diff --git a/DiskArc/FS/HFS-notes.md b/DiskArc/FS/HFS-notes.md
index ab251df..914a90d 100644
--- a/DiskArc/FS/HFS-notes.md
+++ b/DiskArc/FS/HFS-notes.md
@@ -498,6 +498,61 @@ FXInfo / FndrOpaqueInfo (16 bytes)
 +$0c / 4: fdPutAway
 ```
 
+## Boot Blocks ##
+
+The Macintosh looks for a specific structure in block 0 to decide whether a disk can be booted.
+A number of system parameters are stored here, as well as executable code.  The format is
+documented in IM:Files starting on page 2-57.
+
+The block 0/1 layout is:
+
+```
++$00 / 2: bbID - signature bytes, for HFS this must be $4c $4b ('LK')
++$02 / 4: bbEntry - entry point to boot code, expressed as a 68K BRA.S instruction
++$06 / 2: bbVersion - flag byte and boot block version number
++$08 / 2: bbPageFlags - "used internally"
++$0a /16: bbSysName - system filename, usually "System" (stored as string with leading length byte)
++$1a /16: bbShellName - Finder filename, usually "Finder"
++$2a /16: bbDbg1Name - first debugger filename, usually "MacsBug"
++$3a /16: bbDbg2Name - second debugger filename, usually "Disassembler"
++$4a /16: bbScreenName - file containing startup screen, usually "StartUpScreen"
++$5a /16: bbHelloName - name of startup program, usually "Finder"
++$6a /16: bbScrapName - name of system scrap file, usually "Clipboard"
++$7a / 2: bbCntFCBs - number of FCBs to allocate
++$7c / 2: bbCntEvts - number of event queue elements
++$7e / 4: bb128KSHeap - system heap size on 128K Mac
++$82 / 4: bb256KSHeap - "used internally"
++$86 / 4: bbSysHeapSize - system heap size on machines with >= 512K of RAM
++$8a / 2: filler - reserved
++$8c / 4: bbSysHeapExtra - minimum amount of additional System heap space required
++$90 / 4: bbSysHeapFract - fraction of RAM to make available for system heap
++$94 /nn: executable code, if any
+```
+
+The last two heap size fields are only present in "new"-style boot blocks.  A bit in the version
+flags will tell you whether or not they are present.  These values override the earlier fields.
+
+The `bbEntry` value is a 68K branch whose offset is relative to the start of the instruction + 2,
+so `60 00 00 86` is a branch to 4 + $86 + 2 = $8c, appropriate for an "old"-style boot block.
+A "new"-style boot block should be `60 00 00 8e`, branching to $94.
+
+The `bbVersion` field is documented as a 16-bit value, but the first (high) byte holds flags,
+while the second (low) byte holds the boot block version number.  The flags are:
+
+bit | meaning
+--- | -------
+0-4 | reserved, must be 0
+  5 | set if relative system heap sizing is to be used
+  6 | set if the boot code in the boot blocks is to be executed
+  7 | set if the new boot block header format is used
+
+If bit 7 is clear (old format), then bits 5 and 6 are ignored, and the boot code is only executed
+if the version is 0x0d.  If bit 7 is set (new format), then bit 6 determines whether or not the
+code is executed.  IM:Files notes:
+
+> Generally, however, the boot code stored on disk is ignored in favor of boot code stored in a
+> resource in the System file.
+
 ## Miscellaneous ##
 
 HFS volumes can checked with the `fsck.hfs` command.  The x86-64 version found on Linux
diff --git a/DiskArc/FS/HFS.cs b/DiskArc/FS/HFS.cs
index 6badde4..7907fee 100644
--- a/DiskArc/FS/HFS.cs
+++ b/DiskArc/FS/HFS.cs
@@ -590,9 +590,14 @@ public void Format(string volumeName, int volumeNum, bool makeBootable) {
                 throw new ArgumentException("Invalid volume name");
             }
 
-            // Zero out the boot blocks.
-            ChunkAccess.WriteBlock(0, HFS_FileDesc.sZeroBlock, 0);
-            ChunkAccess.WriteBlock(1, HFS_FileDesc.sZeroBlock, 0);
+            // Write a Macintosh boot block, or just zero it out.
+            if (makeBootable && false) {
+                ChunkAccess.WriteBlock(0, sBootBlock0, 0);
+                ChunkAccess.WriteBlock(1, sBootBlock1, 0);
+            } else {
+                ChunkAccess.WriteBlock(0, HFS_FileDesc.sZeroBlock, 0);
+                ChunkAccess.WriteBlock(1, HFS_FileDesc.sZeroBlock, 0);
+            }
 
             // Compute geometry.
             //
@@ -1146,6 +1151,80 @@ internal uint AllocBlockToLogiBlock(uint allocBlockNum) {
             return VolMDB.AllocBlockStart + allocBlockNum * VolMDB.LogicalPerAllocBlock;
         }
 
+        /// <summary>
+        /// <para>Standard Macintosh boot block.  Obtained from "bootblockdata" file in
+        /// <see href="https://github.com/apple-opensource/bless/tree/master/files"/>.</para>
+        /// <para>Copyright Apple Computer, Inc.</para>
+        /// </summary>
+        private static readonly byte[] sBootBlock0 = new byte[512] {
+            0x4c,0x4b,0x60,0x00,0x00,0x86,0x44,0x18,0x00,0x00,0x06,0x53,0x79,0x73,0x74,0x65,
+            0x6d,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x06,0x46,0x69,0x6e,0x64,0x65,
+            0x72,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x07,0x4d,0x61,0x63,0x73,0x42,
+            0x75,0x67,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x0c,0x44,0x69,0x73,0x61,0x73,
+            0x73,0x65,0x6d,0x62,0x6c,0x65,0x72,0x00,0x00,0x00,0x0d,0x53,0x74,0x61,0x72,0x74,
+            0x55,0x70,0x53,0x63,0x72,0x65,0x65,0x6e,0x00,0x00,0x06,0x46,0x69,0x6e,0x64,0x65,
+            0x72,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x09,0x43,0x6c,0x69,0x70,0x62,
+            0x6f,0x61,0x72,0x64,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x0a,0x00,0x14,0x00,0x00,
+            0x43,0x00,0x00,0x00,0x80,0x00,0x00,0x02,0x00,0x00,0x4a,0x78,0x02,0x8e,0x6b,0x46,
+            0x20,0x78,0x02,0xae,0x32,0x28,0x00,0x08,0x7c,0xfe,0x54,0x46,0x30,0x3b,0x60,0x3c,
+            0x67,0x58,0xb2,0x40,0x66,0xf4,0x0c,0x01,0x00,0x76,0x62,0x10,0x20,0x78,0x02,0xa6,
+            0xd1,0xfa,0xff,0xd4,0xa0,0x57,0x21,0xf8,0x02,0xa6,0x01,0x18,0x58,0x4f,0x2e,0x0f,
+            0x61,0x38,0x32,0x3b,0x60,0x22,0x4a,0x40,0x67,0x04,0x32,0x3b,0x60,0x24,0x20,0x78,
+            0x02,0xae,0x4e,0xf0,0x10,0x00,0x70,0x62,0xa9,0xc9,0x00,0x75,0x02,0x76,0x01,0x78,
+            0x03,0x7a,0x06,0x7c,0x00,0x00,0x0a,0x44,0x09,0x0e,0x0f,0x1c,0x30,0xe6,0x1d,0x96,
+            0x0b,0x82,0x0a,0x52,0x11,0xae,0x33,0x6e,0x20,0x3e,0x41,0xfa,0xff,0x0e,0x43,0xf8,
+            0x0a,0xd8,0x70,0x10,0xa0,0x2e,0x41,0xfa,0xff,0x12,0x43,0xf8,0x02,0xe0,0x70,0x10,
+            0xa0,0x2e,0x41,0xfa,0xff,0x56,0x43,0xf8,0x09,0x70,0x21,0xc9,0x09,0x6c,0x70,0x10,
+            0xa0,0x2e,0x30,0x3a,0xff,0x58,0xa0,0x6d,0x30,0x3a,0xff,0x50,0xa0,0x6c,0x20,0x47,
+            0x31,0x78,0x02,0x10,0x00,0x16,0xa0,0x0f,0x66,0x54,0x42,0xa8,0x00,0x12,0x42,0x68,
+            0x00,0x1c,0xa2,0x07,0x66,0x40,0x28,0x68,0x00,0x5e,0x21,0x68,0x00,0x5a,0x00,0x30,
+            0x67,0x10,0x21,0x7c,0x45,0x52,0x49,0x4b,0x00,0x1c,0x70,0x01,0xa2,0x60,0x66,0x26,
+            0xa0,0x15,0x55,0x4f,0xa9,0x95,0x4a,0x5f,0x6b,0x1a,0x59,0x4f,0x2f,0x3c,0x62,0x6f,
+            0x6f,0x74,0x3f,0x3c,0x00,0x02,0xa9,0xa0,0x20,0x1f,0x67,0x12,0x58,0x4f,0x26,0x40,
+            0x20,0x53,0x4e,0xd0,0x70,0x2b,0x3f,0x00,0x20,0x47,0xa0,0x0e,0x30,0x1f,0x4e,0x75,
+            0xda,0xda,0xda,0xda,0xda,0xda,0xda,0xda,0xda,0xda,0xda,0xda,0xda,0xda,0xda,0xda,
+            0xda,0xda,0xda,0xda,0xda,0xda,0xda,0xda,0xda,0xda,0xda,0xda,0xda,0xda,0xda,0xda,
+            0xda,0xda,0xda,0xda,0xda,0xda,0xda,0xda,0xda,0xda,0xda,0xda,0xda,0xda,0xda,0xda,
+            0xda,0xda,0xda,0xda,0xda,0xda,0xda,0xda,0xda,0xda,0xda,0xda,0xda,0xda,0xda,0xda,
+            0xda,0xda,0xda,0xda,0xda,0xda,0xda,0xda,0xda,0xda,0xda,0xda,0xda,0xda,0xda,0xda,
+            0xda,0xda,0xda,0xda,0xda,0xda,0xda,0xda,0xda,0xda,0xda,0xda,0xda,0xda,0xda,0xda,
+            0xda,0xda,0xda,0xda,0xda,0xda,0xda,0xda,0xda,0xda,0xda,0xda,0xda,0xda,0xda,0xda
+        };
+        private static readonly byte[] sBootBlock1 = new byte[512] {
+            0xda,0xda,0xda,0xda,0xda,0xda,0xda,0xda,0xda,0xda,0xda,0xda,0xda,0xda,0xda,0xda,
+            0xda,0xda,0xda,0xda,0xda,0xda,0xda,0xda,0xda,0xda,0xda,0xda,0xda,0xda,0xda,0xda,
+            0xda,0xda,0xda,0xda,0xda,0xda,0xda,0xda,0xda,0xda,0xda,0xda,0xda,0xda,0xda,0xda,
+            0xda,0xda,0xda,0xda,0xda,0xda,0xda,0xda,0xda,0xda,0xda,0xda,0xda,0xda,0xda,0xda,
+            0xda,0xda,0xda,0xda,0xda,0xda,0xda,0xda,0xda,0xda,0xda,0xda,0xda,0xda,0xda,0xda,
+            0xda,0xda,0xda,0xda,0xda,0xda,0xda,0xda,0xda,0xda,0xda,0xda,0xda,0xda,0xda,0xda,
+            0xda,0xda,0xda,0xda,0xda,0xda,0xda,0xda,0xda,0xda,0xda,0xda,0xda,0xda,0xda,0xda,
+            0xda,0xda,0xda,0xda,0xda,0xda,0xda,0xda,0xda,0xda,0xda,0xda,0xda,0xda,0xda,0xda,
+            0xda,0xda,0xda,0xda,0xda,0xda,0xda,0xda,0xda,0xda,0xda,0xda,0xda,0xda,0xda,0xda,
+            0xda,0xda,0xda,0xda,0xda,0xda,0xda,0xda,0xda,0xda,0xda,0xda,0xda,0xda,0xda,0xda,
+            0xda,0xda,0xda,0xda,0xda,0xda,0xda,0xda,0xda,0xda,0xda,0xda,0xda,0xda,0xda,0xda,
+            0xda,0xda,0xda,0xda,0xda,0xda,0xda,0xda,0xda,0xda,0xda,0xda,0xda,0xda,0xda,0xda,
+            0xda,0xda,0xda,0xda,0xda,0xda,0xda,0xda,0xda,0xda,0xda,0xda,0xda,0xda,0xda,0xda,
+            0xda,0xda,0xda,0xda,0xda,0xda,0xda,0xda,0xda,0xda,0xda,0xda,0xda,0xda,0xda,0xda,
+            0xda,0xda,0xda,0xda,0xda,0xda,0xda,0xda,0xda,0xda,0xda,0xda,0xda,0xda,0xda,0xda,
+            0xda,0xda,0xda,0xda,0xda,0xda,0xda,0xda,0xda,0xda,0xda,0xda,0xda,0xda,0xda,0xda,
+            0xda,0xda,0xda,0xda,0xda,0xda,0xda,0xda,0xda,0xda,0xda,0xda,0xda,0xda,0xda,0xda,
+            0xda,0xda,0xda,0xda,0xda,0xda,0xda,0xda,0xda,0xda,0xda,0xda,0xda,0xda,0xda,0xda,
+            0xda,0xda,0xda,0xda,0xda,0xda,0xda,0xda,0xda,0xda,0xda,0xda,0xda,0xda,0xda,0xda,
+            0xda,0xda,0xda,0xda,0xda,0xda,0xda,0xda,0xda,0xda,0xda,0xda,0xda,0xda,0xda,0xda,
+            0xda,0xda,0xda,0xda,0xda,0xda,0xda,0xda,0xda,0xda,0xda,0xda,0xda,0xda,0xda,0xda,
+            0xda,0xda,0xda,0xda,0xda,0xda,0xda,0xda,0xda,0xda,0xda,0xda,0xda,0xda,0xda,0xda,
+            0xda,0xda,0xda,0xda,0xda,0xda,0xda,0xda,0xda,0xda,0xda,0xda,0xda,0xda,0xda,0xda,
+            0xda,0xda,0xda,0xda,0xda,0xda,0xda,0xda,0xda,0xda,0xda,0xda,0xda,0xda,0xda,0xda,
+            0xda,0xda,0xda,0xda,0xda,0xda,0xda,0xda,0xda,0xda,0xda,0xda,0xda,0xda,0xda,0xda,
+            0xda,0xda,0xda,0xda,0xda,0xda,0xda,0xda,0xda,0xda,0xda,0xda,0xda,0xda,0xda,0xda,
+            0xda,0xda,0xda,0xda,0xda,0xda,0xda,0xda,0xda,0xda,0xda,0xda,0xda,0xda,0xda,0xda,
+            0xda,0xda,0xda,0xda,0xda,0xda,0xda,0xda,0xda,0xda,0xda,0xda,0xda,0xda,0xda,0xda,
+            0xda,0xda,0xda,0xda,0xda,0xda,0xda,0xda,0xda,0xda,0xda,0xda,0xda,0xda,0xda,0xda,
+            0xda,0xda,0xda,0xda,0xda,0xda,0xda,0xda,0xda,0xda,0xda,0xda,0xda,0xda,0xda,0xda,
+            0xda,0xda,0xda,0xda,0xda,0xda,0xda,0xda,0xda,0xda,0xda,0xda,0xda,0xda,0xda,0xda,
+            0xda,0xda,0xda,0xda,0xda,0xda,0xda,0xda,0xda,0xda,0xda,0xda,0xda,0xda,0xda,0xda
+        };
+
         #endregion Miscellaneous
     }
 }