diff --git a/atrcopy/ataridos.py b/atrcopy/ataridos.py
index 2abbb32..ef30602 100644
--- a/atrcopy/ataridos.py
+++ b/atrcopy/ataridos.py
@@ -30,11 +30,11 @@ class AtariDosVTOC(VTOC):
     def parse_segments(self, segments):
         self.vtoc1 = segments[0].data
         bits = np.unpackbits(self.vtoc1[0x0a:0x64])
-        log.debug("vtoc before: %s" % bits)
         self.sector_map[0:720] = bits
+        log.debug("vtoc before:\n%s" % str(self))
 
     def calc_bitmap(self):
-        log.debug("vtoc after: %s" % self.sector_map[0:720])
+        log.debug("vtoc after:\n%s" % str(self))
         packed = np.packbits(self.sector_map[0:720])
         self.vtoc1[0x0a:0x64] = packed
         s = WriteableSector(self.sector_size, self.vtoc1)
@@ -175,7 +175,7 @@ class AtariDosDirent(object):
         return True
     
     def get_sectors_in_vtoc(self, image):
-        sector_list = BaseSectorList(image.header.sector_size)
+        sector_list = BaseSectorList(image.header)
         self.start_read(image)
         while True:
             sector = WriteableSector(image.header.sector_size, None, self.current_sector)
diff --git a/atrcopy/diskimages.py b/atrcopy/diskimages.py
index 6a73f7b..58b195c 100644
--- a/atrcopy/diskimages.py
+++ b/atrcopy/diskimages.py
@@ -387,7 +387,7 @@ class DiskImageBase(object):
         try:
             vtoc_segments = self.get_vtoc_segments()
             vtoc = self.vtoc_class(self.header, vtoc_segments)
-            for sector_num, pos, size in vtoc.iter_free_sectors(self.header):
+            for sector_num, pos, size in vtoc.iter_free_sectors():
                 log.debug("shredding: sector %s at %d, fill value=%d" % (sector_num, pos, fill_value))
                 self.bytes[pos:pos + size] = fill_value
         except AtrError:
diff --git a/atrcopy/dos33.py b/atrcopy/dos33.py
index f1adb18..488005d 100644
--- a/atrcopy/dos33.py
+++ b/atrcopy/dos33.py
@@ -92,10 +92,10 @@ class Dos33VTOC(VTOC):
         # so we need to reorder them using numpy's indexing before stuffing
         # them into the sector map
         self.sector_map[0:self.max_sectors] = bits[self.vtoc_bit_reorder_index]
-        log.debug("vtoc before: %s (%d free)" % (self.sector_map[0:35*16], self.num_free_sectors))
+        log.debug("vtoc before:\n%s" % str(self))
 
     def calc_bitmap(self):
-        log.debug("vtoc after: %s (%d free)" % (self.sector_map[0:35*16], self.num_free_sectors))
+        log.debug("vtoc after:\n%s" % str(self))
 
         # reverse the process from above, so swap the order of every 16 bits,
         # turn them into bytes, then stuff them back into the vtoc. The bit
@@ -251,7 +251,7 @@ class Dos33Dirent(object):
     def add_metadata_sectors(self, vtoc, sector_list, header):
         """Add track/sector list
         """
-        tslist = BaseSectorList(header.sector_size)
+        tslist = BaseSectorList(header)
         for start in range(0, len(sector_list), header.ts_pairs):
             end = min(start + header.ts_pairs, len(sector_list))
             log.debug("ts: %d-%d" % (start, end))
@@ -277,7 +277,7 @@ class Dos33Dirent(object):
         return True
 
     def get_track_sector_list(self, image):
-        tslist = BaseSectorList(image.header.sector_size)
+        tslist = BaseSectorList(image.header)
         sector_num = image.header.sector_from_track(self.track, self.sector)
         sector_map = []
         while sector_num > 0:
diff --git a/atrcopy/utils.py b/atrcopy/utils.py
index e2bfbb1..6495426 100644
--- a/atrcopy/utils.py
+++ b/atrcopy/utils.py
@@ -93,8 +93,9 @@ class WriteableSector(object):
 
 
 class BaseSectorList(object):
-    def __init__(self, sector_size):
-        self.sector_size = sector_size
+    def __init__(self, header):
+        self.header = header
+        self.sector_size = header.sector_size
         self.sectors = []
 
     def __len__(self):
@@ -134,7 +135,7 @@ class BaseSectorList(object):
 
 class Directory(BaseSectorList):
     def __init__(self, header, num_dirents=-1, sector_class=WriteableSector):
-        BaseSectorList.__init__(self, header.sector_size)
+        BaseSectorList.__init__(self, header)
         self.sector_class = sector_class
         self.num_dirents = num_dirents
         # number of dirents may be unlimited, so use a dict instead of a list
@@ -236,20 +237,23 @@ class Directory(BaseSectorList):
 
 class VTOC(BaseSectorList):
     def __init__(self, header, segments=None):
-        BaseSectorList.__init__(self, header.sector_size)
+        BaseSectorList.__init__(self, header)
 
         # sector map: 1 is free, 0 is allocated
         self.sector_map = np.zeros([1280], dtype=np.uint8)
         if segments is not None:
             self.parse_segments(segments)
 
+    def __str__(self):
+        return "%s\n (%d free)" % ("\n".join(["track %02d: %s" % (i, line) for i, line in enumerate(str(self.sector_map[0:self.header.tracks_per_disk*self.header.sectors_per_track].reshape([self.header.tracks_per_disk,self.header.sectors_per_track])).splitlines())]), self.num_free_sectors)
+
     @property
     def num_free_sectors(self):
         free = np.where(self.sector_map == 1)[0]
         return len(free)
 
-    def iter_free_sectors(self, header):
-        for i, pos, size in header.iter_sectors():
+    def iter_free_sectors(self):
+        for i, pos, size in self.header.iter_sectors():
             if self.sector_map[i] == 1:
                 yield i, pos, size