Microsoft KB Archive/11276

MS-DOS 3.20: Disk Parameters for 80-Track-Per-Side Drives ID Number: Q11276

3.20 MS-DOS

Problem:

Table 3.2 on Page 3-11 of the “Microsoft MS-DOS Programmer’s Reference” shipped with both the Alpha and Beta versions of MS-DOS Version 3.20 shows some disk parameters for 80-track-per-side drives that differ from versions of the parameters published in the past. Have these parameters changed?

Response:

The parameters have not changed. Some of the information in the table is incorrect. The errors are as follows:


 * 1) The number of root directories for the single-sided 8-sector format (the first column of numbers) and the single-sided 9-sector format (the second column of numbers) should be 112, not 64 as listed in the table.
 * 2) The total number of sectors for the double-sided 9-sector format (the fourth column of numbers) should be 1440, not 1640 as shown in the table.
 * 3) The Media Descriptor for the single-sided 9-sector format (the second column of numbers) should be F8, not FB as shown in the table.
 * 4) The Media Descriptor for the double-sided 8-sector format (the third column of numbers) should be FB, not F8 as shown in the table.

The following is a corrected copy of the table:

Table 3.2 MS-DOS Standard Disk Formats

Disk Size 3.5 or 5.25 5.25 in inches

Tracks/side 80 80 80 80 80

WORD Bytes/ Sector 512 512 512 512 512

BYTE Sectors/ Allocation unit 2 2 2 2 1

WORD Reserved Sectors 1 1 1 1 1

BYTE No. FATs 2 2 2 2 2

WORD Root Dir Entries 112 112 112 112 224

WORD No. Sectors 640 720 1280 1440 2400

BYTE Media Descriptor FA F8 FB F9 F9

WORD Sectors/ FAT 1 2 2 3 7

WORD Sectors/ Track 8 9 8 9 15

WORD No. Heads 1 1 2 2 2

WORD No. Hidden Sectors 0 0 0 0 0