Guide to Running Classic DemosThis detailed information is only to run the most demos that you can, ideally 100%, and perfectly! If you're okay with just going onto the next if one demo glitches, try the stuff that applies to your Amiga below. You can also use WHDLoad, even though you're limited by the demos patched so far, and it takes a fair bit of knowledge to set it up.
See if you can get the general picture, or use it to understand how to get that special demo working correctly.
Remember that new demos are coming for the Amiga 500, and that most of these compatibility tips are not necessary for them.
HistoryMost if not all of the classic demos from the 80s and early 90s were written by teenagers, doing their best with the documentation available and having only their own Amiga to test on.
During and after this came new kickstarts, chipsets, and accelerators. For demos from 87-88, there wasn't much incompatibility information, and some coders just wrote an exe, not caring about chipmem, fastmem, expansion, etc. At the same time, they wanted to use as much memory as possible, even on 512K and 1MB Amigas.
A common solution was to just put the demo in high chipmem and overwrite whatever was there, and whoever wanted to see it would "make his machine demo-compatible". And if you wanted newly released demos to work the first time, that's what you did, you made sure as much high chipmem (within the first 512K chipmem area) as possible was available.
Part of the solution to this is to have some fastmem so the OS goes there instead of occupying chipmem, and use various commands like "Add22k", and disable external drives (which I suppose are not the must-have peripheral they once were, but they do steal a few K of chipmem).
Running from floppy vs harddiskUsually, running demos from floppy, i.e. official release disks and packdisks, takes care of the above tasks. Whoever made the disk prepared it so that the demos would load on a 512k+512k Amiga. Some packdisks have boot menus (try right mouse button on boot) for hardware compatibility options. Some older demos may require you to disable all fastmem.
When running separate executables from harddisk, you must simply mimic this manually. Disconnect external drives, boot without startup-sequence, run Add22k, and then cd and dir your way to the executable. My utility Hogfast allows you to "switch off" fastmem for the older demos mentioned above.
If you write demos to floppy, never use HD disks or HD drives! They're unreliable on all computers and machines from this era. Use DD disks. You can also use disk images directly on floppy emulators such as Gotek or HxC.
KickstartKick 1.3, what else, right? Most demos from 1990 onwards work fine with kick 2.0 and up, while those who came before can guru. 3.1 is almost as compatible as 1.3, but 2.0 can make demos fail for another reason: it uses the most memory of all the kickstarts. Not much more, but it can sometimes make the difference. Compatibility issues with OS versions is normally not a problem for trackmos and megademos, since they turn it off first thing.
But what about kick 1.2? It's fine to use, but you can't use it to start demos from harddisk since it has no harddisk support! Demos from 1987 and early 1988 are the most likely to rely on kick 1.2 and guru on 1.3 and up. Some music players can "freak out" on kick 2.0 and up.
ChipsetOCS is king, no question. Normally, using ECS Amigas (or A500s delivered with some ECS chips!), all demos still run normally but many can show corrupt-looking graphics, and this can be due to experimental copperlists resulting in incorrect "modulo".
On AGA machines, you can select OCS, ECS or AGA, and turn off CPU caches in the Early Boot Menu (both buttons held after reset). You may still get chipset incompatibilities.
Faster CPU/memoryYou may get tearing, skipped frames (and therefore perhaps music running too fast) if an effect is not double-buffered and synced properly.
Recommended mods for max compatible demo machines
- A1000 - solder the filter fix, color burst etc mods to the motherboard, and somehow get hold of some fastmem... should work fine.
- A500 - replace any ECS chips, use kick 1.2 and a 512k expansion with toggle switch and no extra equipment. If you want to use a harddisk/CF, get an expansion where extra memory can be turned off (like the Game Switch on GVP interfaces).
- A500+ - get ACA500 (or possibly a "5.5MB"-jumpered LordV expansion?) for slowmem, either way you'll have no Game Switch, but you can get that with a GVP interface. All three have Faster memory (see above) so those glitches apply, but it's still okay - the next best thing. You should be able to use Kick 1.2 and 1.3 as for A500. Chipset glitches are possible as per above.
- A600 - like A500+, but compatible expansions available are only the 5.5MB LordV expansion (A6055) or SRAM card for PCMCIA.
- A1200 - get an SRAM card or RCA120, enable OCS and disable caches in Early Boot Menu.
- A1500/2000/2500 are basically like A500, with a few small differences, but slowmem is not available, as far as I know.
The Ideal Demo Dream Machine!A Kick 1.3 OCS A500 with kickstart switch to 1.2, 512k slowmem with off switch, and a GVP interface with Game Switch, to write disk images to floppy.
If you follow the advice above, you can get pretty close to this, certainly a Gotek should be rather harmless, if you don't want to spend time on writing floppies), but this setup will give you the least compatibility trouble of all.
SymptomsIf you have maximized your Amiga's compatibility with classic demos, and you still get problems, these are some generic tips:
- Disk inserted, but insert disk screen reappears: try kick 1.2 if you know there is no read error
- Guru ending with address $0000ffff or lower: try changing kickstart, up or down but usually to 1.2.
- Guru ending with address $00080000 - $001fffff: enable fastmem.
- Guru ending with address $00200000 or higher: try disabling fastmem
- Trash graphics (not modulo bug) and/or random noise music: disable fastmem (HogFast is better to use if you can)
- Rolling copperlist: disable fastmem and change kickstart to 1.2.
- Rolling sprites after demo exit: Drag the CLI screen down, or press Amiga+m twice, or try running another demo and exit that.
- Error 103 or exiting without starting: Not enough memory available for the demo to start
- Demo bugs, gurus, or freezes on exit: Not so good, but you got to see the demo at least.