TITLE
    High-Density Disks: Don't Format them in 400K/800K Drives
Article ID:
Created:
Modified: 		3427
12/5/88
8/23/91
TOPIC

DISCUSSION



    TOPIC ------------------------------------------------------------

    This article explains why a high-density disk should not be formatted in 400K
    or 800K drives.

    DISCUSSION -------------------------------------------------------

    If a high-density disk is formatted in a normal 800K or 400K drive, it
    functions as an 800K or 400K disk; however, when such a disk is used in the
    Apple SuperDrive (formerly Apple FDHD), a dialog box appears stating that the
    disk was improperly formatted.

    SuperDrive disks have a special notch which allows the SuperDrive to recognize
    the media as high density (1.4MB). Standard 800K and 400K drives CANNOT detect
    the notch, and will format a high-density disk as a regular 800K or 400K disk.

    High-density media should NOT be formatted in a 800K or 400K drive.

    High-density disks are physically different from double-density disks and
    are tested to a different specification. The coating on high-density disks
    is thinner and has finer particles. These disks require a less intense
    magnetic field from the read/write head to properly align the magnetic
    particles within the data cell during a write cycle.

    The magnetic field generated by Apple 800K and 400K drives is too strong and
    may cause data loss.

    Thus, the SuperDrive, in conjunction with the system software, recognizes that
    the high-density disk was formatted improperly and gives the user the option
    to re-format it or eject it.




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