Editing Acorn Archimedes A4000

{{Infobox computer
| name         = Acorn Archimedes A4000
| image        = [[File:Acorn_Archimedes_A4000.jpg|250px]]
| caption      = Acorn Archimedes A4000
| manufacturer = Acorn Computers Ltd
| type         = Personal Computer
| release date = June 1992
| discontinued = 1993
| price        = £899 (1992)
| cpu          = ARM250 @ 12 MHz
| memory       = 2 MB RAM (expandable to 4 MB)
| storage      = 3.5" floppy drive (1.6 MB), 80 MB IDE hard drive
| display      = 640×512 (16 colours), 640×480 (256 colours), 800×600 (16 colours)
| sound        = 8-channel stereo, 8-bit logarithmic DAC
| dimensions   = 430 mm × 340 mm × 95 mm
| weight       = 6 kg
| os           = RISC OS 3.10
| predecessor  = [[Acorn Archimedes A3000]]
| successor    = [[Acorn A4]]
| codename     = 
| model        = 
}}

The '''Acorn Archimedes A4000''' was a mid-range desktop computer released in June 1992 as part of Acorn's second generation of Archimedes machines. Positioned between the entry-level A3010/A3020 and the professional A5000, the A4000 combined the cost-effective ARM250 processor with a built-in IDE hard drive, making it suitable for small businesses and advanced educational use.

== Overview ==

The A4000 represented Acorn's response to market demands for an affordable machine with built-in mass storage. Unlike the A3010 and A3020 which targeted home and education markets respectively, the A4000 aimed at users requiring a complete system without the expense of the ARM3-based A5000. The inclusion of an 80 MB IDE hard drive as standard distinguished it from its contemporaries, providing sufficient storage for RISC OS 3, applications, and user data without external additions.

Acorn designed the A4000 using the same fundamental architecture as the A3010 and A3020, sharing the ARM250 system-on-chip that integrated the ARM2 core, MEMC memory controller, VIDC video controller, and IOC input/output controller into a single package. This integration reduced manufacturing costs while improving reliability through fewer interconnections.

== Architecture ==

The ARM250 processor formed the heart of the A4000, manufactured using a 1.5µm CMOS process that reduced power consumption to approximately 3 watts. The integration of previously discrete components into a single chip eliminated many timing issues present in earlier designs while enabling the clock speed increase from 8 MHz to 12 MHz.

=== Memory System ===

The A4000's memory architecture differed from both its predecessors and contemporaries through its use of standard 30-pin SIMMs rather than proprietary modules:

{| class="wikitable styled-table" style="width:85%; text-align:center;"
! Configuration !! SIMM Type !! Banks Used !! Total RAM
|-
| Standard || 2× 1MB 30-pin || 2 of 4 || 2 MB
|-
| Expanded || 4× 1MB 30-pin || 4 of 4 || 4 MB
|-
| Alternative || 2× 2MB 30-pin || 2 of 4 || 4 MB
|}

The use of industry-standard SIMMs reduced upgrade costs significantly compared to earlier machines. The memory controller within the ARM250 supported fast page mode access, achieving 50ns access times with 70ns rated SIMMs through careful timing optimization.

== Hardware Design ==

The A4000 motherboard represented a significant redesign from the A3000, optimizing for manufacturing efficiency and the integrated ARM250 processor. The two-layer PCB reduced costs compared to the four-layer boards used in earlier Archimedes models, though this required careful trace routing to minimize signal interference.

=== Integrated Components ===

The ARM250's integration provided several advantages:
* '''Reduced chip count''' - Single chip replaced four major components
* '''Lower power consumption''' - 3W versus 8W for discrete implementation
* '''Improved reliability''' - Fewer solder joints and interconnects
* '''Simplified cooling''' - Passive heatsink sufficient for all conditions
* '''Cost reduction''' - Approximately 40% lower component cost

The integration also introduced limitations. The fixed relationships between processor, memory controller, and video controller prevented independent upgrades, and the 12 MHz clock speed could not be increased without replacing the entire chip.

=== IDE Interface ===

{| class="wikitable styled-table" style="width:85%; text-align:center;"
! Specification !! Details !! Performance
|-
| Controller || 82C711 Multi-I/O chip || PIO Mode 0
|-
| Interface || 40-pin IDE connector || 16-bit data
|-
| Transfer rate || 3.3 MB/s maximum || 1.8 MB/s typical
|-
| Drive supplied || 80 MB Conner CP3084 || 28ms average seek
|-
| File system || ADFS with RISC OS 3 extensions || Long filenames
|}

The IDE interface represented a departure from the SCSI interfaces used in higher-end models. While offering lower performance, IDE drives cost significantly less than equivalent SCSI units, contributing to the A4000's attractive price point. The 82C711 controller also provided the floppy drive interface, serial port, and parallel port, further reducing chip count.

== Video Capabilities ==

The VIDC1a video controller within the ARM250 supported enhanced display modes compared to the original VIDC, with improved timing flexibility for VGA monitors becoming standard in the early 1990s.

=== Display Modes ===

{| class="wikitable styled-table" style="width:90%; text-align:center;"
! Mode !! Resolution !! Colors !! Refresh !! Memory Used
|-
| 12 || 640×256 || 16 || 50 Hz || 80 KB
|-
| 15 || 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 || 16 || 72 Hz || 150 KB
|-
| 28 || 640×480 || 256 || 60 Hz || 300 KB
|-
| 31 || 800×600 || 16 || 60 Hz || 234 KB
|}

The addition of proper VGA timing modes (20, 21, 27, 28) eliminated the need for expensive multisync monitors, allowing the use of standard PC displays. This compatibility improvement significantly reduced total system cost for business users migrating from PC platforms.

== Input/Output Systems ==

The A4000 provided comprehensive I/O capabilities through a combination of integrated and discrete controllers:

=== Standard Ports ===

{| class="wikitable styled-table" style="width:85%; text-align:center;"
! Port !! Type !! Controller !! Features
|-
| Serial || 9-pin D-sub || 82C711 || 115200 bps maximum
|-
| Parallel || 25-pin D-sub || 82C711 || Bidirectional, EPP compatible
|-
| Mouse || 9-pin mini-DIN || IOC quadrature || PS/2 compatible with adapter
|-
| Keyboard || 5-pin DIN || 8051 MCU || PC/AT protocol
|-
| Video || 15-pin D-sub || VIDC1a || Analog RGB, separate syncs
|-
| Audio || 3.5mm jack || VIDC1a || Stereo line output
|-
| Network || Optional || Econet module || 250 kbps half-duplex
|}

The serial port implementation in the 82C711 provided full 16550-compatible buffering, improving reliability at high data rates compared to the unbuffered 6551 used in earlier models. The parallel port's EPP compatibility enabled connection to newer peripherals designed for PC systems.

=== Expansion Options ===

Unlike the A3000 which provided only a single internal expansion slot, the A4000 included:
* '''Single podule slot''' - Standard 96-pin Archimedes expansion
* '''Network slot''' - Internal Econet interface option
* '''RAM expansion''' - Two free SIMM slots
* '''VRAM upgrade''' - Optional 1 MB VRAM for improved video

The single podule slot limitation proved restrictive for users requiring multiple expansions. Common expansion cards included SCSI interfaces for external devices, Ethernet adapters for TCP/IP networking, and MIDI interfaces for music applications.

== Operating System ==

The A4000 shipped with RISC OS 3.10 in 2 MB of ROM, providing immediate access to the desktop environment and core applications without loading from disk. This version introduced several improvements over RISC OS 3.00 used in the A3010/A3020:

=== RISC OS 3.10 Features ===

System enhancements included:
* '''Improved ADFS''' - Better IDE support and faster disk operations
* '''Enhanced printing''' - Bidirectional parallel communication
* '''Bug fixes''' - Resolution of numerous RISC OS 3.00 issues
* '''Application updates''' - Newer versions of Edit, Paint, and Draw
* '''Driver improvements''' - Better third-party hardware support

The 2 MB ROM contained the complete operating system, desktop environment, and bundled applications. This approach provided instant startup, immunity from disk corruption, and consistent system behavior across all machines.

=== Memory Management ===

With 2 MB RAM as standard, RISC OS 3.10 memory allocation typically appeared as:

{| class="wikitable styled-table" style="width:85%; text-align:center;"
! Area !! Size !! Purpose
|-
| Screen memory || 160-300 KB || Depending on mode
|-
| System heap || 128 KB || OS workspace
|-
| Module area || 256 KB || Loaded modules
|-
| Font cache || 64-128 KB || Outline font rendering
|-
| RAM disc || 64 KB || Default size
|-
| Free memory || 1.0-1.2 MB || Applications
|}

The inclusion of a hard drive reduced RAM disc importance, allowing more memory allocation to applications. The system could dynamically adjust memory areas based on requirements, though this occasionally led to fragmentation requiring a restart.

== Software Compatibility ==

The A4000's 2 MB minimum RAM and included hard drive ensured compatibility with virtually all contemporary RISC OS software. The ARM250's instruction set compatibility with ARM2 and ARM3 processors meant existing software ran without modification, though without the performance benefits of the ARM3's cache.

Popular software categories included:
* '''Office applications''' - Impression Publisher, Pipedream, DataPower
* '''Graphics software''' - Artworks, ProArtisan, Photodesk
* '''Programming tools''' - Acorn C/C++, BBC BASIC V, ARM assembler
* '''Educational software''' - Granada Learning titles, Sherston Software
* '''Games''' - Zarch, Lemmings, SimCity

The hard drive transformed software installation and use, eliminating disk swapping and providing space for multiple applications. Users could maintain extensive font collections, clip art libraries, and document archives previously impractical on floppy-only systems.

== Performance Analysis ==

The A4000's performance fell between the A3020 and A5000, offering adequate speed for most applications while lacking the raw processing power of ARM3-based systems:

{| class="wikitable styled-table" style="width:85%; text-align:center;"
! Benchmark !! A3020 (12 MHz ARM250) !! A4000 (12 MHz ARM250) !! A5000 (25 MHz ARM3)
|-
| Dhrystone 2.1 || 5,400 || 5,400 || 21,000
|-
| Screen redraw || 100% || 100% || 180%
|-
| BASIC loop || 1.2 sec || 1.2 sec || 0.3 sec
|-
| File copy (HD) || N/A || 850 KB/s || 1.4 MB/s
|}

The identical processor performance to the A3020 meant the A4000's advantages lay primarily in its storage capabilities and expansion options rather than raw computing power. The IDE interface's lower performance compared to the A5000's SCSI system was rarely noticeable in typical use.

== Manufacturing and Variants ==

Acorn produced the A4000 for approximately 18 months, with minor revisions addressing component availability and cost reduction:

=== Production Timeline ===

{| class="wikitable styled-table" style="width:85%; text-align:center;"
! Period !! Changes !! Notes
|-
| Jun-Dec 1992 || Initial production || Conner CP3084 drives
|-
| Jan-Jun 1993 || Drive change || Western Digital drives
|-
| Jul-Oct 1993 || Component updates || Cost-reduced PSU
|-
| Nov 1993 || End of production || Replaced by Risc PC
|}

Production volumes remained modest, with approximately 15,000 units manufactured. The education market absorbed roughly 40%, with the remainder split between small businesses and advanced home users. The relatively short production run reflected Acorn's transition to the Risc PC architecture announced in 1994.

== Common Issues and Reliability ==

The A4000 exhibited generally good reliability, benefiting from the integrated ARM250 design and improved manufacturing processes. However, several issues emerged over time:

=== Hard Drive Failures ===

The Conner CP3084 drives used in early production proved problematic:
* '''Stiction problems''' - Drives failed to spin up after periods of inactivity
* '''Head crashes''' - Particularly common after 5-7 years of use
* '''Bearing wear''' - Caused increasing noise before complete failure

Replacement with modern IDE drives requires attention to geometry limitations in RISC OS 3.10, which cannot address drives larger than 512 MB without third-party software.

=== Power Supply Issues ===

The internal switch-mode power supply, while more efficient than earlier linear designs, developed characteristic faults:
* '''Capacitor degradation''' - Particularly in the primary section
* '''Thermal stress** - Inadequate ventilation caused component failure
* '''Voltage drift''' - Aging components caused regulation problems

=== Battery Leakage ===

Like all Archimedes machines, the CMOS backup battery posed long-term risks:
* '''Battery type''' - 3.6V lithium (improved from NiCd)
* '''Typical lifetime''' - 7-10 years before replacement needed
* '''Leakage damage''' - Less severe than NiCd but still problematic
* '''Symptoms''' - Settings loss, clock failure, boot problems

== Upgrades and Modifications ==

A4000 owners frequently pursued various upgrades to enhance system capabilities:

=== Memory Expansion ===

Upgrading to 4 MB required adding two 1 MB SIMMs:
* '''Cost in 1993''' - Approximately £80
* '''Installation** - Simple insertion into empty slots
* '''Benefits''' - Improved multitasking, larger RAM disc
* '''Compatibility''' - 70ns or faster SIMMs required

=== Processor Upgrades ===

Several third-party processor upgrades became available:
* '''ARM3 upgrade** - 25-33 MHz ARM3 with cache
* '''FPA coprocessor''' - Hardware floating-point acceleration
* '''Clock speedup''' - Replaced crystal for 16 MHz operation

The ARM3 upgrade provided the most significant performance improvement, offering 3-4 times the processing power of the standard ARM250.

=== Storage Expansion ===

Storage options included:
* '''Larger IDE drives''' - Up to 512 MB with RISC OS 3.10
* '''External SCSI''' - Via podule slot interface
* '''Network storage*** - Using Econet or Ethernet

## Network Options ##

Network connectivity options:
* '''Econet''' - Internal interface card, 250 kbps
* '''Ethernet''' - 10Base2/10BaseT via podule slot
* '''Serial networking''' - SLIP/PPP via serial port

Ethernet gradually replaced Econet in educational settings, offering standard TCP/IP compatibility and higher speeds.

== Educational Use ==

The A4000 found particular success in secondary schools and colleges where the built-in hard drive enabled new teaching approaches. Programming courses benefited from local storage for development tools and student projects. Art and design classes utilized the hard drive for storing large graphics files and font collections.

Network boot capabilities allowed the A4000 to serve as a classroom file server, with diskless A3010 or A3020 stations loading software from the A4000's hard drive via Econet. This configuration reduced total system cost while providing centralized software management.

== Market Position ==

The A4000 occupied a challenging market position, competing against increasingly powerful and affordable PC compatibles. While offering superior ease of use and educational software, the platform's limited business software selection restricted commercial appeal.

Pricing remained competitive with similarly specified PC systems, but the PC platform's economies of scale and broader software availability gradually eroded Acorn's market share. The A4000's discontinuation in late 1993 marked the end of the traditional Archimedes line, with the revolutionary Risc PC representing Acorn's next generation strategy.

== General Maintenance ==
{{Main|Acorn Archimedes A4000 General Maintenance}}

Regular maintenance focuses on thermal management and mechanical components. The internal hard drive requires adequate cooling airflow, making case ventilation cleaning essential. The power supply's switch-mode design generates less heat than linear types but still requires periodic inspection. Battery replacement before leakage prevents motherboard damage. The integrated ARM250 has no socketed components, simplifying maintenance but preventing chip-level repairs.

== Troubleshooting ==
{{Main|Acorn Archimedes A4000 Troubleshooting}}

Common faults include hard drive failures manifesting as boot errors or data corruption, power supply problems causing random resets or failure to start, and video output issues often traced to the VGA output circuitry. The integrated ARM250 design means processor, memory controller, or video controller failures require complete chip replacement. IDE interface problems may prevent hard drive detection, usually resolved by cable replacement or controller chip reseating.

== Capacitor Replacement Guide ==
{{Main|Acorn Archimedes A4000 Capacitor Replacement Guide}}

Critical capacitors requiring replacement after 30 years include power supply primary capacitors (47µF 400V, 100µF 200V), secondary filtering (1000µF 16V ×2, 2200µF 10V), and motherboard electrolytics (100µF 16V ×4, 47µF 16V ×6). The switch-mode power supply requires careful handling of high-voltage components. Unlike earlier models, the A4000's two-layer PCB simplifies trace repair if capacitor leakage causes damage.

== Legacy ==

The A4000 represented the final evolution of the original Archimedes concept before the radical Risc PC redesign. Its combination of integrated processor technology, standard memory modules, and IDE storage influenced subsequent Acorn designs. While commercial success remained limited, the A4000 demonstrated the viability of highly integrated ARM processors, presaging the system-on-chip designs that would eventually dominate mobile computing.

The machine's reliability and expandability ensured many units remained in service well into the 2000s, particularly in educational environments. Modern retro computing enthusiasts appreciate the A4000's balance of capability and affordability, making it a popular entry point for exploring RISC OS and ARM architecture history.

== See Also ==
* [[Acorn Archimedes A3010]]
* [[Acorn Archimedes A3020]]
* [[Acorn Archimedes A5000]]

[[Category:Acorn Computers]]
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