Commodore 128D and 128DCR

The Commodore 128D and the Commodore 128DCR are two desktop forms of the Commodore 128 in which the computer board, a mains power supply and a 5¼-inch disk drive share one system unit, with the keyboard on a cable. Archive descriptions of the power-supply and drive schematics treat the first as a plastic-cased machine and the second as a metal-cased machine whose floppy controller sits on the main board. In North America, Commodore's service literature and the press both called the metal machine the 128D, so the printed model name does not by itself tell the two designs apart.

Naming

Neither of the North American owner's guides examined for this article uses the designation "C128DCR". The November 1987 service manual files its integrated-drive material under "C128D", and its major parts list labels the assembly as an NTSC C128D, yet the same section identifies the board as assembly 250477 and the board drawing carries a C128DCR marking. A German service binder held by the Internet Archive uses C128DCR on its cover, which shows that the longer name also appeared in Commodore-related service paperwork outside the United States.

Later archive descriptions draw the line by case material and board design rather than by printed label. The zimmers.net power-supply index files two internal supply diagrams under "128D (plastic case)" and three under "128DCR (metal case)". Its 1571 page gives the 128DCR's drive electronics a name of their own, 1571CR, and places them on that machine's motherboard; the 128D, by the same page, has a built-in 1571. This article follows that usage: "C128D" means the plastic-cased design unless a source says otherwise, and "C128DCR" means the metal-cased design with the integrated controller, even where a period source calls it a 128D.

Chronology

No Commodore press release or dated announcement for either model was located for this article, so the dates below come from documents and reviews rather than from launch records. They show when each design was documented or on sale in a given territory, not when it was first announced.

• West Germany, 1985. The German service binder includes a parts list for a "C 128 D" power supply whose circuit is dated 22 September 1985. Its reference number matches the German version of the plastic-case 128D supply in the zimmers.net power-supply index.
• Australia, March 1986. The March 1986 newsletter of the Commodore Computer Users Group in Queensland printed a hands-on review of the 128-D, announced a club demonstration of it for 1 April 1986, and carried a dealer notice that offered the machine as new.
• Finland, undated. A Finnish-language brochure from Oy PCI-Data Ab, which describes itself as Commodore's authorised importer for Finland, gives specifications for the 128 D but carries no date.
• United States, 1987. Commodore's English-language introductory guide for the C128D carries a 1987 copyright and an FCC compliance notice, and it tells owners to set a channel-3 or channel-4 selector for a television display. The November 1987 service manual (part number 314001-08) documents the 250477 board under the C128D name.
• United States, 1988. A Howard W. Sams Computerfacts service folder for "Model C128D", copyrighted 1988, covers a unit with the 5710 controller. In May 1988 Compute! reviewed a metal-cased 128D that it said had reached the US more than two years after its European introduction, and it presented the machine as the successor to the flat 128 in Commodore's American range. Commodore's October 1988 diagnostic manual names the 1571 and the C128D together in its title and treats the C128D internal drive as a test subject.

These records leave gaps. The Compute! remark about a European debut more than two years earlier refers to a 128D without saying which case it had, and none of the sources examined dates the move from the plastic case to the metal one in Europe. No source examined documents a plastic-case model on sale in the United States.

C128D (plastic case)

Evidence for the plastic-case model is scattered. The power-supply archive confirms the material and lists German and Japanese versions of its internal switching supply. A hands-on account of the unit as a whole comes from the Australian user-group review of March 1986. It does not name the case material, so linking it to the plastic design depends on its date, which is roughly two years before the metal machine is documented in the US.

The review notes a separate reset switch for the drive, provided because a single on/off switch serves both computer and drive. The separate keyboard plugs into the cabinet's right-hand flank through a multi-pin connector; its lead was one of the reviewer's two complaints, and the reviewer wanted it 20 to 30 cm longer. Two features make the machine portable, according to the review: a handle at the cabinet's left end that stows away when unused, and clips that hold the keyboard beneath the cabinet. Processor board, 1571 drive and power supply all sit in the cabinet, and the reviewer put the unit's weight down to the power supply. A built-in fan provides cooling; the reviewer called it "a bit noisy, but not too bad". A monitor can stand on top. The second complaint, about the drive's device number, is covered below.

The German owner's handbook for the 128 and 128D lists the 128 D's features as a keyboard with a 14-key numeric block and an integrated 5¼-inch double-sided drive. The Finnish importer's brochure gives a 92-key keyboard with 14 numeric keys and eight programmable function keys, and it lists a key that switches between a Scandinavian layout and ASCII. The same brochure gives overall dimensions of 430 × 405 × 100 mm and a weight of 9,240 g. Neither publication is dated or names the case material, so their figures cannot be assigned to one design with certainty.

Board-level classification for this generation, including which main board it shares with other C128 models, is covered in Commodore 128 board profiles.

C128DCR (metal case)

In May 1988 Compute! described the US machine as having its electronics, mains supply and internal 1571 inside a metal cabinet, with a keyboard that unplugs. The reviewer reported that the keyboard keeps the flat 128's layout with a lighter action, also found its cable too short, and noted that the slim case can serve as a monitor stand. According to the magazine, metal construction gave both RF shielding and protection against spilled drinks.

Commodore's 1987 guide for the same market calls the cabinet light tan and the keyboard removable. Its right-hand flank, according to the guide, carries the keyboard and cassette sockets, both joystick ports, and two reset buttons, one for the whole system and one for the drive alone. The expansion port, serial socket, composite video and RF outputs are on the back, together with the power socket and power switch, and the mains lead ends in a three-pronged plug. The guide names neither the case material nor the board, so applying its layout to the metal design rests on the US documentation trail described above rather than on an explicit statement.

Sourced differences from the C128D

• Enclosure. The archive power-supply index labels the 128D as plastic-cased and the 128DCR as metal-cased. Compute! confirms a metal case for the US machine.
• Drive integration. In the 128DCR the drive electronics, called the 1571CR by zimmers.net, are built into the motherboard, and the archive's 1571 page excludes them from its standalone 1571 schematic; for the plastic 128D's built-in 1571, the same page says the schematic is partly applicable. The service manual's C128D section lists computer and drive-controller components on one board assembly.
• Power supply. The power-supply index lists separate internal switching-supply designs for each model: German and Japanese versions for the plastic 128D, and a US version plus two other versions for the metal 128DCR. The service manual's parts list offers supplies from two vendors for the NTSC C128D.

Compute! also reported 64 KB of dedicated 80-column video RAM in the US 128D, against 16 KB in the flat 128. The service manual's component list for the 250477 assembly includes an 8568 CRT controller. No source examined gives the plastic 128D's figure, so video memory is not listed above as a difference between the two designs.

The sources do not show whether the metal model kept the carrying handle and under-case keyboard storage described for the 1986 unit. Neither the 1988 review nor the 1987 guide mentions either feature, but neither says they were removed. Board-level detail of the 250477 assembly belongs to the board-profiles article linked above. The computer's 64, 128 and CP/M modes, which Compute! found to work as on the flat 128, are described in Commodore 128 operating modes.

Drive and controller arrangements

By model

For the plastic C128D, zimmers.net describes a built-in 1571 that its standalone 1571 schematic covers only partly. The 1986 Cursor review, linked to the plastic design by its date as explained above, also names a 1571 inside the unit. None of the sources examined gives a component-level parts list for this drive.

For the C128DCR, the controller is part of the main board. The zimmers.net parts list, which the archive's index identifies as covering the 1571CR (C128DCR) although the file heads that section "C128D Parts", gives the drive section a 6502A processor, two 65C22 interface chips, a 64H156 gate array, a MOS 5710 combined floppy controller and gate array, 2 KB of static RAM, an MC2871A read/write amplifier and a Newtronics D502 mechanism. The standalone 1571 list instead gives a WD1770 or WD1772 floppy controller and a separate 6526A or 8520 CIA. A companion memory map shows the DCR's 5710 taking over the register area of the WD1770; within the address range the standalone drive gives its 6526 CIA, the map places a small 5710 block labelled as a CIA serial port, followed by a second 5710 controller block. The service manual's component list for the 250477 assembly also includes the 5710 and 6522-family parts.

Recording formats

Commodore's C128D System Guide explains that native Commodore DOS disks use group code recording (GCR) and that CP/M disks normally use modified frequency modulation (MFM). By its account, the 128D's internal drive reads disks in both, while the Commodore 1541 is limited to GCR. The guide lists MFM layouts that the 1571 can read, including Epson QX-1, single- and double-sided IBM CP/M-86 formats with eight or nine sectors per track, Kaypro II and IV, and single- and double-sided Osborne formats. It adds that CP/M-86 data files can be read even though CP/M-86 programs cannot run on the Z80.

The guide also explains how CP/M identifies a foreign disk. Recognition is based on how many bytes each sector holds and how many sectors a track contains. When that combination fits several known layouts, CP/M asks the user to pick one from a window, and the choice can be fixed so that later accesses skip the prompt. The wider CP/M environment belongs to the operating-modes article and is not repeated here.

The Finnish brochure gives separate GCR figures for single-sided and double-sided disks: 35 tracks and 174,848 formatted bytes on one side, and 70 tracks and 349,696 bytes on two. It also lists MFM sector sizes from 128 to 1,024 bytes. The German handbook instead gives a formatted capacity of 336 KB, double-density MFM support for CP/M, compatibility with the 1541, and a serial transfer rate of up to 5,200 characters per second. The capacity figures do not match, and neither source explains how its figure was calculated.

Device number, reset and servicing

The 1987 guide gives the internal drive device number 8 and asks owners of extra drives on the rear serial port to set them to 9, 10 or 11. Its separate drive reset button restarts only the drive, leaving the computer running. Both reviews counted the lack of external DIP switches for the internal drive's device number among its drawbacks. The Cursor review likens the drive to the 1541, whose number is also set internally, and calls that route "an option I would not normally recommend". The stand-alone 1571 does have external switches, as Compute! pointed out, and its reviewer questioned Commodore's choice of a permanent device 8 for the internal drive, writing that "users with a 128D and a 1581 drive may not see things that way". The Sams service folder for the C128D with the 5710 controller shows how the number can be changed inside the case: two jumper pads beside one of the drive interface chips are shorted or cut to select addresses 8 to 11. The Finnish brochure says the address can be changed either in software or in hardware.

Commodore's 1988 diagnostic disk supports both the standalone 1571 and the C128D internal drive. It includes separate soft-error tests for GCR and MFM recording, as well as C128D versions of the 80-column, C64-mode and RAM-expander tests. In the guide's loading procedure, the user pulls the drive's front lever down after inserting a disk.

See also

• Commodore 64
• Commodore 64 and 128 periodicals
• C64 and C128 manuals as documentary sources
• Commodore C64 and C128 input and output peripherals

Automation and sourcing note

This article was independently synthesized from the cited sources under c64.wiki publication policy. Historical manuals and source archives were used as citation-only factual evidence; no source prose, code, images, scans, or screenshots were copied into the candidate.