The Argonaut Dual Loading System (ADLS) was heralded as a potential cost-saver for software publishers in the late 1980s. The first game to use it was Rainbird's Starglider 2. ADLS meant that a game disk could be loaded on either an Atari ST or a Commodore Amiga. Both versions shared the same 68000-based code (with appropriate drivers, display code, etc), and so Argonaut devised a disk format and filing system that could work on either machine, resulting in ADLS.
There were plenty of problems to overcome before ADLS became viable though. At the time, there were two types of disk drive available to ST owners - single (360k) and double-sided (720k), compared to the Amiga which only had to worry about one type - double-sided (880k). By abandoning the standard ST disk format, Argonaut managed to squeeze 500k onto one side. Ditching the standard format meant writing new drivers just to load the data from the disk, but thankfully the drivers only occuppied about 20k.
Of course, there were also the usual other hardware differences between the ST and the Amiga to take into consideration (video, sound and so on). All of these differences had to be coded and then included on the same ADLS disk.
Unfortunately, ADLS proved less than reliable when it came down to the disk duplication process. The pressure was on to get Starglider 2 released, but the testers at Telecomsoft kept encountering problems with the pre-production sample disks (pre-prods) that were sent from the disk duplicators. The pre-prods would fail to load on standard STs and Amigas during repeated testing - a failure rate of almost 30% was recorded (three times out of every ten attempts the same disk would fail to load on the same ST or Amiga machine).
The fault was partially due to the disk format being difficult to reproduce, and also down to the variable quality of the internal disk drives supplied with Atari STs and Commodore Amigas. The disk format was tweaked and there were many technical discussions between Argonaut, Rainbird and the disk duplicators. A reliable version was produced in the end, but it was decided to drop the dual loading feature from the packaging and the box format labels for the UK and Europe. However, ADLS remained on the disks and so, in theory, the Amiga version would load on an ST and the ST version would load on an Amiga.
From a quality control and returns view-point, ADLS was a nightmare. Very early on a decision was made that the game would only be guaranteed to load on the machine that was stated on the box. This didn't actually change anything, as not many people owned both machines and the disk could be just as unreliable on an ST as on an Amiga!
The other problem associated with the ADLS used on Starglider 2 was that the save game disks were also meant to be compatible between ST and Amigas. Unfortunately, this also used a propriatory disk format which again fell foul to the same tecnical problems encountered by the game disk. This problem caused further delays to the Starglider 2's release, and put a great deal of pressure on the game testers to give it the thumbs up for full production to go ahead.
ADLS was an experiment which ultimately failed. It was only ever used for Starglider 2, and it caused more headaches than it was worth. Oddly enough, the ADLS remained prominant on the US release where the ST was barely a consideration - it had a tiny percentage of the market compared to the Amiga.