doc: modernize usage of “disk” and “core”

In documentation and comments, don’t assume that secondary storage
devices are disk devices.  Similarly, don’t assume that main memory
uses magnetic cores, which became obsolete in the 1970s.
* src/du.c (usage):
* src/ls.c (usage):
* src/shred.c (usage): Reword to avoid “disk” in usage messages.

1 files changed, 5 insertions, 5 deletions

diff --git a/man/df.x b/man/df.x
index cc2dd9e1c..28214674b 100644
--- a/man/df.x
+++ b/man/df.x
@@ -4,20 +4,20 @@
 '\" of the GNU General Public License <https://www.gnu.org/licenses/gpl.html>.
 '\" There is NO WARRANTY, to the extent permitted by law.
 [NAME]
-df \- report file system disk space usage
+df \- report file system space usage
 [DESCRIPTION]
 This manual page
 documents the GNU version of
 .BR df .
 .B df
-displays the amount of disk space available on the file system
+displays the amount of space available on the file system
 containing each file name argument.  If no file name is given, the
-space available on all currently mounted file systems is shown.  Disk
-space is shown in 1K blocks by default, unless the environment
+space available on all currently mounted file systems is shown.
+Space is shown in 1K blocks by default, unless the environment
 variable POSIXLY_CORRECT is set, in which case 512-byte blocks are
 used.
 .PP
-If an argument is the absolute file name of a disk device node containing a
+If an argument is the absolute file name of a device node containing a
 mounted file system,
 .B df
 shows the space available on that file system rather than on the