diff --git a/build/unixv0.simh b/build/unixv0.simh
index 79ff03c..ddd4927 100644
--- a/build/unixv0.simh
+++ b/build/unixv0.simh
@@ -1,5 +1,11 @@
+set cpu 8k
+set cpu eae
+set cpu history=100
+show cpu
+
 set rb ena
 att rb image.fs
-load -S a.rim
 show dev
+
+load -S a.rim
 dep pc 0100
diff --git a/src/sys/sop.s b/src/sys/sop.s
index 047a1ba..ada9499 100644
--- a/src/sys/sop.s
+++ b/src/sys/sop.s
@@ -39,7 +39,7 @@ lls = 0640600			" EAE: long left shift
 llss = 0660600			" EAE: long left shift, signed
 als = 0640700			" EAE: AC left shift
 alss = 0660700			" EAE: AC left shift, signed
-mul = 0653323			" EAE: multiply
+mul = 0653122			" EAE: multiply
 idiv = 0653323			" EAE: integer divide
 lacq = 0641002			" EAE: load AC with MQ
 clq = 0650000			" EAE: clear MQ
diff --git a/tools/mkfs7 b/tools/mkfs7
index 96b6ae1..e295813 100755
--- a/tools/mkfs7
+++ b/tools/mkfs7
@@ -14,17 +14,13 @@ Getopt::Long::Configure qw(gnu_getopt);
 # Constants
 use constant NUMBLOCKS     => 8000;    # Number of blocks on a surface
 use constant WORDSPERBLK   => 64;      # 64 words per block
-use constant NUMINODEBLKS  => 710;     # Blocks 1 to 710 for i-nodes
-#use constant FIRSTINODEBLK => 1;       # First i-node block number
+use constant NUMINODEBLKS  => 710;     # Number of i-nodes
 use constant FIRSTINODEBLK => 2;       # First i-node block number
 use constant INODESIZE     => 12;      # Size of an i-node
 use constant INODESPERBLK => int(WORDSPERBLK / INODESIZE);
 use constant DIRENTSIZE => 8;          # Size of an directory entry
 use constant DIRENTSPERBLK => WORDSPERBLK / DIRENTSIZE;
 
-use constant ROOT_UID => -1;           # Native root user-id
-use constant MAXINT   => 0777777;      # Biggest unsigned integer
-
 use constant DD_INUM => 2;             # I-number of the dd directory
 
 # i-node field offsets
@@ -148,8 +144,7 @@ sub fill_inode {
     my ( $inum, $perms, $filetype, $uid, $size, @blklist ) = @_;
     die("Too many blocks\n") if ( @blklist > 7 );
 
-    # Deal with the root user-id
-    $uid = MAXINT if ( $uid == ROOT_UID );
+    $uid &= 0777777;		# truncate negative UID to 18 bits
 
     # Calculate the block number and word offset for this
     $inum = allocate_inode() if ( !defined($inum) );
@@ -176,6 +171,12 @@ sub fill_inode {
     return ($inum);
 }
 
+sub increment_file_length {
+    my ( $inum, $incr) = @_;
+    my ( $blocknum, $offset ) = get_inode_block_offset($inum);
+    $Block[$blocknum][ $offset + I_SIZE ] += $incr;
+}
+
 # Convert an ASCII string into an array of 18-bit word values
 # where two characters are packed into each word. Put NUL in
 # if the string has an odd number of characters. Return the array
@@ -241,6 +242,8 @@ sub add_direntry {
     # Move up to the next position in the directory.
     $dirref->[1] += D_NUMWORDS;
 
+    increment_file_length( $dirref->[2], D_NUMWORDS ); # update directory inode i.size
+
     # If we have filled the directory up, allocate another block to it
     if ( $dirref->[1] == WORDSPERBLK ) {
         my ($nextblock) = allocate_blocks(WORDSPERBLK);
@@ -535,6 +538,7 @@ sub dump_image {
         foreach my $blocknum ( 0 .. NUMBLOCKS - 1 ) {
             foreach my $offset ( 0 .. WORDSPERBLK-1 ) {
                 my $word = $Block[$blocknum][$offset] || 0;
+		# SIMH format packs word in a little-endian 32-bit int
                 my $packedword = pack( "CCCC",
                     $word & 0xff,
                     ( $word >> 8 ) & 0xff,