---

NOTE

"Physical" is not the same as "BIOS".
E.g. When calling an INT 13H function against physical hard drive 0, the drive number of 80 hex is used.

---

CONFIGURATION #1

- Physical floppy drive 0
- Physical floppy drive 1
- Physical floppy drive 2  ('external' drive, at end of the cable shown at here.)
- Physical hard drive 0

Floppy count switches on IBM 5160 motherboard set to 2 drives.

Booted to IBM DOS 3.3, with DRIVER.SYS used in CONFIG.SYS to support physical floppy drive 2 (DRIVER.SYS pointed to that drive via /D:2 option)

DOS 3.3's LOGICAL DRIVE ASSIGNMENT SEQUENCE:

Because floppy count switches set to 2, at the time that DOS loaded (but before DRIVER.SYS in CONFIG.SYS was processed), DOS was only informed of two floppy drives (assuming them to be 0 and 1).
Physical floppy drive 0 was assigned A:
Physical floppy drive 1 was assigned B:
Physical hard drive 0 was assigned C:

CONFIG.SYS was then processed, loading DRIVER.SYS, resulting in physical floppy drive 2 being assigned D:

FDIMAGE TOOL:

Used "0:" to access physical floppy drive 0.
Used "1:" to access physical floppy drive 1.
Used "2:" to access physical floppy drive 2.

---

CONFIGURATION #2

Same as configuration as configuration #1, except that the floppy count switches were set to three drives.

DOS 3.3's LOGICAL DRIVE ASSIGNMENT SEQUENCE:

Physical floppy drive 0 was assigned A:
Physical floppy drive 1 was assigned B:
Physical floppy drive 2 was assigned C:
Physical hard drive 0 was assigned D:

FDIMAGE TOOL:

Used "0:" to access physical floppy drive 0.
Used "1:" to access physical floppy drive 1.
Used "2:" to access physical floppy drive 2.

---

CONFIGURATION #3

- Physical floppy drive 0
- Physical floppy drive 1
- Physical floppy drive 3  ('external' drive, at middle of the cable shown at here.)
- Physical hard drive 0

No floppy drive 2.

Floppy count switches on IBM 5160 motherboard set to 2 drives.

Booted to IBM DOS 3.3, with DRIVER.SYS used in CONFIG.SYS to support physical floppy drive 3 (DRIVER.SYS pointed to that drive via /D:3 option)

DOS 3.3's LOGICAL DRIVE ASSIGNMENT SEQUENCE:

Because floppy count switches set to 2, at the time that DOS loaded (but before DRIVER.SYS in CONFIG.SYS was processed), DOS was only informed of two floppy drives (assuming them to be 0 and 1).
Physical floppy drive 0 was assigned A:
Physical floppy drive 1 was assigned B:
Physical hard drive 0 was assigned C:

CONFIG.SYS was then processed, loading DRIVER.SYS, resulting in physical floppy drive 3 being assigned D:

FDIMAGE TOOL:

Used "0:" to access physical floppy drive 0.
Used "1:" to access physical floppy drive 1.
Used "3:" to access physical floppy drive 3.