Acorn Archimedes Computer ~ Hard and Software Plus

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The Acorn Archimedes was Acorn Computers' first general purpose home computer to be based on their own ARM architecture.

Using a RISC design with a 32-bit CPU, at its launch in June 1987, the Archimedes was stated as running at 4 MIPS, with a claim of 18 MIPS during tests.

The name is commonly used to describe any of Acorn's contemporary designs based on the same architecture, even where Acorn did not include Archimedes in the official name.

The first models were released in June 1987, as the 300 and 400 series. The 400 series included 4 expansion slots (although a 2 slot backplane could be added to the 300 series as an official upgrade, and third parties produced their own 4 slot backplanes) and an ST506 controller for an internal hard drive. Both models included the Arthur operating system operating system (later replaced by RISC OS as a paid-for upgrade), BBC BASIC programming language and an emulator for Acorn's earlier BBC Micro, and were mounted in two-part cases with a small central unit, monitor on top, and a separate keyboard and three-button mouse. All models featured onboard 8 channel stereo sound and were capable of displaying 256 colours on screen.

Four models were initially released with different amounts of memory, the A305, A310, A410 and A440. The 540 was unveiled in September 1990, and included higher speed SCSI and provision for connecting Genlock devices. The 300 and 400 were followed by a number of machines with minor changes and upgrades:

A3000 and A5000

Work began on a successor to the Arthur operating system. Initially named Arthur 2, it was renamed to RISC OS 2. New computers were shipped with it pre-installed. A number of new machines were introduced along with RISC OS 2 and in May 1989, the 300 series was phased out in favour of the new Acorn A3000 (the 400 series was kept in production). Earlier models which shipped with Arthur could be upgraded to RISC OS 2 by replacing the ROM chips containing the operating system.

The A3000 used an 8 MHz ARM2 and was supplied with 1 MB of RAM. Unlike the previous models, the A3000 came in a single-part case similar to the BBC Micro, Amiga 500 and Atari ST computers, with the keyboard integrated in the base unit. This kind of housing consumes a lot of desktop space, a problem that Acorn tried to overcome by offering a monitor stand that attached to the base unit. The new model sported only a single internal expansion slot, which was physically different from that of the earlier models, although electronically similar. An external connector could interface to existing expansion cards, although they really needed to be housed in an external case joined to the main unit.

A300 series, A400 series, R140 and A3000 machines had the VIDC1a video chip, which provided a wide variety of screen resolutions:

160 × 256 with 4, 16 or 256 colours
320 × 256 with 2, 4, 16 or 256 colours
640 × 256 with 2, 4, 16 or 256 colours
640 × 512 with 2, 4, 16 or 256 colours
1152 × 896 with 2 colours.

The palette range was 4096 colours (12-bit) and the VIDC1a had 16 hardware palette registers. This meant that in screen modes with sixteen colours or fewer, the colours could be mapped to any of the 4096 available. However, in 256 colour modes, 4 bits of the colour data were hardware derived and could not be adjusted. The net result was 256 colours, but only 16 of them could be assigned as desired, covering a range of the 4096 available colours. It also had no Horizontal sync interrupt, meaning that it was difficult to display additional colours by changing the palette for each scan line, but not impossible, thanks to the 2 MHz IOC timer 1. Many demos managed to display 4096 colour on screen or more with dithering. It had also one hardware sprite, with 32 pixels width and unlimited height, where each pixel is coded on 2 bits: value 0 is for transparency, and the 3 others are freely chosen from the 4096 colour palette.

In 1991, the A5000 was launched. It featured the new 25 MHz ARM3 processor, 2 or 4MB of RAM, either a 40 MB or an 80 MB hard drive and a more conventional 2U rack pizza box-style two-part case (HxWxD: 100 x 430 x 340 mm). Its enhanced video capabilities allowed the A5000 to comfortably display VGA resolutions of up to 800×600 pixels. It was the first Archimedes to feature a High Density capable floppy disc drive as standard. This natively supported various formats including DOS and Atari discs. A later version of the A5000 featured a 33 MHz ARM3, 4 or 8 MB of RAM, an 80 or 120 MB hard drive.

The A5000 initially ran the new 3.0 version of RISC OS, although several bugs were identified; most were shipped with RISC OS 3.10 or 3.11. As before, earlier machines were capable of being upgraded to the new RISC OS 3, though some needed an additional daughterboard installing, as well as the ARM3 CPU. Earlier models could also benefit from the video performance of the A5000 via a third party upgrade.

New range and a laptop

In 1992, a new range was produced, the first ARM macrocell: the ARM250 microprocessor, a single-chip design including an ARM3 chip without cache, and the IOC1 (Input Output Controller), VIDC1a (VIDeo and sound Controller) and MEMC1 (MEMory Controller) chips all integrated into one chip. The increase in clock frequency, from 8 MHz to 12 MHz, gave a performance of 7 MIPS. They run RISC OS 3.10. The A30x0 series had a one-piece design, similar to the A3000 but far smaller, while the A4000 looked like a slightly slimmer A5000. The A3010 model was intended to be a home computing machine, featuring a TV modulator and joystick ports, while the A3020 targeted the home office and educational markets, featuring a built-in 2.5" hard drive and a dedicated network interface socket.

Technically, the A4000 was almost identical to the A3020, only differing in hard disk size (3.5" in the A4000), though it sported a different appearance. All three ARM250-based machines could be upgraded to 4 MB with plug-in chips (though the A3010 was designed for 2 MB, third party upgrades overcame this) and one "mini-podule" slot as used for internal expansion in the A3000.

Also in 1992, Acorn introduced a laptop computer called A4 that featured an ARM3 processor like the A5000, even though it had a slightly lower clock speed, and a LCD screen capable of displaying a maximum resolution of 640 × 480 pixels in 15 levels of grey. However, it did feature a monitor port which offered the same display capabilities as an A5000. A notable omission from the machine was a built-in pointing device, requiring users to navigate with the cursor keys or attach a conventional Acorn three-button mouse.

The A7000, despite its name being reminiscent of the Archimedes naming conventions, was actually more similar to the Risc PC, the line of RISC OS computers that succeeded the Archimedes in 1994. It lacked, however, the DEBI expansion slots and multi-slice case that characterized the RiscPC (though by removing the CDROM, a backplane with one slot could be fitted).

List of models

Model	Memory (RAM)	Hard disk space	ARM core	Launch date	UK retail price at launch	Notes
BBC Archimedes 305	512 KB (512 KB)	-	ARM2	July 1987	£799	-
BBC Archimedes 310	1 MB (1 MB)	-	ARM2	July 1987	£875	-
BBC Archimedes 310M	1 MB	-	ARM2	July 1987	Unknown	Includes PC emulation software
Acorn Archimedes 410	1 MB	-	ARM2	July 1987	£1399	-
Acorn Archimedes 440	4 MB	20 MB	ARM2	July 1987	£2299	-
BBC A3000	1 MB	-	ARM2	May 1989	£649	This model was the last ever BBC Microcomputer
Acorn Archimedes 410/1	1 MB	- (ST506 interface on motherboard)	ARM2	June 1989	£999	Improved MEMC1A memory controller over previous 410 model
Acorn Archimedes 420/1	2 MB	20 MB ST506	ARM2	June 1989	£1099	-
Acorn Archimedes 440/1	4 MB	40 MB ST506	ARM2	June 1989	£1299	Improved MEMC1A memory controller over previous 440 model
Acorn R140	4 MB	47 MB ST506	ARM2	June 1989	£3,500	RISC iX workstation
Acorn Archimedes 540	4 MB (max 16 MB)	100 MB SCSI	ARM3	June 1990	£2499
Acorn R225	4 MB	-	ARM3	July 1990	£3000	RISC iX network workstation
Acorn R260	8 MB	100 MB SCSI	ARM3	July 1990	£5000	RISC iX workstation
Acorn A5000	1, 2, 4 or 8 MB	20 MB to 160 MB IDE	ARM3	September 1991	£999 or £1499	25 or 33 MHz ARM3 processor, launched with various sub-models
Acorn A4	2 MB or 4 MB	40 MB or 60 MB IDE (2.5")	ARM3	June 1992	£1399 or £1699	Notebook model with ARM3 processor clocked at 24 MHz (1 MHz slower than usual), 640x480 greyscale LCD screen
Acorn A3010	1 MB	-	ARM2/ARM250	September 1992	£499	ARM250 processor (early models had an ARM2 mezzanine processor codenamed "Adelaide")
Acorn A3020	2 MB	0 MB - 80 MB IDE (2.5")	ARM250	September 1992	£799
Acorn A4000	2 MB	0 MB - 210 MB IDE	ARM250	September 1992	£999

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