Implementing Directories

• (see Fig. 5 Left)
• A simple directory containing fixed-sized entries with the disk addresses and attributes in directory entry; DOS/Windows
• A directory in which each entry just refers to an inode; UNIX
• Fixed Size Directory Entries;
  • Either too small; Example: DOS 8+3 characters
  • Waste too much space; Example: 255 characters per file name
• Free variable length entries can create external fragmentation in directory blocks; Can compact when block is in RAM

Figure 5: Left: (a) A simple directory containing fixed-sized entries with the disk addresses and attributes in directory entry (b) A directory in which each entry just refers to an inode. Right: Two ways of handling long file names in directory (a) Inline (b) In a heap.