Directories - USB Mass Storage: Designing and Programming Devices and Embedded Hosts - page 204

Table 9-2: The attribute bits in a directory entry provide additional information
about a file.
Bit Name Meaning When Set to 1

0 1

R: read only The file can't be written to. (Some hosts allow writing after

prompting “Are you sure?”)

1 1

H: hidden Hide the file's directory listing from view unless the user has

requested to view hidden files.

2 1

S: system The file is a critical system file. Hide the file's directory listing

from view unless the user has requested to view system files.

3 1

V: volume The entry is for the volume label. A volume can have only one

entry with this attribute. The entry must be in the root directory.
The cluster number for this entry is zero.

4 D: directory The entry is for a directory rather than for a file.

5 A: archive The file hasn't been backed up since the last write operation to the

file. The file-system driver should set this bit to 1 on creating,
renaming, or writing to a file. Backup utilities can set the bit to zero
to indicate that the file has been backed up.

6 - Always zero.

7 - Always zero.

1

If bits 0-3 are all set to 1, the entry is a long-file-name entry.

Date and Time Fields
Three sets of data-and-time fields can store when a file was created, when
the file was last modified, and when the file was last accessed.
On file creation, the file-modified date and time fields (bytes 22 - 25) store
the current date and time. Every time the file's contents are modified, the
file-system driver should update the values to the current date and time. The
time is specified in units of two seconds. These fields were in the original 8.3
entries, and every system that has a real-time clock should store values in
these fields on creating or modifying a file. When copying or moving a file,
this date and time should remain unchanged.
The file-creation date and time fields (bytes 13 - 17) store the date and time
when a file was created. As with the file-modified time, one field stores the
time with a resolution of two seconds. An additional time field stores hun-
dredths of a second (0 - 199). The two values added together give the time.
These fields weren't part of the original 8.3 entries.When copying a file, the
copy's entry should have the current date and time. When moving a file, the