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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...
DuoDisk chart: link to the copy on Disk II (Apple's p. 1.5) instead of repeating it with a wrong page range
 
(4 intermediate revisions by the same user not shown)
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{{Infobox computer peripheral
{{Infobox computer peripheral
| image = [[File:Apple Floppy Disk Drive.jpg]]
| image = [[File:Apple Floppy Disk Drive.jpg|260px|frameless]]
| caption = Macintosh 800K External Drive (Model M0131)
| caption = Macintosh 800K External Drive (M0131)
| manufacturer = Apple Computer, Inc. (Sony mechanism)
| manufacturer = Apple Computer, Inc.
| type = Floppy disk drive
| type = Floppy disk drive
| interface = DB-19 external floppy port
| interface = DB-19 external floppy port
| compatible = Macintosh Plus and later; see below
| media = 3.5-inch disks: 800 KB double-sided, 400 KB single-sided
| compatible = [[Macintosh Plus]], [[Macintosh SE]] and any Macintosh with an external FDHD drive port
| predecessor = [[Apple 400K Drive|Macintosh External Disk Drive (M0130)]]
| predecessor = [[Apple 400K Drive|Macintosh External Disk Drive (M0130)]]
| successor = [[Apple SuperDrive]]
| successor = [[Apple SuperDrive]]
Line 11: Line 12:
}}
}}
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<templatestyles src="Template:StyledTable/styles.css" />
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.<ref name="gmfh9">''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.</ref>
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.<ref name="gmfh9">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.</ref>


== Formats ==
== Formats ==
Line 24: Line 25:
|}
|}


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.<ref name="gmfh9" />
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.<ref name="gmfh9" />


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.<ref name="gmfh9" />
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.<ref name="gmfh9" />


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'''.<ref name="gmfh9" />
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.<ref name="gmfh9" />


== It Controls Its Own Speed ==
== Speed control ==


This is the structural difference from the [[Apple 400K Drive|400K drive]]: '''the 800K drive controls its own motor speed and ignores the PWM speed-control signal''' on pin 10 of the connector.<ref name="gmfh9" /> The 400K drive depends on that signal being generated by the host.
The 800K drive controls its own motor speed and ignores the PWM speed-control signal on pin 10 of the external connector. The [[Apple 400K Drive|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.<ref name="gmfh9" />


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'''.<ref name="gmfh9" /> That makes the M0131 the most widely compatible external floppy drive Apple sold.
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.<ref name="gmfh9" />


== Compatibility ==
== Compatibility ==
Line 46: Line 47:
| Macintosh SE (before the FDHD change) || 1 or 2 || 1
| Macintosh SE (before the FDHD change) || 1 or 2 || 1
|-
|-
| Macintosh II || 1 or 2 || 0 — '''no external floppy connector'''
| Macintosh II || 1 or 2 || None (no external floppy connector)
|}
|}


Plus, per the note above, any model that supports an external FDHD drive.<ref name="gmfh9" />
Any model that supports an external FDHD drive also takes the 800K drive.<ref name="gmfh9" />


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.<ref name="gmfh9" />
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.<ref name="gmfh9" />


=== Current draw ===
=== Current draw ===
'''An Apple 800K drive requires 600 mA at +12 V and 360 mA at +5 V.'''<ref name="gmfh9" /> 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'''.<ref name="gmfh9" />
An 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,<ref name="gmfh9" /> so an 800K drive on its own uses the Plus's whole +12 V allowance.


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.
== Apple 3.5 Drive specifications ==


== The Apple 3.5 Drive Mechanism ==
Apple's service documentation treats the 800K mechanism and the later [[Apple 3.5 Drive Service Source|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,<ref name="ss800" /> and the Apple 3.5 Drive Service Source covers that mechanism used as a Macintosh internal drive.<ref name="ss35">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.</ref> The 800K Drive Service Source contains take-apart procedures and an exploded view only and has no specifications chapter,<ref name="ss800" /> so the nearest Apple figures for the M0131 are those for the Apple 3.5 Drive:
 
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:<ref name="ss35">''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.</ref>


{| class="wikitable styled-table" style="width:80%;"
{| class="wikitable styled-table" style="width:80%;"
Line 68: Line 67:
| Recording surfaces || 2; 80 tracks per inch
| Recording surfaces || 2; 80 tracks per inch
|-
|-
| Seek time, track to track || '''6 ms maximum'''
| Seek time, track to track || 6 ms maximum
|-
|-
| Settle time || '''30 ms maximum'''
| Settle time || 30 ms maximum
|-
|-
| Drive startup time || '''600 ms maximum'''
| Drive startup time || 600 ms maximum
|-
|-
| Head position accuracy || '''±0.035 mm'''
| Head position accuracy || ±0.035 mm
|-
|-
| Formatted capacity || 800K (certified double-sided media)
| Formatted capacity || 800K (certified double-sided media)
Line 80: Line 79:
| Unformatted capacity || 1,246K
| Unformatted capacity || 1,246K
|-
|-
| +12 V || Standby 10 µA; typical 120 mA; '''peak 600 mA during eject only, 2 seconds maximum'''
| +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
| +5 V || Standby 10 mA; typical 360 mA
Line 93: Line 92:
|}
|}


'''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.
== Disassembly ==


== Two Faults With Non-Obvious Causes ==
Apple's procedure for the 800K drive:<ref name="ss800">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.</ref>


These come from Apple's own symptom charts and are the kind of thing that costs hours if you do not know them.
# 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.
=== The cable stripe ===
# Remove the two screws and lift the drive assembly from the cover.
'''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.'''<ref name="ss35" />
# Remove the four screws that hold the drive in the housing and slide the drive out.
 
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".<ref name="ss35" /> 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]].<ref name="ss35" />
 
'''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'''.<ref name="ss35" />


== Restoring Mouse Eject ==
The [[Apple 400K Drive|400K drive]] has six bottom-cover screws.<ref>Apple Computer, ''Apple 400K Drive'' Service Source, hosted as [[:File:Apple 400k drive.pdf]]. Take Apart: "Remove the six screws from the bottom cover."</ref>


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.'''<ref name="ss800">''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.</ref>
=== Restoring mouse eject ===


Apple's correction:<ref name="ss800" />
When 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:<ref name="ss800" />


# Remove the bottom cover and the interface cable.
# 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.
# 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.
# On the underside, locate the spring clip under that wire.
# '''Push in on the spring clip''' and gently pull the wire to remove it.
# Push in the spring clip and gently pull the wire out.
# '''Wrap the connector end of the wire with electrical tape''' to prevent electrical contact.
# Wrap the connector end of the wire in electrical tape so it cannot make 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:<ref name="ss800" />
 
# '''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 [[Apple 400K Drive|400K drive]], which has six.


== Troubleshooting ==
== Troubleshooting ==


Apple's symptom charts for this family:<ref name="ss35" />
Apple'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.<ref name="ss35" />


{| class="wikitable styled-table" style="width:90%;"
{| class="wikitable styled-table" style="width:90%;"
|+'''Symptom charts'''
|+'''Apple 3.5 Drive symptom charts'''<ref name="ss35" />
! Symptom !! Apple's sequence
! 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
| 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
| Reads but does not write || Drive mechanism, then external drive cable
Line 156: Line 135:
| Reads and writes, but does not eject || 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'''
| 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'''
| 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)
|}
|}


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'''.<ref name="ss35" />
=== Cable stripe ===
An 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.<ref name="ss35" />


=== Head cleaning ===
=== Daisy-chain gate array ===
A 3.5-inch head-cleaning disk. Do not over-clean; the heads wear.
When 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).<ref name="ss35" />


=== Will not eject ===
== DuoDisk ==
Use the emergency eject hole first. Then check the eject switch cable assembly before the mechanism — that is Apple's order.<ref name="ss35" />


== What Is Not Documented ==
The 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 [[Disk II#DuoDisk|the Disk II page]].


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.
== Other Apple floppy drive service manuals ==
Three 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.<ref name="sspc525">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.</ref>
* [[Apple SuperDrive/HDI-20 Service Source]]: the external 1.4 MB SuperDrive and the HDI-20, with a symptom chart.


== See Also ==
== See also ==
* [[Apple 400K Drive]]
* [[Apple 400K Drive]]
* [[Apple SuperDrive]]
* [[Apple SuperDrive]]
* [[Apple UniDisk 3.5]]
* [[Apple UniDisk 3.5]]
* [[Disk II]]
* [[Apple 800K Drive Service Source]]
* [[Apple 3.5 Drive Service Source]]
* [[Floppy Drive Repair]]


== References ==
== References ==

Latest revision as of 17:53, 1 October 2026

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

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]

Formats

[edit | edit source]
Apple Table 9-1, the 800K drive[1]
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

[edit | edit source]

The 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 | edit source]
Models using the 800K drive (Apple Table 9-2)[1]
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

[edit | edit source]

An 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

[edit | edit source]

Apple'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:

Apple 3.5 Drive specifications[3]
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

[edit | edit source]

Apple's procedure for the 800K drive:[2]

  1. Remove the four screws from the bottom cover and lift it off.
  2. Remove the screw from the clamp that holds the interface cable, and disconnect the cable.
  3. Remove the two screws and lift the drive assembly from the cover.
  4. 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

[edit | edit source]

When 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]

  1. Remove the bottom cover and the interface cable.
  2. 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.
  3. On the underside, locate the spring clip under that wire.
  4. Push in the spring clip and gently pull the wire out.
  5. Wrap the connector end of the wire in electrical tape so it cannot make contact.

Troubleshooting

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Apple'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]

Apple 3.5 Drive symptom charts[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

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An 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

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When 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

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The 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

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Three further Service Source volumes cover Apple external floppy drives and are hosted here:

See also

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References

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  1. ↑ 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. ↑ 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. ↑ 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.
  4. ↑ Apple Computer, Apple 400K Drive Service Source, hosted as File:Apple 400k drive.pdf. Take Apart: "Remove the six screws from the bottom cover."
  5. ↑ 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.


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