The 6502 CPU's overflow flag explained at the silicon level
1–10 of 34 posts
Re: The 6502 CPU's overflow flag explained at the silicon level
#2Very interesting
And this is 30 year old tech. The 6502, the processor in you cell phone is about 1000x faster than it (and much more capable)
To me the hardest part (apparently) is converting the electronic circuit to the actual chip drawings. Not sure how this is done (how do you route it). And this was done by hand in the 6502, the drawings were done the size of a desk and reduced photographically. (IIRC)
Re: The 6502 CPU's overflow flag explained at the silicon level
#3Very interesting And this is 30 year old tech. The 6502, the processor in you cell phone is about 1000x faster than it (and much more capable) To me the hardest part (apparently) is converting the electronic circuit to the actual chip drawings. Not sure how this is done (how do you route it). And this was done by hand in the 6502, the drawings were done the size of a desk and reduced photographically. (IIRC)
How did you come up with 1000x? With Moore's law we are only 3 orders of magnitude better than a processor from the late 1970s?
Re: The 6502 CPU's overflow flag explained at the silicon level
#4Very interesting And this is 30 year old tech. The 6502, the processor in you cell phone is about 1000x faster than it (and much more capable) To me the hardest part (apparently) is converting the electronic circuit to the actual chip drawings. Not sure how this is done (how do you route it). And this was done by hand in the 6502, the drawings were done the size of a desk and reduced photographically. (IIRC)
Great tale regarding the history of it was posted sometime ago on HN:
Re: The 6502 CPU's overflow flag explained at the silicon level
#5Very interesting And this is 30 year old tech. The 6502, the processor in you cell phone is about 1000x faster than it (and much more capable) To me the hardest part (apparently) is converting the electronic circuit to the actual chip drawings. Not sure how this is done (how do you route it). And this was done by hand in the 6502, the drawings were done the size of a desk and reduced photographically. (IIRC)
How did you come up with 1000x? With Moore's law we are only 3 orders of magnitude better than a processor from the late 1970s?
In terms of clockspeed, the 6502 ran at 1 to 2 MHz. Today's processors are at most running at around 2 to 4 GHz, so in terms of "order of magnitude" 1000x is spot on. Of course, on a clock-for-clock basis modern architecures are a lot wider too, which will also account for better performance. But clockspeed is simple enough.
Re: The 6502 CPU's overflow flag explained at the silicon level
#6Very interesting And this is 30 year old tech. The 6502, the processor in you cell phone is about 1000x faster than it (and much more capable) To me the hardest part (apparently) is converting the electronic circuit to the actual chip drawings. Not sure how this is done (how do you route it). And this was done by hand in the 6502, the drawings were done the size of a desk and reduced photographically. (IIRC)
How did you come up with 1000x? With Moore's law we are only 3 orders of magnitude better than a processor from the late 1970s?
Wikipedia lists the 6502 as having between 1 MHz to 2 MHz and the Samsung Galaxy SII as having around 1.2 GHz.[0] I'm guessing that's where the 1000x comes from... Or, you know, it's just a nice big number. ;P
[0] Of course, that's ignoring multiple cores, better microcode, caches, etc.
Re: The 6502 CPU's overflow flag explained at the silicon level
#7Very interesting And this is 30 year old tech. The 6502, the processor in you cell phone is about 1000x faster than it (and much more capable) To me the hardest part (apparently) is converting the electronic circuit to the actual chip drawings. Not sure how this is done (how do you route it). And this was done by hand in the 6502, the drawings were done the size of a desk and reduced photographically. (IIRC)
How did you come up with 1000x? With Moore's law we are only 3 orders of magnitude better than a processor from the late 1970s?
The 6502 ran at 1 MHz in the Apple ][. Modern processors run at 1 GHz (1000 MHz) and above. That's 1000x, which is 3 orders of magnitude.
Re: The 6502 CPU's overflow flag explained at the silicon level
#8Very interesting And this is 30 year old tech. The 6502, the processor in you cell phone is about 1000x faster than it (and much more capable) To me the hardest part (apparently) is converting the electronic circuit to the actual chip drawings. Not sure how this is done (how do you route it). And this was done by hand in the 6502, the drawings were done the size of a desk and reduced photographically. (IIRC)
How did you come up with 1000x? With Moore's law we are only 3 orders of magnitude better than a processor from the late 1970s?
Moore's law is about the number of transistors. The 6502 had ~3500. Modern desktop CPUs have ~2,500,000,000 (see also http://en.wikipedia.org/wiki/File:Transistor_Count_and_Moore... ).
So that's more like 1,000,000x (thus six orders of magnitude).
Then again, the grandparent was talking about speed, and speed doesn't scale linearly with the number of transistors.
Re: The 6502 CPU's overflow flag explained at the silicon level
#9Very interesting And this is 30 year old tech. The 6502, the processor in you cell phone is about 1000x faster than it (and much more capable) To me the hardest part (apparently) is converting the electronic circuit to the actual chip drawings. Not sure how this is done (how do you route it). And this was done by hand in the 6502, the drawings were done the size of a desk and reduced photographically. (IIRC)
How did you come up with 1000x? With Moore's law we are only 3 orders of magnitude better than a processor from the late 1970s?
Those are (generally accepted to be) the same thing...
One order of magnitude: 10x
Two orders of magnitude: 100x
Three orders of magnitude: 1000x
Re: The 6502 CPU's overflow flag explained at the silicon level
#10Very interesting And this is 30 year old tech. The 6502, the processor in you cell phone is about 1000x faster than it (and much more capable) To me the hardest part (apparently) is converting the electronic circuit to the actual chip drawings. Not sure how this is done (how do you route it). And this was done by hand in the 6502, the drawings were done the size of a desk and reduced photographically. (IIRC)
Almost 38 years, even... If you're interested in the story around MOS and the 6502, the early parts of "Commodore: A Company on the Edge" by Brian Bagnall covers it quite a bit including parts about the manual layout work that Bill Mensch did.
Here's an article about it too: http://research.swtch.com/6502
Not only did they route / layout by hand-drawing, and then cut the Rubylith photomask by hand (it's not a drawing they use to reduce it photographically - they cut out holes..), but Bill Mensch got it right the first time. 3,510 transistors according to the article.
Bill Mensch left MOS to found Western Design Centre quite early, and so is covered less in that book than Chuck Peddle which was instrumental in Commodore for a long time after they acquired MOS. The amazing thing is WDC still sell variations of the 6502 design, including various replacements such as a 16 bit version.
Peddle (the other main designer) and Mensch deserve a lot more attention than they've gotten.
(EDIT: From WDC's website: "Annual volumes in the hundreds (100’s) of millions of units keep adding in a significant way to the estimated shipped volumes of five (5) to ten (10) billion units. " Yikes...)