Editing IBM PS/2 (section)

===Storage===
[[File:IBM PS2 MCA Model 70, riser for floppy and hard drive.jpg|thumb|Some PS/2 models used a quick-attachment socket on the back of the floppy drive which is incompatible with a standard 5.25-inch floppy connector.]]
[[Image:IBM PS2 MCA Model 55 SX, hard drive bus closeup.jpg|thumb|left|Close-up of unusual 72-pin MCA internal hard drive connector]]

Apple had first popularized the 3.5-inch floppy on the Macintosh line and IBM brought them to the PC in 1986 with the [[PC Convertible]]. In addition, they could be had as an optional feature on the XT and AT. The PS/2 line used entirely 3.5-inch drives which assisted in their quick adoption by the industry, although the lack of 5.25-inch drive bays in the computers created problems later on in the 1990s as they could not accommodate internal CD-ROM drives. In addition, the lack of built-in 5.25-inch floppy drives meant that PS/2 users could not immediately run the large body of existing IBM-compatible software.<ref>{{cite web |url=http://www.disktrend.com/pdf/portrpkg.pdf |archive-url=https://web.archive.org/web/20120328044723/http://www.disktrend.com/pdf/portrpkg.pdf |title=100th Anniversary Conference: Magnetic Recording and Information Storage |date=1998-12-14 |access-date=2014-03-24 |archive-date=2012-03-28 |author=Jim Porter |publisher=disktrend.com}}</ref> However IBM made available optional external 5.25-inch drives, with internal adapters for the early PS/2 models, to enable data transfer.
[[File:IBM 3.5-inch DD and HD diskettes.jpg|thumb|3.5-inch DD and HD floppies]]
In the initial lineup, IBM used 720&nbsp;KB double density (DD) capacity drives on the 8086-based models and 1440&nbsp;KB high density (HD) on the 80286-based and higher models. By the end of the PS/2 line they had moved to a somewhat standardized capacity of 2880&nbsp;KB.

The PS/2 floppy drives lacked a capacity detector. 1440&nbsp;KB floppies had a hole so that drives could distinguish them from 720&nbsp;KB floppies, preventing users from formatting the smaller capacity disks to the higher capacity (doing so would work, but with a higher tendency of data loss). Clone manufacturers implemented the hole detection, but IBM did not. As a result of this a 720 KB floppy could be formatted to 1440&nbsp;KB in a PS/2, but the resulting floppy would only be readable by a PS/2 machine.<ref>{{cite web|url=http://ohlandl.ipv7.net/floppy/floppy.html#Format_720K_On_144MB|title=floppy|first=Louis|last=Ohland|website=ohlandl.ipv7.net|access-date=2011-02-19|archive-date=2011-07-23|archive-url=https://web.archive.org/web/20110723160004/http://ohlandl.ipv7.net/floppy/floppy.html#Format_720K_On_144MB|url-status=live}}</ref>

PS/2s primarily used [[Mitsubishi]] floppy drives and did not use a separate Molex power connector; the data cable also contained the power supply lines. As the hardware aged the drives often malfunctioned due to bad quality [[capacitor]]s.{{Citation needed|date=February 2019}}

The PS/2 used several different types of internal hard drives. Early models used [[Modified Frequency Modulation|MFM]] or [[Enhanced Small Disk Interface|ESDI]] drives. Some desktop models used combo power/data cables similar to the floppy drives. Later models used [[DBA ESDI]] or [[Parallel SCSI]]. Typically, desktop PS/2 models only permitted use of one hard drive inside the computer case. Additional storage could be attached externally using the optional SCSI interface.