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Commodore Plus/4

The Commodore Plus/4 was a home computer released by Commodore International in 1984 and intended to replace the Commodore 64 as its flagship computer. It had some success in Eastern Europe, but was less popular in Western Europe and a total flop in the United States.


In the early 1980s, Commodore found itself engaged in a price war in the home computer market. The hot-selling VIC-20 was a design accident resulting from MOS Technologies designing a videogame chip it couldn't sell, and companies like Texas Instruments and Timex undercutting the price of Commodore's PET line. The Commodore 64, the first 64KB computer to sell for under US$600, was another salvo in the price war but it was far more expensive to make than the VIC-20 because it used discrete chips for video, sound, and I/O. Commodore president Jack Tramiel wanted a new computer line that would use fewer chips and at the same time address some of the user complaints about the VIC and C64.

Commodore's third salvo – which, as it turned out, was fired just as most of Commodore's competition was leaving the home computer market – was the C116, C16, and Plus/4. All three computers used a MOS 7501 CPU (6502 compatible) and a MOS 7360 "TED all-in-one video, sound, and I/O chip. The Plus/4's design is thus philosophically closer to that of the VIC-20 than of the C64.

The Plus/4 was the flagship computer of the line. The Plus/4 had 64K of memory while the C-16 and 116 had 16K. The Plus/4 had built-in software, whereas the others did not. The Plus/4 and 16 had full-travel keyboards; the 116 used a rubber chiclet keyboard like less-expensive Timex-Sinclair computers and the original IBM PCjr. The 116 was only sold in Europe. All of the machines were distinguished by their dark cases and light keys.

The Plus/4 was introduced in June 1984 and priced at US$299. It was discontinued in 1985. It is not completely clear whether Commodore's intent was to eventually totally replace the C64 with the Plus/4, or whether they wanted to attempt to expand the home computer market and sell the Plus/4 to users who were more interested in serious applications than gaming. However, the Plus/4 succeeded at neither and quickly disappeared.

Plus/4 strengths

The TED offered 128-color video, which was revolutionary for its time, and 320×200 video resolution, which was standard for computers intended to be capable of connecting to a television. The Plus/4's memory layout gave it a larger amount of user-accessible memory than the C64, and its BASIC programming language was vastly improved, adding sound and graphics commands as well as looping commands that improved program structure. Commodore released a high-speed floppy disk drive for the Plus/4, the Commodore 1551, which offered much better performance than the C64/1541 combination because its data cable plugged into the cartridge port to facilitate direct memory access, rather than using a serial bus.

Unlike the C64, the Plus/4 had a built-in MOS 6551 UART chip (the C64 emulated the 6551 in software). This allowed the Plus/4 to use high-speed modems without additional hardware or software tricks (the C64 required specially written software to operate at 2400 bps). However, since most people only could afford 300 or 1200 bps modems in 1984, this was not an issue. The Plus/4 keyboard had a separately placed "diamond" of four cursor keys, presumably more intuitive in use than the VIC's and C64's two shifted cursor keys. Also, for serious programmers, the Plus/4 featured a ROM-resident machine code monitor (rekindling a tradition from the first Commodore computers, the PET/CBM series).

Plus/4 weaknesses

The Plus/4 had three things against it, which proved fatal: Unlike the C64's VIC II, the TED had no sprite capability, which strongly limited its video game graphics capabilities. Also, its tone generator was much closer to the VIC in quality than to the C64's SID, which, again, made the Plus/4 less attractive to game developers. Finally, the lack of these capabilities made C64 software compatibility impossible. Commodore may not have believed this to be a problem, as the successful C64 was incompatible with most VIC-20 software – but the C64 had developed a large software library by 1984, and while the C64 was a significant upgrade to the VIC-20 in almost every way, the Plus/4 was not.

The Plus/4, unlike the C64 and most other computers of its time (with the notable exception of the Coleco Adam), was equipped with ROM-resident application software (developed for Commodore by TriMicro). The application suite, featuring a word processor, spreadsheet, and database, were unfortunately quite rudimentary, however. It could be argued that it added little or no value to the machine, yet might have hindered the marketing/development of third-party software. The fourth advertised built-in application was the aforementioned machine code monitor, which would mostly be useful to serious programmers and tinkerers; a relatively small demographic (typically owning C64s already).

Most of the developers of the Plus/4 also worked on the Commodore 128 project, which was much more successful.