a Comment