##

    Emulated Hard Disk
    A single hard disk is emulated through a disk image file.  An image file can be as
    large as 71 MB.  If one of the following file sizes is used, the emulator will
    auto-detect the emulated disk geometry (heads, cylinders, sectors).

        Filesize  Heads  Cylinders  Sectors  Disk type
        --------  -----  ---------  -------  ---------
       5,013,504      4        153       16   RD50  5M
       5,326,848      4        153       17   RD50  5M
      10,027,008      4        306       16   RD51 10M
      10,653,696      4        306       17   RD51 10M
      20,152,320      4        615       16   RD31 21M
      21,411,840      4        615       17   RD31 21M
      33,554,432      8        512       16   RD52 36M
      35,651,584      8        512       17   RD52 36M
      40,304,640      6        820       16   RD32 43M
      42,823,680      6        820       17   RD32 43M
      67,108,864      8       1024       16   RD53 71M
      71,303,168      8       1024       17   RD53 71M

    Other sizes may be used, but the disk geometry will have to be specified manually.
    The sector size is 512 bytes, so the following equation applies:

      file_size = heads * cylinders * sectors * 512

    Set the path to the directory that contains the hard disk image file with the "rd_dir"
    variable in the configuration file.  Specify the disk image file to be used with the
    "rd0" variable.  For example, to use the provided Venix 2.0 disk image, from the
    current directory, put the following in the configuration file:

      rd_dir = .
      rd0 = venix2.rd

    As an example, to create a custom 6,144,000 byte image by the name of "image.rd,"
    perform the following from a Linux shell prompt:

      dd if=/dev/zero of=image.rd bs=6144000 count=1

    Then, to attach it to the emulator, as a disk with 6 heads, 200 cylinders and 10
    sectors, specify the following in the configuration file:

      rd0 = image.rd, 6, 200, 10

    Additionally, since this newly-created image is blank,  it would make sense to
    specify a bootable floppy image to boot from (see the "Emulated Floppy Drives"
    section).

    If no configuration file is present, or if no hard disk image is specified, the
    emulator will attempt to use a file by the name of "pos32.rd" in the current
    directory.

    All real hard drives used by the Pro seem to have 17 sectors.  However, neither P/OS
    nor Venix seems to access the 17th sector.  To save disk space, the 16-sector formats
    specified in the table may be used.