‮fet (figg) wrote in misc_tech,

The Truth about Unix: The user interface is horrid

From cincy!duke!decvax!utzoo!datamat!rumor Sat Aug  1 23:37:27 PDT 1981
The Truth about UNIX: fa.unix-wizards

                   The truth about Unix:
                The user interface is horrid

                      Donald A. Norman
                  Department of Psychology
                Program in Cognitive Science
          Center for Human Information Processing
            University of California, San Diego
                 La Jolla, California 92093
                 (to appear in Datamation)

     Unix is a highly touted operating system.  Developed at
the  Bell  Telephone Laboratories and distributed by Western
Electric, it has  become  a  standard  operating  system  in
Universities,  and  it promises to become a standard for the
large micro- mini- systems for  home,  small  business,  and
educational setting.  But for all its virtues as a system --
and it is indeed an elegant system -- Unix is a disaster for
the casual user.  It fails both on the scientific principles
of human engineering and even in just plain   common  sense.
The motto of the designers of Unix towards the user seems to
be "let the user beware."

     If Unix is really to become a general system,  then  it
has got to be fixed.  I urge correction to make the elegance
of the system design be reflected  as  friendliness  towards
the user, especially the casual user.  I have learned to get
along with the vagaries  of  its  user  interface,  but  our
secretarial staff persists only because we insist.  And even
I, a heavy user of computer systems for 20  years  have  had
difficulties:  copying  the old file over the new, transfer-
ring a file into itself  until  the  system  collapsed,  and
removing  all  the  files from a directory simply because an
extra space was typed in the argument string.  In this arti-
cle  I  review  both the faults of Unix and also some of the
principles  of  Cognitive  Engineering  that  could  improve
things,  not just for Unix, but for computer systems in gen-
eral.  But first, the conclusion;  Unix fails several simple

     Consistency: The command names, language, functions and
          syntax are inconsistent.

     Functionality: The command names, formats,  and  syntax
          seem to have no relationship to their functions.

     Friendliness: Unix is a recluse, hidden from the  user,
          silent  in  operation.   "No news is good news" is
          its motto, but as a result, the  user  can't  tell
          what  state  the system is in, and essentially, is
          completely out of touch with things.

     Cognitive Engineering:  The system does not  understand

                       August 2, 1981

                           - 2 -

          about  normal  folks,  the everyday users of Unix.
          Cognitive capabilities are strained  beyond  their
          limits,  the  lack  of  mnemonic structures places
          large loads of memory, and the lack of interaction
          puts  a strain on one's ability to retain mentally
          exactly what state the system is in at any moment.
          (Get  distracted  at  the  wrong time and you lose
          your place -- and maybe your file.)

What is good about Unix?   The system design, the generality
of  programs,  the  file  structure,  the job structure, the
powerful operating system command  language  (the  "shell").
To  bad  the concern for system design was not matched by an
equal concern for the human interface.

     One of the first things you learn  when  you  start  to
decipher  Unix  is  how  to list the contents of a file onto
your terminal.  Now this sounds straightforward enough,  but
in  Unix even this simple operation has its drawbacks.  Sup-
pose I have a file called "testfile".  I want to see what is
inside  of  it.   How would you design a system to do it?  I
would have written a program that listed the  contents  onto
the  terminal,  perhaps  stopping  every 24 lines if you had
signified that you were on a display terminal with only a 24
line  display.   To  the  designers of Unix, however, such a
solution lacks elegance.  Unix has  no  basic  listing  com-
mand,  but  instead you must use a program meant to do some-
thing else.

     In Unix, if you wanted to list the contents of  a  file
called "HappyDays", you would use the command named "cat":
                       cat HappyDays
Why cat? Why not?  After all, said Humpty Dumpty  to  Alice,
who  is to be the boss, words or us?  "Cat", short for "con-
catenate" as in, take file1 and concatenate  it  with  file2
(yielding  one  file,  with the first part file1, the second
file2) and put the result on the "standard output" (which is
usually the terminal):
                         cat file1 file2
Obvious right?  And if you have only one file, why cat  will
put  it  on  the standard output -- the terminal -- and that
accomplishes the goal (except for those  of  us  with  video
terminals  who  watch  helplessly as the text goes streaming
off the display).

     The Unix designers are rather  fond  of  the  principle
that  special purpose functions can be avoided by clever use
of a small set of system primitives.   Their  philosophy  is
essentially,  don't  make  a special function when the side-
effects of other functions will do what you want.  But there
are several reasons why this philosophy is bad;

                       August 2, 1981

                           - 3 -

     1. A  psychological  principle  is  that  names  should
          reflect  function, else the names for the function
          will be difficult to recall;

     2. Side-effects can be used for virtue,  but  they  can
          also  have  unwarranted  effects.  Thus, if cat is
          used unwisely, it will destroy files (more on this
          in a moment).

     3. Special functions can do nice things for users, such
          as  stop  at  the  end  of screens, or put on page
          headings,  or  transform  non-printing  characters
          into  printing  ones, or get rid of underlines for
          terminals that can't do that.

Cat, of course, won't stop at terminal or  page  boundaries,
because  if it did that, why that would disrupt the concate-
nation feature.  But still, isn't it elegant to use cat  for
listing?   Who  needs  a  print or a list command.  You mean
"cat" isn't how you would abbreviate  concatenate?  gee,  it
seems so obvious to us.  Just like

function                        unix command name

c compiler                      cc
change working directory        chdir  (cd in Berkeley Unix)
change password                 passwd
concatenate                     cat
copy                            cp
date                            date
echo                            echo
editor                          ed
link                            ln
move                            mv
remove                          rm
search file for pattern         grep

Notice the lack of consistency in forming the  command  name
from  the  function.   Some  names  are formed  by using the
first two consonants of the function name, unless it is  the
editor  which  is  abbreviated "ed" and concatenate which is
"cat" or "date" or "echo" which are not abbreviated at  all.
Note  how  useful those 2 letter abbreviations are.  See how
much time and effort is saved typing only 2 letters  instead
of  --  heaven  forbid  --  4  letters.  So what is a little
inconsistency among friends, especially when  you  can  save
almost 400 milliseconds per command.

     Similar statements apply  to  the  names  of  the  file
directories.  Unix is a file oriented system, with hierarch-
ical directory structures, so the directory names  are  very
important.   Thus,  this  paper  is  being written on a file
named      "unix"      and       whose       "path"       is
/csl/norman/papers/CogEngineering/unix.  The name of the top
directory is "/", and csl, norman, papers, and  CogEngineer-
ing  are  the  names  of  directories  hierarchically placed

                       August 2, 1981

                           - 4 -

beneath "/".  Note that the symbol "/" has two meanings: the
name  of  the  top  level  directory  and  the  symbol  that
separates levels of the directories.  This is very difficult
to justify to new users.  And those names: the directory for
"users" and "mount" are called, of course, "usr" and  "mnt."
And  there  are  "bin," "lib," and "tmp." (What mere mortals
might call binary, library, and temp).   Unix loves abbrevi-
ations,  even  when the original name is already very short.
To write "user" as "usr" or "temp" as "tmp" saves an  entire
letter:  a  letter  a day must keep the service person away.
But Unix is inconsistent;  it doesn't abbreviate  everything
as   2  or  3  letter commands.  It keeps "grep" at its full
four letters, when it could have been abbreviated as "gr" or
"gp".  (What  does  grep mean, you may ask.  "Global REgular
expression, Print" --  at  least  that's  the  best  we  can
invent,  the  manual  doesn't  even  try  to  say.  The name
wouldn't matter if grep were something obscure, hardly  ever
used, but in fact it is one of the more powerful, frequently
used string processing commands.  But that takes me from  my

     Do I dare tell you about "dsw"?  This also turns out to
be  an important routine.  Suppose you accidentally create a
file whose name has  a non-printing character  in  it.   How
can you remove it?  The command that lists the files on your
directory won't show non-printing characters.   And  if  the
character  is  a space (or worse, a "*"), "rm"  (the program
that removes files) won't accept it.   "dsw"  was  evidently
written  by someone at Bell Labs who felt frustrated by this
problem and hacked up a quick solution.  Dsw  goes  to  each
file  in  your  directory  and asks you to respond  "yes" or
"no," whether to delete the file  or keep it (or  is  it  to
keep it or delete it -- which action does "yes" mean?).  How
do you remember dsw?  What on earth does the name stand for?
The  Unix people won't tell; the manual smiles its wry smile
of the professional programmer and says "The name dsw  is  a
carryover  from the ancient past. Its etymology is amusing."
(The implication, I guess, is that true professionals  never
need  to  use such a program, but they are allowing it to be
released for us  novices  out  in  the  real  world.)  Which
Verification of my charges comes from  the  experiences
of  the  many users of Unix, and from the modifications
that other people have been forced to make to the  sys-
tem.   Thus, the system of Unix I now use is called The
Fourth Berkeley Edition for  the  Vax,  distributed  by
Joy,  Babaoglu, Fabry, and Sklower at the University of
California, Berkeley (henceforth, Berkeley Unix).  They
provide   a  listing  program  that  provides  all  the
features I claim a user would want (except  a  sensible
name  -- but Berkeley Unix even makes it easy to change
system names to anything you prefer).

                       August 2, 1981

                           - 5 -

operation takes place if you say  "yes":  why  the  file  is
deleted  of course.  So if you go through your files and see
important-file, you nod to yourself and say, yes,  I  better
keep that one, type in yes, and destroy it forever. Does dsw
warn you? Of course not.  Does dsw even document itself when
it starts, to remind you which way is which?  Of course not.
That would be talkative, and true Unix programmers are never
talkative.   (Berkeley  Unix, has finally killed dsw, saying
"This little known,  but  indispensible  facility  has  been
taken  over...".   That  is a fitting commentary on standard
Unix: a system that allows an "indispensible facility" to be
"little known.")

     The symbol "*" means "glob" (a typical Unix name:   the
name  tells  you  just what action it does, right?).  Let me
illustrate with our friend, "cat." Suppose  I  want  to  put
together   a  set of files named paper.1 paper.2 paper.3 and
paper.4 into one file.  I can do this with cat:
     cat paper.1 paper.2 paper.3 paper.4 > newfilename
Unix provides "glob" to make  the  job  even  easier.   Glob
means  to  expand the filename by examining all files in the
directory to find all that fit. Thus, I can redo my  command
                  cat paper* > newfilename
where paper* expands to {paper.1 paper.2  paper.3  paper.4}.
This  is  one  of  the  typical virtues of Unix; there are a
number of  quite  helpful  functions.   But  suppose  I  had
decided  to name this new file "paper.all".  After all, this
is a pretty logical name, I am combining the separate  indi-
vidual files into a new one that contains "all" the previous
                   cat paper* > paper.all
Disaster.  I will probably blow  up  the  system.   In  this
case,  paper*  expands  to  paper.1  paper.2 paper.3 paper.4
paper.all, and so I am filling up a file from itself:
 cat paper.1 paper.2 paper.3 paper.4 paper.all > paper.all
Eventually the file will burst.   Does  nice  friendly  Unix
check against this, or at least give a warning?  Oh no, that
would be against the policy of  Unix.   The  manual  doesn't
bother warning against this either, although it does warn of
another, related infelicity: "Beware of 'cat a b  >  a'  and
'cat  b a > a', which destroy the input files before reading
them."  Nice of them to tell us.

     The command to remove all files  that  start  with  the
word "paper"
                         rm paper*
becomes a disaster if a space gets inserted by accident:
                         rm paper *
for now the file "paper" is removed, as well as  every  file
in  the  entire directory (the power of glob).  Why is there
not a check against such things?  I finally had to alter  my

                       August 2, 1981

                           - 6 -

version of rm so that when I said to remove files, they were
actually only moved to a special directory  named  "deleted"
and  they  didn't  actually  get deleted until I logged off.
This gave me lots of time for second thoughts and for catch-
ing  errors.  This also illustrates the power of Unix:  what
other operating system would make it so easy for someone  to
completely  change  the  operation  of  a system command for
their own personal satisfaction?  This also illustrates  the
evils  of Unix: what other operating system would make it so
necessary to do so?  (This is no longer necessary  now  that
we use Berkeley Unix -- more on this in a moment.)

     The standard text editor is called Ed.  What a  problem
that  turned  out  to  be.   It was so lovely that I spent a
whole year using it as an experimental vehicle  to  see  how
people dealt with such awful things.  Ed's major property is
his shyness; he doesn't like to talk.  You invoke Ed by say-
ing,  reasonably  enough,   "ed".  The result is silence: no
response, no prompt, no message, just silence.   Novice  are
never sure what that silence means.  What did they do wrong,
they wonder.  Why doesn't Ed say "thank you, here I am"  (or
at least produce a prompt character)?  No, not Unix with the
philosophy that silence is golden.   No response means  that
everything  is  ok.   If  something  had gone wrong, then it
would have told you (unless the system died, of course,  but
that couldn't happen could it?).

     Then there is the famous append  mode  error.   To  add
text  into  the buffer, you have to enter "append mode."  To
do this, one simply types "a",  followed  by   RETURN.   Now
everything  that  is  typed  on  the  terminal goes into the
buffer.  (Ed, true to form, does not inform you that  it  is
now  in  append mode: when you type "a" followed by "RETURN"
the result is silence, no  message,  no  comment,  nothing.)
When  you are finished adding text, you are supposed to type
a line that "contains only a . on it."  This gets you out of
append  mode.   Want  to  bet  on how many extra periods got
inserted into text files,  or how many commands got inserted
into texts, because the users thought that they were in com-
mand mode and forgot they had not left append mode?  Does Ed
tell you when you have left append mode?  Hah.  This problem
is so obvious that even the designers  knew  about  it,  but
their  reaction  was  to  laugh:  "hah-hah, see Joe cry.  He
just made the append mode error  again."   In  the  tutorial
introduction  to  Ed, written at Bell Labs, the authors joke
about it. Even experienced programmers get screwed this way,
they  say, hah hah, isn't that funny.  Well, it may be funny
to the experienced programmer, but it is devastating to  the
beginning secretary or research assistant or student  who is
trying to use friendly Unix as a word processor,  or  as  an
experimental tool, or just to learn about computers.  Anyone
can use Unix says the programmer, all you need is a sense of

                       August 2, 1981

                           - 7 -

     How good is your sense of humor?  Suppose you have been
working  on a file for an hour and then decide to quit work,
exiting Ed  by saying "q".  The problem  is  that  Ed  would
promptly quit.  Woof, there went your last hour's work. Gone
forever.  Why, if you would have wanted to save it you would
have  said  so,  right?   Thank goodness for all those other
people across the country who immediately rewrote  the  text
editor  so  that us normal people (who make errors) had some
other choices besides Ed, editors  that  told  you  politely
when  they were working, that would tell you if they were in
append or command mode,  and  that  wouldn't  let  you  quit
without  saving  your file unless you were first warned, and
then only if you said you really meant it.

     I could go on.  As I wrote this paper I sent out a mes-
sage on our networked message system and asked my colleagues
to tell me of  their  favorite  peeves.   I  got  a  lot  of
responses,  but  there  is  no  need to go into detail about
them; they all have much the same flavor about them,  mostly
commenting  about  lack  of  consistency,  about the lack of
interactive feedback.  Thus, there is no standardization  of
means  to  exit  programs  (and  because the "shell" is just
another program as far as th system is concerned, it is very
easy to log yourself off the system by accident).  There are
very useful pattern matching features (such as the "glob"  *
function),  but the shell and the different programs use the
symbols in inconsistent ways.  The Unix  copy  command  (cp)
and the related C programming language "stringcopy" (strcpy)
have reversed order of arguments, and  Unix  move  (mv)  and
copy (cp) operations will destroy existing files without any
warning.  Many programs take special  "argument  flags"  but
the  manner of specifying the flags is inconsistent, varying
from program to program.  As I said, I could go on.

     The good news is that we don't use  standard  Unix:  we
use  Berkeley  Unix.   History lists, aliases, a much richer
and more intelligent set of  system  programs,  including  a
list  program,  an  intelligent screen editor, a intelligent
set of routines for interacting with terminals according  to
their  capabilities,  and  a  job control that allows one to
stop jobs right in the middle, startup new ones, move things
from  background  to  foreground  (and  vice versa), examine
files, and then resume jobs.  And the shell has been  ampli-
fied  to  be  a more powerful programming language, complete
with file handling capabilities, if--then--else  statements,
while,  case,  and  all the other goodies of structured pro-
gramming  (see the accompanying box on Unix).

     Aliases are worthy of special comment.  Aliases let the
user  tailor the system to their own needs, naming things in
ways they themselves can remember: self-generated names  are
indeed easier to remember than arbitrary names given to you.

                       August 2, 1981

                           - 8 -

And aliases allow abbreviations that are meaningful  to  the
individual,  without burdening everyone else with your clev-
erness or difficulties.

     To work on this  paper,  I  need  only  type  the  word
"unix,"  for  I  have  set up an alias called "unix" that is
defined to be equal to the correct command to change  direc-
tories,  combined with a call to the editor (called "vi" for
"visual" on this system) on the file:
alias unix "chdir /csl/norman/papers/CogEngineering; vi unix"
These Berkeley Unix features have proven  to  be  indispens-
able:  the  people in my laboratory would probably refuse to
go back to standard Unix.

     The bad news is that Berkeley Unix  is  jury-rigged  on
top  of regular Unix, so it can only patch up the faults: it
can't remedy them.  Grep is not only still grep,  but  there
is  an  egrep  and  an  fgrep.  But worse, the generators of
Berkeley Unix have their problems: if Bell Labs  people  are
smug  and  lean,  Berkeley  people  are cute and overweight.
Programs are wordy. Special features  proliferate.   Aliases
--   the  system  for  setting  them  up  is not easy to for
beginners (who may be the people who need them  most).   You
have  to  set  them  up  in a file called .cshrc, a name not
chosen to inspire confidence!  The "period" in the  filename
means that it is invisible -- the normal method of directory
listing programs won't show it.  The directory listing  pro-
gram, ls, comes with 19 possible argument flags, that can be
used singly or in combinations.  The number of special files
that  must be set up to use all the facilities is horrendus,
and they get more complex with each new release from  Berke-
ley.   It  is vey difficult on new users.  The program names
are cute  rather  than  systematic.   Cuteness  is  probably
better  than the lack of meaning of standard Unix, but there
are be limits.  The listing program is called "more" (as in,
"give  me  more"),  the program that tells you who is on the
system is called "finger", and a keyword help file  --  most
helpful by the way -- is called "apropos."  Apropos! who can
remember that?  Especially when you need it most. I  had  to
make  up  an alias called "help" which calls all of the help
commands Berkeley provides, but  whose  names  I  can  never
remember (apropos, whatis, whereis, which).

The system is now so wordy and  so  large  that  it  no
longer  fits  on  the  smaller machines: our laboratory
machine, a DEC 11/45, cannot hold the latest release of
Berkeley  Unix  (even  with a full complement of memory
and a reasonable amount of disc).  I write  this  paper
on a Vax.

                       August 2, 1981

                           - 9 -

     One reader of a draft of this paper -- a  systems  pro-
grammer   --   complained  bitterly:  "Such  whining,  hand-
wringing, and general bitchiness will cause most  people  to
dismiss  it as over-emotional nonsense. ...  The Unix system
was originally designed by systems programmers for their own
use and with no intention for others using it. Other hackers
liked it so much that eventually a lot of them started using
it.  Word  spread about this wonderful system, etc, the rest
you probably know. I think  that  Ken  Thompson  and  Dennis
Ritchie  could  easily shrug their shoulders and say 'But we
never intended it for other than our personal use.'"

     All the other users of Unix who  have  read  drafts  of
this paper agreed with me.  Indeed, their major reaction was
to forward examples of problems  that  I  had  not  covered.
This  complaint was unique.  I do sympathize with the spirit
of the complaint.  He is correct, but  ...    The  "but"  is
that  the  system  is  nationally  distributed, under strict
licensing agreements, with a very high charge  to  industry,
and  nominal  charges  to  educational  institutes.  Western
Electric doesn't mind getting a profit, but  they  have  not
attempted  to  worry  about the product.  If Unix were still
what it started to be, a simple experiment on  the  develop-
ment  of operating systems, then the complaints I list could
be made in a more friendly, constructive manner.   But  Unix
is  more  than  that.   It  is  taken as the very model of a
proper operating system.  And that is  exactly  what  it  is

     In the development of the system aspects of  Unix,  the
designers  have  done  a  magnificent  job.   They have been
creative, and systematic.  A common theme runs  through  the
development  of  programs, and by means of their file struc-
ture, the development of "pipes" and "redirection"  of  both
input  and  output,  plus the power of the iterative "shell"
system-level commands, one can combine system level programs
into  self-tailored systems of remarkable power with remark-
able ease.

     In the development of the  user  interface  aspects  of
Unix, the designers have been failures.  They have been dif-
ficult and derisive.  A common theme runs through  the  com-
mands: don't be nice to the casual user --  write the system
for the dedicated expert.  The system is a recluse.  It uses
weird  names,  and it won't speak to you, not even if spoken
to.  For system programmers, Unix is a delight.  It is  well
structured,  with  a consistent, powerful philosophy of con-
trol and structure.  My complaint is simple:   why  was  not
the  same  effort  put  into  the design at the level of the
user?  The answer to my complaint is  a  bit  more  complex.
There  really  are no well known principles of design at the
level of the user interface.  So, to remedy the harm that  I
may  have  caused by my heavy-handed sarcasm, let me attempt
to provide some positive suggestions based upon the research

                       August 2, 1981

                           - 10 -

that  has  been done by me and by others into the principles
of the human information processing system.

     Cognitive Engineering is a new discipline, so new  that
it  doesn't  exist:   but it ought to.  Quite a bit is known
about the human information processing system,  enough  that
we  can specify some basic principles for designers.  People
are complex entities and can adapt to almost anything.    As
a  result,  designers  are often sloppy, for they can design
for themselves without realizing the difficulties that  will
be faced by other users.  Moreover, there are different lev-
els of users:  people with a large amount  of  knowledge  of
the  device  they  are about to use are quite different from
those who lack a basic understanding.  Experts are different
than novices.  And the expert who is normally skilled at the
use of some systems but who has not used it for awhile is at
a peculiar level of knowledge, neither novice nor expert.

     The three most important concepts for system design are

     1.  Be consistent.  A  fundamental  set  of  principles
          ought  to  be  evolved  and  followed consistently
          throughout all phases of the design.

     2.  Provide the user with  an  explicit  model.   Users
          develop  mental  models  of the devices with which
          they interact.  If you do not  provide  them  with
          one, they will make one up themselves, and the one
          they make up is apt to be wrong.  Do not count  on
          the  user fully understanding the mechanics of the
          device.  Secretaries  and  scientists  alike  will
          share  a  lack  of knowledge of a computer system.
          The users are not apt to understand the difference
          between  the buffer, the working memory, the work-
          ing files, and the permanent files of a text  edi-
          tor.   They are apt to believe that once they have
          typed something into the system, it is permanently
          in  their  files.   They  are  apt  to expect more
          intelligence from the  system  than  the  designer
          knows  is  there.   And  they are apt to read into
          comments (or the lack of comments) more  than  you
          have  intended.   Feedback  is  of critical impor-
          tance, both in helping to establish the  appropri-
          ate  mental model and in letting the user keep its
          current state in synchrony with the actual system.

     3.  Provide mnemonic aids.  Human memory is  a  fragile
          thing.   Actually,  for  most  purposes it is con-
          venient to think of human memory as consisting  of
          two  parts:   a  short-term memory and a long-term
          memory (modern cognitive psychology is  developing
          more  sophisticated  notions than this simple two-

                       August 2, 1981

                           - 11 -

          stage one, but this is still  a  valid  approxima-
          tion).   Short-term  memory  is,  as the name sug-
          gests, limited in duration  and  quantity:   about
          five  to  seven  items is the limit.  Thus, do not
          expect a user to remember the contents of  a  mes-
          sage  for  much  longer  than it is visible on the
          terminal.  Long-term  memory  is  robust,  but  it
          faces  two difficulties:  getting stuff in so that
          it is properly organized and getting stuff out, so
          that  it  can  be  found when needed.  Learning is
          difficult, unless there is a good  structure,  and
          it is visible to the learner.  The system designer
          must provide sensible assistance to  the  user  so
          that  the  material  can be structured.  There are
          lots of sensible memory aids that can be provided,
          but  the  most  powerful  and  sensible  of all is
          understanding.  Make a system so that  it  can  be
          understood and the memory follows with ease.  Make
          the command names ones  that  can  be  understood,
          where  the  names follow from the function that is
          desired.  If abbreviations must be used,  adopt  a
          consistent policy of forming the abbreviations. Do
          not deviate from the policy, even when it  appears
          that  it  would be easier for a particular command
          to deviate:  inconsistency is an  evil.   Remember
          the  major  problem  of  any large-scale memory is
          finding the information that is  sought,  even  if
          the  information  is there someplace.  We retrieve
          things from  memory  by  starting  off  with  some
          description  of  the information we seek, use that
          description to enter their  memory  system  in  an
          attempt  to match against the desired information.
          If the designer uses cute names  and  non-standard
          abbreviations,  our  ability  to  generate a valid
          description is impaired.  As a result, the  person
          who  is  not  expert and current in the use of the
          system is apt to flounder.

     There are many ways of formatting information on termi-
nals  to  provide  useful  memory and syntax aids for users.
With today's modern terminals, it is possible to use  menus,
multiple  screens  and  windows, highlighted areas, and with
full duplex systems,  automatic  or  semi-automatic  command
completion  systems.   The  principles for these systems are
under active study by a  number  of  groups,  but  none  are
directly  relevant to my critique of the UNIX operating sys-
tem.  UNIX is designed specifically so that it can  be  used
with a wide variety of terminals, including hard copy termi-

     The problem with Unix is more fundamental.   Unix  does
not provide the user with a systematic set of principles; it

                       August 2, 1981

                           - 12 -

does not provide a simple, consistent mental model  for  the
user, consistent not only in the shell but in the major sys-
tem programs and languages; it does  not  provide  the  user
with simple memory aids that can be used to learn the system
structure and then, when  one is not completely  current  in
the  use  of  a  particular  command,  still  to  be able to
retrieve (or better, derive)  what  is  needed.   There  are
essentially  no  user help files, despite the claim that all
the documentation is on-line via the command named man  (for
manual, of course).  But "man" requires you to know the name
of the command you want information about,  although  it  is
the name that is probably just the information you are seek-

     System designers take note.  Design the system for  the
person, not for the computer, not even for yourself.  People
are  also  information  processing  systems,  with   varying
degrees   of   knowledge,  varying  degrees  of  experience.
Remember, people's short-term memories are limited in  size,
and they learn and retrieve things best when there is a con-
sistent reason for the name, the function, and  the  syntax.
Friendly systems treat users as intelligent adults who, like
normal adults, are forgetful, distracted, thinking of  other
things,  and  not  quite as knowledgeable about the world as
they themselves would like  to  be.   Treat  the  user  with
intelligence.   There  is  no need to talk down to the user,
nor to explain everything.  But give the  user  a  share  in
understanding by presenting a consistent view of the system.
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