Apple UniDisk 3.5
| Apple UniDisk 3.5 | |
|---|---|
 |
|
| Apple UniDisk 3.5 | |
| Manufacturer | Apple Computer, Inc. |
| Type | 3.5-inch floppy disk drive |
| Release date | September 1985 |
| Interface | 19-pin D-sub disk port (SmartPort) |
| Compatible | Apple IIc (UniDisk 3.5 ROM or later), Apple IIc Plus, Apple IIGS; Apple IIe and Apple II Plus with the UniDisk 3.5 interface card or, on the IIe, the Apple II 3.5 Disk Controller Card |
| Dimensions | 200 × 120 × 51 mm |
| Weight | 1.2 kg |
| Successor | Apple 3.5 Drive |
| Model | A2M2053 |
| Power | Supplied by the host computer's disk port |
| Storage | 800K, double-sided |
The Apple UniDisk 3.5 (model A2M2053) is Apple's first 800K 3.5-inch floppy drive for the Apple II, released in September 1985.[1][2] It uses a Sony 800K mechanism, but it is an intelligent drive: a 65C02 controller inside the case reads and writes the disk and exchanges data with the host in packets over the SmartPort protocol. The 1 MHz 6502 in the Apple II could not take raw data off the mechanism and decode it fast enough, so Apple put that work inside the drive.[1][3] The same design is why it does not work on a Macintosh, which drives its floppy mechanism directly.[1]
Specifications
Apple's Tech Info Library specification sheet for the drive gives these figures.[4]
| Item | Value |
|---|---|
| Media | 3.5-inch disk, certified double-sided, 2 recording surfaces, 80 tracks per surface |
| Capacity | 800K formatted, 1,246K unformatted |
| Seek time (track to track) | 6 ms maximum |
| Settle time | 30 ms maximum |
| Drive motor start time | 600 ms maximum |
| Transfer rate | 500 kbit/s |
| Eject time | 2 s maximum |
| +12 V | 10 µA standby, 120 mA typical, 600 mA peak during eject |
| +5 V | 170 mA standby, 360 mA typical |
| Head position tolerance | ±0.035 mm |
| Operating temperature | 5 to 50 °C (40 to 120 °F) |
| Non-operating temperature | −40 to 60 °C |
| Humidity | 5 to 90%, maximum wet bulb 29 °C, no condensation |
| Size (L × W × H) | 200 × 120 × 51 mm (7.87 × 4.72 × 2.01 in) |
The owner's manual gives the height as 57 mm (2.2 in) and the weight as 1.2 kg (2.6 lb), and says the drive takes all its power from the computer.[5] The mechanism figures match those Apple later published for the Apple 3.5 Drive; the difference is the +5 V standby current, 170 mA for the UniDisk 3.5 against 10 mA for the Apple 3.5 Drive.[4][6]
Inside the drive
Apple documents the controller at the programming level. Code downloaded into the UniDisk controller runs at slightly under 2 MHz with regular cycle times, and the IWM disk controller's registers sit in the controller's own memory map from $0A00. There is spare controller RAM for custom read, write and ID routines, which the host can download and run through SmartPort. Over SmartPort the drive reports device type $01 and subtype $00; the Apple 3.5 Drive reports $01 and $C0.[3]
A community project that uses the UniDisk as a co-processor lists the chips on the controller board:[7]
| Function | Part |
|---|---|
| Processor | GTE G65SC02P-2 (65C02), PDIP40 |
| RAM | Hitachi HM6116LP-2, 2K static, 120 ns, PDIP24 |
| ROM | A2M2053-V1.0 (TC5365P-8718), 8K, 250 ns, PDIP28 |
| Disk controller | IWM, VLI VF4060-001 / 344-0041-B, PDIP28 |
The same project records that the firmware was written by Michael Askins, who also wrote the software for the "Liron" UniDisk 3.5 interface card.[7]
Hosts and connection
The 19-pin disk port carries Apple's Protocol Converter protocol, later called SmartPort, which lets several intelligent devices share one daisy chain.[8]
| Host | Requirement |
|---|---|
| Apple IIc | The UniDisk 3.5 ROM, introduced in November 1985 and offered free to earlier owners.[8] Apple's test: type PR#7 in BASIC; "AppleTalk Offline" means the new ROM, while an attempt to start an external drive or "Check Disk Drive" means the old one. Machines with serial numbers below F6051GFA2S4000 need the upgrade.[9] The owner's manual allows two UniDisk 3.5 drives, or one UniDisk 3.5 and a Disk IIc.[5]
|
| Apple IIe, Apple II Plus | The UniDisk 3.5 interface card from the accessory kit, which supports two drives; more drives need a second card. A II Plus also needs a two-part connector retaining clamp, service part 655-8112.[5] From 1991 the IIe could use the Apple II 3.5 Disk Controller Card instead.[10] |
| Apple IIGS | Built-in SmartPort. The Apple II 3.5 Disk Controller Card does not support the UniDisk 3.5 under GS/OS; connect it to the built-in port, and do not put the card in slot 5, which is linked to that port.[10] |
| Apple IIc Plus | Built-in; the external port takes UniDisk 3.5, Apple 3.5 and Apple 5.25 drives in any mixture, up to three 3.5-inch and two 5.25-inch drives.[1] |
| Macintosh | Not supported.[1] |
Chain order matters. On a Protocol Converter chain a Disk II is optional and "must be the terminal member of the daisy chain".[7] On an Apple II 3.5 Disk Controller Card, a UniDisk 3.5 chained with a different drive model must be the last drive, plugged into the first drive rather than into the card.[10]
Disk format
The UniDisk 3.5 uses Apple's variable-speed recording, which gains 80K over the 720K otherwise available.[1] Apple describes its format as essentially the Macintosh format, with three differences: Macintosh blocks are 524 bytes and UniDisk blocks 512; Macintosh MFS disks are single-sided; and the Macintosh uses a 2:1 physical interleave where the UniDisk 3.5 uses 4:1. Macintosh blocks can be read through SmartPort with the character READ call.[11] Disks formatted on a UniDisk 3.5 and on an Apple 3.5 Drive work in either, but each is slower with the other's interleave.[1] The UniDisk 3.5 and Apple 3.5 Drive cannot use 1.4 MB high-density disks; only the SuperDrive can.[12]
The Apple 3.5 Drive
The Apple 3.5 Drive (A9M0106) came with the Apple IIGS in September 1986. It is the same 800K mechanism without the UniDisk's 65C02 and buffer: the host computer controls the drive directly.[1][2][3]
Which Apple II models it works on depends on the date of the source. Apple's 1995 Service Source for the drive lists direct connection to the Apple IIGS, "Apple IIe and IIe Plus" and "Apple IIc", alongside the Macintosh 512K enhanced and later Macintosh models.[6] The IIe has no disk port of its own: Apple's 1991 controller card guide says a IIe needs the Apple II 3.5 Disk Controller Card to use the Apple 3.5 Drive, the SuperDrive or the UniDisk 3.5.[10] The IIc Plus accepts the Apple 3.5 Drive on its external port and uses the same mechanism internally.[1] Weyhrich, citing a 1987 Call-A.P.P.L.E. article, says that at the time the Apple 3.5 Drive worked on the IIGS and the Macintosh but not on the IIe or the original IIc.[1]
Identification
Apple identifies each drive type on its underside, and the UniDisk 3.5 by its white case, where the Apple 3.5 Drive and SuperDrive are platinum grey.[10] The front has the disk slot, an eject button, a red "in use" light and a small access hole for ejecting a disk by hand.[5]
Faults and things that are not faults
- The eject button works only when the computer is on and the in-use light is off. Apple designed it that way to prevent data loss. With the power off, eject a disk by pushing a straightened paper clip gently into the access hole to the right of the slot.[5]
- A UniDisk 3.5 that is not recognised on a IIc usually means the machine still has the original ROM; check it with
PR#7as above.[9] - Early UniDisk 3.5 drives could misidentify write-protected disks; the Memory Expansion IIc ROM fixed this on the IIc.[8]
- Slow transfers compared with an Apple 3.5 Drive on a IIGS are normal: the UniDisk 3.5 uses a 4:1 interleave.[1]
- Apple warns that the drive can be seriously damaged if it is dropped, jarred, or plugged in or unplugged while the computer is on. Switch the computer off and unplug it before connecting or disconnecting a drive.[5]
Apple's owner-level troubleshooting stops at checking the cable, the power, the disk and the software.[5] For mechanism repair (cleaning, lubrication, eject faults) see Floppy Drive Repair.
Documentation
- UniDisk 3.5 Owner's Manual (030-1151-A): installation on the IIc, IIe and II Plus, use and care.
- Tech Info Library 1307: specifications and supported configurations.
- Technical Note UniDisk 3.5 #4 and #5: disk format and the differences from the Apple 3.5 Drive.
- Apple II 3.5 Disk Controller Card Owner's Guide (030-5717-A).
- Apple 3.5 Drive Service Source: Apple's service manual for the Apple 3.5 Drive.
- Apple II 3.5 Disk Controller Card Owner's Guide
- Apple II UniDisk 3.5 Owner's Manual
- Apple II Technical Note UniDisk 3.5 4: Accessing Macintosh Disks
- Apple II Technical Note UniDisk 3.5 5: Architectural Differences Between 3.5" Drives
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 Steven Weyhrich, Apple II History, Chapter 9, "Disk Evolution / The Apple IIc Plus", apple2history.org, sections "The UniDisk 3.5 and Apple 3.5" and "The Apple IIc Plus". September 1985 release; Sony-based double-sided 800K drive with Apple's variable-speed modification (an extra 80K over 720K); intelligent drive with its own 65C02 and buffer memory because the 1 MHz 6502 could not keep up; 4:1 interleave against the Apple 3.5 Drive's 2:1; disks usable in either drive but slower on the other; the Apple 3.5 Drive of September 1986 with the processor removed; the IIc Plus disk port taking UniDisk 3.5, Apple 3.5 and Apple 5.25 drives.
- ↑ 2.0 2.1 "Macintosh External Disk Drive", Wikipedia, section "Apple UniDisk 3.5" (model number A2M2053) and "Apple 3.5 Drive" (A9M0106), en.wikipedia.org, retrieved 30 September 2026.
- ↑ 3.0 3.1 3.2 Apple Computer, Apple II Technical Notes, UniDisk 3.5 #5, "Architectural Differences Between 3.5" Drives", Cameron Birse and Mike Askins, October 1986, revised November 1988, pp. 1-2. Hosted as File:Apple II Technical Note UniDisk 3.5 5 Architectural Differences.pdf.
- ↑ 4.0 4.1 Apple Computer, Tech Info Library article 1307, "Apple UniDisk 3.5: Specifications (Discontinued)", created 27 September 1985, revised 13 September 1993. Hosted as File:Apple Tech Info Library 1307 UniDisk 3.5 Specifications.pdf.
- ↑ 5.0 5.1 5.2 5.3 5.4 5.5 5.6 Apple Computer, UniDisk 3.5 Owner's Manual, 030-1151-A, 1985. Hosted as File:Apple II UniDisk 3.5 Owners Manual 1985.pdf.
- ↑ 6.0 6.1 Apple Computer, Apple 3.5 Drive (Service Source), 1995, Specifications, pp. 1-6. Hosted as File:Apple 3.5 drive.pdf; see Apple 3.5 Drive Service Source.
- ↑ 7.0 7.1 7.2 Riccardo Greco, UniDisk 3.5 Apple II co-processor in Merlin Assembler, github.com/rigreco/UniDisk (community project, not an Apple publication). Chip markings, the 527 bytes of gate-array I/O and 15 bytes of IWM registers in the memory map, Michael Askins as author of the firmware and of the Liron card software, and the Protocol Converter daisy-chain rules.
- ↑ 8.0 8.1 8.2 Steven Weyhrich, Apple II History, Chapter 8, "The Apple IIc", apple2history.org. The UniDisk 3.5 ROM upgrade of November 1985 (16K to bank-switched 32K ROM; four 3.5-inch drives, or three 3.5-inch and one 5.25-inch; "AppleTalk Offline" on PR#7), and the later Memory Expansion IIc ROM fixing the misidentification of write-protected disks on early UniDisk 3.5 drives.
- ↑ 9.0 9.1 Apple Computer, Tech Info Library article 10098, "Apple IIc: How to Determine If It Needs ROM Upgrade for UniDisk", 14 April 1992, archive.org.
- ↑ 10.0 10.1 10.2 10.3 10.4 Apple Computer, Apple II 3.5 Disk Controller Card Owner's Guide, 030-5717-A, 1991, Chapter 1 "Overview", p. 2, and Chapter 4 "Special rules for UniDisk 3.5 drives", p. 30. Hosted as File:Apple II 3.5 Disk Controller Card Owners Guide 1991.pdf.
- ↑ Apple Computer, Apple II Technical Notes, UniDisk 3.5 #4, "Accessing Macintosh Disks", Mike Askins, May 1985, revised November 1988, p. 1. Hosted as File:Apple II Technical Note UniDisk 3.5 4 Accessing Macintosh Disks.pdf.
- ↑ Apple Computer, Apple II 3.5 Disk Controller Card Owner's Guide, 030-5717-A, 1991, Chapter 4, "Special rules for SuperDrives", pp. 28-29. Hosted as File:Apple II 3.5 Disk Controller Card Owners Guide 1991.pdf.