Acorn Archimedes A3000
 | |
| Acorn Archimedes A3000 | |
| Specifications | |
|---|---|
| Manufacturer | Acorn Computers Ltd |
| Type | Home Computer |
| Released | May 1989 |
| Discontinued | 1991 |
| Intro price | £649 (1989) |
| CPU | ARM2 (ARM250 in later models) @ 8 MHz |
| Memory | 1 MB RAM (expandable to 4 MB) |
| Storage | 3.5" floppy drive (800 KB/1.6 MB), optional hard drive |
| Display | 640×512 (16 colours), 640×256 (256 colours), 1152×896 (monochrome) |
| Sound | 8-channel stereo, 8-bit logarithmic DAC |
| Dimensions | 430 mm × 340 mm × 95 mm |
| Weight | 5.5 kg |
| OS / Firmware | RISC OS 2.00 (later 3.00) |
| Predecessor | Acorn Archimedes A310 |
| Successor | Acorn A3010 |
The Acorn Archimedes A3000 was a single-box home computer released in May 1989 as part of Acorn's Archimedes range. The first all-in-one Archimedes model, it integrated keyboard, motherboard, and floppy drive in a wedge-shaped case reminiscent of the earlier 8-bit machines while incorporating the revolutionary ARM RISC processor architecture.
Architecture
The A3000 utilized either the discrete ARM2 processor with support chips or the later ARM250, a single-chip solution integrating the ARM2 core, MEMC memory controller, VIDC video controller, and IOC input/output controller into one package.
System Architecture
| Component | Early A3000 | Late A3000 | Function |
|---|---|---|---|
| CPU | ARM2 @ 8 MHz | ARM250 @ 12 MHz | 32-bit RISC processor |
| MEMC | MEMC1a (separate) | Integrated in ARM250 | Memory controller, DMA |
| VIDC | VIDC1a (separate) | Integrated in ARM250 | Video and sound controller |
| IOC | IOC (separate) | Integrated in ARM250 | I/O controller, timers |
| RAM | 1 MB (4× 256K×9) | 1 MB minimum | Fast page mode DRAM |
| ROM | 2 MB (4× 512 KB) | 2 MB | RISC OS, applications |
Memory Map
| Address Range | Size | Function | Access Type |
|---|---|---|---|
| $0000000 – $01FFFFF | 2 MB | Logical RAM space | User mode |
| $0200000 – $02FFFFF | 1 MB | Physical RAM (1 MB model) | Direct |
| $0300000 – $033FFFF | 256 KB | Additional RAM (if fitted) | Direct |
| $0340000 – $035FFFF | 128 KB | VIDC frame buffer | DMA |
| $0360000 – $037FFFF | 128 KB | Sound DMA buffers | DMA |
| $0380000 – $03FFFFF | 512 KB | System space | Supervisor |
| $1000000 – $1FFFFFF | 16 MB | Expansion cards | I/O cycles |
| $2000000 – $2FFFFFF | 16 MB | Expansion cards | Synchronous |
| $3000000 – $33FFFFF | 4 MB | I/O controllers | I/O space |
| $3400000 – $35FFFFF | 2 MB | ROM (low) | Read only |
| $3600000 – $37FFFFF | 2 MB | ROM (high) | Read only |
| $3800000 – $3FFFFFF | 8 MB | ROM (expansion) | Read only |
Hardware Specifications
ARM2 Processor Details
| Feature | Specification | Notes |
|---|---|---|
| Architecture | 32-bit RISC | 26-bit address space |
| Registers | 27× 32-bit | 16 general + PC + status |
| Pipeline | 3-stage | Fetch, decode, execute |
| Cache | None | Direct memory execution |
| Instructions | Fixed 32-bit | Conditional execution |
| Modes | 4 processor modes | User, IRQ, FIQ, Supervisor |
| Performance | 4 MIPS @ 8 MHz | 0.5 instructions per clock |
VIDC (Video Controller)
The VIDC1a provided advanced video capabilities:
| Function | Specification | Implementation |
|---|---|---|
| Palette | 4096 colours | 12-bit RGB (4 bits per channel) |
| Sprites | Hardware pointer | 32×32 pixels, 3 colours |
| DMA | Video, cursor, sound | Cycle-stealing from RAM |
| Pixel rates | 8, 12, 16, 24 MHz | Software programmable |
| Sync generation | H/V sync | Programmable timing |
| Sound channels | 8 stereo | Logarithmic DAC |
Display Modes
| Mode | Resolution | Colours | Refresh | Memory Used |
|---|---|---|---|---|
| 0 | 640×256 | 2 | 50 Hz | 20 KB |
| 1 | 640×256 | 4 | 50 Hz | 40 KB |
| 2 | 640×256 | 16 | 50 Hz | 80 KB |
| 8 | 640×256 | 4 | 50 Hz | 40 KB |
| 9 | 640×256 | 16 | 50 Hz | 80 KB |
| 10 | 640×256 | 256 | 50 Hz | 160 KB |
| 11 | 640×512 | 2 | 50 Hz | 40 KB |
| 12 | 640×512 | 16 | 50 Hz | 160 KB |
| 13 | 640×512 | 256 | 50 Hz | 320 KB |
| 15 | 640×512 | 16 | 50 Hz | 160 KB |
| 18 | 640×512 | 2 | 75 Hz | 40 KB |
| 19 | 640×512 | 4 | 75 Hz | 80 KB |
| 20 | 640×512 | 16 | 75 Hz | 160 KB |
| 21 | 640×512 | 256 | 75 Hz | 320 KB |
| 23 | 1152×896 | Mono | 75 Hz | 132 KB |
Input/Output
Internal Expansion
The A3000 provided limited internal expansion:
| Slot | Type | Purpose | Compatibility |
|---|---|---|---|
| RAM expansion | 4× SIMM sockets | Up to 4 MB total | 256K×9 or 1M×9 SIMMs |
| Mini podule | Proprietary connector | Internal expansion | Network cards, SCSI |
| Serial upgrade | 20-pin header | RS423/RS232 | Optional 6551 ACIA |
| User port | 20-pin IDC | Digital I/O | BBC Micro compatible |
| Econet | 5-pin DIN | Network | Optional module |
External Ports
| Port | Connector | Function | Signals |
|---|---|---|---|
| Monitor | 15-pin D-sub | Analogue RGB | R,G,B, H/V sync |
| Serial | 9-pin D-sub | RS423 | TxD, RxD, CTS, RTS |
| Parallel | 25-pin D-sub | Centronics | 8-bit data + control |
| Mouse | 9-pin mini-DIN | Quadrature | X/Y movement, 3 buttons |
| Keyboard | Built-in | Matrix scan | 102-key extended |
| Headphones | 3.5mm jack | Stereo audio | 8-bit log DAC output |
| Econet | 5-pin DIN | Network | Clock, data (optional) |
Floppy Drive System
The A3000 included an internal 3.5" floppy drive:
| Specification | ADFS Format | DOS Format |
|---|---|---|
| Capacity | 800 KB (D) / 1.6 MB (E) | 720 KB / 1.44 MB |
| Sectors/track | 5 (D) / 10 (E) | 9 / 18 |
| Tracks | 80 | 80 |
| Sides | 2 | 2 |
| Sector size | 1024 bytes | 512 bytes |
| Controller | WD1772 @ 8 MHz | WD1772 |
| Data rate | 250 kbps | 250/500 kbps |
Sound System
The VIDC provided sophisticated audio:
Audio Specifications
- Channels: 8 independent stereo channels
- Sample rate: Variable up to 48 kHz
- Resolution: 8-bit logarithmic (µ-law)
- DMA: Automatic buffer refill
- Stereo positioning: 7 positions per channel
- Output: Internal speaker + headphone jack
Sound DMA System
- Buffer size: 16 bytes per channel
- Interrupt: On buffer empty
- Latency: < 1ms at 20 kHz sample rate
- Total bandwidth: 384 KB/s maximum
Power Supply
Internal switched-mode PSU specifications:
- Input: 220-240V AC, 50 Hz
- Output voltages:
* +5V @ 4A (logic) * +12V @ 1A (drives) * -5V @ 100mA (serial)
- Power consumption: 35W typical, 45W maximum
- Cooling: Passive convection
ROM Software
RISC OS 2.00/3.00
The 2 MB ROM contained:
- RISC OS kernel: Memory management, task switching
- Desktop: WIMP environment (Windows, Icons, Menus, Pointer)
- Filing systems: ADFS, DFS, NetFS, RamFS
- BASIC V: Enhanced BBC BASIC with assembler
- Applications: Edit, Paint, Draw, Configure
- Fonts: Trinity, Homerton, Corpus (outline fonts)
- Printer drivers: Dot matrix, inkjet, laser support
ROM Organization
| Address | Size | Contents |
|---|---|---|
| $3400000 | 512 KB | RISC OS kernel and modules |
| $3480000 | 512 KB | Desktop and WindowManager |
| $3500000 | 512 KB | Applications (Draw, Paint, Edit) |
| $3580000 | 512 KB | Fonts and printing system |
ARM250 Variant
Later A3000 models used the ARM250 integrated processor:
| Feature | ARM2 System | ARM250 System |
|---|---|---|
| Chip count | 4 (ARM2, MEMC, VIDC, IOC) | 1 (ARM250) |
| Clock speed | 8 MHz | 12 MHz |
| Power consumption | 8W (chips only) | 3W |
| Cache | None | 4 KB unified |
| Manufacturing | 3µm | 1.5µm CMOS |
| Cost | Higher | 60% reduction |
Technical Limitations
| Limitation | Cause | Impact |
|---|---|---|
| No hardware FPU | Cost reduction | Slow floating point via software |
| 26-bit addressing | ARM2 design | 64 MB address space limit |
| Single expansion slot | Case constraints | Limited upgrade options |
| No SCSI interface | Cost reduction | External SCSI pods required |
| 8-bit sound | VIDC limitation | Lower quality than CD audio |
| No genlock | Consumer positioning | No video production capability |
Known Hardware Issues
Power Supply Problems
- Capacitor failure: Switchmode PSU capacitors dry out after 30+ years
- Voltage drift: +5V rail drops causing system instability
- Thermal stress: Poor ventilation causes PSU overheating
Battery Leakage
- CMOS battery: 3.6V NiCd prone to leaking alkaline electrolyte
- PCB damage: Battery leakage corrodes nearby traces
- Clock failure: System loses time and configuration
Keyboard Issues
- Membrane failure: Key bounce and non-response
- Controller chip: 8051 microcontroller failures
- Cable stress: Ribbon cable fractures at hinge point
Floppy Drive
- Head alignment: Drift causes read errors
- Belt deterioration: Drive belt turns to sticky mess
- Capacitor leakage: Drive PCB capacitors fail
Manufacturing Variants
| Model | Processor | ROM Version | Production Period |
|---|---|---|---|
| A3000 (early) | ARM2 + support chips | RISC OS 2.00 | May 1989 - Dec 1989 |
| A3000 (mid) | ARM2 + support chips | RISC OS 2.01 | Jan 1990 - Jun 1990 |
| A3000 (late) | ARM250 | RISC OS 3.00 | Jul 1990 - Dec 1991 |
| A3000 (final) | ARM250 | RISC OS 3.10 | Jan 1991 - May 1991 |
Memory Timing
MEMC memory controller timing:
- Page mode: 2-1-1-1 cycles for sequential access
- Random access: 4 cycles (N-cycle)
- Video DMA: Steals 1 in 4 cycles during active display
- Sound DMA: On-demand, priority over CPU
- Refresh: 128 cycles every 4ms
Performance measurements:
- Sequential read: 16 MB/s
- Random read: 8 MB/s
- Video bandwidth: 4 MB/s (mode 13)
- Effective CPU bandwidth: 12 MB/s
General Maintenance
Critical maintenance includes replacing the CMOS battery before leakage occurs, cleaning the case ventilation slots to prevent overheating, and checking the PSU capacitors for bulging or leakage. The keyboard membrane should be inspected for wear, and the floppy drive requires periodic cleaning and lubrication. Internal dust should be removed with compressed air, particularly around the processor and PSU.
Troubleshooting
Common faults include startup failures (check PSU voltages and CMOS battery), corrupted display (VIDC timing or RAM faults), and floppy drive errors (clean heads, replace belt). The "Machine startup held" message indicates CMOS corruption requiring battery replacement. Intermittent crashes often result from PSU capacitor degradation or thermal issues.
Capacitor Replacement Guide
Essential capacitors requiring replacement:
- PSU primary: 220µF 200V, 47µF 50V
- PSU secondary: 2200µF 16V, 1000µF 16V (×2)
- Motherboard: 100µF 16V (×4), 47µF 16V (×6)
- Floppy controller: 10µF 25V (×3)
Expansion Options
Internal Mini-Podule
Compatible expansion cards:
- Econet module: Network interface
- SCSI interface: Hard drive controller
- MIDI interface: Musical instrument connectivity
- User port: Digital I/O interface
External Expansions
- External podule backplane: Adds 2-4 standard podule slots
- Hard drive podule: SCSI or IDE interfaces
- Genlock podule: Video synchronization
- Ethernet podule: 10Base2/10BaseT networking