Does anyone know if...

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OS4 will have built-in emulation for running code for the old 68k line of CPUs on the PPC based A1 and accelerator cards.  The problem is that many older games relied on specialised parts of the Amiga's hardware, such as the Copper, and the built-in emulation won't handle this (it's designed for speed, not features).  Of course, there's nothing to stop someone porting UAE to OS4; it might seem crazy at first, but UAE has full chipset emulation.  Untill then, a lot of games won't work (probably the vast majority of the famous "classic" games).

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Of course, UAE runs on Linux and that runs on the A1.

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At first it probably won't have JIT, and will probably be very unoptimised.  But surely it'd be usable - UAE without JIT worked fine for "classic" games on a PII 333.  It might be unusable on the Cyberstorm cards (but they'll be on a machine with AGA anyway) but I'd imagine it'd be fine on an A1 - you simply don't need Amithlon type speeds for playing all the old stuff.

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Or it could use the JIT in OS4 ? That way, the UAE would "only" need to emulate the OCS/AGA chipset and memory system of the "classic" hardware..

I've said that a few times now, but many people said that either:

a) It couldn't be done
b) It'd somehow make OS4 bloatware
c) There isn't a point

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x86

The family of CPU that is found in PeeCees.  You probably remember the 286/386/486 CPUs - it's the same architecture.  Examples include any Pentium or Athlon.  Other chip families include 68k (classic Amiga) and PPC (AmigaONE, accelerated Amiga, Mac, Pegasos).

UAE

The Universal Amiga Emulator.  Or the Unix Amiga Emulator.  Or, originally, the Useless Amiga Emulator (it couldn't boot).  It's the most popular emulator around, with support for tons of stuff and it can run faster than the fastest "classic" Amiga, due to JIT, which brings us to...

JIT

Stands for Just In Time.  It's a fancy way of emulation, where instructions are cached, and this speeds it up no end.  Newer versions of UAE have JIT, as does ^mithlon.  OS4 will have a built in JIT emulator, for running older applications.  Note that this emulator will only emulate the CPU, not the...

Chipset

When the Amiga was first made, processors weren't exactly fast.  To make a truly multimedia computer, co-processors were used - several different processors for sound, graphics, IO etc.  Together these are called the Custom Chipset, and are what made the Classic Amiga so amazing, by taking load off the main CPU.

OCS

Original Chip Set - the first Amiga chipset, used in the A1000, A500 and A2000.  Very nice for it's time - could display 32 colours at once in "normal" modes, up to 4096 in Hold And Modify (HAM) mode.  OCS was slightly upgraded to the ECS chipset for the A3000/600 and perhaps a few others.

AGA

The last chipset ever produced, used in the A1200 and A4000.  Could display 256 colours at once in "normal" modes, and about 260,000 in HAM.

Fortunately I knew what PPC A1200/4000, those are older Amigas, right?

The A1200 and A4000 were made in the early 90's.  The CPUs the used topped out at about 70Mhz, so in the late 90's PPC accelerators appeared, adding a secondary CPU, at around 200Mhz or so.  AmigaOS4 should run on these.