TMAP presents a graphical display of the fragmentation of
     the clusters on any disk.
     
     What's a Cluster?
     
     In the DOS world, disk space is allocated to files on an as-
     needed basis. The basic storage unit is called a cluster,
     and the size of a cluster varies by type of disk and by disk
     format.  Typical floppy disks have cluster sizes of 1024
     bytes, while on a hard disk a cluster may range from 2048 to
     16384 bytes depending on the capacity of the disk.  There
     are tens of thousands of clusters (allocation units) on a
     hard disk; the FORMAT command determines these sizes.
     
     The clusters are numbered and a file consists of one or more
     clusters.  A directory entry is little more than a file's
     name, date, time and the disk's file allocation table (FAT)
     entry that represents the first cluster of the file's
     contents.  The ordered list of actual cluster numbers for
     the file are coded in the FAT.  This tells the sequence in
     which the clusters must be read or written so the individual
     pieces of the file get accessed in the right order.
     
     What's Fragmentation?
     
     Fragmentation is the natural consequence of creating and
     deleting files on most file systems.  Since a file is made
     up of one or more clusters whose order is known, a file may
     be spread out all over the disk.  Reading and writing the
     file is easy as DOS just follows the chain in the FAT.  But
     jumping all over the disk, reading and writing bits and
     pieces, slows things down.  In addition, if the pieces of a
     file are not together, we say the file is fragmented, and it
     can be extremely difficult to unerase or to recover it if
     destroyed, deleted or lost somehow.
     
     TMAP merely shows the relative level of fragmentation of all
     the files on the disk.  Since there are only 1560 display
     positions on TMAP's display, we make each position represent
     more than one cluster.  The symbol displayed is therefore a
     composite of those adjacent clusters grouped together.  The
     scale, or the number of clusters represented by each symbol,
     is notated above the map.
     
     The idea for TMAP came from a utility program called VMAP
     from Golden Bow Systems of San Diego.  According to a
     representative of Golden Bow, VMAP and its mainstream disk
     de-fragmenter product, VOPT, were distributed together as
     demos (the VOPT demo went through the actions but didn't
     actually change the disk). They ended up on bulletin boards
     around the country.  When VMAP was written (1987 timeframe),
     hard disks were relatively small.  An earlier version of
     VMAP didn't work on disk partitions larger than 32
     megabytes.  A subsequent version only worked properly on
     partitions smaller than 128 Mb.  The reason?  The size of
     the disk's file allocation table (FAT) changes as disk
     partitions get larger. On the version I used, VMAP assumed
     it could read the FAT as a single 64k block.  However, on
     disks larger than 128 Mb, the FAT size exceeded 64k and VMAP
     did not work right.
     
     So, Now What?
     
     Every user of DOS should have a utility program that does
     maintenance on his own hard disk.  Besides frequently
     running CHKDSK to ensure consistency in the file system,
     Golden Bow's VOPT utility does a stellar job of
     defragmenting; I highly recommend it. Norton's Speed Disk
     works great too.  Personally I like ORG, a shareware disk
     organizer written by Grev‚ and Rifkind.  A defragmenter
     comes with DOS 6.
     
     This program was authored by Ronald E. Raikes out of our
     mutual desire to have a "VMAP" that worked with our large
     disks.  Ron wanted it to be a character-based utility that
     would function over his serial port.  With his permission, I
     have modified his character-based version, changing the
     output format, adding color and doing additional testing on
     other hardware and DOS versions using Borland C++.  It looks
     very much like the old VMAP from Golden Bow.
     
     I've tested TMAP with a wide range of types and sizes of
     floppy and hard disks (ESDI, IDE, etc) on a variety of
     machines and display adapters. It executes under DOS 4.01
     and above, including DOS 6.0 and Novell DOS 7 (Beta 4). I
     have not tried it on a Doublespaced volume.
     
     The day prior to the day I planned to upload TMAP, a friend
     gave me a version of VMAP that I didn't even know existed.
     Voila, here was the version I had wanted all along!  I'm
     pleased to report we get the same display...
     
     Thomas M. Allen
     North Orange County Computer Club (NOCCC), Orange CA
     72537.1134@compuserve.com
     13 December 1993