.s1
9. Statistics
.es
The following statistics from \*sUNIX\*n are
presented to show the scale of the system
and to show how a
system of this scale is used.
Those of our users
not involved in document preparation
tend to use the system for
program development, especially language work.
There are few important
``applications'' programs.
.s2
9.1 Overall 
.es
.ta .5i 1.25i
.ti 0
.nf
	72	user population
	14	maximum simultaneous users
	220	directories
	3300	files
	23000	512-byte secondary storage blocks used
.fi
.s2
9.2 Per day \fR(24-hour day, 7-day week basis)
.es
There is a ``background'' process that
runs at the lowest possible priority; it is used
to soak up any idle \*sCPU\*n time.
It has been used to produce a million-digit
approximation to the constant \fIe\fR\(mi2,
and is now generating composite pseudoprimes (base 2).
.pg
.nf
.ti 0
	1800	commands
	4.3	\*sCPU\*n hours (aside from background)
	70	connect hours
	30	different users
	75	logins
.fi
.s2
9.3 Command \*sCPU\*n usage \fR(cut off at 1%)
.es
.in 1.25i
.ti 0
	15.7%	C compiler
.ti 0
	15.2%	users' programs
.ti 0
	11.7%	editor
.ti 0
.ta .5i+\w"1"u 1.25i
.ti 0
	5.8%	Shell (\|used as a command, including command times\|)
.ti 0
	5.3%	chess
.ti 0
	3.3%	list directory
.ti 0
	3.1%	document formatter
.ti 0
	1.6%	backup dumper
.ti 0
	1.8%	assembler
.ti 0
	1.7%	Fortran compiler
.ti 0
	1.6%	remove file
.ti 0
	1.6%	tape archive
.ti 0
	1.6%	file system consistency check
.ti 0
	1.4%	library maintainer
.ti 0
	1.3%	concatenate/print files
.ti 0
	1.3%	paginate and print file
.ti 0
	1.1%	print disk usage
.ti 0
	1.0%	copy file
.ta .5i 1.25i
.in 0
.s2
9.4 Command accesses \fR(cut off at 1%)
.es
.in 1.25i
.ti 0
	15.3%	editor
.ta .5i+\w"1"u 1.25i
.ti 0
	9.6%	list directory
.ti 0
	6.3%	remove file
.ti 0
	6.3%	C compiler
.ti 0
	6.0%	concatenate/print file
.ti 0
	6.0%	users' programs
.ti 0
	3.3%	list people logged on system
.ti 0
	3.2%	rename/move file
.ti 0
	3.1%	file status
.ti 0
	1.8%	library maintainer
.ti 0
	1.8%	document formatter
.ti 0
	1.6%	execute another command conditionally
.ti 0
	1.6%	debugger
.ti 0
	1.6%	Shell (\|used as a command\|)
.ti 0
	1.5%	print disk availability
.ti 0
	1.4%	list processes executing
.ti 0
	1.4%	assembler
.ti 0
	1.4%	print arguments
.ti 0
	1.2%	copy file
.ti 0
	1.1%	paginate and print file
.ti 0
	1.1%	print current date/time
.ti 0
	1.1%	file system consistency check
.ti 0
	1.0%	tape archive
.ta .5i 1.25i
.in 0
.s2
9.5 Reliability
.es
Our statistics on reliability are
much more subjective than the others.
The following results are true to the
best of our combined recollections.
The time span is over one year with
a very early vintage 11/45.
.pg
There has been one loss
of a file system (one disk out of five) caused by software
inability to cope with a hardware
problem causing repeated power fail traps.
Files on that disk were backed up three days.
.pg
A ``crash'' is an unscheduled system reboot or halt.
There is about one crash every
other day;
about two-thirds of them are caused
by hardware-related difficulties
such as power dips and inexplicable processor interrupts
to random locations.
The remainder are software failures.
The longest uninterrupted up time
was about two weeks.
Service calls average one every three weeks,
but are heavily clustered.
Total up time has been about 98% of
our 24 hour, 365 day schedule.
.s1
10. Acknowledgments
.es
We are grateful to R.H. Canaday, L.L. Cherry,
and L.E. McMahon
for their contributions to
\*sUNIX\*n.
We are particularly appreciative
of the inventiveness,
thoughtful criticism,
and constant support of
R. Morris, M.D. McIlroy,
and J.F. Ossanna.
.s1
11. References
.es
.in 3
.ta 3
.nr r 0 1
.ti 0
\n+r.	Digital Equipment Corporation.
.ft I
\*sPDP\*n-11/40 Processor Handbook \fR(1972),
.ft R
and
.ft I
\*sPDP\*n-11/45 Processor Handbook \fR(1971).
.ft R
.br
.ti 0
\n+r.	Deutsch, L.P., and Lampson, B.W.
An online editor.
.ft I
Comm. ACM 10,
.ft R
3 (Dec. 1967),
793-799, 803.
.br
.ti 0
\n+r.	Richards, M.
\*sBCPL\*n: A tool for compiler writing
and system programming.
Proc. AFIPS 1969 SJCC, Vol. 34,
AFIPS Press, Montvale, N.J., pp. 557-566.
.br
.ti 0
\n+r.	McClure, R.M.
\*sTMG\*n\(emA syntax directed compiler.
Proc. ACM 20th Nat. Conf.,
ACM, 1965, New York,
pp. 262-274.
.br
.ti 0
\n+r.	Hall, A.D.
The M6 macroprocessor.
Computing Science Tech. Rep. #2,
Bell Telephone Laboratories,
1969.
.br
.ti 0
\n+r.	Ritchie, D.M.  C reference manual. Unpublished memorandum,
Bell Telephone Laboratories (1973).
.br
.ti 0
\n+r.	Aleph-null. Computer Recreations.
.ft I
Software Practice and Experience 1, \fR2
(Apr.-June 1971), 201-204.
.br
.ti 0
\n+r.	Deutch, L.P. and Lampson, B.W.
\*sSDS\*n 930 time-sharing system
preliminary reference manual.
Doc. 30.10.10, Project \*sGENIE\*n,
Univ. Cal. at Berkeley (Apr. 1965).
.br
.ti 0
\n+r.	Feiertag, R.J., and Organick, E.I.
The Multics input-output system.
Proc. Third Symposium on Operating Systems Principles.
Oct. 18-20, 1971,
ACM, New York, pp. 35-41.
.br
.ti 0
\n+r.	Bobrow, D.G., Burchfiel, J.D., Murphy, D.L., and
Tomlinson, R.S.
\*sTENEX\*n, a paged time sharing system for the \*sPDP\*n-10.
.ft I
Comm. ACM 15.,
.ft R
3 (March 1972) 135-143.
