From 1b5f3f95a92388446d689886d1f9f34818f743a3 Mon Sep 17 00:00:00 2001
From: Denis Molony <dmolony@iinet.net.au>
Date: Fri, 25 Jan 2019 15:57:15 +1100
Subject: [PATCH] DOS 4.1 changes

---
 .../diskbrowser/applefile/SimpleText2.java    |   8 +-
 .../bytezone/diskbrowser/disk/AppleDisk.java  |  10 +-
 .../diskbrowser/disk/AppleDiskAddress.java    |  20 ++-
 .../diskbrowser/dos/AbstractCatalogEntry.java |  30 ++--
 .../diskbrowser/dos/CatalogEntry.java         |   9 +-
 .../diskbrowser/dos/DosCatalogSector.java     | 137 ++++++++++++------
 src/com/bytezone/diskbrowser/dos/DosDisk.java |  80 ++++++----
 .../diskbrowser/dos/DosVTOCSector.java        |  88 ++++++++++-
 .../diskbrowser/gui/DiskLayoutSelection.java  |   3 +-
 .../diskbrowser/utilities/Utility.java        |  20 +++
 10 files changed, 306 insertions(+), 99 deletions(-)

diff --git a/src/com/bytezone/diskbrowser/applefile/SimpleText2.java b/src/com/bytezone/diskbrowser/applefile/SimpleText2.java
index 3833f71..f81112f 100755
--- a/src/com/bytezone/diskbrowser/applefile/SimpleText2.java
+++ b/src/com/bytezone/diskbrowser/applefile/SimpleText2.java
@@ -18,7 +18,7 @@ public class SimpleText2 extends AbstractFile
 
     // store a pointer to each new line
     int ptr = 0;
-    while (buffer[ptr] != -1)
+    while (ptr < buffer.length && buffer[ptr] != -1)
     {
       int length = buffer[ptr] & 0xFF;
       lineStarts.add (ptr);
@@ -37,6 +37,8 @@ public class SimpleText2 extends AbstractFile
 
     for (Integer i : lineStarts)
       text.append (String.format ("%05X  %s%n", i, getLine (i)));
+    if (text.charAt (text.length () - 1) == '\n')
+      text.deleteCharAt (text.length () - 1);
     return text.toString ();
   }
 
@@ -46,8 +48,8 @@ public class SimpleText2 extends AbstractFile
     StringBuilder text = new StringBuilder ();
 
     for (Integer i : lineStarts)
-      text.append (HexFormatter.formatNoHeader (buffer, i, (buffer[i] & 0xFF) + 1)
-          + "\n");
+      text.append (
+          HexFormatter.formatNoHeader (buffer, i, (buffer[i] & 0xFF) + 1) + "\n");
     text.append (HexFormatter.formatNoHeader (buffer, buffer.length - 2, 2) + "\n");
 
     return text.toString ();
diff --git a/src/com/bytezone/diskbrowser/disk/AppleDisk.java b/src/com/bytezone/diskbrowser/disk/AppleDisk.java
index a99e977..b539544 100755
--- a/src/com/bytezone/diskbrowser/disk/AppleDisk.java
+++ b/src/com/bytezone/diskbrowser/disk/AppleDisk.java
@@ -396,7 +396,8 @@ public class AppleDisk implements Disk
     int ptr = 0;
     for (DiskAddress da : daList)
     {
-      if (da != null && da.getBlock () > 0)    // sparse text/PNT/PIC files may have gaps
+      // sparse text/PNT/PIC files may have gaps
+      if (da != null && (da.getBlock () > 0 || ((AppleDiskAddress) da).zeroFlag ()))
         readBuffer (da, buffer, ptr);
       ptr += sectorSize;
     }
@@ -458,6 +459,9 @@ public class AppleDisk implements Disk
   @Override
   public DiskAddress getDiskAddress (int track, int sector)
   {
+    //    track &= 0x3F;
+    //    sector &= 0x1F;
+
     if (!isValidAddress (track, sector))
     {
       System.out.println ("Invalid block : " + track + "/" + sector);
@@ -502,10 +506,14 @@ public class AppleDisk implements Disk
   @Override
   public boolean isValidAddress (int track, int sector)
   {
+    track &= 0x3F;
+    sector &= 0x1F;
+
     if (track < 0 || track >= this.tracks)
       return false;
     if (sector < 0 || sector >= this.sectors)
       return false;
+
     return true;
   }
 
diff --git a/src/com/bytezone/diskbrowser/disk/AppleDiskAddress.java b/src/com/bytezone/diskbrowser/disk/AppleDiskAddress.java
index 4ae196f..7138678 100755
--- a/src/com/bytezone/diskbrowser/disk/AppleDiskAddress.java
+++ b/src/com/bytezone/diskbrowser/disk/AppleDiskAddress.java
@@ -6,6 +6,7 @@ public class AppleDiskAddress implements DiskAddress
   private final int track;
   private final int sector;
   public final Disk owner;
+  private boolean zeroFlag;
 
   public AppleDiskAddress (Disk owner, int block)
   {
@@ -19,15 +20,15 @@ public class AppleDiskAddress implements DiskAddress
   public AppleDiskAddress (Disk owner, int track, int sector)
   {
     this.owner = owner;
-    this.track = track;
-    this.sector = sector;
-    this.block = track * owner.getSectorsPerTrack () + sector;
+    zeroFlag = (track & 0x40) != 0;
+    this.track = track & 0x3F;
+    this.sector = sector & 0x1F;
+    this.block = this.track * owner.getSectorsPerTrack () + this.sector;
   }
 
-  @Override
-  public String toString ()
+  public boolean zeroFlag ()
   {
-    return String.format ("[Block=%3d, Track=%2d, Sector=%2d]", block, track, sector);
+    return zeroFlag;
   }
 
   @Override
@@ -65,4 +66,11 @@ public class AppleDiskAddress implements DiskAddress
   {
     return owner;
   }
+
+  @Override
+  public String toString ()
+  {
+    return String.format ("[Block=%3d, Track=%2d, Sector=%2d, Zero=%s]", block, track,
+        sector, zeroFlag);
+  }
 }
\ No newline at end of file
diff --git a/src/com/bytezone/diskbrowser/dos/AbstractCatalogEntry.java b/src/com/bytezone/diskbrowser/dos/AbstractCatalogEntry.java
index d2928dc..78d8ae9 100644
--- a/src/com/bytezone/diskbrowser/dos/AbstractCatalogEntry.java
+++ b/src/com/bytezone/diskbrowser/dos/AbstractCatalogEntry.java
@@ -1,5 +1,6 @@
 package com.bytezone.diskbrowser.dos;
 
+import java.time.LocalDateTime;
 import java.util.ArrayList;
 import java.util.List;
 
@@ -10,6 +11,7 @@ import com.bytezone.diskbrowser.disk.FormattedDisk;
 import com.bytezone.diskbrowser.dos.DosDisk.FileType;
 import com.bytezone.diskbrowser.gui.DataSource;
 import com.bytezone.diskbrowser.utilities.HexFormatter;
+import com.bytezone.diskbrowser.utilities.Utility;
 
 abstract class AbstractCatalogEntry implements AppleFileSource
 {
@@ -22,6 +24,7 @@ abstract class AbstractCatalogEntry implements AppleFileSource
   protected int reportedSize;
   protected boolean locked;
   protected DataSource appleFile;
+  protected LocalDateTime lastModified;
 
   protected DiskAddress catalogSectorDA;
   protected final List<DiskAddress> dataSectors = new ArrayList<DiskAddress> ();
@@ -34,33 +37,34 @@ abstract class AbstractCatalogEntry implements AppleFileSource
   {
     this.dosDisk = dosDisk;
     this.disk = dosDisk.getDisk ();
-    this.disk = dosDisk.getDisk ();
     this.catalogSectorDA = catalogSector;
 
     reportedSize = HexFormatter.unsignedShort (entryBuffer, 33);
-    int type = entryBuffer[2] & 0xFF;
-    locked = (type & 0x80) > 0;
 
-    if ((type & 0x7F) == 0)
+    int type = entryBuffer[2] & 0x7F;
+    locked = (entryBuffer[2] & 0x80) != 0;
+
+    if (type == 0)
       fileType = FileType.Text;
-    else if ((type & 0x01) > 0)
+    else if ((type == 0x01))
       fileType = FileType.IntegerBasic;
-    else if ((type & 0x02) > 0)
+    else if ((type == 0x02))
       fileType = FileType.ApplesoftBasic;
-    else if ((type & 0x04) > 0)
+    else if ((type == 0x04))
       fileType = FileType.Binary;
-    else if ((type & 0x08) > 0)
+    else if ((type == 0x08))
       fileType = FileType.SS;
-    else if ((type & 0x10) > 0)
+    else if ((type == 0x10))
       fileType = FileType.Relocatable;
-    else if ((type & 0x20) > 0)
+    else if ((type == 0x20))
       fileType = FileType.AA;
-    else if ((type & 0x40) > 0)
+    else if ((type == 0x40))
       fileType = FileType.BB;
     else
-      System.out.println ("Unknown file type : " + (type & 0x7F));
+      System.out.println ("Unknown file type : " + type);
 
     name = getName ("", entryBuffer);
+    lastModified = Utility.getDateTime (entryBuffer, 0x1B);
     // CATALOG command only formats the LO byte - see Beneath Apple DOS pp4-6
     String base = String.format ("%s%s %03d ", (locked) ? "*" : " ", getFileType (),
         (entryBuffer[33] & 0xFF));
@@ -71,6 +75,8 @@ abstract class AbstractCatalogEntry implements AppleFileSource
   {
     StringBuilder text = new StringBuilder (base);
     int max = buffer[0] == (byte) 0xFF ? 32 : 33;
+    if (dosDisk.getVersion () >= 0x41)
+      max = 27;
     for (int i = 3; i < max; i++)
     {
       int c = buffer[i] & 0xFF;
diff --git a/src/com/bytezone/diskbrowser/dos/CatalogEntry.java b/src/com/bytezone/diskbrowser/dos/CatalogEntry.java
index 1428db0..1f12940 100644
--- a/src/com/bytezone/diskbrowser/dos/CatalogEntry.java
+++ b/src/com/bytezone/diskbrowser/dos/CatalogEntry.java
@@ -1,5 +1,6 @@
 package com.bytezone.diskbrowser.dos;
 
+import com.bytezone.diskbrowser.disk.AppleDiskAddress;
 import com.bytezone.diskbrowser.disk.DiskAddress;
 import com.bytezone.diskbrowser.dos.DosDisk.FileType;
 import com.bytezone.diskbrowser.utilities.HexFormatter;
@@ -20,7 +21,7 @@ class CatalogEntry extends AbstractCatalogEntry
       DiskAddress da = disk.getDiskAddress (entryBuffer[0], entryBuffer[1]);
 
       // Loop through all TS-list sectors
-      loop: while (da.getBlock () > 0)
+      loop: while (da.getBlock () > 0 || ((AppleDiskAddress) da).zeroFlag ())
       {
         if (dosDisk.stillAvailable (da))
           dosDisk.sectorTypes[da.getBlock ()] = dosDisk.tsListSector;
@@ -55,7 +56,7 @@ class CatalogEntry extends AbstractCatalogEntry
                 sectorBuffer[i], sectorBuffer[i + 1], name.trim ());
             break loop;
           }
-          if (da.getBlock () == 0)
+          if (da.getBlock () == 0 && !((AppleDiskAddress) da).zeroFlag ())
           {
             if (fileType != FileType.Text)
               break;
@@ -132,6 +133,10 @@ class CatalogEntry extends AbstractCatalogEntry
     String lengthText = length == 0 ? "" : String.format ("$%4X  %,6d", length, length);
     String message = "";
     String lockedFlag = (locked) ? "*" : " ";
+    if (dosDisk.dosVTOCSector.dosVersion >= 0x41)
+    {
+      message = lastModified.toString ().replace ('T', ' ');
+    }
     if (reportedSize != actualSize)
       message += "Bad size (" + reportedSize + ") ";
     if (dataSectors.size () == 0)
diff --git a/src/com/bytezone/diskbrowser/dos/DosCatalogSector.java b/src/com/bytezone/diskbrowser/dos/DosCatalogSector.java
index 86fe5fc..c711634 100755
--- a/src/com/bytezone/diskbrowser/dos/DosCatalogSector.java
+++ b/src/com/bytezone/diskbrowser/dos/DosCatalogSector.java
@@ -4,6 +4,7 @@ import com.bytezone.diskbrowser.disk.AbstractSector;
 import com.bytezone.diskbrowser.disk.Disk;
 import com.bytezone.diskbrowser.disk.DiskAddress;
 import com.bytezone.diskbrowser.utilities.HexFormatter;
+import com.bytezone.diskbrowser.utilities.Utility;
 
 class DosCatalogSector extends AbstractSector
 {
@@ -12,73 +13,119 @@ class DosCatalogSector extends AbstractSector
         "SS file", "Relocatable file", "AA file", "BB file" };
   private static int CATALOG_ENTRY_SIZE = 35;
 
-  public DosCatalogSector (Disk disk, byte[] buffer, DiskAddress diskAddress)
+  private final DosDisk dosDisk;
+
+  public DosCatalogSector (DosDisk dosDisk, Disk disk, byte[] buffer,
+      DiskAddress diskAddress)
   {
     super (disk, buffer, diskAddress);
+    this.dosDisk = dosDisk;
   }
 
   @Override
   public String createText ()
   {
-    StringBuilder text = getHeader ("Catalog Sector");
+    StringBuilder text =
+        getHeader ("DOS " + dosDisk.getVersionText () + " Catalog Sector");
     addText (text, buffer, 0, 1, "Not used");
     addText (text, buffer, 1, 2, "Next catalog track/sector");
     addText (text, buffer, 3, 4, "Not used");
     addText (text, buffer, 7, 4, "Not used");
 
+    boolean dos4 = dosDisk.getVersion () > 3;
+
     for (int i = 11; i <= 255; i += CATALOG_ENTRY_SIZE)
     {
       text.append ("\n");
-      if (true)
-      {
-        if (buffer[i] == (byte) 0xFF)
-        {
-          addText (text, buffer, i + 0, 2,
-              "DEL: file @ " + HexFormatter.format2 (buffer[i + 32]) + " "
-                  + HexFormatter.format2 (buffer[i + 1]));
-          addText (text, buffer, i + 2, 1, "DEL: File type " + getType (buffer[i + 2]));
-          if (buffer[i + 3] == 0)
-            addText (text, buffer, i + 3, 4, "");
-          else
-            addText (text, buffer, i + 3, 4, "DEL: " + getName (buffer, i));
-          addTextAndDecimal (text, buffer, i + 33, 2, "DEL: Sector count");
-        }
-        else if (buffer[i] > 0)
-        {
-          addText (text, buffer, i + 0, 2, "TS list track/sector");
-          addText (text, buffer, i + 2, 1, "File type " + getType (buffer[i + 2]));
-          if (buffer[i + 3] == 0)
-            addText (text, buffer, i + 3, 4, "");
-          else
-          {
-            addText (text, buffer, i + 3, 4, getName (buffer, i));
-            for (int j = 0; j < 24; j += 4)
-              addText (text, buffer, i + j + 7, 4, "");
-            addText (text, buffer, i + 31, 2, "");
-          }
-          addTextAndDecimal (text, buffer, i + 33, 2, "Sector count");
-        }
-        else
-        {
-          addText (text, buffer, i + 0, 2, "");
-          addText (text, buffer, i + 2, 1, "");
-          addText (text, buffer, i + 3, 4, "");
-          addText (text, buffer, i + 33, 2, "");
-        }
-      }
+      if (dos4)
+        createDos4Text (text, i);
+      else
+        createDos3Text (text, i);
     }
 
     text.deleteCharAt (text.length () - 1);
     return text.toString ();
   }
 
-  private String getName (byte[] buffer, int offset)
+  private void createDos4Text (StringBuilder text, int i)
+  {
+    int track = buffer[i] & 0x3F;
+    int sector = buffer[i + 1] & 0x1F;
+    int fileType = buffer[i + 2] & 0x7F;
+
+    boolean deleteFlag = (buffer[i] & 0x80) != 0;
+    boolean zeroTrackFlag = (buffer[i] & 0x40) != 0;
+    boolean lockedFlag = (buffer[i + 2] & 0x80) != 0;
+
+    if (buffer[i] == 0 && !zeroTrackFlag)
+    {
+      addText (text, buffer, i + 0, 2, "");
+      addText (text, buffer, i + 2, 1, "");
+      addText (text, buffer, i + 3, 4, "");
+      addText (text, buffer, i + 33, 2, "");
+    }
+    else
+    {
+      addText (text, buffer, i, 1,
+          String.format ("TS list track (%s, %s)", deleteFlag ? "deleted" : "not deleted",
+              zeroTrackFlag ? "track zero" : "not track zero"));
+      addText (text, buffer, i + 1, 1, "TS list sector");
+      addText (text, buffer, i + 2, 1,
+          String.format ("File type (%s)", lockedFlag ? "locked" : "unlocked"));
+      addText (text, buffer, i + 3, 4, getName (buffer, i + 3, 24));
+      for (int j = 0; j < 20; j += 4)
+        addText (text, buffer, i + 7 + j, 4, "");
+      addText (text, buffer, i + 27, 3,
+          "Date/time initialised: " + Utility.getDateTime (buffer, i + 27));
+      addText (text, buffer, i + 30, 3, "");
+      addTextAndDecimal (text, buffer, i + 33, 2, "File size");
+    }
+  }
+
+  private void createDos3Text (StringBuilder text, int i)
+  {
+    if (buffer[i] == (byte) 0xFF)         // file is deleted
+    {
+      addText (text, buffer, i, 2, "DEL: file @ " + HexFormatter.format2 (buffer[i + 32])
+          + " " + HexFormatter.format2 (buffer[i + 1]));
+      addText (text, buffer, i + 2, 1, "DEL: File type " + getType (buffer[i + 2]));
+      if (buffer[i + 3] == 0)
+        addText (text, buffer, i + 3, 4, "");
+      else
+        addText (text, buffer, i + 3, 4, "DEL: " + getName (buffer, i + 3, 29));
+      addTextAndDecimal (text, buffer, i + 33, 2, "DEL: Sector count");
+    }
+    else if (buffer[i] > 0)               // file exists
+    {
+      addText (text, buffer, i, 2, "TS list track/sector");
+      addText (text, buffer, i + 2, 1, "File type " + getType (buffer[i + 2]));
+      if (buffer[i + 3] == 0)
+        addText (text, buffer, i + 3, 4, "");
+      else
+      {
+        addText (text, buffer, i + 3, 4, getName (buffer, i + 3, 30));
+        for (int j = 0; j < 24; j += 4)
+          addText (text, buffer, i + j + 7, 4, "");
+        addText (text, buffer, i + 31, 2, "");
+      }
+      addTextAndDecimal (text, buffer, i + 33, 2, "Sector count");
+    }
+    else                                  // no file
+    {
+      addText (text, buffer, i + 0, 2, "");
+      addText (text, buffer, i + 2, 1, "");
+      addText (text, buffer, i + 3, 4, "");
+      addText (text, buffer, i + 33, 2, "");
+    }
+  }
+
+  private String getName (byte[] buffer, int offset, int length)
   {
     StringBuilder text = new StringBuilder ();
-    int max = buffer[offset] == (byte) 0xFF ? 32 : 33;
-    for (int i = 3; i < max; i++)
+    //    int max = buffer[offset] == (byte) 0xFF ? 32 : 33;
+    for (int i = offset; i < offset + length; i++)
     {
-      int c = buffer[i + offset] & 0xFF;
+      int c = buffer[i] & 0xFF;
       if (c == 136)
       {
         if (text.length () > 0)
@@ -87,10 +134,10 @@ class DosCatalogSector extends AbstractSector
       }
       if (c > 127)
         c -= c < 160 ? 64 : 128;
-      if (c < 32) // non-printable
+      if (c < 32)                                 // non-printable
         text.append ("^" + (char) (c + 64));
       else
-        text.append ((char) c); // standard ascii
+        text.append ((char) c);                   // standard ascii
     }
     return text.toString ();
   }
diff --git a/src/com/bytezone/diskbrowser/dos/DosDisk.java b/src/com/bytezone/diskbrowser/dos/DosDisk.java
index 427afda..ba2f4e1 100755
--- a/src/com/bytezone/diskbrowser/dos/DosDisk.java
+++ b/src/com/bytezone/diskbrowser/dos/DosDisk.java
@@ -18,7 +18,7 @@ public class DosDisk extends AbstractFormattedDisk
   private static final int CATALOG_TRACK = 17;
   private static final int VTOC_SECTOR = 0;
 
-  private final DosVTOCSector dosVTOCSector;
+  final DosVTOCSector dosVTOCSector;
   private final Color green = new Color (0, 200, 0);
   private final DefaultMutableTreeNode volumeNode;
 
@@ -152,6 +152,12 @@ public class DosDisk extends AbstractFormattedDisk
 
       int track = sectorBuffer[1] & 0xFF;
       int sector = sectorBuffer[2] & 0xFF;
+      if (dosVTOCSector.dosVersion >= 0x41)
+      {
+        track = track & 0x3F;
+        sector = sector & 0x1F;
+      }
+
       if (!disk.isValidAddress (track, sector))
         break;
 
@@ -254,6 +260,28 @@ public class DosDisk extends AbstractFormattedDisk
     return false;
   }
 
+  public String getVersionText ()
+  {
+    switch (getVersion ())
+    {
+      case 0x01:
+        return "3.1";
+      case 0x02:
+        return "3.2";
+      case 0x03:
+        return "3.3";
+      case 0x41:
+        return "4.1";
+      default:
+        return "??";
+    }
+  }
+
+  public int getVersion ()
+  {
+    return dosVTOCSector.dosVersion;
+  }
+
   private static int checkFormat (AppleDisk disk)
   {
     byte[] buffer = disk.readSector (0x11, 0x00);
@@ -272,10 +300,10 @@ public class DosDisk extends AbstractFormattedDisk
     //      //      return 0;
     //    }
 
-    int version = buffer[3];
-    if (version < -1 || version > 4)
+    int version = buffer[3] & 0xFF;
+    if (version > 0x42 && version != 0xFF)
     {
-      System.out.println ("Bad version : " + buffer[3]);
+      System.out.printf ("Bad version : %02X%n", version);
       return 0;
     }
 
@@ -347,7 +375,7 @@ public class DosDisk extends AbstractFormattedDisk
     if (type == tsListSector)
       return new DosTSListSector (getSectorFilename (da), disk, buffer, da);
     if (type == catalogSector)
-      return new DosCatalogSector (disk, buffer, da);
+      return new DosCatalogSector (this, disk, buffer, da);
     if (type == dataSector)
       return new DefaultSector (
           "Data Sector at " + address + " : " + getSectorFilename (da), disk, buffer, da);
@@ -369,7 +397,7 @@ public class DosDisk extends AbstractFormattedDisk
   {
     String newLine = String.format ("%n");
     String line = "- --- ---  ------------------------------  -----  -------------"
-        + "  -- ----  ----------------" + newLine;
+        + "  -- ----  -------------------" + newLine;
     StringBuilder text = new StringBuilder ();
     text.append (String.format ("Disk : %s%n%n", getAbsolutePath ()));
     text.append ("L Typ Len  Name                            Addr"
@@ -405,33 +433,33 @@ public class DosDisk extends AbstractFormattedDisk
   }
 
   /* From http://apple2history.org/history/ah15/
-   * 
-    There were actually three versions of DOS 3.3 that Apple released without 
+   *
+    There were actually three versions of DOS 3.3 that Apple released without
     bumping the version number:
   
     The first version that was released had FPBASIC and INTBASIC files that were 50
     sectors in size.
-    
-    The second version of DOS 3.3, often referred to as “DOS 3.3e”, appeared at the 
-    time the Apple IIe was released. In this version, the FPBASIC and INTBASIC files 
-    were 42 sectors in size. The changes introduced at that time included code to turn 
-    off the IIe 80-column card at boot time, and an attempt to fix a bug in the APPEND 
-    command. This fix reportedly introduced an even worse bug, but as the command was 
-    not heavily used it did not make much of an impact on most programmers. The APPEND 
+  
+    The second version of DOS 3.3, often referred to as “DOS 3.3e”, appeared at the
+    time the Apple IIe was released. In this version, the FPBASIC and INTBASIC files
+    were 42 sectors in size. The changes introduced at that time included code to turn
+    off the IIe 80-column card at boot time, and an attempt to fix a bug in the APPEND
+    command. This fix reportedly introduced an even worse bug, but as the command was
+    not heavily used it did not make much of an impact on most programmers. The APPEND
     fix was applied by utilizing some formerly unused space in the DOS 3.3 code.
-    
-    The third version of DOS 3.3 appeared just before the first release of ProDOS. 
-    The only mention of this in the press was in the DOSTalk column of Softalk magazine. 
-    This final version of DOS 3.3 included a different fix for the APPEND bug, using 
+  
+    The third version of DOS 3.3 appeared just before the first release of ProDOS.
+    The only mention of this in the press was in the DOSTalk column of Softalk magazine.
+    This final version of DOS 3.3 included a different fix for the APPEND bug, using
     another bit of unused space in DOS 3.3.
   
-    With regard to the FPBASIC and INTBASIC files: There were three differences between 
-    the 50 sector and the 42 sector versions of the INTBASIC file. Firstly, the 
-    $F800-$FFFF section was removed. This area was the code for the Monitor, and with 
-    the changes introduced in the Apple IIe, it could cause some things to “break” if 
-    the older Monitor code was executed. Secondly, a FOR/NEXT bug in Integer BASIC was 
-    fixed. Finally, there was a three-byte bug in the Programmer’s Aid ROM #1 chip. 
-    The code for this chip was included in the INTBASIC file, and could therefore be 
+    With regard to the FPBASIC and INTBASIC files: There were three differences between
+    the 50 sector and the 42 sector versions of the INTBASIC file. Firstly, the
+    $F800-$FFFF section was removed. This area was the code for the Monitor, and with
+    the changes introduced in the Apple IIe, it could cause some things to “break” if
+    the older Monitor code was executed. Secondly, a FOR/NEXT bug in Integer BASIC was
+    fixed. Finally, there was a three-byte bug in the Programmer’s Aid ROM #1 chip.
+    The code for this chip was included in the INTBASIC file, and could therefore be
     patched.
    */
 }
\ No newline at end of file
diff --git a/src/com/bytezone/diskbrowser/dos/DosVTOCSector.java b/src/com/bytezone/diskbrowser/dos/DosVTOCSector.java
index 5c68f6f..23415d7 100755
--- a/src/com/bytezone/diskbrowser/dos/DosVTOCSector.java
+++ b/src/com/bytezone/diskbrowser/dos/DosVTOCSector.java
@@ -4,12 +4,13 @@ import com.bytezone.diskbrowser.disk.AbstractSector;
 import com.bytezone.diskbrowser.disk.Disk;
 import com.bytezone.diskbrowser.disk.DiskAddress;
 import com.bytezone.diskbrowser.utilities.HexFormatter;
+import com.bytezone.diskbrowser.utilities.Utility;
 
 class DosVTOCSector extends AbstractSector
 {
   DosDisk parentDisk;
   int volume;
-  int DOSVersion;
+  int dosVersion;       // 1, 2, 3 or 0x41...
   int maxTSPairs;
   int lastAllocTrack;
   int direction;
@@ -25,7 +26,7 @@ class DosVTOCSector extends AbstractSector
     super (disk, buffer, diskAddress);
 
     this.parentDisk = parentDisk;
-    DOSVersion = buffer[3];
+    dosVersion = buffer[3];
     volume = buffer[6] & 0xFF;
     maxTSPairs = buffer[39];
     lastAllocTrack = buffer[48];
@@ -38,6 +39,63 @@ class DosVTOCSector extends AbstractSector
 
   @Override
   public String createText ()
+  {
+    return dosVersion <= 3 ? createDosText () : createOtherText ();
+  }
+
+  private String createOtherText ()
+  {
+    StringBuilder text = getHeader ("DOS 4.1 VTOC Sector");
+    addText (text, buffer, 0, 1, "Not used");
+    addText (text, buffer, 1, 2, "First directory track/sector");
+    addText (text, buffer, 3, 1, "DOS release number");
+    addText (text, buffer, 4, 1, "Build number");
+    addText (text, buffer, 5, 1, "Ram DOS " + (char) (buffer[5] & 0x7F));
+
+    addTextAndDecimal (text, buffer, 6, 1, "Diskette volume");
+    addText (text, buffer, 7, 1, "Volume type " + (char) (buffer[7] & 0x7F));
+
+    int ptr = 8;
+    addText (text, buffer, ptr, 4, "Volume name: " + getName (buffer, ptr));
+    for (int j = 4; j < 24; j += 4)
+      addText (text, buffer, ptr + j, 4, "");
+
+    addText (text, buffer, 0x20, 3,
+        "Date/time initialised: " + Utility.getDateTime (buffer, 0x20));
+    addText (text, buffer, 0x23, 3, "");
+    addText (text, buffer, 0x26, 1, "Not used");
+
+    addTextAndDecimal (text, buffer, 0x27, 1, "Maximum TS pairs");
+    addText (text, buffer, 0x28, 2, "Volume library");
+    addText (text, buffer, 0x2A, 3,
+        "Date/time modified: " + Utility.getDateTime (buffer, 0x2A));
+    addText (text, buffer, 0x2D, 3, "");
+
+    addTextAndDecimal (text, buffer, 0x30, 1, "Last allocated track");
+    addText (text, buffer, 0x31, 1, "Direction to look when allocating the next file");
+    addText (text, buffer, 0x32, 2, "Not used");
+    addTextAndDecimal (text, buffer, 0x34, 1, "Maximum tracks");
+    addTextAndDecimal (text, buffer, 0x35, 1, "Maximum sectors");
+    addTextAndDecimal (text, buffer, 0x36, 2, "Bytes per sector");
+
+    boolean bootSectorEmpty = parentDisk.getDisk ().isSectorEmpty (0);
+    for (int i = 0x38; i <= 0xC3; i += 4)
+    {
+      String extra = "";
+      if (i == 0x38 && bootSectorEmpty)
+        extra = "(unusable)";
+      else if (i == 124)
+        extra = "(VTOC and Catalog)";
+      addText (text, buffer, i, 4, String.format ("Track %02X  %s  %s", (i - 56) / 4,
+          getBitmap (buffer[i], buffer[i + 1]), extra));
+    }
+
+    text.deleteCharAt (text.length () - 1);
+
+    return text.toString ();
+  }
+
+  private String createDosText ()
   {
     StringBuilder text = getHeader ("VTOC Sector");
     addText (text, buffer, 0, 1, "Not used");
@@ -138,11 +196,35 @@ class DosVTOCSector extends AbstractSector
     return block;
   }
 
+  // duplicate of DosCatalogSector.getName()
+  private String getName (byte[] buffer, int offset)
+  {
+    StringBuilder text = new StringBuilder ();
+    int max = 24;
+    for (int i = 0; i < max; i++)
+    {
+      int c = buffer[i + offset] & 0xFF;
+      if (c == 136)
+      {
+        if (text.length () > 0)
+          text.deleteCharAt (text.length () - 1);
+        continue;
+      }
+      if (c > 127)
+        c -= c < 160 ? 64 : 128;
+      if (c < 32)                                 // non-printable
+        text.append ("^" + (char) (c + 64));
+      else
+        text.append ((char) c);                   // standard ascii
+    }
+    return text.toString ();
+  }
+
   @Override
   public String toString ()
   {
     StringBuffer text = new StringBuffer ();
-    text.append ("DOS version      : 3." + DOSVersion);
+    text.append ("DOS version      : 3." + dosVersion);
     text.append ("\nVolume           : " + volume);
     text.append ("\nMax TS pairs     : " + maxTSPairs);
     text.append ("\nLast allocated T : " + lastAllocTrack);
diff --git a/src/com/bytezone/diskbrowser/gui/DiskLayoutSelection.java b/src/com/bytezone/diskbrowser/gui/DiskLayoutSelection.java
index f289543..1d96af7 100755
--- a/src/com/bytezone/diskbrowser/gui/DiskLayoutSelection.java
+++ b/src/com/bytezone/diskbrowser/gui/DiskLayoutSelection.java
@@ -7,6 +7,7 @@ import java.util.Collections;
 import java.util.Iterator;
 import java.util.List;
 
+import com.bytezone.diskbrowser.disk.AppleDiskAddress;
 import com.bytezone.diskbrowser.disk.Disk;
 import com.bytezone.diskbrowser.disk.DiskAddress;
 import com.bytezone.diskbrowser.disk.FormattedDisk;
@@ -152,7 +153,7 @@ class DiskLayoutSelection implements Iterable<DiskAddress>
     highlights.clear ();
     if (list != null)
       for (DiskAddress da : list)
-        if (da != null && da.getBlock () > 0)
+        if (da != null && (da.getBlock () > 0 || ((AppleDiskAddress) da).zeroFlag ()))
           highlights.add (da);
   }
 
diff --git a/src/com/bytezone/diskbrowser/utilities/Utility.java b/src/com/bytezone/diskbrowser/utilities/Utility.java
index af81ef5..6089b18 100644
--- a/src/com/bytezone/diskbrowser/utilities/Utility.java
+++ b/src/com/bytezone/diskbrowser/utilities/Utility.java
@@ -2,6 +2,8 @@ package com.bytezone.diskbrowser.utilities;
 
 import java.awt.Graphics2D;
 import java.awt.geom.AffineTransform;
+import java.time.DateTimeException;
+import java.time.LocalDateTime;
 import java.util.Arrays;
 import java.util.List;
 
@@ -58,6 +60,24 @@ public class Utility
     return false;
   }
 
+  public static LocalDateTime getDateTime (byte[] buffer, int ptr)
+  {
+    try
+    {
+      int[] val = new int[6];
+      for (int i = 0; i < 6; i++)
+        val[i] = Integer.parseInt (String.format ("%02X", buffer[ptr + i] & 0xFF));
+
+      LocalDateTime date =
+          LocalDateTime.of (val[3] + 2000, val[5], val[4], val[2], val[1], val[0]);
+      return date;
+    }
+    catch (DateTimeException e)
+    {
+      return null;
+    }
+  }
+
   public static boolean matches (byte[] buffer, int offset, byte[] key)
   {
     int ptr = 0;