nits

bio.c

@@ -4,7 +4,7 @@
 // holding cached copies of disk block contents.
 // Each buf has two state bits B_BUSY and B_VALID.
 // If B_BUSY is set, it means that some code is currently
-// modifying buf, so other code is not allowed to look at it.
+// using buf, so other code is not allowed to use it.
 // To wait for a buffer that is B_BUSY, sleep on buf.
 // (See bget below.)
 // 

fs.c

@@ -6,7 +6,7 @@
 //   + Directories: inode with special contents (list of other inodes!)
 //   + Names: paths like /usr/rtm/xv6/fs.c for convenient naming.
 //
-// Disk layout is: superblock, inodes, block not-free bitmap, data blocks.
+// Disk layout is: superblock, inodes, block in-use bitmap, data blocks.
 //
 // This file contains the low-level file system manipulation 
 // routines.  The (higher-level) system call implementations