Acorn Archimedes A5000

Acorn Archimedes A5000
	Acorn Archimedes A5000
Specifications
Manufacturer	Acorn Computers Ltd
Type	Personal Computer
Released	September 1991
Discontinued	1993
Intro price	£1,499 (2 MB), £1,999 (4 MB)
CPU	ARM3 @ 25 MHz
Memory	2 MB or 4 MB RAM (expandable to 8 MB)
Storage	3.5" floppy drive (1.6 MB), 40/80/120 MB IDE hard drive
Display	640×480 (256 colours), 800×600 (256 colours), 1024×768 (16 colours)
Sound	8-channel stereo, 8-bit logarithmic DAC
Dimensions	420 mm × 340 mm × 105 mm
Weight	8.5 kg
OS / Firmware	RISC OS 3.00
Predecessor	Acorn Archimedes A540, Acorn Archimedes A420
Successor	Acorn Risc PC

The Acorn Archimedes A5000 was released in September 1991 as a mid-range professional computer, bridging the gap between the entry-level A3000 series and the high-end A540. Featuring the ARM3 processor at 25 MHz with integrated cache, the A5000 combined workstation-class performance with affordability, becoming one of Acorn's most successful second-generation Archimedes models.

Overview

The A5000 addressed market demands for ARM3 performance without the A540's premium pricing. By utilizing IDE storage instead of SCSI and limiting maximum RAM to 8 MB, Acorn reduced costs while maintaining professional capabilities. The machine targeted educational establishments, small businesses, and power users who required more performance than the A3000 series but could not justify the A540's expense.

Acorn offered multiple configurations to suit different markets. The base model with 2 MB RAM and 40 MB hard drive competed with high-end PCs, while the 4 MB/120 MB configuration challenged entry-level workstations. The inclusion of RISC OS 3.00 marked a significant advancement in the operating system, introducing cooperative multitasking improvements and enhanced desktop functionality.

Architecture

The A5000 utilized a refined architecture combining proven components with cost-effective design choices. The ARM3 processor provided the performance foundation, while careful system integration minimized component count and manufacturing costs.

System Design

Component	Implementation	Function
ARM3	25 MHz, 4 KB cache	Central processor
MEMC1a	Single chip	Memory controller, DMA
VIDC1a/VIDC20	Enhanced timing	Video and sound
IOC	Standard implementation	I/O control, timers
COMBO chip	82C711	IDE, floppy, serial, parallel

The integration of multiple I/O functions into the 82C711 COMBO chip reduced board complexity and cost. This chip handled IDE and floppy disk control, serial and parallel ports, and real-time clock functions, eliminating several discrete components used in earlier designs.

Memory Architecture

The A5000's memory system balanced performance with cost:

Configuration	SIMM Type	Slots Used	Total RAM	Expansion Path
2 MB model	2× 1MB 30-pin	2 of 4	2 MB	Add 2 SIMMs
4 MB model	4× 1MB 30-pin	4 of 4	4 MB	Replace all
8 MB upgrade	4× 2MB 30-pin	4 of 4	8 MB	Maximum

The use of industry-standard 30-pin SIMMs reduced memory costs compared to proprietary modules. The MEMC1a controller supported up to 8 MB directly, though RISC OS could only utilize 8 MB total including VRAM.

Hardware Specifications

The A5000 motherboard represented mature Archimedes design, incorporating lessons from five years of production experience.

Processor Subsystem

The ARM3 processor configuration:

Clock frequency: 25 MHz from 50 MHz crystal
Cache: 4 KB unified instruction/data
Cache organization: 64 lines of 16 words
Cache timing: Single-cycle hit, 4-cycle miss
Write strategy: Write-through
Power consumption: 1.4W typical

The cache provided approximately 85% hit rate for typical applications, reducing memory bandwidth requirements substantially. This proved crucial given the memory system's shared bandwidth with video and sound DMA.

IDE Storage System

Specification	Details	Performance
Controller	82C711 COMBO chip	PIO Mode 2
Interface	40-pin IDE connector	16-bit data path
Transfer rate	3.3 MB/s maximum	1.5 MB/s typical
Drive options	40/80/120 MB	Various manufacturers
File system	RISC OS 3 ADFS	Long filenames, 512 MB limit

Common drive configurations:

40 MB: Conner CP3044 or Western Digital WD93044
80 MB: Conner CP3084 or Maxtor 7080A
120 MB: Conner CP30124 or Seagate ST3144A

The IDE interface's simplicity improved reliability compared to SCSI, though with reduced performance and expandability.

Video Capabilities

The A5000 shipped with either VIDC1a or VIDC20 depending on production date:

Video Controller Comparison

Feature	VIDC1a (early units)	VIDC20 (late units)
Maximum colors	256 from 4096	256 from 16.7M
Resolutions	Fixed modes	Flexible timing
Pixel clock	24 MHz	36 MHz
VRAM support	No	Yes (1 MB)
Hardware cursor	32×32×3 colors	32×32×3 colors

VIDC20-equipped machines could utilize 1 MB of VRAM for enhanced performance in high-resolution modes, though this option was rarely fitted due to cost.

Display Modes

Mode	Resolution	Colors	Refresh	Memory Used
12	640×256	16	50 Hz	80 KB
13	640×256	256	50 Hz	160 KB
20	640×480	16	60 Hz	150 KB
21	640×480	256	60 Hz	300 KB
24	800×600	16	56 Hz	234 KB
27	640×480	256	70 Hz	300 KB
28	800×600	256	56 Hz	468 KB

The VGA-compatible modes (20, 21, 27) enabled use of standard PC monitors, significantly reducing total system cost compared to earlier models requiring expensive multisync displays.

RISC OS 3.00

The A5000 introduced RISC OS 3.00, a major operating system upgrade:

New Features

System improvements included:

Application tasks: Improved cooperative multitasking
Drag and drop: System-wide protocol for data transfer
Outline fonts: Scalable font technology
3D look: Enhanced desktop appearance
Pinboard: Desktop background with file shortcuts
Configuration: Non-volatile settings storage

Bundled applications:

Edit: Enhanced text editor
Paint: Improved bitmap editor
Draw: Vector graphics with bezier curves
Maestro: Music composition
Alarm: Calendar and scheduling
Chars: Character map utility

Memory Management

Memory Area	2 MB System	4 MB System	Purpose
Screen memory	160-300 KB	160-468 KB	Display buffer
System heap	256 KB	384 KB	OS workspace
Module area	384 KB	640 KB	Relocatable modules
Font cache	128 KB	256 KB	Outline fonts
Application space	800 KB	2 MB	User programs

The improved memory management allowed multiple applications to coexist more effectively than RISC OS 2, though true preemptive multitasking remained absent.

Expansion Options

The A5000 provided four podule expansion slots:

Common Expansion Cards

Popular expansions included:

SCSI cards: Lingenuity, Morley, Oak Solutions
Ethernet: i-cubed EtherLan 200/500
Sound samplers: Wild Vision AudioDynamics
MIDI interfaces: EMR Studio 24
PC emulators: Aleph One 486 card
Video digitizers: HCCS Vision

The four-slot capacity matched the A540, providing professional expansion capabilities at lower cost.

Network Options

Interface	Speed	Protocol	Typical Use
Econet (module)	250 kbps	Proprietary	Educational networks
Ethernet (podule)	10 Mbps	TCP/IP	Professional networks
Serial SLIP	115.2 kbps	TCP/IP	Internet dial-up
Parallel PLIP	50 KB/s	TCP/IP	Direct connection

Ethernet gradually replaced Econet in educational settings, providing standard networking compatibility and improved performance.

Software Ecosystem

The A5000's performance enabled sophisticated applications:

Professional Software

Key applications included:

Impression Publisher: Professional desktop publishing
Artworks: Vector illustration program
ProArtisan 2: 24-bit image processing
Sibelius 6: Music notation and MIDI
Schema II: Electronic CAD
Eureka 3: Mathematical solver

These applications leveraged the ARM3's performance for tasks previously requiring dedicated workstations.

Development Tools

Programming environments:

Acorn C/C++: ANSI C and C++ compilers
BBC BASIC V: Integrated interpreter/compiler
Desktop Development Environment: Integrated development
GCC: GNU compiler collection port
StrongED: Programmer's editor

The 25 MHz ARM3 provided compilation speeds competitive with contemporary Unix workstations, attracting software developers.

Performance Characteristics

The A5000 delivered impressive performance for its price point:

Benchmark Results

Test	A5000 (25 MHz)	A3020 (12 MHz)	486DX-33	Mac IIci
Dhrystone 2.1	20,000	5,400	16,000	11,000
Screen redraw	320 ms	1,200 ms	450 ms	380 ms
BASIC loop	0.35 sec	1.2 sec	N/A	N/A
File copy (HD)	1.4 MB/s	N/A	1.8 MB/s	1.2 MB/s

The ARM3 cache provided substantial benefits, with cache-friendly code running 4-5 times faster than ARM2 systems at equivalent clock speeds.

Manufacturing History

Production evolved through several phases:

Period	Changes	Drive Options	Notes
Sep 1991-Mar 1992	Initial release	40/80 MB	VIDC1a
Apr-Sep 1992	Component updates	80/120 MB	Some VIDC20
Oct 1992-Mar 1993	Cost reduction	80/120 MB	VIDC20 standard
Apr-Dec 1993	Final production	120 MB only	Clearance sales

Approximately 25,000 units were manufactured, making the A5000 one of Acorn's more successful professional models. Educational purchases accounted for 60% of sales, with the remainder split between business and advanced home users.

Typical Configurations

The A5000 served various roles:

Educational Workstation

Standard classroom configuration:

A5000 2 MB/40 MB base system
4 MB RAM upgrade for multitasking
Econet interface for network boot
Shared printer via network
Educational software suite

Schools often purchased class sets, with one A5000 serving as file server for A3010/A3020 stations.

Desktop Publishing System

Professional DTP configuration:

A5000 4 MB/120 MB system
SCSI podule for external storage
Scanner interface for image acquisition
PostScript printer connection
Impression Publisher software
Font collections on hard drive

The combination provided capabilities competitive with Macintosh systems at lower cost.

Software Development Platform

Developer configuration:

A5000 4 MB/80 MB base
8 MB RAM upgrade essential
SCSI podule for backup
Serial podule for debugging
Ethernet card for networking
Development tools suite

The ARM3 performance made the A5000 viable for serious software development, particularly for RISC OS and embedded ARM applications.

Known Issues

Several characteristic problems affected A5000 systems:

Power Supply Issues

The internal switch-mode PSU exhibited common failures:

Capacitor degradation: Primary and secondary capacitors fail
Regulation drift: Voltage variations under load
Thermal stress: Inadequate cooling in some cases
Startup problems: Difficulty starting when cold

Regular capacitor replacement became essential for long-term reliability.

IDE Interface Limitations

The 82C711 controller imposed restrictions:

Drive size limit: 512 MB maximum per partition
No DMA: Processor-intensive transfers
Compatibility: Some modern drives incompatible
Performance: Limited to PIO Mode 2

These limitations became problematic as drive capacities increased, though third-party solutions eventually addressed some issues.

Battery Failures

The Dallas DS1287 real-time clock module contained an integrated battery:

Lifetime: 7-10 years typical
Failure mode: Complete module replacement required
Symptoms: Date/time loss, configuration reset
Solution: Module modification or replacement

The integrated battery design made replacement challenging compared to earlier removable batteries.

Upgrade Options

Common upgrades extended system capabilities:

Memory Expansion

Upgrading from 2 MB to 4 MB: 1. Purchase two 1 MB 30-pin SIMMs (70ns or faster) 2. Install in empty slots 3 and 4 3. System automatically detects new memory 4. Cost in 1992: approximately £60

Upgrading to 8 MB required replacing all SIMMs with 2 MB modules, costing approximately £200 in 1993.

Processor Enhancements

Limited processor upgrades existed:

ARM3 clock boost: 30-33 MHz possible with cooling
FPA11 coprocessor: Floating-point acceleration
Cache upgrade: Third-party 8 KB cache boards

The clock boost provided 20-30% performance improvement but risked system stability.

Storage Upgrades

Storage expansion options:

Larger IDE drives: Up to 512 MB with RISC OS 3
SCSI podule: External drive support
Network storage: NFS via Ethernet
Removable media: Parallel ZIP drives

Modern solutions include IDE-to-SD adapters, eliminating mechanical drive failures.

Comparison with Competitors

The A5000 competed in a challenging market:

System	Processor	Performance	Price (1991)	Market Position
A5000 2MB	ARM3 25MHz	20,000 Dhry	£1,499	Education/professional
486DX-33	Intel 486	16,000 Dhry	£1,800	Business standard
Mac IIsi	68030 20MHz	11,000 Dhry	£2,100	Creative professional
Amiga 3000	68030 25MHz	12,500 Dhry	£2,000	Multimedia

The A5000 offered superior price-performance but suffered from limited software availability compared to PC and Macintosh platforms.

Reliability Analysis

Long-term reliability studies revealed:

Component Failure Rates

Component	MTBF	Failure Rate (30 years)	Primary Cause
ARM3 processor	>100,000 hrs	<5%	Cache RAM
IDE drive	50,000 hrs	95%	Mechanical wear
PSU capacitors	15,000 hrs	100%	Electrolyte drying
DS1287 RTC	10 years	100%	Battery depletion
VIDC	>100,000 hrs	<2%	Very reliable

Preventive maintenance significantly extended operational life, with properly maintained systems still functional after 30 years.

Educational Impact

The A5000 played a crucial role in UK computing education:

Curriculum Support

The system supported diverse educational activities:

Programming: BBC BASIC and ARM assembly
Graphics: Vector and bitmap creation
Music: Composition and MIDI sequencing
Science: Data logging and analysis
Technology: CAD and electronics design

The integrated development environment encouraged programming education, with many UK programmers learning on A5000 systems.

Tesco Computers for Schools

The A5000 featured prominently in Tesco's voucher scheme:

Program duration: 1992-1994
Voucher collection: Shoppers collected vouchers
School redemption: Vouchers exchanged for computers
Impact: Thousands of A5000s entered schools

This program significantly increased Acorn's educational market penetration, establishing RISC OS in schools previously using BBC Micros.

Service and Support

Acorn provided comprehensive A5000 support:

Documentation

Available documentation included:

User Guide: Comprehensive operating instructions
Programmer's Reference: Complete API documentation
Technical Reference: Hardware specifications
Service Manual: Diagnostic and repair procedures

Documentation quality remained high, enabling third-party development and simplified maintenance.

Diagnostic Software

Diagnostic tools included:

!SysMerge: System module updates
!HForm: Hard drive formatting
!Verify: Disk and memory testing
!Configure: System settings

Third-party utilities like ZIDEFS and Killer provided additional diagnostic capabilities.

General Maintenance

Essential maintenance focuses on power supply capacitor inspection and replacement after 30 years of aging. The DS1287 real-time clock module requires modification or replacement when its integrated battery fails. IDE drive mechanisms need replacement with modern solid-state solutions. Cooling paths require regular cleaning to prevent thermal stress. The ARM3 processor benefits from heatsink compound replacement. Expansion slot contacts need periodic cleaning to maintain reliable podule operation.

Troubleshooting

Common problems include power supply failures manifesting as inability to start or random resets, typically resolved through capacitor replacement. IDE interface errors present as drive not found or data corruption, often caused by cable problems or drive compatibility. Memory errors produce application crashes or system instability, diagnosed through systematic RAM testing. The diagnostic sequence should verify PSU voltages, test memory operation, check drive detection, and validate expansion cards.

Capacitor Replacement Guide

Critical capacitors requiring replacement include PSU primary section (47µF 400V, 100µF 200V), secondary filtering (1000µF 16V ×2, 2200µF 10V ×2, 470µF 25V ×2), and motherboard distribution (100µF 16V ×6, 47µF 16V ×8, 22µF 25V ×4). The switch-mode design requires careful attention to capacitor specifications, particularly ESR ratings. Safety precautions are essential when working with primary-side components.

End of Production

Acorn discontinued the A5000 in December 1993, replacing it with the revolutionary Risc PC. Factors contributing to discontinuation included:

Risc PC development completion
Market demand for higher performance
Competition from Pentium-based PCs
Strategic platform consolidation

Remaining inventory sold through 1994, with educational discounts clearing stock. The Risc PC's modular architecture and superior performance made the A5000 obsolete, though many systems remained in service for years.

Legacy

The A5000 represented the culmination of the traditional Archimedes architecture, combining ARM3 performance with cost-effective design. Its commercial success in education markets validated Acorn's strategy, though broader market penetration remained elusive. The system demonstrated that British companies could produce competitive computers, influencing subsequent ARM development.

Many technological careers began with A5000 experience, particularly in UK schools where the systems remained common through the late 1990s. The combination of accessible programming tools, reliable hardware, and comprehensive documentation created an ideal learning environment.

Modern retrocomputing enthusiasts appreciate the A5000's balance of performance, expandability, and reliability. Unlike earlier models with proprietary components, the A5000's standard memory and IDE interface simplify restoration. The relative abundance compared to other Archimedes models makes the A5000 an accessible entry point for collecting Acorn computers.