A little bit about Gigabyte (GB) and Gibibyte (GiB) in computer storage

I am going to write a little bit about this basic concept in storage: Gigabyte (GB) and Gibibyte (GiB). This is all because of the annoyance between standard and reality.

I can still remember 15 years ago, when I first got in touch with enterprise storage system, the first concept introduced is about the differences between physical disk labelled size and reported size in storage system. No need to calculate, even today, I can still clearly remember a 73GB SAS disk will report 66GB usable capacity in EMC CLARiiON, a large part of this difference is contributed by the difference between GB and GiB.

At that time, GiB is rarely adopted, GB mean GiB in most storage systems. Even today, GB is still widely used in different documents, user manuals and systems with the actual meaning of GiB. This is annoying when I have been asked about what GB means in particular document or system, I have to stop and perform a quick check.

A little bit history, based on Wikipedia,

Prior to 1998, some usage of gigabyte has been ambiguous. To resolve this difficulty, IEC 80000-13 clarifies that a gigabyte (GB) is 109 bytes and specifies the term gibibyte (GiB) to denote 230 bytes


In fact, IEC80000-13 is published in 2008 to replace IEC 60027-2 which was first published January 1999 to define the binary prefixes.

IEC 60027-2 Amendment 2, as published in January 1999, was the first international standard defining the binary prefixes, as proposed by International Electrotechnical Commission (IEC) since 1996 (kibi- (Ki), mebi- (Mi), gibi- (Gi) and tebi- (Ti))[1] but extended them up to pebi (Pi) and exbi- (Ei).”


From my very own point of view, the source of the confusion is all about the standard came late, computer world has already accepted that GB mean 230 bytes in storage for decades.

Even today, 2022, some software and documentations, old or new, still do not bother to use GB with the actual meaning of GiB. A few examples are as below:

VMware ESXi version 7.0

Windows 10

DELL EMC PowerStore

Google Cloud

On the other side, we can see GiB in some systems, for example, in Azure VM.

It looks like the confusion between GiB and GB will still be there in short or long. However, in real world of computer storage, except the physical disk drive labelled size, most GB we can see in storage system and within operating systems are most likely with the meaning of GiB.

But if you need 100% confirmation of the meaning of GB in particular system you are not familiar, you need check the document or perform testing within the system, this is the annoying bits I mentioned in the beginning.

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