Editing Acorn Archimedes A540

{{Infobox computer
| name         = Acorn Archimedes A540
| image        = [[File:Acorn_Archimedes_A540.jpg|250px]]
| caption      = Acorn Archimedes A540
| manufacturer = Acorn Computers Ltd
| type         = Personal Computer
| release date = June 1990
| discontinued = 1992
| price        = £2,495 + VAT (1990)
| cpu          = ARM3 @ 25-26 MHz (variants at 30 MHz, 33 MHz)
| memory       = 4 MB RAM (expandable to 16 MB)
| storage      = 3.5" floppy drive (800 KB), 100 MB SCSI hard drive
| sound        = 8-channel stereo, 8-bit
| os           = RISC OS 2.01
| predecessor  = [[Acorn Archimedes A440]]
| successor    = [[Acorn A5000]]
}}

The '''Acorn Archimedes A540''' was introduced in June 1990 as the flagship model of the Archimedes range. It was Acorn's first machine to be fitted with the ARM3 processor as standard, supporting up to 16 MB of RAM, and included higher speed SCSI and provision for connecting genlock devices.

== Overview ==

The A540 represented Acorn's response to the need for a high-performance workstation in the Archimedes range. It was an anticipated consequence of Acorn's Unix workstation development, offering the same general specification as Acorn's R260 Unix workstation (running RISC iX) but without built-in Ethernet support and running RISC OS 2 instead of Unix. At £2,495 plus VAT, it was positioned as the top-of-the-range model, substantially more expensive than other Archimedes computers but offering unprecedented performance for the platform.

The A540 hardware was essentially identical to the R260 except that RISC iX was not installed; it could be purchased separately and installed on an A540. The machine was designed to appeal to professional users, educational institutions requiring maximum performance, and as a potential Unix workstation.

== Hardware Specifications ==

=== Processor ===
The A540 featured an ARM3 processor on a replaceable CPU card. Initial models shipped with processors running at 25-26 MHz, though variants existed running at 30 MHz and 33 MHz. The 26 MHz version used a 52 MHz oscillator, while some machines used 60 MHz oscillators for 30 MHz operation. The ARM3 included 4 KB of cache memory, providing substantial performance improvements over ARM2-based models.

The CPU card could accommodate an FPA10 (Floating Point Accelerator), with FPA11 also being compatible with later variants. The 33 MHz ARM3 CPU with FPA10 combination represented the highest performance configuration available. The ceramic ARM3 processors used in some machines could be overclocked, with reports of stable operation at up to 40+ MHz.

=== Memory System ===
The A540 had 4 MB RAM by default but could be expanded to 16 MB with additional RAM cards, each with its own 4 MB RAM and MEMC1a memory controller. This unique multi-MEMC configuration allowed the A540 to exceed the 4 MB limitation of single-MEMC systems. 

The memory expansion was achieved through up to three additional RAM cards, giving possible configurations of 4 MB, 8 MB, 12 MB, or 16 MB total. Both Acorn and third-party manufacturers like Simtec produced RAM cards for the system. The memory cards were noted to be somewhat temperamental and liable to become dislodged if the machine wasn't used for extended periods.

=== Storage ===
Unlike the rest of the Archimedes range, the A540 had a SCSI interface as standard, specifically using an NCR 53C90 or 53C90A controller. The machine shipped with a 100 MB SCSI hard disc, with the Acorn AKA31 or AKA32 SCSI interface providing both internal and external SCSI connectivity. The system retained the standard 800 KB double-density 3.5" floppy drive used across the Archimedes range.

=== Video System ===
The A540 used the VIDC1a (Video Controller) chip and included three BNC connectors unique to the A540 and R260 models. The system supported various display modes with resolutions up to 1152×896 pixels and could display 256 colors from a palette of 4096. The memory access frequency was raised to 12 MHz in the A540, compared to 8 MHz in earlier models, providing enhanced system performance.

=== Power Supply and Cooling ===
The A540 featured a larger power supply than standard Archimedes machines, containing two fans for cooling. The system was noted to generate considerable heat, particularly with fully loaded configurations, and the memory cards were susceptible to heat-related issues.

=== Expansion ===
The machine provided four podule (expansion card) slots, with all four remaining available for expansion since SCSI was integrated on the motherboard. The backplane supported various expansion cards including:
* Atomwide Ethernet IV cards for networking
* Computer Concepts Colour Card Gold for enhanced graphics
* Aleph1 386 PC emulation cards
* ScanLight podules for scanning
* MIDI interfaces

== Operating System ==

The A540 was launched with RISC OS 2.01, which included bug fixes and improvements over the earlier 2.00 release. The ROM-based operating system provided:
* ARM3 processor support with cache control
* Native SCSI device handling through the SCSI manager
* Support for memory configurations beyond 4 MB
* Improved printer driver stability and font manager fixes

Many A540s were later upgraded to RISC OS 3.10 or 3.11, with the Acorn Universal Boot system being a popular addition for enhanced functionality. Some machines, particularly ex-Acorn examples, retained RISC OS 2.01 with specialized software such as SJResearch Nexus Level 4 fileserver software for Econet networks.

== RISC iX Capability ==

While sold as a RISC OS machine, the A540 could run RISC iX (Acorn's BSD Unix variant) when purchased separately. The hardware provided genuine Unix workstation capabilities, supporting:
* Multi-user operation via serial terminals
* X Windows System
* Standard Unix development tools
* Network operation via optional Ethernet cards

Performance under RISC iX was reported to be competitive with contemporary Unix workstations, with the ARM3's cache particularly benefiting Unix operations.

== Technical Details ==

=== Motherboard Revisions ===
The A540 motherboard existed in at least two documented versions:
* Issue 1: Initial production version
* Issue 2: Revised version with minor improvements

The motherboard design utilized PAL chips to alter addressing for each MEMC, enabling the multi-MEMC memory configuration. The system used different phases of the memory clock (derived from a 72 MHz oscillator) for each MEMC, with abort signals ANDed together so an abort only occurred if all MEMCs failed to translate an address.

== See Also ==
* [[Acorn Archimedes A440]]
* [[Acorn A5000]]

== External Links ==
* [http://chrisacorns.computinghistory.org.uk/Computers/A540.html Chris's Acorns: Acorn Archimedes A540]
* [http://www.computinghistory.org.uk/ Centre for Computing History]
* [https://www.4corn.co.uk/archimedes.php 4corn Computers: The Acorn Archimedes]

[[Category:Acorn Computers]]