Apple Floppy Disk Drive
The Macintosh 800K External Drive (model M0131) is Apple's external double-sided 3.5-inch floppy drive for the Macintosh. It reads and writes 800 KB double-sided and 400 KB single-sided disks.[1]
| Apple Floppy Disk Drive | |
|---|---|
 |
|
| Macintosh 800K External Drive (M0131) | |
| Manufacturer | Apple Computer, Inc. |
| Type | Floppy disk drive |
| Interface | DB-19 external floppy port |
| Compatible | Macintosh Plus, Macintosh SE and any Macintosh with an external FDHD drive port |
| Predecessor | Macintosh External Disk Drive (M0130) |
| Successor | Apple SuperDrive |
| Model | M0131 |
| Media | 3.5-inch disks: 800 KB double-sided, 400 KB single-sided |
Formats
edit| Disk type | Capacity | File system | Encoding |
|---|---|---|---|
| 3.5-inch single sided | 400 KB | MFS | Apple GCR |
| 3.5-inch double sided | 800 KB | HFS | Apple GCR |
The interface IC in the computer is the IWM (Integrated Woz Machine). It converts between the NRZI serial data used by the drive and the 8-bit parallel data used by the CPU; the Disk Driver software converts between GCR and ordinary bytes.[1]
The IWM is clocked by C8M (7.8336 MHz) on the Macintosh Plus and earlier, and by C16M (15.6672 MHz) on the Macintosh SE and II. At startup, software sets a bit in the IWM to divide the faster clock by two when it drives an 800K drive, a 400K drive or a Hard Disk 20.[1]
The maximum data rate to the drive is about 500 kbit/s. Four bytes of GCR carry three bytes of data, so the effective maximum is about 375 kbit/s.[1]
Speed control
editThe 800K drive controls its own motor speed and ignores the PWM speed-control signal on pin 10 of the external connector. The 400K drive depends on that signal, which the host generates from a disk-speed buffer in RAM: a PAL on the Macintosh Plus, the BBU on the Macintosh SE.[1]
Because it needs no speed signal, the 800K drive also works on later machines. Apple states that an external 800K drive can be connected to any Macintosh model that supports an external FDHD drive.[1]
Compatibility
edit| Model | Internal drives | External drives |
|---|---|---|
| Macintosh Plus | 1 | 1 |
| Macintosh SE (before the FDHD change) | 1 or 2 | 1 |
| Macintosh II | 1 or 2 | None (no external floppy connector) |
Any model that supports an external FDHD drive also takes the 800K drive.[1]
On the Macintosh Plus and SE the external connector also accepts a 400K drive or an Apple Hard Disk 20. The Hard Disk 20 has a pass-through DB-19 with the same pinout, so a floppy drive can be chained behind it.[1]
Current draw
editAn Apple 800K drive draws 600 mA at +12 V and 360 mA at +5 V. Apple limits the combined load of everything connected to a Macintosh Plus to 600 mA at +12 V, 700 mA at +5 V and 10 mA at −12 V,[1] so an 800K drive on its own uses the Plus's whole +12 V allowance.
Apple 3.5 Drive specifications
editApple's service documentation treats the 800K mechanism and the later Apple 3.5 Drive mechanism as interchangeable. The 800K Drive Service Source has a procedure for an Apple 3.5 mechanism fitted in the 800K drive,[2] and the Apple 3.5 Drive Service Source covers that mechanism used as a Macintosh internal drive.[3] The 800K Drive Service Source contains take-apart procedures and an exploded view only and has no specifications chapter,[2] so the nearest Apple figures for the M0131 are those for the Apple 3.5 Drive:
| Parameter | Value |
|---|---|
| Recording surfaces | 2; 80 tracks per inch |
| Seek time, track to track | 6 ms maximum |
| Settle time | 30 ms maximum |
| Drive startup time | 600 ms maximum |
| Head position accuracy | ±0.035 mm |
| Formatted capacity | 800K (certified double-sided media) |
| Unformatted capacity | 1,246K |
| +12 V | Standby 10 µA; typical 120 mA; peak 600 mA during eject only, 2 seconds maximum |
| +5 V | Standby 10 mA; typical 360 mA |
| Size | 2.01 × 4.72 × 7.87 in. (51 × 120 × 200 mm) |
| Weight | 2.8 lb (1.3 kg) |
| Operating temperature | 40–122 °F (5–50 °C) |
| Relative humidity | 5–90%, non-condensing |
Disassembly
editApple's procedure for the 800K drive:[2]
- Remove the four screws from the bottom cover and lift it off.
- Remove the screw from the clamp that holds the interface cable, and disconnect the cable.
- Remove the two screws and lift the drive assembly from the cover.
- Remove the four screws that hold the drive in the housing and slide the drive out.
The 400K drive has six bottom-cover screws.[4]
Restoring mouse eject
editWhen an Apple 3.5 mechanism is installed in an 800K drive, holding down the mouse button during startup no longer ejects a disk. Apple's fix:[2]
- Remove the bottom cover and the interface cable.
- Orient the cable connector as shown in the manual. Locate the last wire on the left side in the lower row; the pin above it is empty.
- On the underside, locate the spring clip under that wire.
- Push in the spring clip and gently pull the wire out.
- Wrap the connector end of the wire in electrical tape so it cannot make contact.
Troubleshooting
editApple's symptom charts for the Apple 3.5 Drive family list cures in order of likelihood. If a replacement module does not cure the symptom, refit the original before trying the next cure.[3]
| Symptom | Apple's sequence |
|---|---|
| Drive does not come on; LED flashes once or does not light | If an Apple 3.5 Drive 800K mechanical assembly is fitted as a Macintosh internal drive, verify the logic-board-to-drive cable is yellow, not red; then drive mechanism, external drive cable, LED assembly |
| Reads but does not write | Drive mechanism, then external drive cable |
| Does not read, but LED comes on | Check software, then drive mechanism |
| Does not eject disk | Drive mechanism, then eject switch cable assembly |
| Functions, but LED does not light | LED assembly, then drive mechanism |
| Ejects known-good system disks, but reads and writes after booting from another disk | Disk, then disk cable, then mechanical assembly |
| Reads and writes, but does not eject | Mechanical assembly |
| Internal 3.5-inch drive on a Macintosh Plus ejects continuously | Verify the cable has a yellow stripe, not a red stripe |
| Apple 3.5 drives daisy-chained to a DuoDisk or UniDisk 5.25 start to spin and can no longer be accessed by an Apple IIGS | Check the gate array on the daisy-chain interface board; replace a Revision A board (CXD1085A) with a Revision B board (CXD1085B) |
Cable stripe
editAn Apple 3.5 Drive 800K mechanical assembly used as a Macintosh internal drive needs a yellow-striped logic-board-to-drive cable. With a red-striped cable the drive may not come on, and an internal drive on a Macintosh Plus can eject continuously.[3]
Daisy-chain gate array
editWhen Apple 3.5 drives are chained to a DuoDisk or UniDisk 5.25 and suddenly spin up and become inaccessible from an Apple IIGS, read the part number on the gate array on the daisy-chain interface board. CXD1085A marks a Revision A board; replace it with a Revision B board (CXD1085B).[3]
DuoDisk
editThe DuoDisk is Apple's dual 5.25-inch drive for the Apple II series, two Disk II-type mechanisms sharing one analogue card. Apple's chip-swapping chart for that card, from the DuoDisk Technical Procedures (p. 1.5), is on the Disk II page.
Other Apple floppy drive service manuals
editThree further Service Source volumes cover Apple external floppy drives and are hosted here:
- Apple 400K Drive Service Source: take-apart and exploded view only; no specifications and no symptom chart.
- Apple PC 5.25 Drive Service Source: the 360K 5.25-inch drive. It gives 300 rpm, a 19 ms average seek, a 250 kbit/s transfer rate and a 0.9 A peak on +12 V.[5]
- Apple SuperDrive/HDI-20 Service Source: the external 1.4 MB SuperDrive and the HDI-20, with a symptom chart.
See also
editReferences
edit- ↑ 1.00 1.01 1.02 1.03 1.04 1.05 1.06 1.07 1.08 1.09 1.10 Apple Computer, Guide to the Macintosh Family Hardware, second edition, Addison-Wesley, 1990, hosted as File:Apple Guide to the Macintosh Family Hardware 2nd Edition 1990.pdf. Chapter 9, "Floppy Disk Interfaces": the 400K drive as a single-sided version of the Apple 800K drive; Table 9-1, drive type against disk type, capacity, file system and encoding; the GCR/NRZI and MFM encoding rules; Tables 9-2 and 9-6, which Macintosh models take which drive and how many internal and external drives each supports; the IWM and SWIM interface ICs, their C8M (7.8336 MHz) and C16M (15.6672 MHz) clocks, the maximum data rate of about 500 kbit/s and the effective GCR rate of about 375 kbit/s; Figure 9-3 and Tables 9-3 and 9-4, the 20-pin internal connector pinouts; Figure 9-4 and Table 9-5, the DB-19 external connector pinout, with PWM motor-speed control on pin 10; the limit on devices connected to a Macintosh Plus of 600 mA at +12 V, 700 mA at +5 V and 10 mA at −12 V, and the 800K drive's requirement of 600 mA at +12 V and 360 mA at +5 V; the PWM speed-control signal, used only by the 400K single-sided drive and generated by a PAL on the Macintosh Plus and the BBU on the Macintosh SE, and the statement that the 800K drive controls its own motor speed and ignores it; the statement that the SWIM does not support the single-sided drive; the statement that an external 800K drive may be connected to any model that supports an external FDHD drive; and the Hard Disk 20 pass-through connector, whose DB-19 pinout is identical to the computer's.
- ↑ 2.0 2.1 2.2 2.3 Apple Computer, Apple 800K Drive Service Source, hosted as File:Apple 800k drive.pdf. Take Apart: four screws in the bottom cover; a screw in the clamp holding the interface cable; two screws releasing the drive assembly from the cover and four holding the drive in its housing. Additional Procedures, "Restoring Mouse Eject": the procedure for an Apple 3.5 mechanism fitted in an 800K drive, and the wire to remove and insulate. Exploded view. No specifications chapter.
- ↑ 3.0 3.1 3.2 3.3 3.4 3.5 Apple Computer, Apple 3.5 Drive Service Source, hosted as File:Apple 3.5 drive.pdf. Specifications, pages 1 to 6: 3.5 in. disk, 2 recording surfaces, 80 tracks per inch; seek time track-to-track 6 ms maximum, settle time 30 ms maximum, drive startup time 600 ms maximum; head position accuracy ±0.035 mm; formatted capacity 800K on certified double-sided media, unformatted 1,246K; the list of directly supported computers, and one additional drive daisy-chained on the Apple IIGS; operating temperature 40–122 °F (5–50 °C), storage −40 to 140 °F with no condensation, relative humidity 5–90%; +12 V standby 10 µA, typical 120 mA, peak 600 mA during eject only for 2 seconds maximum; +5 V standby 10 mA, typical 360 mA; 2.01 × 4.72 × 7.87 in. (51 × 120 × 200 mm), 2.8 lb (1.3 kg). Troubleshooting, Symptom Charts/Miscellaneous, pages 1 to 4: the yellow-versus-red logic-board-to-drive cable checks and the CXD1085A/CXD1085B daisy-chain gate array.
- ↑ Apple Computer, Apple 400K Drive Service Source, hosted as File:Apple 400k drive.pdf. Take Apart: "Remove the six screws from the bottom cover."
- ↑ Apple Computer, Apple PC 5.25 Drive Service Source, 15 pages, PDF distilled 14 December 1995, described at Apple PC 5.25 Drive Service Source (File:Apple pc 5.25 drive.pdf). Specifications: average seek 19 ms; transfer rate 250 kbit/s; rotational speed 300 rpm; average startup 500 ms; 360K formatted, 2 surfaces, 40 tracks per surface, 48 tpi; +12 V ±10% maximum 0.6 A, peak 0.9 A, typical 0.36 A; +5 V ±5% maximum 0.65 A, typical 0.5 A.