Acorn Archimedes A310

Acorn Archimedes A310

Archimedes 300-series system unit. The A305 and A310 are physically identical; only the DRAM fitment differs.
Specifications
Manufacturer	Acorn Computers Ltd
Type	Personal computer (three-box desktop)
Released	June 1987
Discontinued	1989
Intro price	£875 ex VAT (base), £1,075 ex VAT with colour monitor
CPU	ARM2 @ 8 MHz (24 MHz master oscillator)
Memory	1 MB RAM (32 × 4464 DRAM); larger third-party upgrades available
Storage	3.5" floppy drive, 1 MB unformatted (800 KB ADFS E)
Display	Analogue RGB, mono composite; 640×256 in 256 colours, 640×512 in 16 colours on a multisync
Sound	8-channel, 8-bit logarithmic (VIDC1a)
Dimensions	362 mm wide × 406 mm deep × 97 mm high (main unit, excluding feet)
OS / Firmware	Arthur 0.30, then Arthur 1.20; upgradeable to RISC OS 2 and, with a carrier board, RISC OS 3
Predecessor	BBC Master series (no page yet)
Successor	Acorn Archimedes A3000
Model no.	AKB15

The Acorn Archimedes A310 was launched in June 1987 alongside the A305. The two machines share the 276,000 motherboard and differ only in the amount of DRAM fitted: 1 MB in the A310, 0.5 MB in the A305. They were the first RISC-processor computers sold to the general public.

This page covers the parts specific to the A310. The chip set, screen modes, expansion, backup batteries, power rails, Acorn field changes and capacitor values are shared with the A305 and are documented on the Acorn Archimedes A305 page.

Prices

From Acorn's 1987 retail price list, ex VAT:

Product code	Configuration	RRP ex VAT	RRP inc VAT
AKB15	A310, no monitor	£875.00	£1,004.00
AKB15/AKF01	A310 with mono monitor	£925.00	£1,061.50
AKB15/AKF11	A310 with colour monitor	£1,075.00	£1,234.00

The figure of £999 that circulates for the A310 is the price of an A305 with a colour monitor, not an A310 of any kind.

A variant, the A310M Archimedes Music Workstation, was sold under product code AKB30.

Processor and memory

The ARM2 is a 32-bit processor with 26-bit addressing, clocked at 4 or 8 MHz from a single 24 MHz master oscillator depending on the memory cycle. Acorn quoted system performance as "typically 4 MIPS".

The A310 has the full complement of thirty-two 4464 DRAMs — 64K × 4 bits at 120 ns — giving 1 MB. This is the maximum the board takes as Acorn shipped it. Several third parties sold 2 MB and 4 MB upgrades; the smaller ones augmented the on-board memory and the larger ones replaced it entirely. Chris Whytehead's restored A310s carry IFEL 4 MB boards, one with the original MEMC1 and the others with MEMC1a.

ROM is 512 KB as standard in four 32-pin sockets.

Operating system

A310s shipped first with Arthur 0.30 and, from September 1987, Arthur 1.20. Acorn's own Arthur ROM fitting instructions make clear that Arthur 1.10 and Arthur 1.20 are the same release.

Arthur 1.20's desktop was written in BASIC and was very limited — a palette selector, calculator, notepad, clock, calendar and diary, with an icon bar that could format discs. RISC OS 2.00, dated 5 October 1988, replaced it and introduced the cooperative multitasking desktop proper. RISC OS 2 is a straight ROM swap on this board. RISC OS 3.10 and later need a ROM carrier board — IFEL's is the one usually found — because the RISC OS 3 ROM set does not fit the board's native four sockets.

Expansion

The A310 ships with no expansion slots. The Acorn AKA01 backplane (part 0176,040) adds two podule positions; third-party four-slot backplanes for the 305/310, such as IFEL's, came later. Total draw from the backplane must not exceed 20 W, and coprocessor podules are not supported on this board.

The area on the middle right of the motherboard is where the hard disc controller would sit — it is not fitted on any 300-series machine, unlike the A440. A hard disc on an A310 means the AKD52 podule-based upgrade or a third-party SCSI or IDE podule.

Decoupling capacitors C37, C38 and C39

Acorn specified three 100 µF 16 V 20% tantalum capacitors, part 0611,101, at C37, C38 and C39 as supply decoupling on the main PCB. C37 decouples the 12 V line, so a 16 V part sits at only 1.33 times the rail it is decoupling. Tantalums are intolerant of over-voltage and fail short, and these positions are the ones most often found burnt on surviving 300-series boards, typically presenting as a machine that will not start.

If you replace them, a higher-voltage part is a sensible substitution in the C37 position. Check the PSU rails at PL5 (+12 V), PL6 (0 V), PL7 (+5 V) and PL8 (−5 V) before and after.

The full capacitor list for this board is on the A305 page, from Acorn's component-level parts list.

Measured performance

Chris Whytehead's documented A310s give the only published measurements taken on a known configuration of this board:

Machine	CPU	Memory controller	OS	ARMSi v4.0 MIPS	SICK Dhrystone/s	kWhetstone/s
A310 (2)	ARM2 8 MHz	MEMC1a	RISC OS 2.00	4.80	4,797	—
A310 (3)	CJE Micros ARM3 25 MHz	MEMC1a	RISC OS 3.10	12.75	17,326	213

Acorn's own marketing figure was 4 MIPS. Higher figures quoted for the Archimedes at launch — 4.5 MIPS, and in some contemporary reports 18 MIPS — are peak or synthetic numbers and are not supported by any measurement on a documented machine.

The MEMC1a

Later 300-series machines and all A400/1 machines use the MEMC1a in place of the original MEMC1. Acorn described the change as giving "a slight performance improvement". The frequently repeated claim of a 10% gain is not supported by the measured figures: an ARM2 A310 with MEMC1a returns 4.80 MIPS on ARMSi and a MEMC1a A3000 4.82, against 4.56 for a MEMC1 A440. The MEMC1a's real significance is that it will run at a 12 MHz memory clock, which is what the A540 and A5000 use; on the A310 the memory clock stays at 8 MHz.

Where the MEMC1a matters on this board is that it is required for the larger third-party memory upgrades.

Maintenance and repair

• Remove the two AA alkaline cells from the holder riveted to the base metalwork. Acorn specified annual replacement; cells left in for decades leak and attack the board. See Battery Explosion, Capacitor or Corrosion Damage.
• Check C37, C38 and C39 — see above.
• Check the PSU rails at PL5–PL8. A clicking PSU means a short between outputs or a failed supply.
• Check the ROM type links LK2, LK6 and LK12 after any ROM change.
• Floppy drive — see Floppy Drive Repair.
• Tools — see Recommended Tools.

Acorn's documented production faults and field change orders for this board — the speaker noise modification, the RGB level change, the video noise diode, the Q9/Q11 audio transistor issue and the Issue 1 serial port links — are listed on the A305 page.

Component-level fault-finding is in the Archimedes 300 Series Service Manual Component Level Supplement; module-level procedures are in the Archimedes 300 Series Service Manual.

See also

• Acorn Archimedes A305 — the same board with half the memory
• Acorn Archimedes A440 — 4 MB flagship of the same 1987 range
• Acorn Archimedes A3000 — the 1989 replacement for the 300 series
• Archimedes 300 Series Service Manual