Acorn Archimedes
The Acorn Archimedes was a computer series produced by the British company Acorn from 1987 to the mid-1990s .
microprocessor
Acorn began developing its own 32-bit RISC processor in 1983 , the Acorn RISC Machine . This was first used in series in the Archimedes, which became the first computer with a RISC CPU that was accessible to a large group of buyers . The processor was characterized by a very high speed for home computers at the time .
The operating speed of the Archimedes, which was clocked at 8 MHz and then cost around 3500 DM, exceeded most other computer systems in the price range up to around 20,000 DM. The first Archimedes models (A305 and A310) and the A3000 still had the Archimedes logo on the keyboard the words "British Broadcasting Corporation Microcomputer System" and had the red function keys typical of BBC computers .
A PC emulator made it possible to run PC programs.
With the introduction of the Acorn A3000 in spring 1989, a variant appeared, the shape of which was based on the desk housing of the Amiga 500 or the Atari 520ST and 1040ST . The price of the A3000 was also significantly more convenient for private users than the more professional machines of the A300 and A400 series. This shape was also used on the A3010 and A3020 models. All other Archimedes devices are designed as classic 3-box computers with a separate keyboard, computer and monitor.
System components
The high performance of the computer was also due to the additional system chips coordinated with the ARM processor and its mode of operation (32-bit, load-store architecture). These are MEMC (the memory controller), IOC (the input output controller) and VIDC (the video controller). In their original version in the first Archimedes models, these still bear the proper names ANNA, ALBION and ARABELLA. They later received a simple chip numbering from the manufacturer VLSI Technology .
graphic
The Acorn Archimedes was capable of higher resolutions of up to 1152 × 896 with two colors and 640 × 512 with 256 colors even without interlace . With his graphics chip (VIDC), resolutions and color depths could be programmed as desired within wide limits, which, however, required a correspondingly flexible monitor (the Multisync II from NEC was very popular ; the luxury model was probably the Eizo 9060).
The Archimedes could choose from a total of 4096 colors, of which 2, 4, 16 or 256 could be displayed simultaneously, depending on the mode. A defined palette of 16 color values is used for the desktop under RISC OS, which is composed of 8 gray values (including black and white) and 8 real colors. The 256 colors are formed by 64 real color values, each of which can be displayed by the video chip in 4 different brightnesses. The operating system contains code to determine the most suitable color value in the RGB spectrum (24 bit) from the current displayable color palette (ColourTrans module). Simple dithering can be used for black and white displays (in high resolutions).
The Archimedes could only handle one hardware sprite (which was primarily used as a mouse pointer). In addition, it did not have any special graphics chips, so developing games was difficult. Nevertheless, there were also elaborately designed games at Archimedes, including conversions of Amiga games that corresponded to their originals.
The RISC OS operating system already supported vector fonts and many other functions, so it was relatively easy for programmers to use them in complex applications. The program ! Draw contained in the ROM of the Archimedes is impressive. It was able to compete functionally with the versions of Corel Draw at the time, but also ran faster and was completely contained in the ROM of the computer.
Sound and music
As is common with today's sound hardware, the Archimedes only offered one DMA channel and had to combine the audio data of the individual channels using software before output. The output of the samples was not implemented linearly, but logarithmically, which is closer to the human ear than the linear mapping commonly used today. This enabled a dynamic range of approx. 12 bits to be achieved with the 8-bit samples. The Archimedes' operating system provided 8 voices. 16-voice trackers like the ! Coconizer were available.
operating system
The RISC OS operating system resided in ROM . In addition to the entire graphical user interface, it already contained numerous additional programs such as ! Paint (a bitmap drawing program) ,! Draw (a vector-oriented DTP program) and ! Edit (a writing program). The Archimedes programs started in the so-called taskbar , which Microsoft licensed for Windows 95 . Also included were a CLI (command line interpreter), a complex, Unix-based operating system shell , which could execute batch processing , and the BBC BASIC , which also supported an inline assembly language .
RISC OS 2 made it possible to start the system without a hard disk drive or floppy disks . Settings were in a battery CMOS - RAM stored. RISC OS 3 could also be booted without floppy disks or hard disk, but boot disks were included that loaded various extensions.
The operating system offered cooperative multitasking . Cooperative means that the applications were called by the RISC OS and independently ended a cycle so that the RISC OS could pass on to the next application. The memory controller MEMC of Archimedes was able to switch the entire memory ( memory mapping ), so that each program was apparently executed in the same memory area without affecting the other programs.
The operation was done almost exclusively with a mouse, which was equipped with three buttons. The middle mouse button opened context menus for all objects on the desktop and in the programs . The operating system supported drag and drop throughout .
The task manager of the RISC OS listed all programs and their resource consumption .
A disadvantage of cooperative multitasking compared to preemptive multitasking (such as with Amiga , Windows NT or Unix derivatives ) is that the programs have to independently transfer control back to the operating system and thus a program error has serious consequences for the entire system may have. However, at least with later RiscOS versions it is possible in this case to end the hanging program with a key combination in order to avoid a crash of the entire operating system.
The system stability is also due to the lack of dynamic link libraries , the other functionality of which was provided by the routines in the unchangeable ROM . In addition, the MEMC (hardware-based) prevented errors in which programs threaten to overwrite the memory area of the operating system; Such errors can in principle lead to a system crash in systems without comparable hardware support.
The default setting for the character set is ISO 8859-1 with proprietary extensions. It is possible to switch to other character sets.
Programming of Archimedes
The BBC BASIC built into the ROM also supports inline assembly language . The graphical user interface of the first Archimedes operating system, ARTHUR , was partly programmed in BBC BASIC. The later operating system RISC OS was finally written entirely in assembly language.
For the operating system calls, the ARM offered its own assembler command, the SWI (software interrupt). Operating system functions from the assembler in the form z. B. SWI "OS_WriteC" (for write characters) can be called. The 16 registers of the ARM were used as parameters. Detailed manuals listed all SWIs of RISC OS and documented the inputs and outputs of the registers and the functions.
Own operating system calls could be programmed via new modules and the operating system could be expanded as required.
Extensions
All Archimedes computers can in principle be expanded. There are, however, at least three different ways of installing additional cards, and also - especially for the early models - variants whose installation requires experience in electronics and which were originally intended for installation by the specialist dealer. Installation was often included in the price.
Plug-in card expansions
.jpg)
The classic expansion port for plug-in cards on the Archimedes is a 64-pin bus with 16-bit data width in which so-called podules can be used. Visually and in terms of the connector, this is reminiscent of the VMEbus system of industrial and CP / M computers. In order to be able to use these podules, a riser card , called a backplane , must be installed. In particular, the early A305 and A310 models sometimes only have a backplane with 2 slots or no backplane at all. In principle, the housing allows a large backplane with 4 slots, but power consumption and other factors must be taken into account when converting. Devices of the 400 series have i. A. the backplane with 4 slots, as well as the A5000. The A3000 has an external bus to which a Podule can be connected. However, there were also so-called extenders that allow the use of several podules in an external housing on the A3000. With the A7000, for reasons of space (small housing), only either a CD-ROM drive or a backplane with connection options for a single module can be installed.
.jpg)
The podules themselves can have a single width or extend over the entire width and thus over two slots. The hidden slot becomes unusable, although theoretically it would still be free. In general, it is not necessary to install a device driver because the plug-in cards have their driver on an EPROM , which is automatically loaded when the system starts. However, it is entirely possible to deactivate the software stored on the EPROM and to use the Podule with a newer driver version from the hard disk. This can often make sense with Ethernet cards or drive connections such as SCSI or IDE cards. Some of the newer podules have Flash EEPROMs instead of EPROMs, so that the latest driver version can be written directly to the podule.
The spectrum of such podules ranges from all types of I / O cards such as B. serial connections with particularly high data transfer rates , IDE and SCSI cards, joystick modules, MIDI cards to video digitizers , genlocks or sound cards with synthesizer functions . There are also podules on which a complete small computer is located for hardware emulation . Cards with a mathematical coprocessor or for special network cabling are rare variants .
Typical cards for an early Archimedes system were disk buffer cards for connecting external disk drives, cards with a user port compatible with the BBC Micro for self-made extensions and EPROM banks on podules or combined EPROM and RAM banks, whereby the RAM has been battery-backed . These podules were used particularly in schools in the United Kingdom , with the Archimedes functioning as a large computer and file server , which worked using Acorn's LAN system Econet .
.jpg)
A3000, A3010, A3020 and A4000 have a modification of this bus system, which however only has 8 bit data width and is connected via a special connection, a pin header. So-called mini podules can be installed in it.
The third variant is the Micro-Podules from HCCS. In contrast to the aforementioned original Acorn connections, they require a carrier board that is connected either as a podule or as a mini-podule and on which up to three micro-podules can be plugged. Although this format saves space, it is not very common. In addition, the selection of micro podules is quite limited.
Conversion extensions
The Archimedes computers of the first series in particular have often been modified in many ways by users and specialist dealers.
.jpg)
.jpg)
An important expansion was RAM expansions that go hand in hand with more complex soldering work in the computers of the A300 and A400 series . Later models from the A3000 can be equipped with more memory by simply plugging memory chips directly onto the motherboard or using special plug-in RAM cards or, in the case of the A7000, with SIMM modules. Remarkable are those conversions that exceed a limit of 4 Mbytes. Since a single MEMC memory controller can only address up to 4 Mbytes of RAM, a second MEMC is required to use 8 Mbytes, which is not intended, with the exception of the A540 and the Unix devices. This is accompanied by desoldering the MEMC, if it is unsocketed, attaching a base and plugging in a special board, which then houses the original MEMC and the supplementary MEMC and establishes a connection to the expansion RAM. This means that 8 MB can be installed in Archimedes computers with the usual conversion kits. For devices in which this is already provided (slots for RAM cards with MEMC and 4 Mbytes each), an expansion to 16 Mbytes is possible.
Another important reason for rebuilding the MEMC is the desire to run a RISC OS on a first-edition Archimedes. Since this in principle requires a MEMC 1a, this must be retrofitted in the machine. Without MEMC 1a, only Arthur can be used as the operating system.
In devices with an ARM250, the MEMC is integrated into the main processor and therefore it is difficult to add a second one. Therefore, extensions of the A3010, A3020, A4000 are only possible up to 4 Mbytes. The A5000 is available in a variant with a socketed MEMC, which makes such conversions easier. There, 8 Mbytes were already quite common in professional DTP machines and more were possible, but very cost-intensive.
.jpg)
An important modification that made the Archimedes series into real long-term runners was the possibility of upgrading the CPU to ARM 3. This is possible because the built-in ARM 2 and ARM 3 do not differ significantly and belong to the same processor version. The ARM 3 is purely formally an ARM v2a. The main difference between the two is the cache integrated in the ARM 3 as well as an additional instruction that allows the contents of two registers to be swapped (SWP for swap, good e.g. for sorting processes). In addition, the ARM 3 can be operated with significantly higher clock rates. Depending on the chip version, a clock rate of up to 36 MHz was possible, 20 or 25 MHz were more common. This conversion has been made in many Archimedes of the A300 and A400 series and also often in the A3000. Similar to the RAMs above, the actual CPU is unsoldered and a new socket is inserted. This in turn contains an adapter, via which a small circuit board with the ARM-3 upgrade including the necessary quartz oscillators is connected. The result is a computer at (almost) the level of an A5000 with around 12.5 MIPS integer performance while retaining all the investments that have already been made on the device.
The third major modification was the upgrade of the operating system RISC OS 2 to the more modern version RISC OS 3. Since this has a lot more software, 4 ROMS are required, for which the first Archimedes are not prepared. Therefore a so-called ROM carrier board had to be installed for RISC OS 3, into which the 4 ROMS could be plugged.
In contrast, the so-called VIDC enhancer is an extension that is easier to install. This is a crystal oscillator that is built into the system in such a way that the video chip can then be operated at higher frequencies (hardware overclocking ). The advantages are the higher achievable resolutions or higher refresh rates in lower resolutions. Disadvantages are the decreasing service life of the chip due to overclocking and sometimes problems with sound reproduction, as this is generated by the VIDC and is based on the video clock.
Archimedes models
- Archimedes A305 (1987), the entry-level or original model with ARM2 -CPU with 8 MHz, 512 kB RAM , was usually upgraded to 1 MByte by the dealer in Germany (whereby the A305 lettering was covered with an A310 lettering)
- Archimedes A310 (1987), like A305, only with 1 MByte RAM
- Archimedes A410, was announced (several times), but was (presumably) never actually available
- Archimedes A440 (1987), like A310, but with 4 MB RAM, ST506 hard disk controller and a 20 MB hard disk
- Archimedes A410 / 1 (1989), like A440, but with a new (about 10% faster) memory controller MEMC1a, 1 MByte RAM and no hard disk
- Archimedes A420 / 1 (1989), like A410 / 1, but with 2 Mbytes
- Archimedes A440 / 1 (1989), like A410 / 1, but with 4 MByte RAM and with an ST506 hard disk with 53 MByte
- Archimedes A540 (1990), the first Archimedes with ARM3 CPU with 26 MHz, 4 MByte RAM (expandable to 16 MByte) and optional math coprocessor , SCSI hard disk with 100 MByte
The following models were not called Archimedes by Acorn, but are technically largely identical to the Archimedes:
- A3000 (1989), keyboard computer, similar to the Amiga 500 (or the BBC Master 128)
- R140 (1989), like A440 / 1, but with a 60 MB hard disk and (in addition to RISC OS) with RISCix ( Unix derivative)
- R260 (1990), like A540, but 8 MByte RAM, a SCSI hard disk with 100 MByte, Ethernet interface and RISCix
- R225 (1990), like R260, but with 4 MB RAM and without drives
- A5000 (1991), ARM3 with initially 25 MHz (so that the A540 was retained as the top model), later with up to 33 MHz and optionally with a mathematical coprocessor (FPA10), first model with standard IDE controller and 2 MB (gross) floppy disk drive
- A4 (1992), the notebook that was technically the forerunner of the A5000 (although it came on the market after it), with ARM3 (24 MHz), 4 Mbytes of RAM and a grayscale display with 640 × 480 pixels, the Housing was identical to the Walkstation 386SX from Triumph-Adler and the S20 from Olivetti (at the time Acorn was 79% owned by Olivetti, which also included TA). Together with its sister models S20 and Walkstation 386SX, it is one of the first notebooks with an integrated touchpad.
The following models use an ARM250 as the main chip. This is an IC that combines the functions CPU (ARM) + memory controller (MEMC) + video (VIDC) + input / output control (IOC) on one piece of silicon and thus in principle the entire computer in one chip " bundles ". It is therefore also referred to as a system-on-a-chip .
- A3010 (1992), keyboard computer, designed for private use, ARM250 (processor ARM2a, memory controller MEMC1a, IO controller IOC and graphics chip VIDC1a combined in one chip), 12 MHz, 1 MB RAM, 1.6 MB floppy disk drive, first and only " Archimedes ”with built-in joystick ports and TV modulator
- A3020 (1992), variant of the A3010 for schools, 2 MB RAM (expandable to 4 MB), no joystick ports, no TV modulator, but with a built-in IDE controller and optional hard drive and an additional slot for an ECONET network card
- A4000 (1992), office version of the A3020 with identical hardware as the A5000 but with a separate keyboard
The 7000s are more formally a continuation of the Archimedes devices. Technically, they correspond more to the successor device RiscPC, although its modular structure and expandability are missing here. In addition, the video chip is slowed down by the lack of VideoRAM. The 7000 series was also available with a built-in FPA (Floating Point Accelerator), i.e. H. mathematical co-processor, which allows higher computing speeds for certain applications (spreadsheet etc.) than with a StrongARM RiscPC. In principle, the entire computer is again united in one IC.
- A7000 (1995)
- A7000 + (1997)
The successors were the Risc PCs from Acorn.
Web links
- Acorn Archimedes 3010 at www.heimcomputer.de
- Collection of information on the Acorn Archimedes (English)
- Comprehensive presentation of the Acorn Archimedes by Dusty Bits with comparison Amiga 500 vs. Acorn A3010 (German)
Individual evidence
- ↑ VL86C010 (ARM2)
- ↑ MEMC Datasheet
- ^ IOC Datasheet
- ↑ VIDC Datasheet
- ↑ possibly first RISC OS Flyer (English)
- ↑ http://www.riscos.com/support/users/userguide3/bookb/book_6.html
- ↑ Latin1 standard character set of Archimedes
- ^ Archimedes' promotional brochure
- ↑ A310 advertising brochure
- ↑ A440 brochure (English)
- ↑ Flyer for the A4xx / 1 series (English)
- ↑ Brochure for the 4xx / 1 series (English)
- ↑ A3000 advertisement (English)