Schneider CPC6128

Purely by chance, I have now also acquired another significant computer from the history of 8-bit computing—the Schneider CPC6128. I received it together with the “GT 65” green-screen monitor, an external 3-inch floppy disk drive, and a stack of 3-inch floppy disks. I was able to test the computer immediately—though not the external floppy drive, as the connecting cable to the CPC is missing.

History

The devices originated in England—where they were produced and distributed by the company Amstrad—while for Germany, the company Schneider handled the distribution. Incidentally, the abbreviation CPC stands for "Colour Personal Computer." The first model in the series was the Schneider CPC464, released in 1984 with 64 KB of memory. It featured an integrated cassette drive; the 3-inch floppy disk drive (FD1)—along with its controller (DDI1)—was available separately. In 1985, the machine was voted Computer of the Year.

In 1985, the CPC664 model was released, featuring a slightly improved keyboard as well as an internal 3-inch floppy disk drive. Shortly thereafter, its successor—the CPC6128 (also released in 1985)—hit the market. In addition to the integrated floppy drive, this model now boasted 128 KB of RAM (organized as 2 × 64 KB via bank switching).

The computer was usually sold as a bundle with a monitor—consequently, the CPC was very attractively priced. The C64 was more expensive, as both the floppy disk drive and a monitor always had to be purchased separately.

Technically, the Schneider (Amstrad) was state-of-the-art and could hold its own against the Commodore 64. In some respects, it was even superior—save for the lack of hardware support for sprites.

Technical Specifications

Inside, a 4 MHz *Zilog Z80A* is at work—though, due to the wait states that the *Gate Array* imposes on the processor during memory access, the effective speed is somewhat lower. A *Motorola 6845* (CRTC) handles the video output, working in conjunction with the Ferranti *Gate Array* characteristic of the CPC. The latter serves as the true heart of the computer, controlling video timing, mode switching, and memory access. Additionally, an *Intel 8255 PPI* is present to handle I/O tasks.

Three graphics modes are available:

• Mode 0: 160 × 200 pixels with 16 colors
• Mode 1: 320 × 200 pixels with 4 colors
• Mode 2: 640 × 200 pixels with 2 colors

The complete range comprises 27 colors.

Upon switching on the **CPC**, you land directly in *Locomotive Basic*, which is embedded in the ROM—specifically version 1.1 on the 6128 (the CPC464 still featured version 1.0). Thanks to the *Z80* processor used, the system also offered compatibility with the operating systems *CP/M 2.2* (64 KB) or *CP/M 3.0/Plus* (128 KB), which could be loaded via floppy disk. Incidentally, *AMSDOS*—supplied by Amstrad—is not a distinct operating system layer in its own right, but rather a floppy disk extension for Locomotive Basic.

The 3-inch floppy disk format

The 3-inch floppy disk format (CF-2), developed by Hitachi, never truly managed to gain widespread traction; due to its limited distribution, the price of the disks remained high—at the time, they cost between 7 and 20 DM. The disks themselves were double-sided and had a capacity of 360 kB (180 kB per side). Since the CPC computers were equipped with single-sided drives, the disks had to be physically flipped over in order to write to the second side.

Apart from the CPC models, the 3-inch format also appeared in the Sinclair ZX Spectrum +3 and the Schneider Joyce (Amstrad PCW)—meaning my collection includes several representatives of this idiosyncratic design. 🙂

Sound

Sound in the CPC is handled by an AY-3-8912 chip from General Instrument. The chip generates three tone channels plus a noise generator. The signal is output in mono via the built-in speaker; stereo output—featuring hard-wired panning (Channel A left, Channel B center, Channel C right)—is available only through the 3.5mm headphone jack.

Incidentally, Yamaha's *YM2149F*—which was built into the *Atari ST*—also hails from the same chip family; while both chips are closely related, they are not identical. The 8912 in the CPC, for instance, features only one I/O port, whereas the 8910 (or YM2149) has two.

Power Supply

The power supply of the CPC is implemented in an unusual manner. The computer itself features neither a built-in power supply unit nor a direct power connection. Instead, the monitor is utilized to provide power. To this end—taking the **GT65** as an example—two cables emerge: one serves as the connection for the monitor, while the other supplies the 5 volts required by the computer. The **CPC** itself is equipped with a cable that connects to the 12-volt input located on the front of the monitor.

As a result, it isn't quite so simple to connect the CPC to a TV using an RGB SCART cable, since the Schneider also needs to be supplied with power. 🙂

Incidentally, there were two lines of monitors: the green monochrome monitors GT64/GT65 and the color monitors CTM640/644. Anyone who wanted a color monitor had to dig significantly deeper into their pockets.

Market Performance and the End of the Model Series

Around 3 million CPCs were sold worldwide—a remarkable success. In 1990, the series came to an end with the Plus series (CPC 464Plus, CPC 6128Plus) and the dedicated game console, the Amstrad GX4000. Incidentally, I also have the GX4000 in my collection.

My Copy – The Typical Quirks

With my particular unit, I encountered a problem where no floppy disks could be read. Whenever I attempted to access the disks, I consistently received a "Bad Command" error. The disks themselves were in good working order (having been tested on a **Sinclair ZX Spectrum +3**), and the seller assured me that everything had been working fine on his end. My initial suspicion fell on the drive belt of the CPC's floppy drive; however, upon opening the computer, the belt appeared to be in excellent condition (it had likely been replaced previously). After examining the floppy drive more closely, I spotted a threaded "metal pin" connected to a guide mechanism leading to the read/write head. Because the guide had slipped out of its proper position within the threads, the read/write head was unable to move, resulting in the aforementioned error message. I believe this issue was caused by the shipping process. 🙂

After receiving a connection cable to link the FD-1 to my CPC, I unfortunately discovered that the drive was displaying nothing but read errors on the screen. So far, I haven't been able to repair the drive. I would be grateful for any tips—or for a helpful CPC specialist who might be able to fix it. 🙂

Since I had never worked with the Schneider CPC before, this is uncharted territory for me—and I will certainly dedicate an article to one or two of my experiences. 🙂