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1500 questions
29
votes
3 answers
What are uses of the byte after BRK instruction on 6502?
The BRK instruction on the MOS 6502 seems to be one of the more
ill-documented features of the processor. The 1976 preliminary data
sheet from MOS indicates that it's a 1-byte instruction using
the "implied" addressing mode (i.e., it has no…
cjs
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29
votes
4 answers
Did Apple really advise customers to lift up and then drop their computers?
This led to the infamous technical note where Apple recommended users facing problems with the Apple III to lift the computer two inches and then drop it, as this would set the circuits back in place.[1]
I couldn't find that technical note in the…
snips-n-snails
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29
votes
3 answers
Why did Intel abandon unified CPU cache?
When Intel introduced the 80486 in 1989, they included their first on-chip cache, ostensibly to compete better with Motorola, who had been including on-chip caches for 5 years (MC68020, 1984).
Unlike the Motorola CPUs, Intel went with unified L1…
Brian H
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29
votes
1 answer
In the original Z80 layout, where are the "traps" located? And what are their effects?
According to Zilog Oral History, Zilog only had a tight schedule to design the Z80. Facing the potential competition, Federico Faggin and Masatoshi Shima were worrying about Japanese semiconductor corporations copying their design: if they managed…
比尔盖子
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29
votes
9 answers
How did early x86 BIOS programmers manage to program full blown TUIs given very few bytes of ROM/EPROM?
I've always wondered how so much functionality and relative luxuries(CMOS Configuration Utilities. See: https://geekprank.com/bios/ for an example) included with most popular x86 BIOSes could be packed into such a tight space. According to Wikipedia…
video_error
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28
votes
4 answers
Was the Stack Exchange "Happy April Fools" page fitting with the '90's code?
We nostalgia fans were all treated to a nineties-esque page on the various Stack Exchange sites, complete with guest books, obnoxious tiled backgrounds, Comic Sans, etc.
However, when I went to view the source code, I was expecting to see tables…
komodosp
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28
votes
3 answers
Why separate cursor keys?
The original IBM PC keyboard didn't have separate cursor keys; the numeric keypad doubled as such. It wasn't long, however, until a new keyboard was introduced that did have separate cursor keys (so effectively two sets when num lock was turned…
rwallace
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28
votes
6 answers
How did the early Macintosh computers update the display?
This question is about the Macintosh 128k, but if you can give an answer which describes one of the other very similar machines, that's good too.
The bitmap was 512 by 384 pixels. Assuming that one byte stores eight pixels, so that the CPU can read…
Omar and Lorraine
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28
votes
5 answers
Why are Windows 95 installation disks not uniquely bound to a single product key?
I was installing the OEM version of Windows 95 on VirtualBox the other day for reminiscence sake, and for some reason I had two different product keys. I tested both of them to see which one mapped to the CD, and to my surprise both product keys…
Retro Gamer
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28
votes
2 answers
Are there runnable Multics systems available?
I've always read that Multics was a failed precurser of Unix, and was interested in seeing how it looks (as in, what features did Unix remove that Multics had, and did more modern Unixen bring them back when hardware improved).
Multics code was open…
multics
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28
votes
4 answers
How did 8 bit processors perform 16 bit arithmetic?
How did 8 bit processors such as the Z80 and 8080 perform 16 bit arithmetic? They have an 8 bit data bus, so how does the ALU perform 16 bit arithmetic on the register pairs?
Z80 architecture diagram (from Wikipedia):
Jet Blue
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28
votes
2 answers
The start of x86: Intel 8080 vs Intel 8086?
Why is it said that all modern Intel processors of the x86 family are said to descend from the Intel 8086 and not the Intel 8080? From the Wikipedia article on the Intel 8086,
The 8086 gave rise to the x86 architecture, which eventually became…
Evan Carroll
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28
votes
2 answers
Why does this BASIC program declare variables for the numbers 0 to 4?
On pages 150 to 154 of William Tang's (1982) Spectrum Machine Language for the Absolute Beginner, there are these lines of code. (Note GOTO 9000 is the first non-REM statement in the program).
9000 REM
9010 REM initialisation
9020 LET ze= PI - PI:…
harlandski
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28
votes
7 answers
Over its lifetime, how many Apple II computers were sold?
It would be nice to break it down by model if possible.
nevster
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28
votes
3 answers
How did the "rub joystick port to continue" in the Creatures 2 infinite lives cheat work?
The game Creatures 2 on the Commodore 64 had an unusual cheat to get infinite lives which unlike most things on the Internet that are said to "really work" really worked!
What you had to do was lick your finger and then rub it on the joystick port.…
komodosp
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