## Physical Sector I/O

A special pathlist can be used to perform “raw” physical I/O operations on a disk. The pathlist consists of the device name immediately followed by an “@” character (without a “/” in between), for example:

/d1@

When this pathlist is used, the entire disk media is treated as one logical file. Any byte or sector on the disk can be read or written without regard for the actual file structure. This feature is widely used by utility programs sush as dir, attr, mfree, etc., to access sectors of the disk which are not part of data areas of a file (such as header sectors).

### Warning

Use extreme caution when using physical sector I/O. Because any sector can be written on, it is possible to severely damage the file structure and data on a disk.

Also, using “@” completely defeats the file security and record locking systems.

To convert a logical sector number of an “@1” file to a byte number, multiply the sector number by 256 (the number of bytes per sector). Conversely, the logical sector number of a byte address is the byte address divided by 256 (integer division).

As an example, the following command will give a complete “dump” of every data byte on disk device “d0”:

    dump /d0@