Amstrad PCW

Amstrad PCW

The Amstrad PCW series ("Personal Computer Word processor") was British company Amstrad's versatile line of home/personal microcomputers pitched as a complete, integrated home/office solution. It was first sold in 1985.

Some models were also affectionately known as "Joyce", especially in Germany; the name is that of a secretary of Alan Sugar, the founder of Amstrad, and was the codename of the machine while it was in development.

General features

The PCWs came as complete setups bundled with a full-size word processor keyboard, high resolution monochrome CRT monitor, printers of various types, and floppy disk drive(s). The motherboard and disk drives were incorporated into the casing of the monitor. Although it lacked a built-in operating system, the package included bootable floppy disks containing LocoScript word processing software, and the CP/M operating system, including the Mallard BASIC dialect of the BASIC programming language and the Digital Research implementation of Seymour Papert's LOGO programming language.The floppy disk drives on early models were the relatively obscure 3-inch 'compact floppy' format. Later models replaced these with standard 3½" 'microfloppy' drives. During the PCWs lifetime, many commercially-produced upgrades were available for the 3" disk models to add one or two 3.5" drives, either internally or externally. Often these were manually switchable to select which drives were 'A' and 'B'; some even had extra electronics that could do this automatically when the machine was switched on. It is also possible to fit a standard 3.5" floppy drive as a DIY upgrade; this however requires a number of modifications to the PCW's internal cabling and the external cabinet. Some modern PC floppy drives do not support the control signals that the PCW expects, and this can require extra circuitry or other methods to work around.

In order to allow a bundled printer to be included with every PCW, Amstrad devised a new, lower-level printer control protocol, placing the majority of the printer drive electronics inside the PCW cabinet. Instead of having a relatively sophisticated microcontroller inside the printer casing, the printer consisted only of electromechanical components and high current driver electronics; the power supply was fed from inside the PCW, and pin and motor drive signals were driven by a very small and simple microcontroller on the PCW mainboard. Most models of PCW were bundled with a 9-pin dot matrix printer mechanism, with the later 9512 and 9512+ models using a daisywheel (with a different cable; the printers were not interchangeable with the dot matrix models). These PCW printers could not, of course, be used on other computers, and the original PCW lacked a then-standard Centronics printer port. Instead, the Z80 bus and video signals were brought to an edge connector socket at the back of the cabinet. Many accessories including parallel and serial ports were produced for this interface. Some of the later models included a built-in parallel port; these could be bundled with either the dedicated Amstrad printer, or a Canon Bubblejet model.

The machines were built around the 8-bit Zilog Z80 processor, running at 4 MHz, and managed the relatively large amount of RAM main memory using a technique known as bank switching (allowing access to more than the Z80's normal 16-bit address bus reach of 64 kB). The PCW divided RAM into 16 kB sections, of which four could be accessed at any time. In CP/M, the memory used for the display was switched out while programs were running, giving more than 60 kB of usable RAM. While the Joyce architecture was designed with configurations of 128 kB and 256 kB of RAM in mind, no PCW was ever sold with 128 kB of RAM.

The PCWs were definitely not designed to play games, although some software authors considered this a minor detail, releasing games like "Batman", "Head Over Heels", and "Bounder". The PCW video system was not at all suited to games. In order that it be able to display a full 80 column page plus margins, the display's addressable area was 90 columns and the display had 32 lines. The display was, in fact, monochrome and bitmapped, giving a resolution of 720 by 256. Even with one bit per pixel, this occupied 23 kB of RAM, making software scrolling far too slow for fluid text manipulation. In order to improve this, the PCW implemented roller RAM, with a 512-byte area of RAM used to hold the address of each line of display data, effectively allowing very rapid scrolling. The video system also fetched data in a special order designed so that plotting a character eight scan lines high would touch eight contiguous addresses. This meant that very fast Z80 copy instructions like LDIR could be used. Unfortunately, it meant that drawing lines and other shapes could be very complicated.

The original PCW did not have ROM software. On boot, the onboard microcontroller normally used to run the integrated printer was connected to the data port of the main processor, feeding it instructions, allowing it to start running. This code had to be very small in order to fit into the limited ROM of the microcontroller, and as a consequence it has no character generation code; this is why the Amstrad PCW machines do not display text to indicate the loading of software from floppy disk. Instead, they display a bright screen which is progressively filled by black stripes as the code is loaded.

The PcW16 does not share any hardware with the original PCW series, other than the Z80 CPU, and should be considered to be a completely different machine.

PCW models

* The PCW8256 or "Joyce" (1985) featured 256 kilobytes of RAM and one 3-inch single-sided floppy drive that could store 180 kilobytes on each side of the disk (the disk had to be turned over, "flipped", to access alternate sides). The 8256 had a green screen monitor.
* The PCW8512 or "Joyce Plus" (1985) came with 512 kB RAM and two 3-inch floppy drives, the second of which could store 720 kB on an 80-track double-density floppy without needing the disk to be turned over.
* The PCW9512 (1987) was supplied with a daisy wheel printer instead of the 9-pin dot matrix of the 8000 series. It had a single 3-inch 720 kB floppy drive, and a white-screen monochrome display. The visual appearance was significantly changed. It came with a parallel printer port as standard.
* The PcW9256 (1991) had a modern, smaller case design similar to the 9512, but had 256 kB RAM, a single 3½-inch 720 kB floppy drive, a dot-matrix printer, and no parallel port.
* The PcW9512+ (1991) was a rework of the older PCW9512, with a 3.5" floppy instead of 3". As a deriative of the 9512, it retained the parallel port. It was offered with the choice of the PCW9512 daisywheel or Canon Bubblejet printer.
* The PcW10 (1993) was a 9256 with 512 kB RAM and a parallel port.
* The PcW16 or "Anne" (1996) was a radical departure from earlier machines. The Z80 CPU was retained, but ran at 16 MHz and had 1 MB of Flash RAM. The system supported 1.44 MB 3½-inch floppy disks, and came bundled with an entirely rewritten GUI software suite ("Rosanne") and a mouse. It did not, however, come with a printer, and nor did it run software designed for the earlier machines. (An implementation of CP/M was later developed for running certain text-based programs such as Mallard BASIC.)

Market impact

The PCW series was extremely successful in addressing its particular market. These machines were not sold as general-purpose computers but rather as simple word processors. They were not bought in preference to a PC or an Amiga; but rather in preference to an electric typewriter. The PCW screen displayed 32 lines with 90 characters each (256 lines of 720 pixels), so more text could appear on a single screen simultaneously than on the 80×25 layout used on other machines.

Despite this they were capable microcomputers which were used for database management, online services, spreadsheets, programming, and even graphics and desktop publishing. The Sage Group's early growth was largely due to the demand for its PCW-based accounts package.Fact|date=August 2007 The PCW introduced a generation of British writers to computers who might not have otherwise become involved with them.

See also

* Amstrad CPC
* SymbOS

External links

* [ PCW Joyce Computer Club]
* [ Info about early PCWs]
* [ Info about final PcW16 model]
* [ Screen shots of the PcW16's "Rosanne" GUI]
* [ PCW nostalgia. BBC Web page.]

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