CopyDisk is a program for copying entire disk packs.  It will copy from
one drive to another on the same machine, or between drives on separate
machines via a network.

1. History

The  first Alto  CopyDisk  was called  Quick  and was  written  by Gene
McDaniel in 1973.   During the summer of  1975 Graeme Williams  wrote a
new CopyDisk adding the ability to copy disks over the network.  During
the  summer of  1976 David  Boggs redesigned  the network  protocol and
added the  ability to copy  Trident disks.  In  the spring of  1980 the
network protocol was extended  to speak to CopyDisk servers  in Interim
File  Systems  (and  eventually Tape  servers).   The  CopyDisk network
protocol is specified in

2. Concepts and Terminology

In a disk copy operation, the information on a 'Source' disk  is copied
to a  'Destination' disk,  destroying any  previous information  on the
destination.  A copy operation usually consists of two steps:

     [Copy] Step one  copies bit-for-bit the information  from the
     source disk to the destination disk.

     [Check] Step two reads  the destination disk and  checks that
     it  is indentical  with the  source disk.   This step  can be
     omitted at the user's peril.

Copying a disk from one  machine (or 'host') to another over  a network
requires the  active cooperation  of programs on  both machines.   In a
typical scenario,  a human  user invokes a  program called  a 'CopyDisk
User' and directs it to  establish contact with a 'CopyDisk  Server' on
another machine.  Once contact has been established, the  CopyDisk User
initiates  requests  and  supplies  parameters  for  the   actual  copy
operation which the User and  Server carry out together.  The  User and
Server roles differ  in that the CopyDisk  User interacts with  a human
user  (usually  through  some  keyboard  interpreter)  and   takes  the
initiative  in User/Server  interactions, whereas  the  CopyDisk Server
plays a comparatively passive  role.  The question of which  machine is
the CopyDisk User  and which is the  CopyDisk Server is  independent of
the direction in which data moves.

The  Alto  CopyDisk  subsystem  contains both  a  CopyDisk  User  and a
CopyDisk Server, running as independent processes.  Therefore to copy a
disk  from one  machine to  another you  should start  up  the CopyDisk

                   Copyright Xerox Corporation 1980

CopyDisk                   November 12, 1980                          2

subsystem on both machines and then type commands to one of them, which
becomes  the  CopyDisk  User.   Subsequent  operations  are  controlled
entirely from the User end, with no human intervention required  at the
Server machine.  This  arrangement is similar to  the way the  Alto FTP
subsystem works, and different from the way the older CopyDisk worked.

3. Calling CopyDisk

CopyDisk can be  run in two modes:  interactive mode in  which commands
come from the keyboard, and non-interactive mode in which commands come
from the command line (   The general form of the  command line
to invoke CopyDisk looks like:

  CopyDisk [ [/