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RX(4)											    RX(4)

       rx - DEC RX02 floppy disk

	    NRX  rx_units  # RX02

	    #Name Unit# Addr   Vector Br Handler(s)	 # Comments
	    rx	  ?	177170 264    5  rxintr 	 # rx02

       major device number(s):
	    raw: 17
	    block: 8
       minor device encoding:
	    bit 01 specifies drive: <rx_drive>
	    bit 02 specifies density: single: 0, double: 1

       The  rx	device provides access to a DEC RX02 floppy disk unit with M8256 interface module
       (RX211 configuration).  The RX02 uses 8-inch,  single-sided,  soft-sectored  floppy  disks
       (with pre-formatted industry-standard headers) in either single or double density.

       Floppy  disks  handled by the RX02 contain 77 tracks, each with 26 sectors (for a total of
       2,002 sectors).	The sector size is 128 bytes for single density,  256  bytes  for  double
       density.   Single density disks are compatible with the RX01 floppy disk unit and with IBM
       3740 Series Diskette 1 systems.

       Files with minor device numbers 0 and 1 refer to drives 0 and 1 in  single  density  mode;
       minor devices 2 and 3 refer to drives 0 and 1 in double density mode.  The standard device
       names begin with ``rx'' followed by the drive number and then a letter a-b for single  and
       double  density access to the drive respectively.  The character ? stands here for a drive
       number in the range 0-1.

       The block 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' interface
       which provides for direct transmission between the disk and the user's read or write  buf-
       fer.   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
       files conventionally begin with an extra `r.'

       In  raw I/O the buffer must begin on a word (even) boundary, and counts should be a multi-
       ple of the disk's sector size (either 128 or 256 bytes  depending  on  selected	density.)
       Likewise seek calls should specify a multiple of the disk's sector size.

       In addition to normal (`block' and `raw') i/o, the driver supports formatting of disks for
       either density.

       The rx driver does not support pseudo-disks (partitions).  Each file rx?[ab] refers to the
       entire  drive  as  a single sequentially addressed file.  The physical disk sector size is
       128 bytes for single density and 256 bytes for double density.  The logical block size  is
       1024 bytes.  Each diskette has 250 logical blocks in single density and 500 logical blocks
       in double density.

       The size and density of the disks are specified as follows:

	    disk  minor device	unit  density
	    rx0a  0		0     single
	    rx1a  1		1     single
	    rx0b  2		0     double
	    rx1b  3		1     double

       Even though the storage capacity on a floppy disk is quite small, it is possible  to  make
       file systems on them.  For example, the commands
	      % rxformat /dev/rrx0a
	      % newfs /dev/rrx0a
	      % rxformat /dev/rrx1b
	      % newfs /dev/rrx1b
       format  and  make file systems on the single density disk in the left drive and the double
       density disk in the right drive with 241 and 486 kbytes available, respectively, for  file
       storage.   Using  tar(1)  gives somewhat more efficient utilization of the available space
       for file storage.  The RX02 disks are primarily useful for small archives and transfer  of
       small systems or distributions.

       An ioctl(2) call is available is available to format RX02 disks:
	      #include <pdpuba/rxreg.h>
	      ioctl(fildes, RXIOC_FORMAT)
       The density is determined by the device opened.

       /dev/rx[01][ab]	   block files
       /dev/rrx[01][ab]    raw files
       /dev/MAKEDEV	   script to create special files
       /dev/MAKEDEV.local  script to localize special files

       hk(4),  ra(4),  ram(4),	rk(4), rl(4), rp(4), si(4), xp(4), dtab(5), autoconfig(8), rxfor-

       rx2%d: hard error sn%d cs=%b er=%b.  An unrecoverable error occurred  during  transfer  of
       the  specified  sector of the specified disk.  The contents of the two error registers are
       also printed in octal and symbolically with bits decoded.  The error was either unrecover-
       able, or a large number of retry attempts could not recover the error.

       In  raw	I/O  read and write(2) truncate file offsets to disk sector size block boundaries
       (either 128 or 256 bytes depending on the selected density), and write  scribbles  on  the
       tail of incomplete blocks.  Thus, in programs that are likely to access raw devices, read,
       write and lseek(2) should always deal in disk sector size multiples.

       DEC-standard error logging should be supported.

       A program to analyze the logged error information (even in its present  reduced	form)  is

       The 4.3BSD rx driver which supports more capabilities should be ported to 2.11BSD.

3rd Berkeley Distribution		 January 27, 1996				    RX(4)
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