Digital Storage Measurements

You’ve probably noticed that network speeds, hard drive capacity, and memory size all use different measurements. What do these measurements mean, and how can conversions be made between them?

Networking speed is commonly measured in gigabits, megabits or kilobits per second. This is a different measurement than that which is commonly used for hard drive capacity, or gigabytes. The difference lies in the fact that one byte = 8 bits. Kilobits, megabits, and gigabits are all multiples of bits, whereas kilobytes, megabytes, and gigabytes stem from the byte. This means that networking speed measurements are 1/8th of storage space measurements, which is why downloading a 30 megabyte file over a 30 megabit per second Internet connection takes eight seconds instead of one second.

Now let’s compare hard drive capacity vs. memory capacity. This is a confusing issue that involves mislabeled storage sizes.

A gigabyte is actually 1000 megabytes, despite the common misconception that it is 1024 megabytes. The proper terms for the 1024-based measurements are kibibytes, mebibytes, gibibytes, and so on. Megabytes are decimal values, and mebibytes are binary values. The misconception arises from the JEDEC memory standards that label binary memory sizes (64, 128, 256, 512, 1024, etc.) using the decimal terms kilobyte, megabyte, gigabyte, and so on. Hard drive manufacturers also use the terms megabytes and gigabytes, but measure hard drive space using decimal values. Because of this, one gigabyte of hard drive space is 1,000,000,000 bytes whereas one gigabyte of RAM is actually 1,073,741,824 bytes.

Of course, the actual storage space on a hard drive will be less than the advertised capacity after it is formatted, further adding to the confusion.

This is why I can never simply answer the question, “How many megabytes are in a gigabyte?”