I say Petabyte, You say Pebibyte…

Let's call the whole thing off

It turns out that we right first time with our assertion here that 144,115,188,075,855,872 bytes equals 144 Petabytes. A large number of you wrote to tell us that it's actually 128 Petabytes.

But as correspondent Philip Skov Knudsen points out "Just because hundreds of people claim something to be true, that doesn't necessarily make it so."

"Actually, what you did by accident, drive manufacturers have been doing for quite some time. I.e. reporting drive capacities in powers of ten
rather than powers of two. So most drive manufacturers really would have marketed it as 144 petabytes," writes Brinton Sherwood.

According to the SI - not the Situationist International unfortunately, but the International System of Units best known for looking after the metric system - recognized a standard set of names for binary multiples in December 1998.

These had originally been devised by the International Electrotechnical Commission, or IEC. So 144,115,188,075,855,872 bytes equals 144.115118 Petabytes (PB). Or thereabouts, and it's actually 128 Pebibytes (PiB).

The SI's list follows, and with the correct abbreviations:-

One kibibit (1 Kibit) is 2^10, or 1024 bits
One kilobit (1 kbit) is 10^3, or 1000 bits
One mebibyte (1 MiB) is 2^20, or 1,048,576 bytes
One megabyte (1 MB) is 10^6, or a round million bytes
One gibibyte (1 GiB) is 2^30, or 1,073,741,824 bytes
One gigabyte (1 GB) is 10^9 or a round billion (thousand million - that battle's over, we guess) bytes.

Muddy waters

Unfortunately the drive industry looks likely to continue marketing the decimal rather than the binary definition. After all, they probably feel that they got there first.

As the SI note explains:- "... storage devices were not constructed on binary trees, which meant that, for many practical purposes, binary arithmetic was less convenient than decimal arithmetic."

There are actually three definitions of a Megabyte, one decimal, one binary, and one that refers specifically to 1.44MB floppoes.

"The sloppy use of kilo-, mega-, giga-, tera, and peta- wouldn't normally complain about it," writes correspondent John W Kennedy, "but if people like your correspondents are actually going to turn snarky on the subject, then I feel obliged to point out that it's flat wrong."

"It makes for a great pitch, but it is frustrating dealing with customers who want refunds or replacements for their drives because they were 'ripped off', adds Brinton.

So be forewarned when you're shopping. ®