Apple Floppy Disk Drive: Difference between revisions
Rebuild from Guide to the Macintosh Family Hardware ch.9 + the Apple 800K Drive and Apple 3.5 Drive Service Sources, both already hosted here but unused. Connector is DB-19 not DE-19. Added Apples real mechanism specifications (6 ms seek, 30 ms settle, 600 ms startup, +-0.035 mm head accuracy, 600 mA eject peak), the yellow-not-red drive cable fault that makes a Mac Plus eject continuously, the CXD1085A -> CXD1085B daisy-chain gate array fix, and the Restoring Mouse Eject procedure. Deleted u... |
cite the PC 5.25 and SuperDrive Service Source volumes inline (P4 orphan fix) |
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No Apple figures for the M0131's release date, retail price, discontinuation date or part number could be traced, and none are stated here. The M0131's own Service Source contains take-apart procedures and an exploded view only — '''no specifications chapter at all'''<ref name="ss800" /> — which is why the figures above are drawn from the closely related Apple 3.5 Drive manual and are labelled as such. | No Apple figures for the M0131's release date, retail price, discontinuation date or part number could be traced, and none are stated here. The M0131's own Service Source contains take-apart procedures and an exploded view only — '''no specifications chapter at all'''<ref name="ss800" /> — which is why the figures above are drawn from the closely related Apple 3.5 Drive manual and are labelled as such. | ||
== Apple's other external floppy drive manuals == | |||
Three further ''Service Source'' volumes cover Apple external floppy drives and are hosted here. None of them duplicates the others: | |||
* [[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 is the only one with a rotational-speed figure: '''300 rpm''', with a 19 ms average seek, a 250 kbit/s transfer rate and a '''0.9 A peak on +12 V'''.<ref name="sspc525">''Apple PC 5.25 Drive'', Apple ''Service Source'', 15 pages, PDF distilled 14 December 1995 - hosted on this wiki as [[Apple PC 5.25 Drive Service Source]], file [[: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.</ref> | |||
* [[Apple SuperDrive/HDI-20 Service Source]] - the external 1.4 MB SuperDrive and the HDI-20, and the only Apple external floppy drive volume with a symptom chart. | |||
== See Also == | == See Also == | ||
Revision as of 07:56, 25 September 2026
| Apple Floppy Disk Drive | |
|---|---|
 |
|
| Macintosh 800K External Drive (Model M0131) | |
| Manufacturer | Apple Computer, Inc. (Sony mechanism) |
| Type | Floppy disk drive |
| Interface | DB-19 external floppy port |
| Compatible | Macintosh Plus and later; see below |
| Predecessor | Macintosh External Disk Drive (M0130) |
| Successor | Apple SuperDrive |
| Model | M0131 |
The Macintosh 800K External Drive (model M0131) is Apple's double-sided 800 KB external 3.5-inch drive. It reads and writes both 800 KB double-sided and 400 KB single-sided floppies.[1]
Formats
| 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 is the IWM (Integrated Woz Machine). It converts between the NRZI serial data used to talk to drives and the 8-bit parallel data used by the CPU; the Disk Driver software converts between GCR and ordinary bytes.[1]
The IWM's clock is C8M, 7.8336 MHz on the Macintosh Plus and earlier, and C16M, 15.6672 MHz on the Macintosh SE and II — twice as fast. During startup, software sets a bit in the IWM to divide the faster clock by two when using the 800K drive, the single-sided 400K drive or the Hard Disk 20.[1]
Maximum data rate to the drive is approximately 500 kbit/s; because four bytes of GCR correspond to three bytes in RAM the effective maximum is about 375 kbit/s.[1]
It Controls Its Own Speed
This is the structural difference from the 400K drive: the 800K drive controls its own motor speed and ignores the PWM speed-control signal on pin 10 of the connector.[1] The 400K drive depends on that signal being generated by the host.
Because of that, the 800K drive works on machines that provide no speed-control line — and Apple states explicitly that on all Macintosh models that support an external FDHD drive, you can connect an external 800K drive instead.[1] That makes the M0131 the most widely compatible external floppy drive Apple sold.
Compatibility
| Model | Internal drives | External drives |
|---|---|---|
| Macintosh Plus | 1 | 1 |
| Macintosh SE (before the FDHD change) | 1 or 2 | 1 |
| Macintosh II | 1 or 2 | 0 — no external floppy connector |
Plus, per the note above, any model that supports an external FDHD 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 an identical pinout so both can be used together.[1]
Current draw
An Apple 800K drive requires 600 mA at +12 V and 360 mA at +5 V.[1] The combined load of everything connected to a Macintosh Plus must not exceed 600 mA at +12 V, 700 mA at +5 V and 10 mA at −12 V.[1]
An 800K drive therefore uses the Macintosh Plus's entire +12 V allowance on its own. If you are chasing an intermittent fault on a Plus with several things plugged in, start here.
The Apple 3.5 Drive Mechanism
The mechanism Apple later shipped as the Apple 3.5 Drive is the same family and is properly specified in its own Service Source, which is useful because the M0131's own manual is not:[2]
| 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 |
The 600 mA eject peak is the number that matters in service. A drive that ejects weakly, or that resets the machine when it ejects, is a power problem rather than a mechanical one.
Two Faults With Non-Obvious Causes
These come from Apple's own symptom charts and are the kind of thing that costs hours if you do not know them.
The cable stripe
If an Apple 3.5 Drive 800K mechanical assembly is being used as a Macintosh internal drive, the logic-board-to-drive cable must be YELLOW, not RED.[2]
The related symptom is unmistakable: an internal 3.5-inch drive on a Macintosh Plus that ejects continuously — Apple's remedy is to "verify that cable has yellow stripe, not red stripe".[2] A drive that spits out every disk you feed it is almost certainly wearing the wrong cable, not failing.
The daisy-chain gate array
Symptom: one or more Apple 3.5 drives are daisy-chained to a DuoDisk or to one or more UniDisk 5.25 drives, and the drives suddenly start to spin and can no longer be accessed by the Apple IIGS.[2]
Cause and fix: check the part number on the gate array on the daisy-chain interface board. If it reads CXD1085A that is a Revision A board; replace it with a Revision B board, CXD1085B.[2]
Restoring Mouse Eject
An obscure but genuinely useful procedure from Apple's own manual. When an Apple 3.5 mechanism is installed in an 800K drive, you cannot eject a disk by holding down the mouse button during boot up.[3]
Apple's correction:[3]
- 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.
- Look at the bottom and locate the spring clip under that wire.
- Push in on the spring clip and gently pull the wire to remove it.
- Wrap the connector end of the wire with electrical tape to prevent electrical contact.
The wire is removed and insulated, not cut. Reversing the change is a matter of pushing it back into the connector.
Disassembly
Apple's procedure:[3]
- 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.
Four bottom screws distinguishes this drive from the 400K drive, which has six.
Troubleshooting
Apple's symptom charts for this family:[2]
| 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 internally, verify the 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 spin up and become inaccessible on an Apple IIGS | Replace a Revision A CXD1085A daisy-chain gate array board with Revision B CXD1085B |
Note the ordering principle Apple uses throughout: cure in order of most likely first, and if a replaced module does not fix the symptom, reinstall the original before moving on.[2]
Head cleaning
A 3.5-inch head-cleaning disk. Do not over-clean; the heads wear.
Will not eject
Use the emergency eject hole first. Then check the eject switch cable assembly before the mechanism — that is Apple's order.[2]
What Is Not Documented
No Apple figures for the M0131's release date, retail price, discontinuation date or part number could be traced, and none are stated here. The M0131's own Service Source contains take-apart procedures and an exploded view only — no specifications chapter at all[3] — which is why the figures above are drawn from the closely related Apple 3.5 Drive manual and are labelled as such.
Apple's other external floppy drive manuals
Three further Service Source volumes cover Apple external floppy drives and are hosted here. None of them duplicates the others:
- 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 is the only one with a rotational-speed figure: 300 rpm, with a 19 ms average seek, a 250 kbit/s transfer rate and a 0.9 A peak on +12 V.[4]
- Apple SuperDrive/HDI-20 Service Source - the external 1.4 MB SuperDrive and the HDI-20, and the only Apple external floppy drive volume with a symptom chart.
See Also
References
- ↑ 1.00 1.01 1.02 1.03 1.04 1.05 1.06 1.07 1.08 1.09 1.10 1.11 Guide to the Macintosh Family Hardware, second edition, Apple Computer, Inc. / Addison-Wesley, 1990 — hosted on this wiki as File:Apple Guide to the Macintosh Family Hardware 2nd Edition 1990.pdf. Chapter 9, "Floppy Disk Interfaces": the description of 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 method; 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 approximately 500 kbit/s and the effective GCR rate of approximately 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; the warning that all devices connected to a Macintosh Plus must not draw more than 600 mA at +12 V, 700 mA at +5 V and 10 mA at −12 V, that a single-sided floppy drive requires 500 mA at +12 V and 500 mA at +5 V and that an Apple 800K drive requires 600 mA at +12 V and 360 mA at +5 V; the PWM motor-speed-control line, used only by 400K single-sided drives and generated by a PAL on the Macintosh Plus and the BBU on the Macintosh SE from values in the disk-speed buffer in RAM, with the statement that the 800K drive controls its own motor speed and ignores the signal; the statement that the SWIM does not support the single-sided floppy disk 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 arrangement, whose DB-19 pinout is identical to the computer's.
- ↑ 2.0 2.1 2.2 2.3 2.4 2.5 2.6 2.7 2.8 Apple 3.5 Drive Service Source, Apple Computer, Inc. — hosted on this wiki as File:Apple 3.5 drive.pdf. Specifications: disk diameter 3.5 in., 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 and unformatted 1,246K, with the note that disks should be certified double-sided media; the list of directly supported computers and the note that one additional drive can be 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%; electrical +12 V standby 10 µA, typical 120 mA, peak 600 mA during eject only for a 2-second maximum, and +5 V standby 10 mA, typical 360 mA; size 2.01 × 4.72 × 7.87 in. (51 × 120 × 200 mm) and weight 2.8 lb (1.3 kg). Troubleshooting symptom charts, including the yellow-versus-red logic-board-to-drive cable checks and the CXD1085A/CXD1085B daisy-chain gate-array revision.
- ↑ 3.0 3.1 3.2 3.3 Apple 800K Drive Service Source, Apple Computer, Inc. — hosted on this wiki 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 identification of the wire to remove and insulate.
- ↑ Apple PC 5.25 Drive, Apple Service Source, 15 pages, PDF distilled 14 December 1995 - hosted on this wiki as Apple PC 5.25 Drive Service Source, file 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.