First, the device-driver attempts to read the diskette using the characteristics of the default diskette for the drive type. If this fails, the device-driver changes its characteristics and attempts to read until it has read the diskette successfully or until it has tried all the possibilities supported for the drive type by the device driver. An r prefix on a special file name means that the drive is accessed as a raw device rather than a block device. Also, all lseek subroutine calls made to the raw diskette device driver must result in a file offset value that is a multiple of the sector size. For the diskette types supported, the sector length is always 512 bytes.
Possible values are fd and rfd , where the r indicates raw access to the special file.
X Drive number indicator. Possible values of 0 and 1 indicate drives 0 and 1, respectively. Y Diskette format indicator. Possible values depend on the type of diskette being used. Either a single character or a decimal point followed by numeric characters is allowed.