Top 10 List of Week 03
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[What happens when you open a file on your computer?]
Information about currently open files is stored in an open file table, containing the following: (1) File pointer - records the current position in the file, for the next read or write access, (2) File-open count - How many times has the current file been opened and not yet closed? When this counter reaches zero the file can be removed from the table, (3) Disk location of the file, and (4) Access rights -
[File locking]
Some OS provide support for file locking such as the following: (1) A shared lock is for reading only, (2) exclusive lock is for writing as well as reading, (3) advisory lock is informational only, and not enforced. ( A “Keep Out” sign, which may be ignored. ), (4) mandatory lock is enforced. ( A truly locked door. ). UNIX used advisory locks, and Windows uses mandatory locks. -
[File types]
Windows caters a lot of file types with its special extension to indicate the type of each file. Some of the types are executable(exe,com,bin) which is a ready-to-run machine-language program, object(obj,o) as compiled or machine language, source code(c,cc,java) as source code in various languages, batch (bat,sh) as commands to the command interpreter, markup (xml, html,tex) as textual data or documents and others which can be found on the above link. https://www.computerhope.com/issues/ch001789.htm -
[File Structure]
Some files contain an internal structure, which may or may not be known to the OS. For the OS to support particular file formats increases the size and complexity of the OS. UNIX treats all files as sequences of bytes, with no further consideration of the internal structure. ( With the exception of executable binary programs, which it must know how to load and find the first executable statement) -
[Access Methods]
There is sequential access which generally supports a few operations: (1) read next - read a record and advance the tape to the next position,(2) write next - write a record and advance the tape to the next position, (3) rewind, and (4) skip n records - May or may not be supported. Another method is direct access. It works by jumping to any record and read that record. It has the following operations: (1) read n - read record number n., (2) write n - write record number n, (3) jump to record n - could be 0 or the end of file, (4) Query current record - used to return back to this record later. -
[Directory Structure]
Directory, as what you might have known, is a container to keep folders and files. It organizes files and folders into hierarchical manner. There are some structures including Single-level directory ( the linear, simple one), two-level directory, and others which can be read in geeksforgeeks(https://www.geeksforgeeks.org/structures-of-directory-in-operating-system/#:~:text=A%20directory%20is%20a%20container,folders%20into%20a%20hierarchical%20manner). They are clearly and concisely written! -
[FTP]
I bet you are familiar with this term. But what is it really? FTP stands for File Transfer Protocol (FTP), a standard network protocol used for the transfer of computer files between a client and server on a computer network. FTP is built on a client-server model architecture using separate control and data connections between the client and the server.(Wikipeda). . Ftp can be either account and password controlled, or anonymous, not requiring any user name or password. -
[DNS]
When we are talking about remote file systems, particularly the distributed information systems, Domain Names Systems (DNS) is a key part. DNS is a phonebook of the internet. It provides for a unique naming system across all of the Internet such as when Web browsers interact through Internet Protocol (IP) addresses, DNS translates domain names to IP addresses so browsers can load Internet resources. How does it work? Check this out -> https://www.cloudflare.com/learning/dns/what-is-dns/ -
[LDAP]
A newer approach is the Lightweight Directory-Access Protocol, LDAP, which provides a secure single sign-on for all users to access all resources on a network. This is a secure system which is gaining in popularity, and which has the maintenance advantage of combining authorization information in one central location -
[Failures in local disk vs remote file]
When a local disk file is unavailable, the result is generally known immediately, and is generally non-recoverable. The only reasonable response is for the response to fail. However when a remote file is unavailable, there are many possible reasons, and whether or not it is unrecoverable is not readily apparent. Hence most remote access systems allow for blocking or delayed response, in the hopes that the remote system ( or the network ) will come back up eventually.