Editing Binary prefix (section)

==== Hard disks ====
In specifying disk drive capacities, manufacturers have always used conventional decimal SI prefixes representing powers of 10. Storage in a rotating [[disk drive]] is organized in platters and tracks whose sizes and counts are determined by mechanical engineering constraints so that the capacity of a disk drive has hardly ever been a simple multiple of a power of 2. For example, the first commercially sold disk drive, the [[IBM 350]] (1956), had 50 physical disk platters containing a total of {{val|50000}} sectors of 100 characters each, for a total quoted capacity of 5 million characters.<ref name="IBM1956" />

Moreover, since the 1960s, many disk drives used IBM's [[Count Key Data|disk format]], where each track was divided into blocks of user-specified size; and the block sizes were recorded on the disk, subtracting from the usable capacity. For example, the IBM 3336 disk pack was quoted to have a 200-megabyte capacity, achieved only with a single {{val|13030}}-byte block in each of its 808 × 19 tracks.

Decimal megabytes were used for disk capacity by the CDC in 1974.<ref name="CDC1974" /> The Seagate [[ST-412]],<ref name="seag1982" /> one of several types installed in the [[IBM PC/XT]],<ref name="CSN1984" /> had a capacity of {{val|10027008|u=bytes}} when formatted as 306 × 4 tracks and 32 256-byte sectors per track, which was quoted as "10&nbsp;MB".<ref name="mall2011" /> Similarly, a "300&nbsp;GB" hard drive can be expected to offer only slightly more than {{val|300|e=9}} = {{val|300000000000}}, bytes, not {{nowrap|300 × 2<sup>30</sup>}} (which would be about {{val|322|e=9}} bytes or "322&nbsp;GB"). The first terabyte (SI prefix, {{val|1000000000000}} bytes) hard disk drive was introduced in 2007.<ref name="hita2007" /> Decimal prefixes were generally used by information processing publications when comparing hard disk capacities.<ref name="RDD1977" />

Some programs and operating systems, such as [[Microsoft Windows]], still use "MB" and "GB" to denote binary prefixes even when displaying disk drive capacities and file sizes, as did [[Classic Mac OS]]. Thus, for example, the capacity of a "10 MB" (decimal "M") disk drive could be reported as "{{nowrap|9.56 MB}}", and that of a "300&nbsp;GB" drive as "279.4&nbsp;GB". Some operating systems, such as [[Mac OS X]],<ref>{{cite web |title=How iOS and macOS report storage capacity |url=https://support.apple.com/en-us/HT201402 |website=Apple Support |access-date=9 January 2022 |language=en |date=27 February 2018 |archive-date=9 April 2020 |archive-url=https://web.archive.org/web/20200409170256/https://support.apple.com/en-us/HT201402 |url-status=live }}</ref> [[Ubuntu]],<ref>{{cite web |title=UnitsPolicy |url=https://wiki.ubuntu.com/UnitsPolicy |website=Ubuntu Wiki |publisher=Ubuntu |access-date=9 January 2022 |archive-date=18 November 2021 |archive-url=https://web.archive.org/web/20211118114902/https://wiki.ubuntu.com/UnitsPolicy |url-status=live }}</ref> and [[Debian]],<ref>{{cite web |title=ConsistentUnitPrefixes |url=https://wiki.debian.org/ConsistentUnitPrefixes |website=Debian Wiki |access-date=9 January 2022 |archive-date=3 December 2021 |archive-url=https://web.archive.org/web/20211203075715/https://wiki.debian.org/ConsistentUnitPrefixes |url-status=live }}</ref> have been updated to use "MB" and "GB" to denote decimal prefixes when displaying disk drive capacities and file sizes. Some manufacturers, such as [[Seagate Technology]], have released recommendations stating that properly-written software and documentation should specify clearly whether prefixes such as "K", "M", or "G" mean binary or decimal multipliers.<ref name="seaga2011" /><ref name="seag2010" />