page_title: IBM Personal System/2
section_title: Storage
hierarchical_section_title: IBM Personal System/2 / Technology / Storage
caption_attribution_description: English: Closeup of the unusual IBM PS/2 Micro-Channel Architecture (MCA) connector on a PS/2 hard drive. This single connector conveys both power and data to the drive; mounting a generic IDE or MFM hard drive inside a stock PS/2 was impossible because separate 4-wire power connectors were not provided. (Building an adapter was technically possible.) The actual communication standard is unknown, but it is strongly suggested to have been ESDI. PS/2 systems could accept only one hard drive; no further internal expansion of capacity was permitted.
context_page_description: The Personal System/2 or PS/2 is IBM's third generation of personal computers. Released in 1987, it officially replaced the IBM PC, XT, AT, and PC Convertible in IBM's lineup. Many of the PS/2's innovations, such as the 16550 UART, 1440 KB 3.5-inch floppy disk format, Model M keyboard layout, 72-pin SIMMs, the PS/2 keyboard and mouse ports, and the VGA video standard, went on to become standards in the broader PC market.
  The PS/2 line was created by IBM partly in an attempt to recapture control of the PC market by introducing the advanced yet proprietary Micro Channel architecture on higher-end models. These models were in the strange position of being incompatible with the IBM-compatible hardware standards previously established by IBM and adopted in the PC industry. However IBM's initial PS/2 computers were popular with target market corporate buyers, and by 30th September 1988 IBM reported that it had sold 3 million PS/2 machines. This was only 18 months after the new range had been introduced.
  Most major PC manufacturers balked at IBM's licensing terms for MCA-compatible hardware, particularly the per-machine royalties.
context_section_description: Apple had first popularized the 3.5" 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" drives which assisted in their quick adoption by the industry, although the lack of 5.25" 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" floppy drives meant that PS/2 users could not immediately run the large body of existing IBM compatible software. However IBM made available optional external 5.25" drives, with internal adapters for the early PS/2 models, to enable data transfer.
  In the initial lineup, IBM used 720 KB double density (DD) capacity drives on the 8086-based models and 1440 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 KB.
  The PS/2 floppy drives lacked a capacity detector. 1440 KB floppies had a hole so that drives could identify them from 720 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 KB in a PS/2, but the resulting floppy would only be readable by a PS/2 machine.
  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 capacitors.
  The PS/2 used several different types of internal hard drives. Early models used MFM or 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 by using the optional SCSI interface.
caption: Close-up of unusual 72-pin MCA internal hard drive connector.
exif: {}