diff --git a/code/lab1/boot/bootasm.S b/code/lab1/boot/bootasm.S
index 35647f5..8db1909 100644
--- a/code/lab1/boot/bootasm.S
+++ b/code/lab1/boot/bootasm.S
@@ -27,23 +27,23 @@ start:
     #  address line 20 is tied low, so that addresses higher than
     #  1MB wrap around to zero by default. This code undoes this.
 seta20.1:
-    inb $0x64, %al                                  # Wait for not busy
+    inb $0x64, %al                                  # Wait for not busy(8042 input buffer empty).
     testb $0x2, %al
     jnz seta20.1
 
     movb $0xd1, %al                                 # 0xd1 -> port 0x64
-    outb %al, $0x64
+    outb %al, $0x64                                 # 0xd1 means: write data to 8042's P2 port
 
 seta20.2:
-    inb $0x64, %al                                  # Wait for not busy
+    inb $0x64, %al                                  # Wait for not busy(8042 input buffer empty).
     testb $0x2, %al
     jnz seta20.2
 
     movb $0xdf, %al                                 # 0xdf -> port 0x60
-    outb %al, $0x60
+    outb %al, $0x60                                 # 0xdf = 11011111, means set P2's A20 bit(the 1 bit) to 1
 
-    movb $0xdf, %al                                    # 0xdf -> port 0x60
-    outb %al, $0x60
+    movb $0xdf, %al                                 # 0xdf -> port 0x60, do it again!
+    outb %al, $0x60                                 # 0xdf = 11011111, means set P2's A20 bit(the 1 bit) to 1
 
     # Switch from real to protected mode, using a bootstrap GDT
     # and segment translation that makes virtual addresses
diff --git a/code/lab2/boot/bootasm.S b/code/lab2/boot/bootasm.S
index f1852c3..6f769b7 100644
--- a/code/lab2/boot/bootasm.S
+++ b/code/lab2/boot/bootasm.S
@@ -28,20 +28,20 @@ start:
     #  address line 20 is tied low, so that addresses higher than
     #  1MB wrap around to zero by default. This code undoes this.
 seta20.1:
-    inb $0x64, %al                                  # Wait for not busy
+    inb $0x64, %al                                  # Wait for not busy(8042 input buffer empty).
     testb $0x2, %al
     jnz seta20.1
 
     movb $0xd1, %al                                 # 0xd1 -> port 0x64
-    outb %al, $0x64
+    outb %al, $0x64                                 # 0xd1 means: write data to 8042's P2 port
 
 seta20.2:
-    inb $0x64, %al                                  # Wait for not busy
+    inb $0x64, %al                                  # Wait for not busy(8042 input buffer empty).
     testb $0x2, %al
     jnz seta20.2
 
     movb $0xdf, %al                                 # 0xdf -> port 0x60
-    outb %al, $0x60
+    outb %al, $0x60                                 # 0xdf = 11011111, means set P2's A20 bit(the 1 bit) to 1
 
 probe_memory:
     movl $0, 0x8000
diff --git a/code/lab3/boot/bootasm.S b/code/lab3/boot/bootasm.S
index f1852c3..6f769b7 100644
--- a/code/lab3/boot/bootasm.S
+++ b/code/lab3/boot/bootasm.S
@@ -28,20 +28,20 @@ start:
     #  address line 20 is tied low, so that addresses higher than
     #  1MB wrap around to zero by default. This code undoes this.
 seta20.1:
-    inb $0x64, %al                                  # Wait for not busy
+    inb $0x64, %al                                  # Wait for not busy(8042 input buffer empty).
     testb $0x2, %al
     jnz seta20.1
 
     movb $0xd1, %al                                 # 0xd1 -> port 0x64
-    outb %al, $0x64
+    outb %al, $0x64                                 # 0xd1 means: write data to 8042's P2 port
 
 seta20.2:
-    inb $0x64, %al                                  # Wait for not busy
+    inb $0x64, %al                                  # Wait for not busy(8042 input buffer empty).
     testb $0x2, %al
     jnz seta20.2
 
     movb $0xdf, %al                                 # 0xdf -> port 0x60
-    outb %al, $0x60
+    outb %al, $0x60                                 # 0xdf = 11011111, means set P2's A20 bit(the 1 bit) to 1
 
 probe_memory:
     movl $0, 0x8000
diff --git a/code/lab4/boot/bootasm.S b/code/lab4/boot/bootasm.S
index f1852c3..6f769b7 100644
--- a/code/lab4/boot/bootasm.S
+++ b/code/lab4/boot/bootasm.S
@@ -28,20 +28,20 @@ start:
     #  address line 20 is tied low, so that addresses higher than
     #  1MB wrap around to zero by default. This code undoes this.
 seta20.1:
-    inb $0x64, %al                                  # Wait for not busy
+    inb $0x64, %al                                  # Wait for not busy(8042 input buffer empty).
     testb $0x2, %al
     jnz seta20.1
 
     movb $0xd1, %al                                 # 0xd1 -> port 0x64
-    outb %al, $0x64
+    outb %al, $0x64                                 # 0xd1 means: write data to 8042's P2 port
 
 seta20.2:
-    inb $0x64, %al                                  # Wait for not busy
+    inb $0x64, %al                                  # Wait for not busy(8042 input buffer empty).
     testb $0x2, %al
     jnz seta20.2
 
     movb $0xdf, %al                                 # 0xdf -> port 0x60
-    outb %al, $0x60
+    outb %al, $0x60                                 # 0xdf = 11011111, means set P2's A20 bit(the 1 bit) to 1
 
 probe_memory:
     movl $0, 0x8000
diff --git a/code/lab5/boot/bootasm.S b/code/lab5/boot/bootasm.S
index f1852c3..6f769b7 100644
--- a/code/lab5/boot/bootasm.S
+++ b/code/lab5/boot/bootasm.S
@@ -28,20 +28,20 @@ start:
     #  address line 20 is tied low, so that addresses higher than
     #  1MB wrap around to zero by default. This code undoes this.
 seta20.1:
-    inb $0x64, %al                                  # Wait for not busy
+    inb $0x64, %al                                  # Wait for not busy(8042 input buffer empty).
     testb $0x2, %al
     jnz seta20.1
 
     movb $0xd1, %al                                 # 0xd1 -> port 0x64
-    outb %al, $0x64
+    outb %al, $0x64                                 # 0xd1 means: write data to 8042's P2 port
 
 seta20.2:
-    inb $0x64, %al                                  # Wait for not busy
+    inb $0x64, %al                                  # Wait for not busy(8042 input buffer empty).
     testb $0x2, %al
     jnz seta20.2
 
     movb $0xdf, %al                                 # 0xdf -> port 0x60
-    outb %al, $0x60
+    outb %al, $0x60                                 # 0xdf = 11011111, means set P2's A20 bit(the 1 bit) to 1
 
 probe_memory:
     movl $0, 0x8000
diff --git a/code/lab6/boot/bootasm.S b/code/lab6/boot/bootasm.S
index f1852c3..6f769b7 100644
--- a/code/lab6/boot/bootasm.S
+++ b/code/lab6/boot/bootasm.S
@@ -28,20 +28,20 @@ start:
     #  address line 20 is tied low, so that addresses higher than
     #  1MB wrap around to zero by default. This code undoes this.
 seta20.1:
-    inb $0x64, %al                                  # Wait for not busy
+    inb $0x64, %al                                  # Wait for not busy(8042 input buffer empty).
     testb $0x2, %al
     jnz seta20.1
 
     movb $0xd1, %al                                 # 0xd1 -> port 0x64
-    outb %al, $0x64
+    outb %al, $0x64                                 # 0xd1 means: write data to 8042's P2 port
 
 seta20.2:
-    inb $0x64, %al                                  # Wait for not busy
+    inb $0x64, %al                                  # Wait for not busy(8042 input buffer empty).
     testb $0x2, %al
     jnz seta20.2
 
     movb $0xdf, %al                                 # 0xdf -> port 0x60
-    outb %al, $0x60
+    outb %al, $0x60                                 # 0xdf = 11011111, means set P2's A20 bit(the 1 bit) to 1
 
 probe_memory:
     movl $0, 0x8000
diff --git a/code/lab7/boot/bootasm.S b/code/lab7/boot/bootasm.S
index f1852c3..6f769b7 100644
--- a/code/lab7/boot/bootasm.S
+++ b/code/lab7/boot/bootasm.S
@@ -28,20 +28,20 @@ start:
     #  address line 20 is tied low, so that addresses higher than
     #  1MB wrap around to zero by default. This code undoes this.
 seta20.1:
-    inb $0x64, %al                                  # Wait for not busy
+    inb $0x64, %al                                  # Wait for not busy(8042 input buffer empty).
     testb $0x2, %al
     jnz seta20.1
 
     movb $0xd1, %al                                 # 0xd1 -> port 0x64
-    outb %al, $0x64
+    outb %al, $0x64                                 # 0xd1 means: write data to 8042's P2 port
 
 seta20.2:
-    inb $0x64, %al                                  # Wait for not busy
+    inb $0x64, %al                                  # Wait for not busy(8042 input buffer empty).
     testb $0x2, %al
     jnz seta20.2
 
     movb $0xdf, %al                                 # 0xdf -> port 0x60
-    outb %al, $0x60
+    outb %al, $0x60                                 # 0xdf = 11011111, means set P2's A20 bit(the 1 bit) to 1
 
 probe_memory:
     movl $0, 0x8000
diff --git a/code/lab8/boot/bootasm.S b/code/lab8/boot/bootasm.S
index f1852c3..6f769b7 100644
--- a/code/lab8/boot/bootasm.S
+++ b/code/lab8/boot/bootasm.S
@@ -28,20 +28,20 @@ start:
     #  address line 20 is tied low, so that addresses higher than
     #  1MB wrap around to zero by default. This code undoes this.
 seta20.1:
-    inb $0x64, %al                                  # Wait for not busy
+    inb $0x64, %al                                  # Wait for not busy(8042 input buffer empty).
     testb $0x2, %al
     jnz seta20.1
 
     movb $0xd1, %al                                 # 0xd1 -> port 0x64
-    outb %al, $0x64
+    outb %al, $0x64                                 # 0xd1 means: write data to 8042's P2 port
 
 seta20.2:
-    inb $0x64, %al                                  # Wait for not busy
+    inb $0x64, %al                                  # Wait for not busy(8042 input buffer empty).
     testb $0x2, %al
     jnz seta20.2
 
     movb $0xdf, %al                                 # 0xdf -> port 0x60
-    outb %al, $0x60
+    outb %al, $0x60                                 # 0xdf = 11011111, means set P2's A20 bit(the 1 bit) to 1
 
 probe_memory:
     movl $0, 0x8000
diff --git a/doc/lab1.pdf b/doc/lab1.pdf
index 2c81fdf..5a10b09 100644
Binary files a/doc/lab1.pdf and b/doc/lab1.pdf differ
diff --git a/doc/lab2.pdf b/doc/lab2.pdf
index df6e7e5..d832fca 100644
Binary files a/doc/lab2.pdf and b/doc/lab2.pdf differ