diff --git a/DuetPkg/BootSector/bootsect.asm b/DuetPkg/BootSector/bootsect.asm
index 8fb7236bc1..1b8c15bc80 100644
--- a/DuetPkg/BootSector/bootsect.asm
+++ b/DuetPkg/BootSector/bootsect.asm
@@ -9,9 +9,22 @@
 ;*   THE PROGRAM IS DISTRIBUTED UNDER THE BSD LICENSE ON AN "AS IS" BASIS,                     
 ;*   WITHOUT WARRANTIES OR REPRESENTATIONS OF ANY KIND, EITHER EXPRESS OR IMPLIED.             
 ;*   
-;*    bootsect.asm
-;*  
-;*   Abstract:
+;*   bootsect.asm
+;*    
+;*   bootsect.asm is built as 16-bit binary file in 512 bytes and patched to disk/partition's 
+;*   first section - boot sector. 
+;*
+;*   The startup sequence for DUET disk boot sector is:
+;*
+;*   1, LegacyBios check 0xAA55 signature at boot sectore offset 0x1FE to judget 
+;*      whether disk/partition is bootable.
+;*   2, LegacyBios will load boot sector to 0x7c00 in real mode, pass BPB data and
+;*      hand off control to 0x7c00 code.
+;*   3, boot sector code simply parse FAT format in boot disk and find EfiLdr binary file 
+;*      and EfiVar.bin if exists. For first boot, EfiVar.bin does not exist.
+;*   4, boot sector load the first sector of EfiLdr binary which is start.com to
+;*      0x2000:0x0000 address.
+;*   5, boot sector handoff control to 0x2000:0x0000 for start.com binary.
 ;*
 ;------------------------------------------------------------------------------