Working and commented.

hello32.s

@@ -3,7 +3,7 @@
     ;; Link with: ld -m elf_i386 -o hello hello.o
     ;; Run with: ./hello
 
-    ;; sys/syscall.h
+    ;; sys/unistd_32.h
 %define     SYS_write	4
 %define     SYS_exit	1
 
@@ -17,11 +17,11 @@ section .text
     global _start
 
 _start:
-    mov     edx, 26d            ; Length of the message
-    mov     ecx, msg            ; Address of the message
+    mov     edx, 26d            ; Length of the message.  The 'd' means 'decimal'
+    mov     ecx, msg            ; Address of the message (not the content)
     mov     ebx, STDOUT         ; using STDOUT (see definition above)
     mov     eax, SYS_write      ; Using WRITE in 32-bit mode?
-    int     80h
+    int     80h                 ; Interrupt target. The 'h' means 'hexidecimal'
 
     mov     ebx, 0
     mov     eax, SYS_exit

hello64.s

@@ -3,7 +3,7 @@
     ;; Link with: ld -m elf_i386 -o hello hello.o
     ;; Run with: ./hello
 
-    ;; sys/syscall.h
+    ;; sys/unistd_64.h
 %define     SYS_write	1
 %define     SYS_exit	60