CompuServe Messages

Roger, The book I used was the AmigaDOS manual, published by Bantam books, written by Commodore. There is no file header block list per-se. What there is, is the root block since all filenames start at the root block of a filesystem. The root block contains a list of header blocks for files/directories attached directly to the root block of the filesystem. The file or directory name is run thru a hashing algorithm and the result is an offset within the root block. Located at that offset is the key number of the block that contains a header block. That header block can be either a file header, or a directory header. If it's a file header, it contains pointers to what blocks the file itself is using. If it's a directory header, it then acts like the root block. It contains pointers (the key numbers) to files and/or directories attached directly to that directory. Again a file or directory name would be hashed, and offset generated and a jump to the keynumber at that offset would be another header block…again, it could be either a file or directory block. Let's take the filename: df0:junk/downloads/files/george The filesystem first "moves" to df0: and grabs the root block. It then hashes the name "junk" and jumps to the header found at the hash generated offset in the root block. It then hashes the name "downloads" and jumps to the header found at the hash generated offset in the "junk" directory block. The name "files" is now hashed, the offset located within the "downloads" directory block and another jump is made. Finally, "george" is hashed, the offset in the "files" directory is used to locate the header block of the file "george". The system then reads the pointers to the blocks containing "george" from that header, and starts to read them in. The above is a simplification of what goes on. There are extension blocks for long files, extension blocks for hash offset collisions and so forth. But it should give you a bit of a clue as to what's going on. Don