IBM 1130 User Manual page 588

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of other characteristics. Thus a great many fac-
tors play a role in determining the efficiency and
speed of a sort program.
Among the more important data file characteris-
tics, the following may be cited: the degree of
original ordering of the file (that is, is it in random
order or do natural sequences exist?); the length,
range, and location of control word data; and the
number and length of the records.
Equally important in influencing sort perform-
ance are the characteristics of the storage facilities
and the CPU of the computer. Among storage char-
acteristics of interest are the capacity of the main
internal storage and the mode of addressing it, as
well as the availability and access times of exter-
nal storage devices, such as disk files. Relevant
machine and CPU characteristics include simul-
taneous read, write, and processing capability; the
basic processing speeds of compare, add, and
move operations; the structure of the OP-code set;
and the availability of indexing, table lookup, etc.
For a given sorting method, the data file charac-
teristics influence the primary sorting statistics,
such as the total number of arithmetic operations
or comparisons and the total number of passes.
For a file of a given size, each method also has
some inherent characteristics that influence the
complexity and speed of the sort -- for example,
the required working storage, the required number
of comparisons, transfers, and exchanges, etc.
Finally, realistic sorting objectives must con-
sider the specific data processing requirements,
as well as the complexity and cost of the sort pro-
gramming effort. A specific sort program should
try to provide an optimum match between the speci-
fied data file, the given machine configuration, and
the chosen technique. In sorting large files, a
single sorting technique cannot always provide this
optimum match. Frequently, therefore, a program
combines two methods in order to take advantage of
special machine features, minimize the effects of
storage limitations, and provide increased speed.