Editing Apple 400K Drive

{{Infobox computer peripheral
| image = [[File:Apple 400K Drive.jpg]]
| caption = Macintosh External Disk Drive (Model M0130)
| manufacturer = Apple Computer, Inc. (Sony mechanism)
| type = Floppy disk drive
| released = May 4, 1984
| 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 = [[Apple Floppy Disk Drive|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:

{| class="wikitable"
|-
! 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 ==

{| class="wikitable"
|-
! 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 ===

{| class="wikitable"
|-
! 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

== See Also ==
* [[Macintosh 128K]]
* [[Apple Floppy Disk Drive]]
* [[Apple SuperDrive]]
* [[Disk II]]

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

[[Category:Apple Vintage Accessories]]

{{Navbox-AppleVintageAccessories}}