The hs files access the disk via the system's normal buffering mechanism and may be read and written without regard to physical disk records. There is also a `raw' inteface which provides for direct transmission between the disk and the user's read or write buffer. A single read or write call results in exactly one I/O operation and therefore raw I/O is considerably more efficient when many words are transmitted. The names of the raw HS files begin with rhs. The same minor device considerations hold for the raw interface as for the normal interface.
In raw I/O the buffer must begin on a word boundary, and counts should be a multiple of 512 bytes (a disk block). Likewise lseek calls should specify a multiple of 512 bytes.