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MOS Technology specialists claimed that their processor was up to 4 times faster than the 6800. I find this questionable: the 6502 can work much faster with memory, but the 6800's second accumulator greatly accelerated many calculations. I can assume on estimation that the 6502 was on average no more than 2 times faster.
The 6800 and the 6502 are roughly the same speed, if you're speaking generally. I'm not sure where you got "the 6502 can work much faster with memory." It does usually handle array-to-array operations of 256 bytes or less faster than the 6800, which is not an uncommon case, but nor is it a huge part of almost every program out there.
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...the 6501 and 6502 in particular, did not support working with three output states and therefore could not be used directly, for example with hardware with direct memory access.
Well, that was pretty easily fixed with couple of external buffers. The Apple II used DMA for the video system in exactly this way. If leaving a tri-state address bus off of the 6502 resulted in significant cost savings (I have heard this, but have seen no conclusive evidence) then it certainly made sense to leave that to external parts that could be left off on systems that don't need that feature.
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Although a "bug" strictly speaking it was not. Of course for a specialist accustomed to the comfortable processors of large systems of those years one of the features that is quite relevant and even useful among microprocessors, could seem something annoying, a bug. But in fact this behavior of hurting someone's feelings was described in the official documentation from 1976....
Well, I don't think there's any plausible description of the indirect jump bug other than "bug." It was a
documented bug, certainly, but the behaviour caused problems that needed to be worked around and offered no advantages to anyone except people trying to obfuscate code.
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I raised this question on the forum 6502.org, where some participants had familiarity with the Apple ][ computers. I asked if anyone could give an example when the "bug" crashed the program. I received only emotional and general comments, a specific example was never offered.
Well the nature of the bug is that it would exhibit as "something is mysteriously wrong somewhere in the program" and would likely vanish if small changes were made to the program, so someone saying "I specifically encountered that" is low, but there could be many people who encountered it but never traced it down to that.
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On the other hand, the absolute majority of the new instructions only occupied the code space, adding almost nothing to the capabilities of the 6502, which left fewer free opcodes for possible further upgrades.
That's not a huge deal; there's no reason that little-used opcodes couldn't be removed in a new version of the CPU, to be replaced with other more useful things, should someone think of and implement them. The CMOS versions never had complete compatibility with each other anyway; Rockwell had instructions that Signetics did not have and so on.
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The last scene of the drama with the participation of the 6502 was featured in the prevention of computers based on the 6502 with a frequency of 2 MHz on the US market in the first half of the 80's. This affected the English BBC Micro, their manufacturing company Acorn made a large batch of computers for the United States, but as it turned out, in vain. Some kind of lock was triggered and the computers had to be urgently redone to European standards.
This sounds a bit dodgy, as if there's some sort of conspiracy involved or something. And, "Some kind of lock was trigered"? Do you have any documentation of this story?
Much of this part of the article comes across as quite speculative. Perhaps you should give your references for this stuff.
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The instruction system 6502 in some particular ways is unusually asymmetric, for example, there is an instruction to load register Y, LDY addr,X, but there is no pairwise unload to it. There is an instruction to reset the overflow flag, but there is no paired instruction to set it.
Both of these make perfect sense if you think about the design goals of the CPU (take out anything unnecessary in order to reduce cost) and how the instructions were used. Directly setting and clearing the overflow flag isn't something you'd typically want to do. But the 6502 does have an external pin that sets the overflow flag for use as a signal input, so of course you would want CLV to be able to clear that. LDY aaaa,X is conceivably useful for loading indices from a table, but there seems little call to
store indicies to a table.
Given that the design deliberately left out much more useful instructions, such as BRA, to keep costs down, it's no suprise that they left out more obscure and less useful instructions.
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The main drawback of the 6502 is the small stack size, only 256 bytes. However, for a system with a memory capacity of 64 KB, this, as practice has shown, is usually quite enough.
I wouldn't call that its main drawback. As it turns out, for the kinds of things done on the 6502 the small stack
isn't a drawback in most cases, much less its
main drawback. And I don't see it as related to the memory capacity of the machine.
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The Commodore PET in the development of which Chuck Peddle was actively involved appeared on sale half a year earlier than the Apple ][, although its mass production started only half a year later than the Apple ][.
My understanding is that the PET was not for sale at all until 1977-10 (4 months after the Apple II); up to that point they were only demoing it. BTW, the Apple II is generally written as "Apple II"; the stylized "][" was only ever used on the boot screen, and never in Apple documentation or advertising as far as I'm aware.
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Interestingly, of the three mass PCs that appeared in 1977, "the holy trinity", two were based on the 6502 and only one on the Z80. Unfortunately, the most important American computer manufacturers (Apple, Tandy RadioShack, IBM), from the 80's did not publish information about the number of PCs they produced.
None the less, this information is available. See, for example, some of the information I dug up in
this thread on retrocomputingforum.com. (EDIT: Link fixed to point to the right thread, and Ed has also mentioned
this thread.) For what it's worth, especially through about 1980, the TRS-80 was by far the biggest seller of the Trinity, and Apple by far the smallest.
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However, it was unclear why it was then to implement support for decimal arithmetic, which is completely superfluous in controllers.
Is it? Are controllers never used for processes that count and display in decimal?
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One can only try to fantasize about what would have happened if the 6502 had developed at the same pace as its competitors.
It seems to me it more or less did, and went the way of the other systems that also tried to maintain binary compatibility.
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Why the 6502 was slowed down in its development and deprived of a much brighter future?
I don't think it was slowed down in its development; if anything it was one of the two 8-bit processors (along with the Z80) that had any real future at all in computers (as opposed to microcontroller systems, where the 6800 descendants pretty much stomped both of them).
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I think I came across it again not long ago. Now I just need to remember where I filed it.
