diff --git a/kernel/syscall.c b/kernel/syscall.c
index ee94696..ed65409 100644
--- a/kernel/syscall.c
+++ b/kernel/syscall.c
@@ -79,6 +79,7 @@ argstr(int n, char *buf, int max)
   return fetchstr(addr, buf, max);
 }
 
+// Prototypes for the functions that handle system calls.
 extern uint64 sys_fork(void);
 extern uint64 sys_exit(void);
 extern uint64 sys_wait(void);
@@ -101,6 +102,8 @@ extern uint64 sys_link(void);
 extern uint64 sys_mkdir(void);
 extern uint64 sys_close(void);
 
+// An array mapping syscall numbers from syscall.h
+// to the function that handles the system call.
 static uint64 (*syscalls[])(void) = {
 [SYS_fork]    sys_fork,
 [SYS_exit]    sys_exit,
@@ -133,6 +136,8 @@ syscall(void)
 
   num = p->trapframe->a7;
   if(num > 0 && num < NELEM(syscalls) && syscalls[num]) {
+    // Use num to lookup the system call function for num, call it,
+    // and store its return value in p->trapframe->a0
     p->trapframe->a0 = syscalls[num]();
   } else {
     printf("%d %s: unknown sys call %d\n",