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Old 02 March 2017, 19:45   #139
matthey
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Join Date: Jan 2010
Location: Kansas
Posts: 1,284
Quote:
Originally Posted by Zetr0 View Post
Cat amongst the pidgins idea -

Why not port 3.x and or 4.x to x86?

Money would be made - shits would be given and possibly a very cool x86 would produce some wonderful creativity!
As Olaf hinted at, compatibility would be lost without sandboxing 68k programs (with an emulator like UAE) as AROS x86 did. Little endian (LE) would be a major porting hurdle to overcome. The x86 ISA only has 8 GP registers limiting Amiga like register usage or use x86_64 and have more problems with 64 bit pointers and code density deteriorates to RISC like. You are not going to have an efficient little AmigaOS in the end. If you go big, you need expensive high end hardware because smaller is faster and more energy efficient. As soon as an OS is on x86/x86_64 hardware everyone expects drivers for all the commodity hardware (some lacking info to program drivers) where the AmigaOS would not be competitive. I suppose SMP, memory protection and resource tracking support could be added at the same time as 64 bit and the LE change since all compatibility would be broken anyway. This would put the AmigaOS ahead of AROS x86 except that AROS x86 already has some software (mostly ports). IMO, you would have nothing competitive, nothing unique and nothing innovative. Many Amiga users would not even make the transition to such a platform.

Is it even necessary to go big with 64 bit physical addressing? Pointers need twice as much space and 8 byte alignment gives better performance with 64 bit pointers so more space is wasted aligning data (and code). The DCache is filled with many NOPs and zeros for only a few extra bits of addressing (usually only 40 bits of physical addressing is used). Code density drops significantly when moving to 64 bit wasting valuable ICache. Less than 10% of code and data is used often (probably much less on a small footprint OS like the 68k) so an MMU could quickly swap data between memory >4GB and the 32 bit 68k physical memory (memory<->disk is slow but memory<->memory is relatively fast) with the only limitation being that only 4GB of memory could be addressed at a time per task/process (this is a small limitation on an OS with a small footprint). The savings could be large for a multi-core CPU like an enhanced 68k where a 16kB L1 ICache and 16kB L1 DCache per core would likely significantly outperform that for most 64 bit ISA hardware (smaller caches are faster to access too). IMO, the 68k AmigaOS is a good candidate for such hardware as the AmigaOS does not currently use the MMU, backward compatibility could be maintained without sandboxing and the footprint of the AmigaOS is small enough that little MMU swapping would be necessary anyway and the 68k can improve code density to reduce L1 cache requirements and maximize the advantage of such a setup. An FPU and SIMD would still be able to process 64 bit datatypes. I don't want the 68k Amiga to follow the crowd to big and slow. I want it to be small, fast and friendly (lean and mean in a nice way).

Quote:
Originally Posted by OlafSch View Post
Many people (especially when using real hardware) do not use and like 3.9.
Most of the people who chose to stay with AmigaOS 3.1 have low end 68k hardware. The AmigaOS 3.9 glow icons are bigger, slower and don't look better with ECS/AGA unless slower screen modes are used (PeterK's icon.library partially offsets this disadvantage). More memory is required as some modules grew and a double reboot is necessary without a new kickstart ROM. The changes were good overall and a move in the right direction but Amiga users with high end hardware (RTG and accelerators) benefited more. It would be possible to optimize the 68k AmigaOS so that an AmigaOS 3.9 enhanced AmigaOS is faster and uses less memory than AmigaOS 3.1.

Quote:
Originally Posted by wawa View Post
class act is not a part of os3.9. its a freely available third party contribution. same as third party mui classes you may be using with your os3 or aros respectively.
Reaction is a part of AmigaOS 3.9 and is only a moderately enhanced ClassAct.

Last edited by matthey; 02 March 2017 at 19:57.
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