diff --git a/Bitmap.cpp b/Bitmap.cpp
new file mode 100644
index 0000000..3767539
--- /dev/null
+++ b/Bitmap.cpp
@@ -0,0 +1,66 @@
+#include "Bitmap.h"
+
+#include <cstring>
+
+namespace ProDOS {
+
+/*
+ * 
+ *
+ *
+ */
+
+Bitmap::Bitmap(unsigned blocks) :
+    _bitmap(NULL), _blocks(blocks), 
+    _bitmapSize((blocks + 4096 - 1) >> 12)
+{
+    // 1 block = 512 bytes = 4096 bits 
+    _bitmap = new uint8_t[_bitmapSize];
+
+    // mark every requested block as free.
+    unsigned bytes = blocks >> 3;
+    std::memset(_bitmap, 0xff, bytes);
+
+    // all trailing blocks are marked as used.
+    std::memset(_bitmap + bytes, 0x00, _bitmapSize - bytes);
+    
+    // and handle the edge case...
+    /*
+     * 0 -> 0 0 0 0  0 0 0 0
+     * 1 -> 1 0 0 0  0 0 0 0
+     * 2 -> 1 1 0 0  0 0 0 0
+     * 3 -> 1 1 1 0  0 0 0 0
+     * ...
+     * 7 -> 1 1 1 1  1 1 1 0
+     */
+     //unsigned tmp = (1 << (8 - (blocks & 0x07))) - 1;
+     //_bitmap[bytes] = ~tmp & 0xff;
+
+     _bitmap[bytes] = 0 - (1 << (8 - (blocks & 0x07)));
+
+    //_bitmap[bytes] = (0xff00 >> (blocks & 0x07)) & 0xff;
+}
+
+Bitmap::~Bitmap()
+{
+    delete[] _bitmap;
+}
+
+
+bool Bitmap::markBlock(unsigned block, bool inUse)
+{
+    if (block >= _blocks) return false;
+
+    unsigned index = BlockIndex(block);
+    unsigned mask = BlockMask(block);
+    uint8_t data = _bitmap[index];
+
+    if (inUse) data &= ~mask;
+    else data |= mask;
+
+    _bitmap[index] = data;
+
+    return true;
+}
+} // namespace
+
diff --git a/Bitmap.h b/Bitmap.h
new file mode 100644
index 0000000..d5e6b08
--- /dev/null
+++ b/Bitmap.h
@@ -0,0 +1,57 @@
+#ifndef __PRODOS_BITMAP_H__
+#define __PRODOS_BITMAP_H__
+
+#include <stdint.h>
+
+namespace ProDOS {
+
+class Bitmap {
+public:
+    Bitmap(unsigned blocks);
+    ~Bitmap();
+
+    bool blockFree(unsigned block) const;
+    bool markBlock(unsigned block, bool inUse);
+
+    unsigned blocks() const;
+    unsigned bitmapBlocks() const;
+
+private:
+    static unsigned BlockMask(unsigned block);
+    static unsigned BlockIndex(unsigned block);
+
+    uint8_t *_bitmap;
+    unsigned _blocks;
+    unsigned _bitmapSize;
+};
+
+inline unsigned Bitmap::blocks() const
+{
+    return _blocks;
+}
+
+inline unsigned Bitmap::bitmapBlocks() const
+{
+    return _bitmapSize >> 12;
+}
+
+inline unsigned Bitmap::BlockMask(unsigned block)
+{
+    return 0x80 >> (block & 0x07);
+}
+
+inline unsigned Bitmap::BlockIndex(unsigned block)
+{
+    return block >> 3;
+}
+
+inline bool Bitmap::blockFree(unsigned block) const
+{
+    if (block >= _blocks) return false;
+    return (_bitmap[BlockIndex(block)] & BlockMask(block)) != 0;
+}
+
+} // namespace
+
+#endif
+