Add more comment in mbr

mbr.asm

@@ -94,26 +94,26 @@ main:
     mov bx, copy_target;target pointer
     int 0x13
 
-    cli ; clear interruption flag
+    cli ; disable interruption when setting GDT
 
     ; switch in 32 bits
     lgdt [gdt_pointer] ; switch in 32bits here
     mov eax, cr0
     or eax,0x1; set the protected mode bit on special CPU reg cr0
     mov cr0, eax
-    jmp CODE_SEG:boot2
+    jmp CODE_SEG:boot2 ; In protected mode we need to add the segment selector
 
 ; GDT table desciption could be found http://wiki.osdev.org/Global_Descriptor_Table
 ; here we define the 3 64bits segment needed: null segment, code segment and data segment
 gdt_start: ;null segment
 	dq 0x0
 gdt_code:  ;code segment
-	dw 0xFFFF
-	dw 0x0
-	db 0x0
-	db 10011010b
-	db 11001111b
-	db 0x0
+	dw 0xFFFF	; limit [0:15]
+	dw 0x0		; base [0:15]
+	db 0x0		; base [16:23]
+	db 10011010b    ; access byte:  Present(1)| Priv(2) 0 ->kernel 3->userspace | 1 | Executable(1) | Direction/Conformity (1) | RW(1) | Accessed(1)
+	db 11001111b	; Granularity(1) | Size (1) 0-> 16bit mode 1->32protected mode | 0 | 0 | Limit [16:19]
+	db 0x0		; base [24:31]
 gdt_data:
 	dw 0xFFFF
 	dw 0x0
@@ -135,12 +135,12 @@ dw 0xaa55
 copy_target:
 bits 32
 boot2:
-	mov ax, DATA_SEG
-	mov ds, ax
-	mov es, ax
-	mov fs, ax
-	mov gs, ax
-	mov ss, ax
+	mov ax, DATA_SEG ; set all segments to point to DATA_SEG https://en.wikipedia.org/wiki/X86_memory_segmentation
+	mov ds, ax       ; Data segment
+	mov es, ax	 ; Extra Segment (for string operation)
+	mov fs, ax	 ; No Specific use
+	mov gs, ax	 ; No Specific use
+	mov ss, ax	 ; stack segment
 	mov esi,hello32
 	mov ebx,0xb8000 ; Cannot use BIOS anymore, use VGA Text buffer instead