Every other file and hence directory, since a directory is a file is somewhere beneath the root. But it's way too late to change Unix now; we all just live with it.
There are actually other reasons for doing it that way [the inventors of Unix were pretty bright]; but that's way beyond our scope here. Anyway, the very first slash in a fully qualified path or file name is actually by itself the name of a directory, namely the root; while all the other slashes just separate the names of each successive directory from the next one beneath it in the path.
Another way to think of it, is that a slash after the end of a filename indicates that it is the name of a directory file. If you were silly enough, you could get away with creating and naming a directory " root ". In any event, nobody wants to type those long, fully qualified file names out all the time so Unix has a convention regarding a " working directory ", also known as the current directory, and sometimes even as various combinations of those terms like, current working directory.
At given instant, you and Unix agree on a working directory I'll explain how in a moment and when you enter a command and give it just an unqualified or basic or simple file name like prog1. If there is no file by that name in the current directory, Unix gives you some sort of error message.
So, referring back to Figure 1, if the current working directory were CS , you could display that file named prog1. That would be true even if the current working directory also contained a file whose basic name was prog1. You control the working directory. When you login to Unix, your initial working directory, before you start moving around, is some directory created for you by a system administrator when your Unix account was created. Your system administrator is said to have created a home directory for you.
Anyway, back to directories: You can make new sub directories with the mkdir command. You can change the current working directory via the cd command. You can get Unix to tell you the name of the current working directory by means of the pwd command. You can get a list of the files including other directories within the current directory by means of the ls command.
All these commands and others are explained more fully in the Basic Unix Shell Commands section. But first, there's one last type of path name to learn. If it can't start at the root, about the only other place it knows about for sure is the current working directory. The first and the last sectors of the file system contain its settings the boot record or the superblock. This format uses 48 and 64 bit values to reference files, thus being able to support data storages with extremely high capacity.
ReFS has high tolerance to failures due to new features included into it. The most noteworthy one among them is Copy-on-Write CoW : no metadata is modified without being copied; data is not written over the existing data — it is placed to another area on the disk. After any modifications, a new copy of metadata is saved to a free area on the storage, and then the system creates a link from older metadata to the newer copy.
Thus, a significant quantity of older backups are stored in different places, providing easy data recovery unless this storage space is overwritten. In contrast to FAT, which simply allocates any first free cluster on the disk for the file fragment, HPFS seeks to arrange the file in contiguous blocks, or at least ensure that its fragments referred to as extents are placed maximally close to each other.
At the beginning of HPFS, there are three control blocks occupying 18 sectors: the boot block , the super block and the spare block. The remaining storage space is divided into parts of contiguous sectors referred to as bands taking 8 MB each.
A band has its own sector allocation bitmap showing which sectors in it are occupied 1 — taken, 0 — free. Each file and directory has its own F-Node located close to it on the disk — this structure contains the information about the location of a file and its extended attributes.
A special directory band located in the center of the disk is used for storing directories, while the directory structure itself is a balanced tree with alphabetical entries. Hint: The information concerning data recovery perspectives of the FS types used by Windows can be found in the articles on data recovery specificities of different OS and chances for data recovery.
For detailed instructions and recommendations, please, read the manual devoted to data recovery from Windows. Volumes are divided into sectors, typically bytes in size, then they are grouped into allocation blocks, the number of which depends on the size of the entire volume. The information concerning free and used allocation blocks is kept in the Allocation File. All allocation blocks assigned to each file as extends are recorded in the Extends Overflow File.
And, finally, all file attributes are listed in the Attributes file. Data reliability is improved through journaling which makes it possible to keep track of all changes to the system and quickly return it back to the working state in case of unexpected events. Among other supported features are hard links to directories, logical volume encryption, access control, data compression, etc.
The Apple file system is aimed to address fundamental issues present in its predecessor and was developed to efficiently work with modern flash storages and solid-state drives.
This bit format uses the copy-on-write method to increase performance, which allows to copy each block before the changes to it are applied, and offers a lot of data integrity and space-saving features. The Container Superblock stores information about the number of blocks in the Container, the block size, etc.
Information about all allocated and free blocks of the Container is managed with the help of Bitmap Structures. Each volume in the Container has its own Volume Superblock which provides information about this volume.
All files and folders of the volume are recorded in the File and Folder B-Tree , while the Extents B-Tree is responsible for extents — references to file contents file start, its length in blocks. Hint: The details related to the possibility of data recovery from these FS types can be found in the articles about the peculiarities of data recovery depending on the operating system and chances for data recovery.
Open-source Linux aims at implementing, testing and using different types of file systems. The most popular formats for Linux include:. Ext2, Ext3, Ext4 are simply different versions of the "native" Linux Ext file system. This type falls under active developments and improvements. Ext3 is just an extension of Ext2 that uses transactional file writing operations with a journal. Ext4 is a further development of Ext3, extended with the support of optimized file allocation information extents and extended file attributes.
This FS is frequently used as a "root " one for most Linux installations. ReiserFS - an alternative Linux file system optimized for storing a huge number of small files. It has good search capabilities and enables compact allocation of files by storing their tails or simply very small items along with metadata in order to avoid using large FS blocks for this purpose.
However, this format is no longer actively developed and supported. A file is a collection of data. They are created by users using text editors, running compilers etc. All the files are grouped together in the directory structure. The file-system is arranged in a hierarchical structure, like an inverted tree.
In the diagram above, we see that the home directory of the undergraduate student "ee51vn" contains two sub-directories docs and pics and a file called report. The full path to the file report. The kernel The kernel of UNIX is the hub of the operating system: it allocates time and memory to programs and handles the filestore and communications in response to system calls.
The shell The shell acts as an interface between the user and the kernel. The tcsh shell has certain features to help the user inputting commands. A process is an executing program identified by a unique PID process identifier.
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