SI-Based Units of Measurement: What Are These 'Bits?'

Have you ever been confused by the terms bits, bytes, megabytes, gigabytes, terabytes, petabytes, MB, Mb/s, Kb/s? Well you aren't alone. This simple guide will clear everything up for you.

A 'bit' is the smallest thing in a computer. It is represented as a 1 or a 0, technically representing a high(+5v) or low(+2v) current in a computer component. A bit also refers to a digit in the binary number system, but that's not what this article focuses on. A bit, as I said, is the smallest unit of storage or speed in memory.A nybble is 4 bits, and a byte is 2 nybbles or 8 bits.

From there it just progresses with suffixes. A Kilobyte(or KB) is 1000 bytes. As a sidenote, if you've ever seen the abbreviation KiB, this refers to the SI definition of an n-byte to be multiples of 1024. So a kilobyte(KiB) would actually be 1024 bytes (this is because all calculations are actually done on the bit level, which means every unit of measurement has to be a power of 2). This changes storage measurements somewhat, so most people go with the more popular MB or KB, despite the SI definitions being more accurate.A Megabyte(MB) is 1000 Kilobytes(KB). A Gigabyte(GB) is 1000 Megabytes. A Terabyte(TB) is 1000 Gigabytes. Yes, there is a pattern, each ascending suffix is 1000x as large as the previous.

The 'speed' measurements are also similarly hierarchical. There are clock speed measurements (Hz) and bandwidth measurements (b/s). Hertz(or Hz) are the number of rotations in a second. So, a 2.4Ghz processor switches from 1 to 0 2.4 billion times a second! Bandwidth measurements are always given in a bit per second form. 54Mb/s is 54 megabits per second, and is NOT bytes per second. That means 54,000,000 BITS per second. Bytes are 8x as large as bits so to get bytes-per-second you need to divide by 8 to get MB/s.