Apple 400K Drive

Apple 400K Drive
	Macintosh External Disk Drive (Model M0130)
Manufacturer	Apple Computer, Inc. (Sony mechanism)
Type	Floppy disk drive
Discontinued	1986
Price	US$495
Interface	DE-19 floppy port
Compatible	Macintosh 128K, 512K, 512Ke, Plus
Dimensions	~200 mm × 180 mm × 50 mm
Weight	~900 g
Predecessor	None (first Mac external drive)
Successor	Macintosh 800K External Drive (M0131)
Model	M0130

The Macintosh External Disk Drive (model M0130) was Apple's first external 3½-inch floppy drive, introduced alongside the original Macintosh 128K in January 1984. The single-sided 400 KB drive matched the internal drive of the original Macintosh and used Sony's newly standardized 3.5-inch format with Apple's proprietary GCR encoding.

Background

The Macintosh External Disk Drive was announced with the Macintosh on January 24, 1984, but did not ship until May 4, 1984—sixty days after Apple's promised delivery date. Bill Fernandez served as project manager for the drive's design and production.

The Macintosh originally used Apple's ill-fated Twiggy drive, but this was replaced with Sony's more reliable 3.5-inch mechanism before shipping. The external drive used the same Sony mechanism as the internal drive.

Design

Physical Construction

The M0130 features:

Beige case matching original Macintosh
Bulkier profile than later 800K drives
Single DE-19 connector
Auto-eject mechanism

Sony Mechanism

The 400K drive uses a single-sided Sony mechanism:

Single read/write head (bottom side only)
GCR (Group Coded Recording) variable-speed format
80 tracks
8-12 sectors per track (zoned)

Format

The 400K format differs from industry-standard PC floppy formats:

Parameter	Apple 400K	PC 360K (5.25")
Encoding	GCR variable speed	MFM fixed speed
Tracks	80	40
Sectors/track	8-12 (zoned)	9 (fixed)
Capacity	400 KB	360 KB

Zoned CAV System:

5 zones of 16 tracks each
Inner zone: 8 sectors/track (slower)
Outer zone: 12 sectors/track (faster)
Disk speed varies by zone

This design maximizes capacity and improves reliability on inner tracks by reducing data density.

File System

400K disks use MFS (Macintosh File System):

Flat file structure (no folders, just visual grouping)
Limited to approximately 50 files per disk
Superseded by HFS with the Macintosh Plus

While 400K disks can technically be formatted with HFS, they:

Cannot be booted from
Are unreadable on 64K ROM Macs (128K/512K)

Compatibility

External Drive Limitation

The original Macintosh supports only one external floppy drive, limiting total mounted disks to two.

Systems

Macintosh 128K — Native support
Macintosh 512K — Native support
Macintosh 512Ke — Native support
Macintosh Plus — Supported (reads 400K in 800K drive)
Macintosh SE — Not compatible (SuperDrive controller issues)

The 400K external drive does not work with Macs equipped with the high-density SuperDrive controller (SE FDHD and later) due to electrical interface changes.

Daisy-Chaining

Apple's Hard Disk 20 includes pass-through ports allowing the external floppy drive to be daisy-chained.

Specifications

Parameter	Value
Model number	M0130
Capacity	400 KB
Sides	Single-sided
Tracks	80
Sectors	8-12 per track (zoned)
Encoding	GCR variable speed
Rotation	394-590 RPM (variable)
Interface	DE-19 floppy port
Case color	Beige
Mechanism	Sony single-sided
Price (1984)	US$495

Copy Protection

Copy protection on Macintosh software was less elaborate than on Apple II:

Mac drives offered less low-level control
Apple did not publish Mac OS ROM source listings
Mac OS disk access routines were more complex
Disk access synchronized with mouse/keyboard operations

Maintenance

Head Cleaning

Use a 3.5-inch head cleaning disk. The single head is on the bottom of the mechanism.

Eject Mechanism

Early drives are prone to eject mechanism failure:

Symptoms: Disk won't eject
Emergency: Insert paperclip into eject hole
Common cause: Lubricant dried out, motor failure

Common Issues

Problem	Cause	Solution
Won't read	Dirty head	Clean head
Won't eject	Mechanism failure	Paperclip emergency eject
Not recognized	SE FDHD or later Mac	Use on earlier Mac
Speed errors	Worn mechanism	Replace drive

Historical Significance

The Macintosh External Disk Drive (with its internal counterpart) introduced Sony's 3.5-inch format to mainstream computing. The format became the industry standard, though Apple's GCR encoding differed from the MFM encoding adopted by IBM PC compatibles.

The 3.5-inch disk's rigid plastic shell and protective metal shutter were major improvements over the 5.25-inch format's flexible envelope design.

Collecting

Identification

Model M0130 on label
Beige case (not Platinum)
Bulkier than M0131 (800K drive)
Single-sided mechanism

Condition Assessment

Mint: Original box, functional, clean
Excellent: Functional, minimal yellowing
Good: Functional, cosmetic wear
Fair: Partially functional
Poor: Non-functional

Rarity

Less common than 800K drives due to:

Short production period (1984-1986)
Limited compatibility with later Macs
Many upgraded to 800K systems

References

Wikipedia — Macintosh External Disk Drive
Bill Fernandez Portfolio — Mac External Drive
Folklore.org — Macintosh development stories