Amstrad CPC 664

Amstrad CPC 664

Amstrad CPC 664 with the CTM-644 colour monitor
Specifications
Developer	Amstrad
Manufacturer	Amstrad
Type	Home computer
Released	April 1985
Discontinued	August 1985 (~6 months on the market)
Intro price	£339 monochrome (GT-64/65) / £449 colour (CTM-644)
CPU	Zilog Z80A @ 4 MHz
Memory	64 KB RAM + 32 KB ROM (OS v2 + Locomotive BASIC 1.1) on the main board, 16 KB AMSDOS ROM on the disc-controller daughter
Storage	One built-in Hitachi-mechanism 3-inch single-sided floppy drive, 178 KB per side
Display	RGB and luminance + sync video (6-pin DIN); 27-colour palette, three modes (160×200×16, 320×200×4, 640×200×2)
Sound	General Instrument AY-3-8912 (3 channels + noise)
OS / Firmware	Amstrad Firmware v2 + Locomotive BASIC 1.1 + AMSDOS / CP/M 2.2
Predecessor	Amstrad CPC 464
Successor	Amstrad CPC 6128
Model no.	664

The Amstrad CPC 664 (also branded Schneider CPC 664 in West Germany, Switzerland and Austria) is the second computer in the CPC line. It was announced in April 1985 and replaced the Amstrad CPC 464's integrated cassette deck with a built-in Hitachi-mechanism 3-inch single-sided floppy drive, and upgraded the operating system to firmware v2 with Locomotive BASIC 1.1 and the AMSDOS disc operating system in a separate 16 KB ROM. The Z80A CPU, the 64 KB system RAM, the AY-3-8912 sound chip, the 6845 CRTC and the Gate Array are otherwise unchanged from the CPC 464.

The CPC 664 had an unusually short production life: it was replaced after only six months on the market by the Amstrad CPC 6128, which doubled the RAM to 128 KB and changed the case mouldings. Total production was small — survivors are scarcer than either the 464 or the 6128.

History

By late 1984 the CPC 464 was selling strongly in the UK, France, West Germany and Spain, but the integrated cassette deck was a serious limitation for business and education uses where the AMSOFT / Locomotive Software business titles (e.g. Tasword 464, AMSCALC, AMSWORD) needed floppy storage to be practical. The external Amstrad DDI-1 disc interface had been offered since November 1984, but it added a separate box, a 22-pin floppy ribbon, and a second power adapter.

The CPC 664 was Amstrad's response: a single all-in-one case with the cassette deck physically replaced by a Hitachi 3-inch drive mechanism, the disc interface electronics moved onto the main PCB (instead of being on a separate DDI-1 unit), and the OS extended with built-in AMSDOS support. The original list price (April 1985) was £339 with a GT-64 / GT-65 green monochrome monitor and £449 with the CTM-644 colour monitor — a £90 premium over the equivalent CPC 464.

In August 1985 Amstrad announced the CPC 6128, which doubled the RAM to 128 KB and used a more compact case in the European style. The CPC 6128 was sold concurrently with the CPC 664 for a short period before the 664 was discontinued. As a result the CPC 664 was only on the market for approximately six months and remains the rarest of the original three CPC machines.

Architecture

The CPC 664 shares its core architecture with the Amstrad CPC 464. The differences are concentrated around the floppy disc subsystem and the ROM map.

• CPU: Zilog Z80A at 4 MHz. The main system clock is generated by the Gate Array from a 16 MHz crystal (X101). Same chip as in the CPC 464.
• RAM: 64 KB organised as eight 64K×1 dynamic RAM chips (4164 / HM4864P-2 family) at the IC117–IC124 positions on the main PCB. Same as CPC 464. The upper 16 KB is also used as video RAM; the Gate Array multiplexes Z80 and video access. No bank-switching hardware — the 64 KB is the full main-RAM ceiling.
• ROM: 32 KB on the main PCB at IC103, holding Amstrad Firmware v2 (16 KB OS) and Locomotive BASIC 1.1 (16 KB) in a single mask ROM (Amstrad part number 40012). The CPC 664 BASIC 1.1 is forwards-compatible with the CPC 464 BASIC 1.0 but adds the disc commands (LOAD"!", SAVE"!", CAT, ERA, REN, |DIR, |ERA, |REN, |USER and so on).
• Disc ROM: An additional 16 KB AMSDOS ROM (Amstrad part number 40015) is fitted at a separate socket on the disc-controller area of the main PCB. AMSDOS is the Amstrad implementation of disc I/O, providing the firmware that handles file system, directory, sector read/write and disc command operations through the | (bar) command extensions. Same AMSDOS ROM is used in the CPC 664 and the CPC 6128.
• Sound: General Instrument AY-3-8912 at IC102, clocked at 1 MHz from the Gate Array. 3 channels of square-wave + 1 channel of noise, programmable envelope. Same chip as in the CPC 464.
• CRT controller: 6845-family CRTC at IC108, clocked at 1 MHz. Most CPC 664s ship with the Type 0 HD6845SP CRTC, although some later units ship with Type 1 (UM6845R). See the CRTC type table on CPCWiki for the rare programming differences between types.
• PIO: Intel 8255A-5 (or M5L8255AP-5) at IC107 for keyboard input, AY-3-8912 control, cassette motor + printer strobe (the cassette interface is still wired through to the expansion port even though the deck itself is removed), and DIP switch reading.
• Gate Array: 40010 or 40007 (occasionally 40226 on later units). The Gate Array generates all system clocks, the video pixel pipeline, and the 8 KB Mode Lookup Table for the three video modes.
• Floppy disc controller: NEC uPD765A (or compatible NEC D765AC-2). Provides FM/MFM, single and double-density read/write, single-track support. The CPC 664 firmware uses MFM single-sided at 250 kbit/s, giving 178 KB per side on a 3-inch 40-track diskette.
• Floppy disc drive: Built-in Hitachi HD3 family 3-inch drive (typically HD3.5R-1 or compatible). 40 tracks, 9 sectors of 512 bytes per track, single-sided. The disc is the same Maxell / Amsoft / Panasonic 3-inch hard-shell media that became identified with Amstrad and was the only commercially successful application of the format.

The 664 main PCB silkscreen is part-number Z70200 / MC0030 (or similar by region). The PCB layout is electrically identical to the CPC 6128 main PCB except for the smaller RAM bank (8 chips instead of 16) and the absence of the RAM bank-switching logic at IC131.

Storage

The integrated 3-inch single-sided drive:

• Mechanism: Hitachi HD3.5R-1 or equivalent. Single-motor design with a rubber drive belt between the motor pulley and the drive spindle.
• Capacity: 178 KB per disc side, 40 tracks × 9 sectors × 512 bytes. Each diskette is flipped manually to access the second side ("flip side").
• Interface: Single-cable connection from the drive to the main PCB at the rear of the disc bay.
• Speed: 300 rpm.
• Data rate: 250 kbit/s MFM.
• Disc formats supported by AMSDOS: System format (178 KB, with reserved boot sector and CP/M 2.2 file system), Data format (178 KB, no boot sector), IBM format (160 KB, MS-DOS-style).
• Disc cost: Maxell, Amsoft and Panasonic were the principal manufacturers; new old-stock blank 3-inch discs remain available in 2025 from dedicated Amstrad / Spectrum +3 retailers, but at premium prices.

A second external 3-inch (or 3.5-inch) drive can be added through the expansion port using the standard CPC FDC chain — the Amstrad DDI-3 add-on or a third-party Dragonfly / Hxc / GoTek emulator.

Display

The CPC 664 uses the same video subsystem as the CPC 464. Output is on a 6-pin DIN connector at J101 with:

• Pin 1: Red
• Pin 2: Green
• Pin 3: Blue
• Pin 4: Sync (composite)
• Pin 5: GND
• Pin 6: Luminance (for the green GT-64 / GT-65 monitor)

Video modes:

• Mode 0: 160 × 200, 16 colours from the 27-colour palette. 20 columns of 8×8 text.
• Mode 1: 320 × 200, 4 colours. 40 columns of 8×8 text.
• Mode 2: 640 × 200, 2 colours. 80 columns of 8×8 text.

Refresh is 50 Hz interlaced (UK/EU PAL units) or 60 Hz (US/Japan NTSC units — rare). Vertical resolution is 200 lines doubled to 400 lines on the monitor for non-flickering display.

The CPC 664 supports light-pen input via the LPEN line on the expansion port (pin 47), but no light-pen was officially sold for the 664.

Keyboard

74 keys in QWERTY layout. Same key matrix as the CPC 464 with a slight cosmetic difference: the function keys on the right-hand side keypad are blue plastic on the 664 (vs grey on the 464). The "JOY 0" and "JOY 1" labels on the cursor cluster are also blue.

National variants: QWERTY (English), QWERTY (Spanish), QWERTY (Danish), AZERTY (French). Each is paired with a different firmware ROM (40012 English, 40037 Spanish, 40050 French) and a different keyboard membrane.

Audio

Same audio chain as the CPC 464:

• AY-3-8912 at IC102 generates three independent square-wave channels plus a noise generator.
• Mono internal speaker through IC301 (LA4140) with volume control VR301 (20 kΩ).
• Stereo line output on 3.5 mm jack J103, mixed from the three AY channels (left = A, centre = B, right = C is the most common wiring).

Connectors

• J101 (6-pin DIN female): RGB + sync + luminance. Power-supply output also routed through this DIN to the matching monitor on later units.
• J102 (DB-9 male): joystick. Compatible with Atari 9-pin joysticks. Includes Fire 3 on pin 5 (undocumented) and Joystick 2 ground on pin 9.
• J103 (3.5 mm stereo jack): line-level audio output.
• J104 (2.1 mm DC socket, centre positive): 5 V DC, 2 A system supply. On the 664 this also supplies the floppy drive logic. The drive's motor is separately powered through the same DC input.
• Printer port (34-pin PCB edge connector): Centronics parallel printer port, 7-bit data (D7 grounded), same as CPC 464.
• Expansion port (50-pin PCB edge connector): general-purpose system bus. The floppy drive is now internal so the expansion port no longer routes /EXP-FDC, but a second drive can be added through the expansion bus.

Power Supply

The CPC 664 system unit takes 5 V DC, 2 A on a 2.1 mm centre-positive jack at J104. This is supplied by the matching monitor:

• GT-64 / GT-65 green monitor: supplies 5 V/2 A and the +12 V driver for the cathode.
• CTM-644 colour monitor: supplies 5 V/2 A and additional rails for the colour CRT.

Unlike the CPC 464, the CPC 664 also needs +12 V at ≈0.6 A for the floppy drive motor and stepper. This is supplied through a separate pin on the modified DC cord, on units with a CTM-644; on GT-64/GT-65-only configurations, a dedicated 12 V supply was bundled. The exact pin assignment depends on the regional variant.

If using a third-party display, a stand-alone 5 V / 2 A + 12 V / 1 A dual-output PSU is required.

Submodels and Regional Variants

• Amstrad CPC 664 (UK) — QWERTY keyboard, English firmware (40012).
• Schneider CPC 664 (West Germany, Austria, Switzerland) — QWERTZ keyboard, German firmware. The Schneider brand was applied to all CPCs sold by Schneider Computer Division in the DACH region under a licensing agreement until 1988.
• Amstrad CPC 664 (Spain) — QWERTY keyboard, Spanish firmware (40037), Spanish manuals.
• Amstrad CPC 664 (France) — AZERTY keyboard, French firmware (40050), French manuals.

The 664 was not sold in the US.

General Maintenance

Floppy drive belt replacement, head cleaning, keyboard and PCB cleaning, contact maintenance, and the floppy mechanism stepper lubrication are documented in Amstrad CPC 664 Maintenance Guide.

Troubleshooting

Symptom-based diagnostic, FDC failure analysis, drive belt symptoms, common AMSDOS errors and the Gate Array / RAM / CRTC failure analysis are documented in Amstrad CPC 664 Troubleshooting Guide.

Capacitor Replacement

The CPC 664 main PCB inherits most of the Amstrad CPC 464 capacitor positions and adds a small number of new capacitors on the disc-controller area. Full list with values, designators and the AMSDOS-area additions is in Amstrad CPC 664 Capacitor Replacement Guide.

Gallery

• 
  Amstrad CPC 664 with CTM-644 colour monitor
• 
  CPC 664 system unit (close view of the floppy drive bay)
• 
  CPC 664 1985 catalogue product photo

Related Pages

• Amstrad CPC 664 Maintenance Guide
• Amstrad CPC 664 Troubleshooting Guide
• Amstrad CPC 664 Capacitor Replacement Guide
• Amstrad CPC 464 — predecessor
• Amstrad CPC 6128 — successor
• Amstrad CTM-644 colour monitor

Service Manual

The official Amstrad Service Manual for this machine is available on the wiki: Amstrad CPC 664 Service Manual.

References

• Amstrad CPC — Wikipedia. Reference for the CPC line chronology, the 6-month production lifetime of the 664, and the relationship between the 464, 664 and 6128.
• CPC old generation, CPCWiki. Source for the 664 release date (April 1985), the 6-month production window, the hardware differences from the 464 (built-in 3-inch floppy + 16 KB AMSDOS ROM), and the integration of AMSDOS into firmware v2.
• Amstrad CPC hardware documentation, Grimware. Source for the connector pinouts and the schematic-level architecture shared with the 464.
• CPC hardware revisions, CPCWiki / cpctech.org.uk. Reference for the Gate Array variants (40007 / 40010 / 40226) and the per-revision IC list.
• Amstrad CPC664 Service Manual (1985, Amstrad Consumer Electronics). Authoritative source for the disc controller area schematic, the disc drive parts list, drive alignment instructions and the electrical parts list (matches the CPC 464 main PCB for the non-disc areas).
• Amstrad noob — CPC 664 category. Field-experience source for the most-common drive belt and CRTC failure modes on the CPC 664.