diff --git a/DOS33.pm b/DOS33.pm
index c5e3787..065a3f0 100644
--- a/DOS33.pm
+++ b/DOS33.pm
@@ -2,6 +2,14 @@
 
 package DOS33;
 
+#
+# DOS33.pm:
+#
+# Module to access Apple II DOS 3.3 disk images.
+#
+# 20190115 LSH
+#
+
 use strict;
 
 use DSK;
diff --git a/DSK.pm b/DSK.pm
index dbf7920..e25ba54 100644
--- a/DSK.pm
+++ b/DSK.pm
@@ -2,6 +2,14 @@
 
 package DSK;
 
+#
+# DSK.pm:
+#
+# Module for low level access to Apple II .DSK and .DO disk image file (DOS Order).
+#
+# 20190115 LSH
+#
+
 use strict;
 
 use Exporter::Auto;
diff --git a/PO.pm b/PO.pm
index aa20a1d..fed821c 100644
--- a/PO.pm
+++ b/PO.pm
@@ -2,6 +2,14 @@
 
 package PO;
 
+#
+# PO.pm:
+#
+# Module for low level access to Apple II .PO disk images (ProDOS Order)
+#
+# 20190115 LSH
+#
+
 use strict;
 
 use Exporter::Auto;
@@ -10,7 +18,7 @@ my $debug = 0;
 
 my $min_blk = 0;  # Minimum block number
 my $max_blk = 280;  # Maximum block number
-my $blk_size = 512;
+my $blk_size = 512;  # Block size
 
 #
 # Read entire .po image.
diff --git a/ProDOS.pm b/ProDOS.pm
index 5a61678..aecbb78 100644
--- a/ProDOS.pm
+++ b/ProDOS.pm
@@ -2,6 +2,14 @@
 
 package ProDOS;
 
+#
+# ProDOS.pm:
+#
+# Module to access Apple II ProDOS volumes.
+#
+# 20190115 LSH
+#
+
 use strict;
 
 use PO;
@@ -12,6 +20,8 @@ my $debug = 0;
 
 # ProDOS file types
 my %ftype = (
+  # $0x Types: General
+
   # 00        Typeless file
   0x00 => '   ',
   # 01    BAD Bad block(s) file
@@ -35,6 +45,8 @@ my %ftype = (
   # f    DIR Directory file
   0x0f => 'DIR',
 
+  # $1x Types: Productivity
+
   # 19    ADB AppleWorks data base file
   0x19 => 'ADB',
   # 1a    AWP AppleWorks word processing file
@@ -42,6 +54,8 @@ my %ftype = (
   # 1b    ASP AppleWorks spreadsheet file
   0x1b => 'ASP',
 
+  # $2x Types: Code
+
   # $20 TDM Desktop Manager File
   0x20 => 'TDM',
   # $21 IPS Instant Pascal Source
@@ -64,11 +78,15 @@ my %ftype = (
   # $2E P8C ProDOS 8 Code Module
   0x2e => 'P8C',
 
+  # $4x Types: Miscellaneous
+
   # $41 OCR Optical Character Recognition
   0x41 => 'OCR',
   # $42 FTD File Type Definitions
   0x42 => 'FTD',
 
+  # $5x Types: Apple IIgs General
+
   # $50 GWP Apple IIgs Word Processing
   0x50 => 'GWP',
   #    $5445 - Teach
@@ -123,6 +141,8 @@ my %ftype = (
   # $5E DVU Development Utility
   0x5e => 'DVU',
 
+  # $6x Types: PC Transporter
+
   # $60 PRE PC Pre-Boot
   0x60 => 'PRE',
   # $6B BIO PC BIOS
@@ -136,6 +156,8 @@ my %ftype = (
   # $6F HDV PC Hard Disk Image
   0x6f => 'HDV',
 
+  # $7x Types: Kreative Software
+
   # $70 SN2 Sabine's Notebook 2.0
   0x70 => 'SN2',
   # $71 KMT
@@ -174,6 +196,8 @@ my %ftype = (
   # $7F JCP
   0x7f => 'JCP',
 
+  # $8x Types: GEOS
+
   # $80 GES System File
   0x80 => 'GES',
   # $81 GEA Desk Accessory
@@ -199,6 +223,8 @@ my %ftype = (
   # $8D GEW Formatting Data
   0x8d => 'GEW',
 
+  # $Ax Types: Apple IIgs BASIC
+
   # $A0 WP  WordPerfect
   0xa0 => 'WP ',
   # $AB GSB Apple IIgs BASIC Program
@@ -208,6 +234,8 @@ my %ftype = (
   # $AD BDF Apple IIgs BASIC Data
   0xad => 'BDF',
 
+  # $Bx Types: Apple IIgs System
+
   # $B0 SRC Apple IIgs Source Code
   0xb0 => 'SRC',
   # $B1 OBJ Apple IIgs Object Code
@@ -245,6 +273,8 @@ my %ftype = (
   # $BF DOC Apple IIgs Document
   0xbf => 'DOC',
 
+  # $Cx Types: Graphics
+
   # $C0 PNT Apple IIgs Packed Super HiRes
   0xc0 => 'PNT',
   #    $0001 - Packed Super HiRes
@@ -277,6 +307,8 @@ my %ftype = (
   # $CA ICN Apple IIgs Icon File
   0xca => 'ICN',
 
+  # $Dx Types: Audio
+
   # $D5 MUS Music
   0xd5 => 'MUS',
   # $D6 INS Instrument
@@ -295,6 +327,9 @@ my %ftype = (
 
   # $DB DBM DB Master Document
   0xdb => 'DBM',
+
+  # $Ex Types: Miscellaneous
+
   # $E0 LBR Archive
   0xe0 => 'LBR',
   #    $0000 - ALU
@@ -314,6 +349,8 @@ my %ftype = (
   # ef    PAS ProDOS PASCAL file
   0xef => 'PAS',
 
+  # $Fx Types: System
+
   # f0    CMD ProDOS added command file
   0xf0 => 'CMD',
   # f1-f8     User defined file types 1 through 8
@@ -325,6 +362,10 @@ my %ftype = (
   0xf6 => 'UD6',
   0xf7 => 'UD7',
   0xf8 => 'PRG',
+
+  # $F9 P16 ProDOS-16 System File
+  0xf9 => 'P16',
+
   # fa    INT Integer BASIC Program
   0xfa => 'INT',
   # fb    IVR Integer BASIC Variables
@@ -339,6 +380,9 @@ my %ftype = (
   0xff => 'SYS',
 );
 
+#
+# Months for catalog date format.
+#
 my %months = (
    1, 'JAN',
    2, 'FEB',
@@ -354,6 +398,7 @@ my %months = (
   12, 'DEC',
 );
 
+# Default key volume directory block.
 my $key_vol_dir_blk = 2;
 
 #
diff --git a/README b/README
index cea7ea2..c6e6d29 100644
--- a/README
+++ b/README
@@ -1,12 +1,15 @@
 TODO:
 
-catalog -- mostly working
-read -- mostly working for simple text files
-write
-umlock
-lock
-rename
-delete
-copy
-disk zap/sector editor -- partially working
+catalog.pl -- mostly working
+freemap.pl -- mostly working
+dos33read.pl -- mostly working for simple text files
+dos33write.pl
+dos33umlock.pl
+dos33lock.pl
+dos33rename.pl
+dos33delete.pl
+dos33copy.pl
+zap.pl -- partially working
+prozap.pl -- partially working
+procat.pl -- partially working
 
diff --git a/catalog.pl b/catalog.pl
index 88aec14..0065b18 100644
--- a/catalog.pl
+++ b/catalog.pl
@@ -1,5 +1,13 @@
 #!/usr/bin/perl -w
 
+#
+# catalog.pl:
+#
+# Utility to get a 'catalog' (directory) of an Apple II DOS 3.3 disk image.
+#
+# 20190115 LSH
+#
+
 use strict;
 
 use DOS33;
diff --git a/dos33read.pl b/dos33read.pl
index 74ccda0..270ec63 100644
--- a/dos33read.pl
+++ b/dos33read.pl
@@ -1,5 +1,13 @@
 #!/usr/bin/perl -w
 
+#
+# dos33read.pl:
+#
+# Utility to read a file out of an Apple II DOS 3.3 disk image.
+#
+# 20190115 LSH
+#
+
 use strict;
 
 use DOS33;
@@ -9,19 +17,25 @@ my $conv = 1;
 my $debug = 0;
 
 while (defined $ARGV[0] && $ARGV[0] =~ /^-/) {
+  # Mode
   if ($ARGV[0] eq '-m' && defined $ARGV[1] && $ARGV[1] ne '') {
+    # Text
     if ($ARGV[1] eq 'T') {
       $mode = 'T';
       $conv = 1;
+    # Integer BASIC
     } elsif ($ARGV[1] eq 'I') {
       $mode = 'I';
       $conv = 0;
+    # Applesoft
     } elsif ($ARGV[1] eq 'A') {
       $mode = 'A';
       $conv = 0;
+    # Binary
     } elsif ($ARGV[1] eq 'B') {
       $mode = 'B';
       $conv = 0;
+    # S
     } elsif ($ARGV[1] eq 'S') {
       $mode = 'S';
       $conv = 0;
@@ -30,9 +44,11 @@ while (defined $ARGV[0] && $ARGV[0] =~ /^-/) {
     }
     shift;
     shift;
+  # Convert (carriage return to linefeed)
   } elsif ($ARGV[0] eq '-c') {
     $conv = 0;
     shift;
+  # Debug
   } elsif ($ARGV[0] eq '-d') {
     $debug = 1;
     shift;
diff --git a/freemap.pl b/freemap.pl
index 1e76e2a..b340149 100644
--- a/freemap.pl
+++ b/freemap.pl
@@ -1,5 +1,13 @@
 #!/usr/bin/perl -w
 
+#
+# freemap.pl:
+#
+# Utility to get a free sector map of an Apple II DOS 3.3 disk image.
+#
+# 20190115 LSH
+#
+
 use strict;
 
 use DOS33;
diff --git a/procat.pl b/procat.pl
index 0162ca9..8c7e146 100644
--- a/procat.pl
+++ b/procat.pl
@@ -1,5 +1,13 @@
 #!/usr/bin/perl -w
 
+#
+# procat.pl:
+#
+# Utility to get a 'catalog' (directory listing) of an Apple II ProDOS volume.
+#
+# 20190115 LSH
+#
+
 use strict;
 
 use ProDOS;
diff --git a/prozap.pl b/prozap.pl
index 0c8438e..b3d059c 100644
--- a/prozap.pl
+++ b/prozap.pl
@@ -1,5 +1,13 @@
 #!/usr/bin/perl -w
 
+#
+# prozap.pl:
+#
+# Utility to edit a ProDOS block (.PO image).
+#
+# 20190115 LSH
+#
+
 use strict;
 
 use PO;
@@ -13,17 +21,21 @@ my $write = 0;
 my @mods = ();
 
 while (defined $ARGV[0] && $ARGV[0] =~ /^-/) {
+  # Debug
   if ($ARGV[0] eq '-d') {
     $debug = 1;
     shift;
+  # Block to read
   } elsif ($ARGV[0] eq '-b' && defined $ARGV[1] && $ARGV[1] =~ /^\d+$/) {
     $blk = $ARGV[1];
     shift;
     shift;
+  # Destination block
   } elsif ($ARGV[0] eq '-db' && defined $ARGV[1] && $ARGV[1] =~ /^\d+$/) {
     $dst_blk = $ARGV[1];
     shift;
     shift;
+  # Allow modifying data.
   } elsif ($ARGV[0] =~ /^-m([ahA])/ && defined $ARGV[1] && $ARGV[1] ne '') {
     my $typ = $1;
     print "$ARGV[1] typ=$typ\n" if $debug;
@@ -46,13 +58,18 @@ $dst_blk = $blk unless $dst_blk >= 0;
 
 my $buf;
 
+# Read the block
 if (read_blk($pofile, $blk, \$buf)) {
+  # Display the data in the block.
   dump_blk($buf);
 
+  # Allow modifying the data.
   if ($write) {
     print "WRITING $dst_blk\n" if $debug;
+    # Unpack the data in the block
     my @bytes = unpack "C512", $buf;
 
+    # Process each modification.
     foreach my $mod (@mods) {
       my @mbytes = ();
       if ($mod->{'typ'} eq 'a') {
@@ -76,10 +93,14 @@ if (read_blk($pofile, $blk, \$buf)) {
       }
     }
 
-    my $buf = pack "C*", @bytes;
+    # Re-pack the data in the block
+    $buf = pack "C*", @bytes;
 
+    # Write the destination block (default to block read).
     if (write_blk($pofile, $dst_blk, $buf)) {
+      # Read the block back in.
       if (read_blk($pofile, $dst_blk, \$buf)) {
+        # Display the data in the modified block.
         dump_blk($buf);
       } else {
         print "Failed final read!\n";
diff --git a/zap.pl b/zap.pl
index 9d351d1..a85320e 100644
--- a/zap.pl
+++ b/zap.pl
@@ -1,5 +1,13 @@
 #!/usr/bin/perl -w
 
+#
+# zap.pl:
+#
+# Utility to edit a DOS 3.3 sector (.DSK or .DO disk image).
+#
+# 20190115 LSH
+#
+
 use strict;
 
 use DSK;
@@ -15,25 +23,31 @@ my $write = 0;
 my @mods = ();
 
 while (defined $ARGV[0] && $ARGV[0] =~ /^-/) {
+  # Debug
   if ($ARGV[0] eq '-d') {
     $debug = 1;
     shift;
+  # Track
   } elsif ($ARGV[0] eq '-t' && defined $ARGV[1] && $ARGV[1] =~ /^\d+$/) {
     $trk = $ARGV[1];
     shift;
     shift;
+  # Sector
   } elsif ($ARGV[0] eq '-s' && defined $ARGV[1] && $ARGV[1] =~ /^\d+$/) {
     $sec = $ARGV[1];
     shift;
     shift;
+  # Destination track
   } elsif ($ARGV[0] eq '-dt' && defined $ARGV[1] && $ARGV[1] =~ /^\d+$/) {
     $dst_trk = $ARGV[1];
     shift;
     shift;
+  # Destination sector
   } elsif ($ARGV[0] eq '-ds' && defined $ARGV[1] && $ARGV[1] =~ /^\d+$/) {
     $dst_sec = $ARGV[1];
     shift;
     shift;
+  # Allow modifying data.
   } elsif ($ARGV[0] =~ /^-m([ahA])/ && defined $ARGV[1] && $ARGV[1] ne '') {
     my $typ = $1;
     print "$ARGV[1] typ=$typ\n" if $debug;
@@ -59,10 +73,13 @@ $dst_sec = $sec unless $dst_sec >= 0;
 my $buf;
 
 if (rts($dskfile, $trk, $sec, \$buf)) {
+  # Display the data in the sector.
   dump_sec($buf);
 
+  # Allow modifying data.
   if ($write) {
     print "WRITING $dst_trk $dst_sec\n" if $debug;
+    # Unpack the data in the sector.
     my @bytes = unpack "C256", $buf;
 
     foreach my $mod (@mods) {
@@ -88,10 +105,14 @@ if (rts($dskfile, $trk, $sec, \$buf)) {
       }
     }
 
-    my $buf = pack "C*", @bytes;
+    # Re-pack the data in the sector.
+    $buf = pack "C*", @bytes;
 
+    # Write the sector.
     if (wts($dskfile, $dst_trk, $dst_sec, $buf)) {
+      # Read the sector back in.
       if (rts($dskfile, $dst_trk, $dst_sec, \$buf)) {
+        # Display the data in the modified sector.
         dump_sec($buf);
       } else {
         print "Failed final read!\n";