Mac OS 9 Drive Setup: Format and Partition Drives

In Apple’s classic Mac OS 9, Drive Setup served as the default utility for preparing, partitioning, and formatting both internal and external storage media. This utility handled the critical tasks of writing low-level Mac disk drivers, dividing physical drives into logical volumes using the Mac OS Extended (HFS+) or Mac OS Standard (HFS) file systems, and configuring disks for system booting. Understanding this process highlights how classic Macintosh systems established the foundational drive structures required before installing System Folders and applications.

Drive Detection and Interface Compatibility

When launched, Drive Setup automatically scanned all active storage buses—including internal ATA/IDE channels, legacy SCSI chains, and external interfaces like FireWire (IEEE 1394) and USB. The main interface presented a clean list identifying each connected drive by its bus type, ID/channel, and drive model.

While earlier iterations of Drive Setup restricted formatting to Apple-branded OEM drives, the versions bundled with Mac OS 9 (primarily Drive Setup 1.7 through 2.0.4) were significantly more compatible with generic, third-party drives. Once a user selected an uninitialized, corrupted, or secondary drive from the list, the configuration options became active.

The Partitioning Process

To partition a drive into distinct volumes, users clicked the Custom Setup… button. This opened the volume configuration window:

  1. Volume Layout: Users chose from preset partitioning schemes (such as 2, 3, or 4 partitions) or manually dragged partition dividers to allocate specific block sizes.
  2. File System Selection: Drive Setup allowed users to assign a file system to each partition:
    • Mac OS Extended (HFS+): Introduced to drastically reduce block allocation sizes on larger drives, this was the primary recommendation for Mac OS 9 installations.
    • Mac OS Standard (HFS): The legacy 16-bit format, primarily reserved for compatibility with older 68k Macs or system volumes smaller than 1 GB.
    • ProDOS / A/UX: Options were also available for legacy Apple II compatibility or Unix-based A/UX partitions.
  3. Partition Locking: Users could configure specific volumes as read-only or lock them to prevent accidental modifications.

Installing Mac OS Disk Drivers

A vital function performed by Drive Setup during the preparation process was writing the Mac OS disk driver directly onto the storage media's partition map.

Without this proprietary driver embedded in the drive's preliminary blocks, the classic Mac OS ROM and system software could not mount the drive or use it as a startup disk. Drive Setup provided a dedicated menu command—Update Driver—which allowed users to update existing drive software to the latest version without erasing the underlying data partitions, a common maintenance step when upgrading from older Mac OS versions.

Initialization and Bad-Block Allocation

Once the partitions and formats were configured, the user clicked Initialize. Drive Setup then offered advanced options under the Initialization Options… menu:

  • Zero all data: Wrote zeroes across the entire drive surface, effectively sanitizing previous data and forcing the drive's controller to detect and remap bad sectors.
  • Low-Level Format: Primarily used for SCSI drives to reset sector boundaries and establish proper interleave settings (this option was automatically disabled for modern ATA and FireWire drives).

Upon confirming the initialization warning, Drive Setup unmounted the drive, rewrote the partition table, installed the disk driver, and wrote the new file system catalog and allocation files. Once the progress bar completed, the individual partition volumes immediately mounted to the Mac OS 9 desktop, fully prepped for storage or an OS installation.