Apple UniDisk 3.5
The Apple UniDisk 3.5 (model A2M2053) was the first 800 KB 3.5-inch drive Apple shipped for the Apple II, released in September 1985 - before the 800 KB drive for the Macintosh.[1]
| Apple UniDisk 3.5 | |
|---|---|
 |
|
| Apple UniDisk 3.5 (model A2M2053) | |
| Manufacturer | Apple Computer, Inc. (Sony mechanism) |
| Type | Floppy disk drive |
| Interface | 19-pin D-sub disk port, SmartPort protocol |
| Compatible | Apple IIc with the November 1985 firmware or later; Apple IIe and II Plus with a Liron card; Apple IIGS; Apple IIc Plus |
| Predecessor | Disk II |
| Model | A2M2053 |
It is an intelligent drive: it contains its own processor, RAM and firmware, and the host issues high-level commands rather than driving the mechanism directly. That is why it works on a 1 MHz Apple II at all, and it is also why it will not work on a Macintosh despite using the same Sony mechanism.
Why it exists
editA 1 MHz 6502 cannot take raw data off a 3.5-inch drive, de-nibblise it and hand it to the operating system fast enough. Apple's answer was to put the work inside the drive: a small computer buffers the data and talks to the host over a simple protocol.[1] The cost is speed - the extra processing means the UniDisk works best at a 4:1 interleave, where the later, dumber Apple 3.5 Drive uses 2:1 and is faster.[1]
Apple's design also departs from Sony's: the rotation speed varies with the track being accessed, which packs the inner tracks tightly enough to gain an extra 80 KB over the 720 KB otherwise available - hence 800 KB.[1]
Inside the drive
editThe drive's internals have been documented in detail by a community project that uses the UniDisk as a co-processor for an Apple II:[2]
| Function | Device |
|---|---|
| Processor | 65C02 at 2.0 MHz - GTE G65SC02P-2, PDIP40 |
| RAM | 2 KB static - Hitachi HM6116LP-2, 120 ns, PDIP24 |
| ROM | 8 KB firmware - A2M2053-V1.0 / TC5365P-8718, 250 ns, PDIP28 |
| Disk controller | IWM - VLI VF4060-001 / 344-0041-B, PDIP28 |
The processor's memory map also carries 527 bytes of gate-array I/O locations and 15 bytes of IWM registers.[2] The firmware was written by Michael Askins, who also wrote the software for the Liron controller card.[2]
SmartPort and the daisy chain
editThe 19-pin D-sub disk port carries Apple's Protocol Converter protocol, later renamed SmartPort. The host sends high-level commands; the drive does the low-level work; and several devices can be chained.[2][3]
A Disk II in the chain must be last. The Protocol Converter bus is a daisy chain of the disk port, one or more intelligent devices, and optionally one Disk II, which "must be the terminal member of the daisy chain and remains dormant when a bus resident is addressed".[2] A 5.25-inch drive in the middle of the chain will not work, and that is a configuration error rather than a fault.
On an Apple IIc with the November 1985 firmware the port supports four 3.5-inch drives, or three 3.5-inch drives and one 5.25-inch drive.[3]
Compatibility
edit| Host | What is needed |
|---|---|
| Apple IIc | The November 1985 firmware (the 32 KB "UniDisk 3.5" ROM) or later. The original 16 KB firmware drives one external 5.25-inch drive and nothing else[3] |
| Apple IIe, Apple II Plus | A Liron controller card. A Disk II controller will not do[2][1] |
| Apple IIGS | Native SmartPort support[1] |
| Apple IIc Plus | Native; the external port takes three 3.5-inch drives and two 5.25-inch drives[1] |
| Macintosh | Not supported. The mechanism is the same Sony 800 KB unit, but the Macintosh drives its floppy hardware directly and cannot talk to an intelligent drive[1] |
Format
edit| Parameter | Value |
|---|---|
| Capacity | 800 KB |
| Sides | Double-sided |
| Tracks | 80 per side |
| Encoding | GCR, with the rotation speed varying by track group |
| File system | ProDOS on the Apple II; the Macintosh 800 KB format is the same physical format |
Disks formatted on a UniDisk 3.5 and on an Apple 3.5 Drive are interchangeable, but each is slower reading the other's interleave.[1]
The successor: Apple 3.5 Drive
editThe Apple 3.5 Drive (A9M0106), introduced with the Apple IIGS in September 1986, is the same mechanism with the intelligence removed: no 65C02, no buffering, and the host does the work. That makes it cheaper and, on a machine fast enough to keep up, faster - 2:1 interleave against the UniDisk's 4:1. It works on the Apple IIGS and the Macintosh, but not on the Apple IIe or the original Apple IIc.[1]
Apple's published figures for that drive give a sense of what the mechanism itself does:[4]
- Track-to-track seek 6 ms maximum, settle 30 ms maximum, startup 600 ms maximum
- Head position accuracy ±0.035 mm
- 800 KB formatted, 1,246 KB unformatted
- +12 V at 120 mA typical, rising to 600 mA during eject for up to 2 seconds; +5 V at 360 mA typical
- Operating temperature 5 to 50 °C
Those are the Apple 3.5 Drive's numbers. Apple did not publish an equivalent specification sheet for the UniDisk 3.5, and the UniDisk's own electronics draw more, so do not apply the current figures to it.
Maintenance
editHeads
editClean the heads with a proper 3.5-inch cleaning disk, or with isopropyl alcohol on a lint-free swab with the drive opened and unpowered. Both surfaces have a head; clean both.
The eject mechanism
editThe commonest mechanical fault on any Sony 800 KB mechanism is the eject and loading gear becoming stiff with old grease. Clean the old grease out completely and regrease with a light plastic-safe grease. See Floppy Drive Repair for the general procedure.
Firmware
editThe 8 KB ROM is a mask-programmed A2M2053-V1.0.[2] Replacements are scarce. A drive whose intelligence has failed can be converted to a "dumb" drive for Macintosh use, which destroys its value as a UniDisk but keeps a working mechanism in service.
Common faults
edit| Symptom | Likely cause | What to do |
|---|---|---|
| Not recognised at all | Host does not support SmartPort | Check the firmware revision on a IIc, or that a IIe has a Liron card |
| Not recognised in a chain | Wrong chain order | A Disk II must be last in the chain[2] |
| Read errors | Dirty or worn heads, or degraded media | Clean the heads; try a known-good disk |
| Disk will not eject, or grinds | Hardened grease in the eject mechanism | Strip, clean and regrease |
| Slow compared with a IIGS with an Apple 3.5 | Normal | 4:1 interleave against 2:1[1] |
Identification
edit- A2M2053 on the label
- 19-pin D-sub disk connector with a pass-through for daisy-chaining
- Manual eject button
- Case colour matching the Apple IIc rather than the later platinum
An Apple 3.5 Drive (A9M0106) looks similar but has no internal processor; if a drive is being sold as a UniDisk, the model number on the label is the thing to check.
Apple's own parts list for this drive
editApple published an Illustrated Parts List for the UniDisk as Section 4 of its UniDisk Technical Procedures, which is held here inside the Service Support Training Programs binder described at Service Support Tranning Programs Laserwriter Technical Procedures Jan 1985.[5] Apple's part numbers, as printed:
| Part | Number |
|---|---|
| Analog card, UniDisk | 661-0287 |
| Uni/DuoDisk disk mechanism assembly | 661-72128 |
| Assembly, cable, LED, D1 | 590-0140 |
| Assembly, cable, drive to CPU | 590-0327 |
| Sub-bezel, Uni/DuoDisk | 970-1258 |
| Shield, bottom | 805-0890 |
| Shield, top | 805-0891 |
| Subassembly, bottom cover | 675-5101 |
| Top case assembly | 675-5103 |
| Label, drive number, Uni/DuoDisk | 825-0548 |
| Spring | 870-0023 |
| Load button | U815-0064 |
The same binder carries the DuoDisk Analog Card Chip Swapping Chart, which is component-level and applies to the closely related DuoDisk analogue card. Apple's warning there is worth carrying across to this drive as well: inspect the card for melted or broken components before changing anything, because a card connected to a computer with the power on typically shows "fuzz" and an exploded capacitor.[5]
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 1.11 Steven Weyhrich, Apple II History, Chapter 9, "The Apple IIc Plus", apple2history.org, sections "The UniDisk 3.5 and Apple 3.5" and "Advances in Apple II disk storage". The September 1985 release; the order of Apple's four 3.5-inch drives (400K Mac drive, 800K UniDisk 3.5, 800K Mac drive, Apple 3.5); the intelligent-drive design with its own 65C02 and buffer memory, and why the 1 MHz 6502 needed it; the variable-speed modification to Sony's design that gains the extra 80K over 720K; the Apple 3.5's removal of the processor and its 2:1 interleave against the UniDisk's 4:1; the statement that the Apple 3.5 worked on the Apple IIGS and the Macintosh but not on the IIe and the original IIc; the IIc Plus disk port supporting three external 3.5-inch drives and two 5.25-inch drives.
- ↑ 2.0 2.1 2.2 2.3 2.4 2.5 2.6 2.7 Riccardo Greco, UniDisk 3.5 Apple II co-processor in Merlin Assembler, github.com/rigreco/UniDisk. This is a community project, not an Apple publication. It documents the UniDisk 3.5 board's devices and their markings (GTE G65SC02P-2 65C02 at 2.0 MHz in PDIP40; Hitachi HM6116LP-2 2 KB 120 ns static RAM in PDIP24; A2M2053-V1.0 / TC5365P-8718 8 KB 250 ns ROM in PDIP28; VLI VF4060-001 / 344-0041-B IWM in PDIP28), the 527 bytes of gate-array I/O locations and 15 bytes of IWM registers in the memory map, the authorship of the firmware (Michael Askins) and the Liron design team, and the rule that a Disk II in a Protocol Converter daisy chain must be the terminal device and stays dormant while a bus resident is addressed.
- ↑ 3.0 3.1 3.2 Steven Weyhrich, Apple II History, Chapter 8, "The Apple IIc", apple2history.org. The UniDisk 3.5 firmware upgrade for the IIc in November 1985, the move from a 16K to a bank-switched 32K ROM, and the resulting support for four 3.5-inch drives, or three 3.5-inch drives and one 5.25-inch drive.
- ↑ Apple 3.5 Drive Service Source, Apple Computer, Inc. - hosted on this wiki at Apple 3.5 Drive Service Source. Specifications chapter: 80 tracks per inch and two recording surfaces; track-to-track seek time 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 capacity 1,246K; electrical figures for +12 V (10 µA standby, 120 mA typical, 600 mA peak during eject only for a maximum of 2 seconds) and +5 V (10 mA standby, 360 mA typical); operating temperature 5 to 50 °C; size 51 × 120 × 200 mm and weight 1.3 kg. These are the Apple 3.5 Drive's figures, not the UniDisk 3.5's.
- ↑ 5.0 5.1 Apple Computer, Apple LaserWriter Printer Technical Procedures, preliminary version for internal use only, sections stamped rev. Jan 85 and rev. Feb 85. Held on this wiki inside the Service Support Training Programs binder scan, described at Service Support Tranning Programs Laserwriter Technical Procedures Jan 1985 (File:Service_Support_Tranning_Programs_Laserwriter_Technical_Procedures_Jan_1985.pdf).