Source : Free On-Line Dictionary of Computing

Commodore 1581
     
         {Commodore Business Machines}'s 3.5 inch {disk
        drive} for the {Commodore 64} and {Commodore 128}.  The drive
        stores 800 {kilobytes} using an {MFM} format which is
        different from both {messy-dos} 720 kb, and the {Amiga} 880 kb
        formats.
     
        The 1581 supports a poor imitation of {directories} which are
        really just {partitions} and largely unused.  It also supports
        burst loading like the {Commodore 1571}, but is actually
        faster as it is better designed.  It has 3160 {blocks} free
        when formatted.
     
        The 1581 is the highest density C64 serial bus drive made by
        Commodore.  However Creative Micro Designs (CMD) make the
        {FD2000} (1.6MB) and (until recently) the {FD4000} (3.2MB)
        3.5" disk drives.  {GEOS} users like 1581s as they are very
        fast when used with GEOS.
     
        See also {Commodore 1541}, {Commodore 1571}.
     
        (1998-12-23)