Diskcopy, Copy and Xcopy

                From The Fox Valley PC Association-Illinois,                     
                   Fox Tales via SJIBMPCUG Bits & Bytes

     One of the things we learn almost immediately when confronted with
     a computer is that there are files and we're supposed to do something
     about them.  Even if we have no idea at all what they are, the reference
     manual usually gets us involved with them via the install section.

     Unfortunately, most reference manuals present DISKCOPY or COPY as
     the way to install program files without any explanation of what’s
     happening in the underlying environment.

     To understand the idea of copying, we need to know that pieces of
     information (files) reside in two areas of the computer system: on
     the disk, as a magnetic imprint which keeps the information even when
     there is no electricity, and in RAM (Random Access Memory) which is
     a sort of twilight zone of computer technology and only works when
     there is a supply of electricity.

     When we start a program, or retrieve a file into a word processor
     or spreadsheet, the computer makes a copy of the information from
     the disk and puts that copy in RAM.  There, we can manipulate and
     change all sorts of things without any impact on the magnetism still
     sitting on the disk -- until we save to the disk.

     So at most times, there exists a magnetic map of a program, or a 
     letter we wrote, or our current checkbook.  Then if we're using the 
     computer to make changes to the checkbook or letter, there exists 
     also a copy of that in RAM.  Some programs write to disk immediately 
     upon going to the next record (database),or check (accounting).  
     Many programs wait and let us press the Save key.

     As we build more files, or install more and more programs, we realize
     we need to move things around, or delete the files, or even (oddly
     enough) back up our data files.  Here, once again, we come in contact
     with the concept of copying files.  Drawing on our first experience,
     we might assume that DISKCOPY is the way to go -- particularly if
     that is what our first reference manual suggested, or we may choose
     the plain COPY command.

     DISKCOPY

     DISKCOPY is designed to make an exact copy of a disk to another disk
     of exactly the same type (360 to 360, 1.44 to 1.44, etc.).  It will
     completely overwrite all information on the destination (target) disk
     with all the information on the source disk -- including bad sectors,
     [fragmentation] and other errors.
     
     While DISKCOPY works even on single floppy drive systems, you can't
     ISKCOPY a directory to a floppy disk.  DISKCOPY is a separate program
     and needs to be accessible in the path before it will work.

     COPY

     When we use DOS COPY command, DOS goes to the file we are trying to
     copy; reads up to 64K of it into RAM; then writes that 64K onto the
     destination disk. After that, the cycle begins again until the 
     original source file is copied to the destination.  If we are 
     copying a large number of files, DOS still will read only 64K, then 
     write 64K, over and over.  In addition, DOS doesn’t care at all if 
     the source file is different but has the same name as what you 
     designate as the destination. DOS COPY will overwrite or combine 
     multiple files into a single file and never blink.  [COPY is an 
     internal DOS command available as soon as COMMAND.COM is loaded].

     XCOPY

     To get around this [64K limit], if we're copying large numbers of
     files or a very large single file, we have XCOPY, which came into
     being with DOS 3.2.  XCOPY reads as much information into RAM as 
     there is room, then writes the whole chunk to the destination.  If 
     we have five files, each 80K, and there is 400K of RAM, the whole 
     operation is done in one read and one write.  COPY on the other hand 
     will require seven read/writes.  XCOPY will also ask us if a 
     destination is a file or a directory, if we try to copy 30 files to 
     a non-existent directory. [XCOPY is an external DOS program which 
     needs to be accessible in the path].  Remember: if you are running 
     DOS 5.0, a screenful of help is available for any DOS command simply 
     by appending the /? switch.