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What does it mean to mark a partition as "active"?
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Posted 31 May 2003 - 05:06 AM
A good look at the change the ACTIVE flag makes to a partition table can be found here:
C:\>DEBUG - A 100 xxxx:xxxx MOV AX,201 (ignore xxxx:xxxx segment:offset values on left) xxxx:xxxx MOV BX,200 xxxx:xxxx MOV CX,1 xxxx:xxxx MOV DX,80 (or use 81 for 2nd drive, 82 for 3rd, 83 for 4th) xxxx:xxxx INT 13 xxxx:xxxx INT 3 (press ENTER an extra time here to return to dash prompt) - G=100 (ignore register dump) - D 3BE 3FF (following output is a hex dump of the partition table) x1 x2 xxxx:xxxx x3 x4 x5 x6 x7 x8 x9 10-11 12 13 14 15 16 xx xx xxxx:xxxx xx xx xx xx xx xx xx xx-xx xx xx xx xx xx xx xx xxxx:xxxx xx xx xx xx xx xx xx xx-xx xx xx xx xx xx xx xx xxxx:xxxx xx xx xx xx xx xx xx xx-xx xx xx xx xx xx 55 AA - Q (quits back to DOS prompt) The hex dump resulting from above procedure shows the partition table for the first hard drive. The above values 1 through 16 are the 16 bytes (each represented by 2 digits of hexadecimal) that hold the information for one partition. There are four 16-byte slots - so that four paritions can be defined on the drive - for instance, a Primary DOS parition and an Extended DOS partition may be defined, as well as partitions created by other operating systems. These four 16-byte slots are followed by the the values 55 AA which identifies this as a valid partition table. The 55 AA also indicates the end of the boot sector. The fifth byte in each slot (5 above) indicates the partition type. Here are the partition types used by MS-DOS as indicated in Q69912: Type: Size: FAT type: First used in: 01 - PRI DOS 0-15MB 12-bit FAT MS-DOS 2.0 04 - PRI DOS 16-32MB 16-bit FAT MS-DOS 3.0 05 - EXT DOS 0-2GB n/a MS-DOS 3.3 06 - PRI DOS 32MB-2GB 16-bit FAT MS-DOS 4.0 0E - PRI DOS 32MB 16-bit FAT Windows 95 0F - EXT DOS 0-2GB n/a Windows 95 Here are what some of the other values indicate: 1 - Active Status 80 = Active 00 = Not Active 2 - Starting Head of Partition 3/4 - Starting Cylinder and Sector (combined) 5 - Partition Type 6 - Ending Head of Partition (1 less than total number of heads) 7/8 - Ending Cylinder and Sector (combined) 9/10/11/12 - Relative Partition Sector Start (no. of sectors between partition table and start of partition) 13/14/15/16 - Size of Partition (in sectors)
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