Tuesday, September 29, 2020

Color blindness

Color blindness is an inaccurate term. Most color-blind people can see color, they just don't see the same colors as everyone else.

There have been a number of articles written about how to improve graphs, charts, and other visual aids on computers to better serve color-blind people. That is a worthwhile endeavor, and the people writing them mean well, but I suspect very few of them are color-blind because the advice is often poor and sometimes wrong. The most common variety of color blindness is called red-green color blindness, or deuteranopia, and it affects about 6% of human males. As someone who has moderate deuteranopia, I'd like to explain what living with it is really like.


The answer may surprise you.


I see red and green just fine. Maybe not as fine as you do, but just fine. I get by. I can drive a car and I stop when the light is red and go when the light is green. (Blue and yellow, by the way, I see the same as you. For a tiny fraction of people that is not the case, but that's not the condition I'm writing about.)


If I can see red and green, what then is red-green color blindness?


To answer that, we need to look at the genetics and design of the human vision system. I will only be writing about moderate deuteranopia, because that's what I have and I know what it is: I live with it. Maybe I can help you understand how that impairment—and it is an impairment, however mild—affects the way I see things, especially when people make charts for display on a computer.


There's a lot to go through, but here is a summary. The brain interprets signals from the eye to determine color, but the eye doesn't see colors. There is no red receptor, no green receptor in the eye. The color-sensitive receptors in the eye, called cones, don't work like that. Instead there are several different types of cones with broad but overlapping color response curves, and what the eye delivers to the brain is the difference between the signals from nearby cones with possibly different color response. Colors are what the brain makes from those signals.


There are also monochromatic receptors in the eye, called rods, and lots of them, but we're ignoring them here. They are most important in low light. In bright light it's the color-sensitive cones that dominate.


For most mammals, there are two color response curves for cones in the eye. They are called warm and cool, or yellow and blue. Dogs, for instance, see color, but from a smaller palette than we do. The color responses are determined, in effect, by pigments in front of the light receptors, filters if you will. We have this system in our eyes, but we also have another, and that second one is the central player in this discussion.


We are mammals, primates, and we are members of the branch of primates called Old World monkeys. At some point our ancestors in Africa moved to the trees and started eating the fruit there. The old warm/cool color system is not great at spotting orange or red fruit in a green tree.  Evolution solved this problem by duplicating a pigment and mutating it to make a third one. This created three pigments in the monkey eye, and that allowed a new color dimension to arise, creating what we now think of as the red/green color axis. That dimension makes fruit easier to find in the jungle, granting a selective advantage to monkeys, like us, who possess it.


It's not necessary to have this second, red/green color system to survive. Monkeys could find fruit before the new system evolved. So the red/green system favored monkeys who had it, but it wasn't necessary, and evolutionary pressure hasn't yet perfected the system. It's also relatively new, so it's still evolving. As a result, not all humans have equivalent color vision.


The mechanism is a bit sloppy. The mutation is a "stutter" mutation, meaning that the pigment was created by duplicating the original warm pigment's DNA and then repeating some of its codon sequences. The quality of the new pigment—how much the pigment separates spectrally from the old warm pigment—is determined by how well the stutter mutation is preserved. No stutter, you get just the warm/cool dimension, a condition known as dichromacy that affects a small fraction of people, almost exclusively male (and all dogs). Full stutter, you get the normal human vision with yellow/blue and red/green dimensions. Partial stutter, and you get me, moderately red-green color-blind. Degrees of red-green color blindness arise according to how much stutter is in the chromosome.


Those pigments are encoded only on the X chromosome. That means that most males, being XY, get only one copy of the pigment genes, while most females, being XX, get two. That means that if an XY male inherits a bad X, a likely result if he has a color-blind father, he will be color-blind too. An XX female, though, will be much less likely to get two bad copies. But some will get a good one and a bad one, one from the mother and one from the father, giving them four pigments. Such females are called tetrachromatic and have a richer color system than most of us, even than normal trichromats like you.


The key point about the X-residence of the pigment, though, is that men are much likelier than women to be red-green color-blind.


Here is a figure from an article by Denis Baylor in an essay collection called Colour Art & Science, edited by Trevor Lamb and Janine Bourriau, an excellent resource.


The top diagram shows the pigment spectra of a dichromat, what most mammals have. The bottom one shows the normal trichromat human pigment spectra. Note that two of the pigments are the same as in a dichromat, but there is a third, shifted slightly to the red. That is the Old World monkey mutation, making it possible to discriminate red. The diagram in the middle shows the spectra for someone with red-green color blindness. You can see that there are still three pigments, but the difference between the middle and longer-wave (redder) pigment is smaller.


A deuteranope like me can still discriminate red and green, just not as well. Perhaps what I see is a bit like what you see when evening approaches and the color seems to drain from the landscape as the rods begin to take over. Or another analogy might be what happens when you turn the stereo's volume down: You can still hear all the instruments, but they don't stand out as well.


It's worth emphasizing that there is no "red" or "green" or "blue" or "yellow" receptor in the eye. The optical pigments have very broad spectra. It's the difference in the response between two receptors that the vision system turns into color.


In short, I still see red and green, just not as well as you do. But there's another important part of the human visual system that is relevant here, and it has a huge influence on how red-green color blindness affects the clarity of diagrams on slides and such.


It has to do with edge detection. The signals from receptors in the eye are used not only to detect color, but also to detect edges. In fact since color is detected largely by differences of spectral response from nearby receptors, the edges are important because that's where the strongest difference lies. The color of a region, especially a small one, is largely determined at the edges.


Of course, all animals need some form of visual processing that identifies objects, and edge detection is part of that processing in mammals. But the edge detection circuitry is not uniformly deployed. In particular, there is very little high-contrast detection capability for cool colors. You can see this yourself in the following diagram, provided your monitor is set up properly. The small pure blue text on the pure black background is harder to read than even the slightly less saturated blue text, and much harder than the green or red. Make sure the image is no more than about 5cm across to see the effect properly, as the scale of the contrast signal matters:



In this image, the top line is pure computer green, the next is pure computer red, and the bottom is pure computer blue. In between is a sequence leading to ever purer blues towards the bottom. For me, and I believe for everyone, the bottom line is very hard to read.


Here is the same text field as above but with a white background:



Notice that the blue text is now easy to read. That's because it's against white, which includes lots of light and all colors, so it's easy for the eye to build the difference signals and recover the edges. Essentially, it detects a change of color from the white to the blue. Across the boundary the level of blue changes, but so do the levels red and green. When the background is black, however, the eye depends on the blue alone—black has no color, no light to contribute a signal, no red, no green—and that is a challenge for the human eye.


Now here's some fun: double the size of the black-backgrounded image and the blue text becomes disproportionately more readable:



Because the text is bigger, more receptors are involved and there is less dependence on edge detection, making it easier to read the text. As I said above, the scale of the contrast changes matters. If you use your browser to blow up the image further you'll see it becomes even easier to read the blue text.


And that provides a hint about how red-green color blindness looks to people who have it.


For red-green color-blind people, the major effect comes from the fact that edge detection is weaker in the red/green dimension, sort of like blue edge detection is for everyone. Because the pigments are closer together than in a person with regular vision, if the color difference in the red-green dimension is the only signal that an edge is there, it becomes hard to see the edge and therefore hard to see the color. 


In other words, the problem you have reading the blue text in the upper diagram is analogous to how much trouble a color-blind person has seeing detail in an image with only a mix of red and green. And the issue isn't between computer red versus computer green, which are quite easy to tell apart as they have very different spectra, but between more natural colors on the red/green dimension, colors that align with the naturally evolved pigments in the cones.


In short, color detection when looking at small things, deciding what color an item is when it's so small that only the color difference signal at the edges can make the determination, is worse for color-blind people. Even though the colors are easy to distinguish for large objects, it's hard when they get small.


In this next diagram I can easily tell that in the top row the left block is greenish and the right block is reddish, but in the bottom row that is a much harder distinction for me to make, and it gets even harder if I look from father away, further shrinking the apparent size of the small boxes. From across the room it's all but impossible, even though the colors of the upper boxes remain easy to identify.



Remember when I said I could see red and green just fine? Well, I can see the colors just fine (more or less). But that is true only when the object is large enough that the color analysis isn't being done only by edge detection. Fields of color are easy, but lines and dots are very hard.


Here's another example. Some devices come with a tiny LED that indicates charging status by changing color: red for low battery, amber for medium, and green for a full charge. I have a lot of trouble discriminating the amber and green lights, but can solve this by holding the light very close to my eye so it occupies a larger part of the visual field. When the light looks bigger, I can tell what color it is.


Another consequence of all this is that I see very little color in the stars. That makes me sad.


Remember this is about color, just color. It's easy to distinguish two items if their colors are close but their intensities, for example, are different. A bright red next to a dull green is easy to spot, even if the same red dulled down to the level of the green would not be. Those squares above are at roughly equal saturations and intensities. If not, it would be easier to tell which is red and which is green.


To return to the reason for writing this article, red/green color blindness affects legibility. The way the human vision system works, and the way it sometimes doesn't work so well, implies there are things to consider when designing an information display that you want to be clearly understood.


First, choose colors that can be easily distinguished. If possible, keep them far apart on the spectrum. If not, differentiate them some other way, such as by intensity or saturation.


Second, use other cues if possible. Color is complex, so if you can add another component to a line on a graph, such as a dashed versus dotted pattern, or even good labeling, that helps a lot.


Third, edge detection is key to comprehension but can be tricky. Avoid difficult situations such as pure blue text on a black background. Avoid tiny text.


Fourth, size matters. Don't use the thinnest possible line. A fatter one might work just as well for the diagram but be much easier to see and to identify by color.


And to introduce one last topic, some people, like me, have old eyes, and old eyes have much more trouble with scattered light and what that does to contrast. Although dark mode is very popular these days, bright text on a black background scatters in a way that makes it hard to read. The letters have halos around them that can be confusing. Black text on a white background works well because the scatter is uniform and doesn't make halos. It's fortunate that paper is white and ink is black, because that works well for all ages.


The most important lesson is to not assume you know how something appears to a color-blind person, or to anyone else for that matter. If possible, ask someone you know who has eyes different from yours to assess your design and make sure it's legible. The world is full of people with vision problems of all kinds. If only the people who used amber LEDs to indicate charge had realized that.


Saturday, April 04, 2020

Smiles

(Another resurrected post from the my old Google+ stream, which appeared on or about Dec 6, 2011.)

For unknown reasons, someone asked me if had a copy of this file today. I didn't, but I remembered it was in dmr's home directory, and asked a friend there to find it. I remembered correctly. I don't know why it was touched in 1993, but the .v (mips object file) was created in late 1992. I leave the significance of that date as an exercise for the reader.

By the way, sizeof(void) is illegal, so I'm unsure how it was compiled; my friend assures me the compilers from then didn't accept it either.

Because G+ refuses to leave the indentation alone and screws up the ls formatting, I'm posting a screen grab here, but i'll include the source code, poorly formatted and rudely scrubbed of indentation, so you can play with the bytes. Just for fun, after the first screen grab I'll post a second screen grab of this post in edit mode before I hit save.

#include <u.h>
#include <libc.h>

typedef int ☺☹☻;
typedef void ☹☺☻;
enum
{
    ☹☻☺ = sizeof(☺☹☻),
    ☻☺☹ = sizeof(☹☺☻),
};

☹☺☻
main(☹☺☻)
{
    ☺☹☻ ☺☻☹;

    for(☺☻☹=☻☺☹; ☺☻☹<☹☻☺; ☺☻☹++)
        print("☺☻☹ = %d\n", ☺☻☹);
    exits(☻☺☹);
}




Sunday, January 26, 2020

UTF-8 turned 20 years old (in 2012)

(Another resurrected post from the my old Google+ stream, which appeared on or about Sep 4, 2012. Thirty years of age isn't too far off now.)


UTF-8 turned 20 years old yesterday.

It's been well documented elsewhere (http://www.cl.cam.ac.uk/~mgk25/ucs/utf-8-history.txt) that one Wednesday night, after a phone call from X/Open, Ken Thompson and I were sitting in a New Jersey diner talking about how best to represent Unicode as a byte stream. Given the experience we had accumulated dealing with the original UTF, which had many problems, we knew what we wanted. X/Open had offered us a deal: implement something better than their proposal, called FSS/UTF (File System Safe UTF; the name tells you something on its own), and do so before Monday. In return, they'd push it as existing practice.

UTF was awful. It had modulo-192 arithmetic, if I remember correctly, and was all but impossible to implement efficiently on old SPARCs with no divide hardware. Strings like "/*" could appear in the middle of a Cyrillic character, making your Russian text start a C comment. And more. It simply wasn't practical as an encoding: think what happens to that slash byte inside a Unix file name.

FSS/UTF addressed that problem, which was great. Big improvement though it was, however, FSS/UTF was more intricate than we liked and lacked one property we insisted on: If a byte is corrupted, it should be possible to re-synch the encoded stream without losing more than one character. When we claimed we wanted that property, and sensed we could press for a chance to design something right, X/Open gave us the green light to try.

The diner was the Corner Café in New Providence, New Jersey. We just called it Mom's, to honor the previous proprietor. I don't know if it's still the same, but we went there for dinner often, it being the closest place to the Murray Hill offices. Being a proper diner, it had paper placemats, and it was on one of those placemats that Ken sketched out the bit-packing for UTF-8. It was so easy once we saw it that there was no reason to keep the placemat for notes, and we left it behind. Or maybe we did bring it back to the lab; I'm not sure. But it's gone now.

I'll always regret that.

But that's my only regret in this story. UTF-8 has made the world a better place and I am delighted to have been a facilitator in its creation.

So tonight, please give a toast to a few quickly sketched boxes on a placemat in a New Jersey diner that today define how humans represent their text to be sent across international boundaries (http://googleblog.blogspot.com/2012/02/unicode-over-60-percent-of-web.html), and especially to the X/Open folks for giving us the chance and the Unicode consortium and IETF for pushing it so successfully.

Signed,
-rob
U+263A '☺' white smiling face


Wednesday, January 22, 2020

Unix Quiz answers

(Here's the next resurrected post, this time from Jun 8, April 30, 2012.)

A while back I posted the questions from the 1984 Unix/mpx Exit quiz: https://commandcenter.blogspot.com/2020/01/unix-quiz.html

Here they are again, with annotated answers. The answers are in the form of the simplified pattern that the mpx exit program used to verify them.

Note: I have never seen a correct set of answers posted on line except when they originated from this list. In other words, I don't believe anyone ever got all the questions correct, even with a web search engine. It may not even be possible.

1. Q:The source code motel: your source code checks in, but it never checks out. What is it?
A:sccs
The Source Code Control System. The reference is to the Roach Motel.

2. Q:  Who wrote the first Unix screen editor?
A: irons
Ned Irons wrote a full-screen editor (the first?) at IDA in the 1960s and a Unix version, perhaps a translation, at Yale a few years later.

3. Q:  Using TSO is like kicking a {what?} down the beach.
A: dead whale
The quote is from Steve Johnson. For those of you who never experienced TSO, it's an accurate characterization.

4. Q:  What is the filename created by the original dsw(1)?
A: core
Setting the file's i-number using the switches on the front panel was the other half of its user interface.

5. Q:  Which edition of Unix first had pipes?
A: third | 3
Look it up.

6. Q:  What is =O=?
A: empire
Empire was a large-scale strategy game developed at Reed College and made a computer game by Peter Langston (and perhaps others?).

7. Q:  Which Stephen R. Bourne wrote the shell?
A: software | 1138 | regis
There were two people named Stephen R. Bourne working at SGI in the early 1980s. The one who wrote software (as opposed to designing hardware), who had worked in BTL Center 1138, or whose middle name was Regis: he wrote the shell.

8. Q:  Adam Buchsbaum's original login was sjb. Who is sjb?
A: sol & buchsbaum
Adam was one of many Unix room kids with parents who worked at the Bell Labs. Adam was unusual because his father was executive vice president but apparently didn't have enough clout to get his kid his own login.

9. Q:  What was the original processor in the Teletype DMD-5620?
A: mac & 32
The 5620 was the productized Blit. Trick question: most people thought the 5620, like the Blit, had a 68000 but it used the much less suitable yet more expensive BELLMAC-32.

10. Q:  What was the telephone extension of the author of mpx(2)?
A: 7775
The (2) here is important. Greg Chesson wrote mpx(2); I wrote mpx(8).

11. Q:  Which machine resulted in the naming of the "NUXI problem"?
A: series 1 | series one
The IBM Series/1 was big-endian. Swap the bytes of "UNIX", the first text printed as Unix booted.

12. Q:  What customs threat is dangerous only when dropped from an airplane?
A: belle | chess machine
Ken Thompson took Belle (the chess machine) to the Soviet Union for a tour. Well, he tried: the machine was impounded by U.S. customs and never left American soil. Ken's trip was not much fun.

13. Q:  Who wrote the Bourne Shell?
A: bourne
The only real gimme in the list. Feels like a trick question though.

14. Q:  What operator in the Mashey shell was replaced by "here documents"?
A: pump
Sometimes better ideas do win out.

15. Q:  What names appear on the title page of the 3.0 manual?
A: dolotta & petrucelli & olsson
This refers to System 3, two before System V. It always makes your technology seem more modern when you use Roman numerals.

16. Q:  Sort the following into chronological order: a) PWB 1.2, b) V7, c) Whirlwind, e) System V, f) 4.2BSD, g) MERT.
A: cagbef
Whirlwind is a ringer.

17. Q:  The CRAY-2 will be so fast it {what?} in 6 seconds.
A: infinite | np-complete | p=np
What can I say? The whole exercise was juvenile.

18. Q:  How many lights are there on the front panel of the original 11/70?
A: 52
We counted.

19. Q:  What does FUBAR mean?
A: failed unibus address register
It's really a register name on the VAX-11/780. Someone at DEC liked us.

20. Q:  What does "joff" stand for?
A: jerq obscure feature finder
Tom Cargill's debugger changed its name soon after we were pressured by management to change Jerq to Blit.

21. Q:  What is "Blit" an acronym of?
A: nothing
Whatever people thought, even those who insisted on spelling it BLIT, Blit was not an acronym.

22. Q:  Who was rabbit!bimmler?
A: rob
See Chapter 1 of The Unix Programming Environment for another theory.

23. Q:  Into how many pieces did Ken Thompson's deer disintegrate?
A: three | 3
During takeoff at Morristown airport, propeller meets deer; venison results.

24. Q:  What name is most common at USENIX conferences?
A: joy | pike
Sun Microsystems made these obnoxious conference badges that said, "The Joy of UNIX". We retaliated.

25. Q:  What is the US patent number for the setuid bit?
A: 4135240
Dennis Ritchie was granted the only patent that came out of Research Unix.

26. Q:  What is the patent number that appears in Unix documentation?
A: 2089603
I'm not a fan of this stuff. Look it up yourself.

27. Q:  Who satisfied the patent office of the viability of the setuid bit patent?
A: faulkner
At a time when software patents were all but unknown, Roger Faulkner demonstrated to a judge that the patent was sufficiently well explained by taking a Unix kernel without it and putting it in, given the patent text. A clean-room recreation, if you will.

28. Q:  How many Unix systems existed when the Second Edition manual was printed?
A: 10 | ten
It's right there in the introduction.

29. Q:  Which Bell Labs location is HL?
A: short hills
Easy for Labbers, not so easy for others. MH was Murray Hill.

30. Q:  Who mailed out the Sixth Edition tapes?
A: biren | irma
Packages from Irma Biren were very popular in some circles.

31. Q:  Which University stole Unix by phone?
A: waterloo
Software piracy by modem. I'm not telling.

32. Q:  Who received the first rubber chicken award?
A: mumaugh
I don't remember what this was about, and the on-line references are all about this quiz.

33. Q:  Name a feature of C not in Kernighan and Ritchie.
A: enum | structure assignment | void
K&R (pre-ANSI) was pretty old.

34. Q:  What company did cbosg!ccf work for?
A: weco | western
Western Electric. Chuck Festoon was created by Ron Hardin as a political statement about automated document processing.

35. Q:  What does Bnews do?
A: suck | gulp buckets
Obscure now, but this was a near-gimme at the time.

36. Q:  Who said "Sex, Drugs, and Unix?"
A: tilson
Mike Tilson handed out these badges at an earlier USENIX. They were very popular, although the phrase doesn't scan in proper Blockhead style.

37. Q:  What law firm distributed Empire?
A: dpw | davis&polk&wardwell
Peter Langston worked for this Manhattan law firm, whose computer room had a charming view of FDR Drive.

38. Q:  What computer was requested by Ken Thompson, but refused by management?
A: pdp-10 | pdp10
Sic.

39. Q:  Who is the most obsessed private pilot in USENIX?
A: goble | ghg
Cruel but fair.

40. Q:  What operating system runs on the 3B-20D?
A: dmert | unix/rtr
DMERT gives you dial tone. The D stands for dual, as in dual-processor for redundancy. In a particular Bell System way, it was an awesome machine.

41. Q:  Who wrote find(1)?
A: haight
Dick Haight also wrote cpio(1), which to my knowledge was the first Unix program that did nothing at all unless you gave it options.

42. Q:  In what year did Bell Labs organization charts become proprietary?
A: 83
And soon after, PJW appeared.

43. Q:  What is the Unix epoch in Cleveland?
A: 1969 & dec & 31 & 19:00
Easy.

44. Q:  What language preceded C?
A: nb
Between B and C was NB. B was interpreted and typeless. NB was compiled and barely typed. C added structs and became powerful enough to rewrite the Unix kernel.

45. Q:  What language preceded B?
A: bon | fortran
BCPL is not the right answer.

46. Q:  What letter is mispunched by bcd(6)?
A: r
This trick question was used to verify that a Unix knock-off was indeed a clean-room reimplementation. Or maybe they just fixed the bug.

47. Q:  What terminal does the Blit emulate?
A: jerq
Despite what Wikipedia claims at the time I'm writing this, the Blit did not boot up with support for any escape sequences.

48. Q:  What does "trb" stand for (it's Andy Tannenbaum's login)?
A: tribble
I honestly never knew why this moniker was applied to Andy (no, the other one), although I can guess.

49. Q:  allegra!honey is no what?
A: lady
Peter Honeyman is many things, but ladylike, no.

50. Q:  What is the one-line description in vs.c?
A: screw works interface
From the man page for the driver for the Votrax speech synthesizer.

51. Q:  What is the TU10 tape boot for the PDP-11/70 starting at location 100000 octal?
A: 012700 172526 010040 012740 060003 105710 012376 005007
It's in the book. There was a sad time when I not only had this memorized, it was in muscle memory.

52. Q:  What company owns the trademark on Writer's Workbench Software?
A: at & t communications
AT&T never could decide what it was to call itself.

53. Q:  Who designed Belle?
A: condon | jhc
Joe Condon, hardware genius, died just a few months ago. Belle was the first computer to achieve international master status, using (roughly speaking) Joe's hardware and Ken's software.

54. Q:  Who coined the name "Unix"?
A: kernighan | bwk
This one is well known.

55. Q:  What manual page mentioned Urdu?
A: typo
I miss the typo command and occasionally think of recreating it.

56. Q:  What politician is mentioned in the Unix documentation?
A: nixon
The Nixon era was a dark period for people maintaining time zone tables.

57. Q:  What program was compat(1) written to support?
A: zork | adventure
My memory is rusty on this one and I don't have the 6th Edition manual to hand.

58. Q:  Who is "mctesq"?
A: michael & toy & esquire
Michael Toy wrote rogue...

59. Q:  What was "ubl"?
A: rogue | under bell labs
... which Peter Weinberger renamed ubl when he imported it. The renaming made sense to anyone who worked at Murray Hill.

60. Q:  Who bought the first commercial Unix license?
A: rand
The RAND Corporation led the way.

61. Q:  Who bought the first Unix license?
A: columbia
Columbia University.

62. Q:  Who signed the Sixth Edition licenses?
A: shahpazian
He was the lawyer who literally signed off on the licenses.

63. Q:  What color is the front console on the PDP-11/45 (exactly)?
A: puce
That's what DEC called it. It's not puce at all, which is why it's a good trivia question.

64. Q:  How many different meanings does Unix assign to '.'?
A: lots | many | countless | myriad | thousands
Ken's favorite character on the keyboard.

65. Q:  Who said "Smooth rotation butters no parsnips?"
A: john & tukey
John Tukey discovered/invented the Fast Fourier Transform algorithm, coined the term "bit" for Claude Shannon, and of course uttered this unforgettable gem.

66. Q:  What was the original name for cd(1)?
A: ch
You answered chdir, didn't you? You were wrong.

67. Q:  Which was the first edition of the manual to be typeset?
A: 4 | four
The old phototypesetting process was much smellier than a modern printer.

68. Q:  Which was the first edition of Unix to have standard error/diagnostic output?
A: 5 | five
The idea came remarkably late. Also, back then shell scripts bound standard input to the script, not the terminal.

69. Q:  Who ran the first Unix Support Group?
A: maranzano
USG was a force for internal and commercial Unix development in AT&T.

70. Q:  Whose Ph.D. thesis concerned Unix paging?
A: ozalp & babaoglu
The name was well known; the trick was spelling it correctly when you were in a hurry to get home.

71. Q:  Who (other than the obvious) designed the original Unix file system?
A: canaday
Rudd Canaday was there at the beginning.

72. Q:  Who wrote the PWB shell?
A: mashey
John Mashey, inventor of the pump operator.

73. Q:  Who invented uucp?
A: lesk
In so doing, Mike Lesk created the job category of (amateur) network operations engineer.

74. Q:  Who thought of PWB?
A: evan ivie
Evan Ivie pushed on the Software Tools metaphor to instigate the Programmer's Workbench. It feels quaint now.

75. Q:  What does grep stand for?
A: global regular expressions print
I've read countless incorrect etymologies for 'grep'. It's just the ed command g/re/p. The reference here is the spelling on the original man page. That final 's' is key to getting this one right.

76. Q:  What hardware device does "dsw" refer to?
A: console & 7
The profound "delete from switches" program was in its purest form on the PDP-7 in the First Edition.

77. Q:  What was the old name of the "/sys" directory?
A: ken
Ken and...

78. Q:  What was the old name of the "/dev" directory?
A: dmr
... Dennis divided their work this way until the Seventh Edition.

79. Q:  Who has written many random number generators, but never one that worked?
A: ken | thompson
Sorry, Ken, but it's true and you know it.

80. Q:  Where was the first Unix system outside 127?
A: patent
The Bell Labs patent office truly benefited from automated document processing made possible in the early versions of Research Unix. I believe they started using it when the kernel was still in assembler.

81. Q:  What was the first Unix network?
A: spider
You thought it was Datakit, didn't you? But Sandy Fraser had an earlier project.

82. Q:  What was the original syntax for ls -l | pr -h?
A: ls -l>"pr -h"> | <"ls -l"Notation is important. Ken's introduction of the pipe symbol (not to be confused with the | of the pattern here) was a masterstroke.

83. Q:  Why is there a comment in the shell source /* Must not be a register variable */?
A: registers & longjmp
You should be able to understand this.

84. Q:  What is it you're not expected to understand?
A: 6 | 5 & process
What's amazing to me now is hard this was to understand, let alone to invent, yet within a few years we all realized it could be done almost trivially with setjmp and longjmp.

Sunday, January 19, 2020

Unix Quiz

(Here's another resurrected post from April 30, 2012. Answers in a followup.)


People objected that there was no Exit item on the main menu for the mpx program that put windows on the Blit; see http://en.wikipedia.org/wiki/Blit_(computer_terminal) (which mistakenly says it implemented cursor addressing when turned on - as if!) and http://www.cs.bell-labs.com/cm/cs/doc/83/mpx.ps.gz. It seemed unnecessary, since you could just power cycle. Why clutter the menu? (Those were simpler times.)

After hearing too much complaining, I decided to implement Exit, but did it a special way. Late one night, with help from Brian Redman (ber) and Pat Parseghian (pep), I cranked out a set of trivia questions to drive the Exit control. Answer the question right, you can exit; get it wrong, you're stuck in mpx for a little longer. To make this worthwhile, the questions had to be numerous and hard, and had to be verified by the machine, so the quiz code included a little pattern matcher. It also had to be tiny, since the machine only had 256KB and the display took 100KB of that. (Those were simpler times.)

The response was gratifying. I'll never forget seeing someone, who shall remain nameless, a vociferous complainer about the lack of Exit, burble with excitement when he saw the menu item appear, only to crumble in despair when the question arrived. I forget which question it was, but it doesn't matter: they're all hard.

The questions were extended by lots of suggestions from others in the Unix lab, and then in 1984 they were handed out as a bloc in a trivia contest at the USENIX conference in Salt Lake City. To quote an observer, "The submission with the most correct answers (60) was from a team comprising David Tilbrook, Sam Leffler, and presumably others. Jim McKie had the best score for an individual (57) and was awarded an authenticated 1972 DECtape containing Unix Version 2. Finally, Ron Gomes had 56 correct answers and received an original engraved "Bill Joy" badge, which once belonged to Bill himself, from Sun Microsystems." That score of 57 was so impressive we hired Jim a little later, but that's another story.

How much Unix trivia do you know? Test your mettle; the questions appear below. This may be one of the hardest quizzes ever to originate outside of King William's College.

I've disabled comments because people will just send in spoilers. If you want to discuss or collaborate, do so elsewhere. I'll publish the computer-readable, pattern-matching answers here in a few days.

Good luck, and may your TU-10 never break your 9-track boot tape.

-rob


1. The source code motel: your source code checks in, but it never checks out. What is it?
2. Who wrote the first Unix screen editor?
3. Using TSO is like kicking a {what?} down the beach.
4. What is the filename created by the original dsw(1)?
5. Which edition of Unix first had pipes?
6. What is =O=?
7. Which Stephen R. Bourne wrote the shell?
8. Adam Buchsbaum's original login was sjb. Who is sjb?
9. What was the original processor in the Teletype DMD-5620?
10. What was the telephone extension of the author of mpx(2)?
11. Which machine resulted in the naming of the "NUXI problem"?
12. What customs threat is dangerous only when dropped from an airplane?
13. Who wrote the Bourne Shell?
14. What operator in the Mashey shell was replaced by "here documents"?
15. What names appear on the title page of the 3.0 manual?
16. Sort the following into chronological order: a) PWB 1.2, b) V7, c) Whirlwind, d) System V, e) 4.2BSD, f) MERT.
17. The CRAY-2 will be so fast it {what?} in 6 seconds.
18. How many lights are there on the front panel of the original 11/70?
19. What does FUBAR mean?
20. What does "joff" stand for?
21. What is "Blit" an acronym of?
22. Who was rabbit!bimmler?
23. Into how many pieces did Ken Thompson's deer disintegrate?
24. What name is most common at USENIX conferences?
25. What is the US patent number for the setuid bit?
26. What is the patent number that appears in Unix documentation?
27. Who satisfied the patent office of the viability of the setuid bit patent?
28. How many Unix systems existed when the Second Edition manual was printed?
29. Which Bell Labs location is HL?
30. Who mailed out the Sixth Edition tapes?
31. Which University stole Unix by phone?
32. Who received the first rubber chicken award?
33. Name a feature of C not in Kernighan and Ritchie.
34. What company did cbosg!ccf work for?
35. What does Bnews do?
36. Who said "Sex, Drugs, and Unix?"
37. What law firm distributed Empire?
38. What computer was requested by Ken Thompson, but refused by management?
39. Who is the most obsessed private pilot in USENIX?
40. What operating system runs on the 3B-20D?
41. Who wrote find(1)?
42. In what year did Bell Labs organization charts become proprietary?
43. What is the Unix epoch in Cleveland?
44. What language preceded C?
45. What language preceded B?
46. What letter is mispunched by bcd(6)?
47. What terminal does the Blit emulate?
48. What does "trb" stand for (it's Andy Tannenbaum's login)?
49. allegra!honey is no what?
50. What is the one-line description in vs.c?
51. What is the TU10 tape boot for the PDP-11/70 starting at location 100000 octal?
52. What company owns the trademark on Writer's Workbench Software?
53. Who designed Belle?
54. Who coined the name "Unix"?
55. What manual page mentioned Urdu?
56. What politician is mentioned in the Unix documentation?
57. What program was compat(1) written to support?
58. Who is "mctesq"?
59. What was "ubl"?
60. Who bought the first commercial Unix license?
61. Who bought the first Unix license?
62. Who signed the Sixth Edition licenses?
63. What color is the front console on the PDP-11/45 (exactly)?
64. How many different meanings does Unix assign to '.'?
65. Who said "Smooth rotation butters no parsnips?"
66. What was the original name for cd(1)?
67. Which was the first edition of the manual to be typeset?
68. Which was the first edition of Unix to have standard error/diagnostic output?
69. Who ran the first Unix Support Group?
70. Whose Ph.D. thesis concerned Unix paging?
71. Who (other than the obvious) designed the original Unix file system?
72. Who wrote the PWB shell?
73. Who invented uucp?
74. Who thought of PWB?
75. What does grep stand for?
76. What hardware device does "dsw" refer to?
77. What was the old name of the "/sys" directory?
78. What was the old name of the "/dev" directory?
79. Who has written many random number generators, but never one that worked?
80. Where was the first Unix system outside 127?
81. What was the first Unix network?
82. What was the original syntax for ls -l | pr -h?
83. Why is there a comment in the shell source /* Must not be a register variable */?
84. What is it you're not expected to understand?

Saturday, January 18, 2020

Old things made new

A while back, Google Plus (google+?) lost its public face, removing from public view too much material. But Google, for all its faults, also has virtues, and it let me capture all my posts using its "takeout" feature before plus went negative.

I'm going to publish a few of the more worthwhile or at least fun ones here over the next little while.

To get things going, here's a link I posted from September 30, 2011:

Fashion for Work at the Google Headquarters

There's little merit and less verisimilitude in this, so file it under the fun category.

Color blindness

Color blindness is an inaccurate term. Most color-blind people can see color, they just don't see the same colors as everyone else. Ther...