DOS Command Sys
Type: External (1.0 and later)
SYNTAX
SYS [source] d:
Purpose: Transfers the operating system files to another
disk. The three files that are transferred are IO.SYS, MSDOS.SYS,
and COMMAND.COM (if you are using IBM's version of DOS, they are
named IBMIO.SYS, IBMDOS.SYS, and COMMAND.COM).
Discussion
Using versions of DOS prior to version 4, the disk had to have
enough contiguous free space on it for the three files to be
transferred. In the newer versions that is no longer necessary.
You may not be able to reliably transfer system files to a disk that
already has a different version of DOS on it.
The system files IO.SYS and MSDOS.SYS are hidden files that do not
appear when you use the DIR command to display a directory of a
system disk.
In versions of DOS prior to version 5, when you use the SYS command
to transfer the system files to a disk, the file COMMAND.COM (which
contains the command processor) is not transferred. When using those
earlier versions, you must use the COPY command to transfer
COMMAND.COM.
A system disk can also be transferred (along with all the files
stored on it) using the DISKCOPY command.
If an error is encountered, SYS will not transfer the system files.
DOS will report one of the following error messages:
Message: No room for system on target disk
Meaning: This message means that there is not enough room on the
target disk for the system files.
Message: Incompatible system size
Meaning: The system files do not take up the same amount of space on
the target disk as the new system will need. This can happen if you
try to transfer system files to a disk that already has a different
version of DOS on it.
You may receive other error messages if DOS cannot find the required
system files at the source location specified or if you try to use
the SYS command to transfer the system files to compressed drives or
networked drives.
This page is from http://www.easydos.com. I pasted it on my website to avoid possible broken links. For further help with DOS commands, Check easydos.com out.