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SYS.COM Requirements in MS-DOS versions 2.0-6.0

This article was previously published under Q66530
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This article was written about products for which Microsoft no longer offers support. Therefore, this article is offered "as is" and will no longer be updated.
SUMMARY
The following is a description of the requirements needed to use theMS-DOS SYS command (SYS.COM) to transfer the MS-DOS system files.Changes that have been made to the SYS command since its introductionin MS-DOS version 2.0 are described below.
MORE INFORMATION
System files are used to boot MS-DOS. For safety, the system files aremarked with the hidden, system, and read-only attributes, and cannotbe changed using the ERASE, DEL, or COPY command. For a disk to bootMS-DOS, these files must occupy a specific location on the disk. Thenames of these system files vary among original equipmentmanufacturers (OEMs). The most common names used are:
   IO.SYS and MSDOS.SYS				
-or-
   IBMBIO.COM and IBMDOS.COM				
A disk can only be made bootable in MS-DOS by using the FORMAT /S,DISKCOPY, or SYS command.

SYS Original Functionality

The following is a brief overview of the SYS command's originalfunctionality:

SYS.COM copies the hidden system files from the default drive to thespecified destination drive and updates the boot sector of thedestination drive. Each version of SYS only recognizes system filesthat have the same filenames as its version of MS-DOS. The MS-DOS bootsequence requires that the system files be the first files in the diskdata area, that they be contiguous (that is, not fragmented), and thatthey occupy the first two entries in the root directory.

SYS copies the files to the destination if there is empty space forthem at the beginning of the disk. If the destination disk is alreadybootable and its system files have the same names, SYS replaces theexisting system files. SYS does not copy COMMAND.COM. To make abootable C drive, boot with the original MS-DOS disk, and enter thefollowing at the drive A prompt:
   sys c:   copy command.com c:\ 				

Changes to SYS

Changes to SYS include the following (by MS-DOS version number):
   Version   Description of Changes   -------   ----------------------   3.3       MS-DOS allows system files to be noncontiguous             (fragmented). However, the system files must still occupy             the first two directory entries, and the first three             sectors of IO.SYS (or IBMBIO.COM) must be located             in the first three sectors of the disk data area.   4.0       When either or both of the following conditions are met,             - The first three sectors are allocated, and not to the               first system file, but there is enough free space on               the drive to copy the system files over.             - The SYS command does not recognize the first two files               in the root directory as system files, but the root               directory is not full.             the SYS command will, if necessary, move the first two             directory entries and/or the data located in the first             three sectors of the disk to another location, and then             copy the system files. This allows you to use SYS to             change from PC-DOS to MS-DOS; however, the PC-DOS system             files will not be deleted.             The SYS command will execute properly in earlier versions             of MS-DOS if the drive formats are compatible; however,             this is not guaranteed in all circumstances. If it is             impossible to boot MS-DOS 4.0 before running SYS, using             the SYS command on a floppy drive is the safest course of             action.   5.0       MS-DOS 5.0 SYS.COM recognizes both the Microsoft system             file names (IO.SYS and MSDOS.SYS) and the IBM system file             names (IBMBIO.COM and IBMDOS.COM) as system files. So,             when using the SYS command to transfer MS-DOS to a system             that booted with PC-DOS, IBMBIO.COM and IBMDOS.COM will             be deleted.             The first three sectors of IO.SYS do not need to be in             the first three sectors of the data area; however, they             must be contiguous.             SYS copies COMMAND.COM to the destination disk.             An optional second parameter to specify the source of the             system files is supported when running in MS-DOS 5.0.             Again, running the SYS command without booting MS-DOS 5.0             is not recommended. If you cannot boot MS-DOS 5.0, use             the SYS command on a disk in drive A, and use that disk             to boot MS-DOS 5.0.   6.0       SYS copies DBLSPACE.BIN to the destination disk, as well             as copying IO.SYS, MSDOS.SYS, and COMMAND.COM.				
2.00 3.10 3.20 3.30 3.30a 4.00 5.00 6.0 6.20 6.21 6.22 no room on destination disk
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Article ID: 66530 - Last Review: 05/12/2003 21:03:14 - Revision: 2.0

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