Kubernetes size definitions: What's the difference of "Gi" and "G"?

From Kubernetes source:

Limits and requests for memory are measured in bytes. You can express memory as a plain integer or as a fixed-point integer using one of these suffixes: E, P, T, G, M, K. You can also use the power-of-two equivalents: Ei, Pi, Ti, Gi, Mi, Ki. For example, the following represent roughly the same value:

128974848, 129e6, 129M, 123Mi

So those are the "bibyte" counterparts, like user2864740 commented.

A little info on those orders of magnitude:

The kibibyte was designed to replace the kilobyte in those computer science contexts in which the term kilobyte is used to mean 1024 bytes. The interpretation of kilobyte to denote 1024 bytes, conflicting with the SI definition of the prefix kilo (1000), used to be common.

So, as you can see, 5G means 5 Gigabytes while 5Gi means 5 Gibibytes. They amount to:

• 5 G = 5000000 KB / 5000 MB
• 5 Gi = 5368709.12 KB / 5368.70 MB

Therefore, in terms of size, they are not the same.

Exactly, one of them (G) is power of ten, while the other one (Gi) is power of two. So,

• 10^3 is power of ten. the result is 1000, or 1G
• 2^10 is power of two. the result is 1024, or 1Gi

These are different units - one of the are in Binary prefix and the other are in Decimal prefix.

Simply said, the units such as M, G, T are based on power of 10 - multiplies of 1000. The units such as Mi, Gi, Ti are based on power of 2 - multiplies of 1024.