TMAP version 1.02 960420, (C) Thomas M. Allen

     TMAP presents a graphical display of the fragmentation of the
     clusters on any floppy or hard disk using DOS' FAT file system.

     What's a Cluster?

     In the DOS world, disk space is allocated to files on an as-
     needed basis. The basic allocation storage unit is called a
     cluster, and the size of a cluster varies by the type of disk,
     its format and the disk's size.  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 may be tens of thousands of clusters (allocation
     units) on a hard disk; the FORMAT command determines these sizes.

     The clusters are numbered and a file on the disk consists of one
     or more of these allocation units.  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 contents.  This ordered list of cluster numbers
     comprising the file are coded in the FAT, and is 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.  Resaving the file from, say, a word processor,
     writes the file somewhere else on the disk, freeing up the
     original space to be used for something else.  DOS merely follows
     the current chain of cluster numbers in the FAT to read or write
     the file.  It doesn't care how many pieces there are nor how
     they're scattered around the disk.  But jumping all over the disk
     to read and write the bits and pieces slows things down.  If the
     pieces of a file are not located together, we say the file is
     fragmented, and being fragmented can make it extremely difficult
     to unerase or to recover it if destroyed, deleted or lost
     somehow.

     TMAP shows the relative level of fragmentation of all the files
     on the disk, nothing more.  It doesn't write to the disk nor is
     there any user interaction.  If the display from TMAP looks like
     a bad case of acne, you are long overdue for running a cleanup
     utility on your disk!

     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 demo programs (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.

     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 noted above the map.

     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 and I highly
     recommend it. Norton's Speed Disk works great too.  The
     defragmenter that comes with DOS (defrag) is suitable too.
     Personally I like ORG, a shareware disk organizer written by
     Grev‚ and Rifkind.

     TMAP was authored primarily by Ronald E. Raikes out of our mutual
     desire to have a "VMAP" that worked with our large disks.  He
     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++.  Its output 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 (SCSI, ESDI, IDE) on a variety of machines and
     display adapters. It executes under DOS 4.01 and above, including
     the Novell implementations of DOS. It does not work on a CD-ROM
     (CDs don't use the FAT file system) nor on a networked drive.  I
     have not tried it on a Doublespaced volume.

     Just before releasing the first version of 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
     thos@deltanet.com / 72537.1143@compuserve.com
     North Orange County Computer Club (NOCCC)
     Orange, California

     1.02  20 April 1996: Fixed a condition where the computer would
           lock up when reading the file allocation table of a large
           hard disk partition.

     1.01  13 December 1993