Quote:
Originally Posted by litwr
Intel architecture is not perfect but it has less oddity than Motorola.
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Certainly not. Intel architecture is the governor of the oddity land.
Their protected mode is a total ununderstandable mess.
The registers all have special purpose and while we have AL, AH, we don't have anything to access any other byte, nor the upper word of EAX.
Addressing modes are quite irregular.
Segment registers weren't exactly the best thing they invented either.
So yes 68k isn't perfect, but has less oddities than Intel.
Quote:
Originally Posted by litwr
The dedicated address registers, two carry flags, two stacks, ... - all this stuff looks like an implementation of some bad theory.
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But isn't.
The dedicated registers allow encoding regs in only 3 bits instead of 4, allowing twice the amount of instructions be encoded in the same space, that for the price of a very minor annoyance. And as data/address regs don't behave the same, it's often, in fact, useful to have them separate.
Two stacks are *necessary*. When an interrupt occurs, do you really want its data being pushed to the user program's stack ? There is only one supervisor stack but as many user stacks as we have programs (but perhaps you don't know how it works in a multitasking environment ?). Not having two stack pointers would simply mess things up.
Well, with all this said, i agree that two carry flags wasn't the exact best idea they could have - but guess what, x86 also has two carry flags (it even has useless parity flag, and its overflow bit isn't in user land) so it has no lesson to give here.
Quote:
Originally Posted by litwr
Only 6502 and ARM have more clear architecture than Intel x86.
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Clear, but a lot too spartan and therefore weak.
And just everyone has more clear architecture than Intel x86 (8086 wasn't so bad but the more x86 advanced, the worse it became).
Now if you don't agree - i believe this will be the case
- it could be interesting to compare cpu families by comparing the same code for all of them (spigot seems too simple for this).
Maybe worth opening a thread - I will if enough people want to write code for non-68k cpus. Good idea or not ?