In
this chapter will continue to look through the lens
of the user and see some more characterics.
File
Access.
Historically,
when magnetic tapes were the devices used as persitent media, the way
to access these devices was sequential. One
could not skip to a particular section
in the media to access information but has to always start from the
beginning and read data in order until desired position. They could
be rewound however.
With
the introduction of magnetic disks, sequential files became obsolete
and random access files dawned. In this method there were explicit
indices or keys use to locate the records on the media.
We'd
never have to deal with sequential files. We will only be using
random access files mostly. There are two ways to specify the
position to start reading in the file.
1.
The read operation is performed and for every read the position is
specified.
2.
Using seek operation the position is set and the read operation is
performed.
This
piece of information bears no significance to a designer now. We all
are going to design file systems with Random Access Files.
Next.
Although all through the last post and the current we were seeing
attributes of files, there are still many special attributes assigned
to a file that provide different options to the user. The following
is the list.
1.
Protection mode: Dictates can access the file.
2.
Password: Password if the file is password protected.
3.
Creator: Id of the creator of the file.
4.
Owner: Id of the current owner of the file.
5.
Readonly
or read/write
6.
Hidden or not
7.
System file or a normal file
8.
ASCII or binary file
9.
Random access or sequential
10.
Temporary or permanent
11.
Creation time
12.
Time of last access
13.
Time of last change
14.
Current size
15.
Maximum size:
Attributes
11 to 13 are useful in scenarios where a tool such as Make must know
if there was a change in the source file after it's last build. Then
the file will be considered for compilation
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