Great Hierophant
Veteran Member
Tandy 1000 HX came with one 3.5" drive standard and came with Tandy MS-DOS 2.11.26 loaded in ROM and on a non-bootable disk. In the Tandy 1000 line, the other machines in the pre TL/SL line came with the following DOS versions:
1000 - 2.11.22
EX - 2.11.24
SX - 3.2.0
TX - 3.2.21
The SX and the TX obviously support the 3.5" drive because they use DOS 3.2, which was the official first version with that support. If you bought an EX, with room for only one 5.25" floppy drive, you could attach an external 5.25" or 3.5" drive, with the latter requiring DOS 3.2 to support 80 tracks. Ditto for the original 1000, except it would need an internal upgrade.
For the HX, the machine supported three floppy drives. There is official BIOS support for the 3.5" drive. The setup program required the user to specify which type of drive each was, and a drive could be either type. It had room for two 3.5" drives inside the machine an an external 5.25" or 3.5" drive. It could boot from either the first internal or the external drive. The DOS-in-ROM contained only what was necessary to boot to DOS and the menu (64KB used in E000-EFFF).
DOS 2-3 would assign drive letters to floppy drives first, then hard drives. If you had more than two floppy drives, then the third would be C:, the fourth would be D:, then the hard drives would have letters assigned. In a stock HX with only one 3.5" drive, it is drive A and the ROM is drive C. If you add a second internal 3.5" drive, it becomes drive B. If you add a external, third, drive, it becomes drive C and the ROM is now drive D.
The bootable part of DOS 3.2 does not fit into 64KB, never mind the menu, so I believe that Tandy used the 2.11 and added 720K/80 track functionality where needed. This had to included patches to FORMAT, DISKCOPY, BASICA, BASIC, DISKCOMP, CHKDSK and others external programs. This saved money and PCB space on extra ROM and paging functionality. (The BIOS uses 64KB from F000-FFFF).
1000 - 2.11.22
EX - 2.11.24
SX - 3.2.0
TX - 3.2.21
The SX and the TX obviously support the 3.5" drive because they use DOS 3.2, which was the official first version with that support. If you bought an EX, with room for only one 5.25" floppy drive, you could attach an external 5.25" or 3.5" drive, with the latter requiring DOS 3.2 to support 80 tracks. Ditto for the original 1000, except it would need an internal upgrade.
For the HX, the machine supported three floppy drives. There is official BIOS support for the 3.5" drive. The setup program required the user to specify which type of drive each was, and a drive could be either type. It had room for two 3.5" drives inside the machine an an external 5.25" or 3.5" drive. It could boot from either the first internal or the external drive. The DOS-in-ROM contained only what was necessary to boot to DOS and the menu (64KB used in E000-EFFF).
DOS 2-3 would assign drive letters to floppy drives first, then hard drives. If you had more than two floppy drives, then the third would be C:, the fourth would be D:, then the hard drives would have letters assigned. In a stock HX with only one 3.5" drive, it is drive A and the ROM is drive C. If you add a second internal 3.5" drive, it becomes drive B. If you add a external, third, drive, it becomes drive C and the ROM is now drive D.
The bootable part of DOS 3.2 does not fit into 64KB, never mind the menu, so I believe that Tandy used the 2.11 and added 720K/80 track functionality where needed. This had to included patches to FORMAT, DISKCOPY, BASICA, BASIC, DISKCOMP, CHKDSK and others external programs. This saved money and PCB space on extra ROM and paging functionality. (The BIOS uses 64KB from F000-FFFF).