The SET MAX_SOURCE_FILES command specifies the number of source
    files that PCA can have open at one time. Opening a source file
    requires the use of an I/O channel, which is a limited system
    resource. Using the SET MAX_SOURCE_FILES command, you can specify
    how many I/O channels PCA can use to read source files. If PCA
    reaches this limit, it must close one source file before it can
    open and read another one. In such cases, source display still
    works, but at some performance cost.

    By default, PCA keeps up to ten source files open at any one
    time. Normally there is no need to change this value.