What the LZ said about implementing dual-boot between the two seems to be installing DOS also on the C drive where XP is located. But I have divided the hard disk into two primary partitions. One is the C drive (NTFS format, with XP installed), and the other is the G drive (FAT32 format, with MS-DOS 7.10 installed). The active partition is the C drive. I used the PROBE tool in the XP installation disk to read the content of the first sector of the G drive (it is said to be the boot sector of the DOS system), and saved it as the file BOOTSECT.DOS to C:\. Then I also added "C:\BOOTSECT.DOS="MS-DOS7.10"" at the end of BOOT.INI. There is a dual-boot menu for selection when starting up later, but only the default XP can be started. When selecting MS-DOS7.10, DOS cannot be started. There is just a cursor at the top, and nothing else, and waiting for a long time has no response. May I ask everyone what is going on? Where is the problem? Urgent...