Every file stored on a permanent storage device is attributed a name that will be used to retrieve the file. File names are unique as this will help distinguish one file from another. There is a convention for naming files computer systems based on the operating systems. The base name is obligatory and the extension is optional.
The extension is usually used to indicate the type of file, example: doc is the extension for Ms Word files, xl is the extension for Ms Excel files. The naming systems have been changing over time. Now these limitations do not apply to the current versions of operating systems. Another way to locate file easily is by creating a directory or folder in which can be held files relating to the same field. On the same directory, it can also be created sub- directories. The naming convention for directories is the same as for files.
Regarding the organization of files, it is noted that files can be organized on a directory in a hierarchical structure for an easy management. There will be a main directory with other directories sub-directories and files. As for software, there are two categories: application and system software. Application software is a software that is conceived to generate information, fix a problem, or support a decision making process for individuals or organizations.
When it comes about system software, it is designed to enhance the effectiveness and efficiency of the computer system. Hardware and software are thus the setup of the computer.
At the heart of the computer is the hardware; the system software is acted as a buffer between the hardware and the outer layer application software which is used by the user to interacts with the computer. In this interactivity between the user and the computer system, the operating system plays a fundamental role.
Actually, the operating system, available on all computers, is the main controlling software of the system and helps the user to communicate and access data in the computer system. There are two broad categories of programming languages: low level and high level languages. Low level languages are designed to operate at a low level, either directly or close to the hardware.
They are machine-dependent and comprise two types: machine language and assembly language. The machine language which is native for any computer comprises a series of binary digits that represent the instructions and data given to the hardware. As for assembly language promoted due to difficulties to work with machine language, it comprises English-like mnemonics devices used to aid recall for instructions.
Any programme in an assembly language needs an assembler which transforms the language into the equivalent machine language code before the computer can operate it. High level languages can be classified in various ways, including the following: compiled language, interpreter, Java, procedural programming language, object oriented programming language, declarative language. Their fast development has led inevitably to the breakthrough of a multitude of applications adapted to industrial needs.
In many fields viz. With these resources computers appear to be vital in nowadays communication. However, computers can only perform tasks that can be described algebraically. As a substantial description of computers, their components, organization and functioning is made, it is also important to understand their evolution. To retrace this history of computers, we need first to have an overview on the period preceding their coming.
Thus, before computers people over the world used different methods including primitive materials like papyrus, a crude form of paper by ancient Egyptians.
At this age, Sumerians used boxes of stones to represent numbers. Chinese invented the abacus in B. Many other methods and techniques were used at this period, but with the genius of human being, invention with regard to computing was launched. A number of scientists Wilhelm Schickard, Blaise Pascal, Leibnitz, Ada Lovelace worked on the field, improving progressively the computer systems in terms quality and space.
In John Napier invented logs for calculations. In , Ada Lovelace began the study of scientific computation. She developed a programming language Ada, named after her. The creation and spread of companies specialized on the field brought a higher dimension to computing machines. However, the breakthrough of computers came almost in the second half of the twentieth century from , with the use of binary maths and Boolean logic. In this regard, the evolution of computers went with the major technological breakthroughs, generations after generations.
People started talking about digital computers that are smaller and more powerful. The first generation of the digital computers was under WW2 and the need to process timely immense data.
Hence, the advancements carried out were the conception of programmes and programming languages. As the devices working with vacuum tubes remained still too large, requiring vast space and lot energy, there was a need for improvement.
This led to the second generation of computers where great progresses were made in the early second half of the 20th century. Computer systems became more and more powerful miniaturization. Transistors quickly replaced the vacuums tubes. They required less space, less energy and processed more data in shorter time. High level languages were used; operating systems replaced human operators. The performance was , to , calculations per second.
Batch processing and time sharing started. Being extremely motivated to meliorate computer products, engineers marked later the third generation with more sophisticated computers IBM The use of integrated circuit IC was the key characteristic of the third generation, but computers got also more single and cheaper, with broader range of programmes.
As for the fourth generation, it was characterized by the utilization of microprocessor and microcomputers. The engineers tended then to build on applications that qualified this generation of computers with the use of artificial intelligence and expert systems. Sophistication of software and expansion of communication qualified also this computer development age. In the fifth generation, specified by further miniaturization, computers reached a new dimension with the artificial intelligence which is defined as the ability of computer system to display behaviour that appears to be from an intelligent individual group.
Partitioning isn't just a way of installing multiple operating systems and tools, though; It also helps us keep critical system files apart from ordinary ones. So no matter how many games you install on your computer, it won't have any effect on the operating system's performance - since they reside in different partitions. Back to the office example, having a call center and a tech team in a common area would harm both teams' productivity because each team has its own requirements to be efficient.
For instance, the primary partition on Windows on which Windows is installed is known as C :, or drive C. In Unix-like operating systems, however, partitions appear as ordinary directories under the root directory - we'll cover this later. In the next section, we'll dive deeper into partitioning and get to know two concepts that will change your perspective on file systems: system firmware and booting. Regardless of what partitioning scheme you choose, the first few blocks on the storage device will always contain critical data about your partitions.
The system's firmware uses these data structures to boot up the operating system on a partition. A firmware is a low-level software embedded into electronic devices to operate the device, or bootstrap another program to do it. Firmware exists in computers, peripherals keyboards, mice, and printers , or even electronic home appliances. In computers, the firmware provides a standard interface for complex software like an operating system to boot up and work with hardware components.
However, on simpler systems like a printer, the firmware is the operating system. The menu you use on your printer is the interface of its firmware. The mission of the firmware among other things is to boot up the computer, run the operating system, and pass it the control of the whole system.
A firmware also runs pre-OS environments with network support , like recovery or diagnostic tools, or even a shell to run text-based commands. The first few screens you see before your Windows logo appears are the output of your computer's firmware, verifying the health of hardware components and the memory. The initial check is confirmed with a beep usually on PCs , indicating everything is good to go.
On MBR-partitioned disks, the first sector on the storage device contains essential data to boot up the system. Once the program is on the memory, the CPU begins executing it.
Having the boot loader and the partition table in a predefined location like MBR enables BIOS to boot up the system without having to deal with any file. If you are curious about how the CPU executes the instructions residing in the memory, you can read this beginner-friendly and fun guide on how the CPU works. Additionally, 64 bytes are allocated to the partition table, which can contain information about a maximum of four partitions. That said, sophisticated boot loaders like GRUB 2 on Linux split their functionality into pieces or stages.
The smallest piece of code known as the first-stage boot loader is stored in the MBR. It's usually a simple program, which doesn't require much space. The responsibility of the first-stage boot loader is to initiate the next and more complicated stages of the booting process. GRUB calls this the stage 1. Stage 1. The second stage boot loader, which is now capable of working with files, can load the operating system's boot loader file to boot up the respective operating system.
A common workaround is to make an extended partition beside the primary partitions, as long as the total number of partitions won't exceed four. An extended partition can be split into multiple logical partitions. Making extended partitions is different across operating systems. Over this quick guide Microsoft explains how it should be done on Windows. And every partition can be the size of the biggest storage device available in the market - actually a lot more. This sector is called Protective MBR.
This is where the first-stage boot loader would reside in an MBR-partitioned disk. The GPT entries and the GPT header are backed up at the end of the storage device, so they can be recovered if the primary copy gets corrupted. Once the EFI partition is found, it looks for the configured boot loader - usually, a file ending with. You can use the parted command on Linux to see what partitioning scheme is used for a storage device.
Formatting involves the creation of various data structures and metadata used to manage files within a partition. Alright, let's get back file systems with our new background about partitioning, formatting, and booting.
A file system is a set of data structures, interfaces, abstractions, and APIs that work together to manage any type of file on any type of storage device, in a consistent manner. Starting from Windows NT 3. So basically, if you have a removable disk you want to use on Windows, Mac, and Linux, you need to format it to exFAT. The Extended File System ext family of file systems was created for the Linux kernel - the core of the Linux operating system.
The first version of ext was released in , but soon after, it was replaced by the second extended file system ext2 in In the s, the third extended filesystem ext3 and fourth extended filesystem ext4 were developed for Linux with journaling capability. The physical layer is the concrete implementation of a file system; It's responsible for data storage and retrieval and space management on the storage device or precisely: partitions. The physical file system interacts with the storage hardware via device drivers.
The virtual file system provides a consistent view of various file systems mounted on the same operating system. It's common for a removable storage medium to have a different file system than that of a computer. For instance, when you open up your file explorer program, you can copy an image from an ext4 file system and paste it over to your exFAT-formatted flash memory - without having to know that files are managed differently under the hood. This convenient layer between the user you and the underlying file systems is provided by the VFS.
A VFS defines a contract that all physical file systems must implement to be supported by that operating system. However, this compliance isn't built into the file system core, meaning the source code of a file system doesn't include support for every operating system's VFS. Instead, it uses a file system driver to adhere to the VFS rules of every file system.
A driver is a program that enables software to communicate with another software or hardware. Although VFS is responsible for providing a standard interface between programs and various file systems, computer programs don't interact with VFS directly. On the other hand, VFS provides a bridge between the logical layer which programs interact with and a set of the physical layer of various file systems.
Then, it creates a virtual directory tree and puts the content of each device under that directory tree as separate directories. The act of assigning a directory to a storage device under the root directory tree is called mounting , and the assigned directory is called a mount point.
That said, on a Unix-like operating system, all partitions and removable storage devices appear as if they are directories under the root directory. If the mount-point directory already contains files, those files will be hidden for as long as the device is mounted. In Unix-like systems, the metadata is in the form of data structures, called inode.
Each file on the storage device has an inode, which contains information about it such as the time it was created, modified, etc. The inode also includes the address of the blocks allocated to the file; On the other hand, where exactly it's located on the storage device. In an ext4 inode, the address of the allocated blocks is stored as a set of data structures called extents within the inode.
Each extent contains the address of the first data block allocated to the file and the number of the continuous blocks that the file has occupied. Once the inode is fetched, the file system starts to compose the file from the data blocks registered in the inode.
You can use the df command with the -i parameter on Linux to see the inodes total, used, and free in your partitions:. To see the inodes associated with files in a directory, you can use the ls command with -il parameters.
The number of inodes on a partition is decided when you format a partition. That said, as long as you have free space and unused inodes, you can store files on your storage device. It's unlikely that a personal Linux OS would run out of inodes.
However, enterprise services that deal with a large number of files like mail servers have to manage their inode quota smartly. Every file has at least one entry in MFT, which contains everything about it, including its location on the storage device - similar to the inodes table.
For instance, when you right-click on a file on Mac OS, and select Get Info Properties in Windows , a window appears with information about the file. A sector is the minimum storage unit on a storage device and is between bytes and bytes Advanced Format.
However, file systems use a high-level concept as the storage unit, called blocks. Blocks are an abstraction over physical sectors; Each block usually consists of multiple sectors. The most basic storage unit in ext4-formatted partitions is the block. However, the contiguous blocks are grouped into block groups for easier management. Ext4 file system even takes one step further comparing to ext3 , and organizes block groups into a bigger group called flex block groups.
The data structures of each block group, including the block bitmap, inode bitmap, and inode table, are concatenated and stored in the first block group within each flex block group. Having all the data structures concatenated in one block group the first one frees up more contiguous data blocks on other block groups within each flex block group. These concepts might be confusing, but you don't have to master every bit of them.
It's just to depict the depth of file systems. When a file is being written to a disk, it is written to one or more blocks within a block group. Managing files at the block group level improves the performance of the file system significantly, as opposed to organizing files as one unit. Have you ever noticed that your file explorer displays two different sizes for each file: size, and size on disk. One block is the minimum space that can be allocated to a file. This means the remaining space of a partially-filled block cannot be used by another file.
This is the rule! Since the size of the file isn't an integer multiple of blocks , the last block might be partially used, and the remaining space would remain unused - or would be filled with zeros.
Based on the output, the allocated block is about 4kb, while the actual file size is bytes. This means each block size on this operating system is 4kb. These frequent changes in the storage medium leave many small gaps empty spaces between files. These gaps are due to the same reason file size and file size on disk are different. Some files won't fill up the full block, and lots of space will be wasted. And over time there' won't be enough consequent blocks to store new files.
File Fragmentation occurs when a file is stored as fragments on the storage device because the file system cannot find enough contiguous blocks to store the whole file in a row.
Now, if you add more content to myfile. Since myfile. In that case, the new content of myfile. File fragmentation puts a burden on the file system because every time a fragmented file is requested by a user program, the file system needs to collect every piece of the file from various locations on a disk.
The fragmentation might also occur when a file is written to the disk for the first time, probably because the file is huge and not many continuous blocks are left on the partition. Modern file systems use smart algorithms to avoid or early-detect fragmentation as much as possible. Ext4 also does some sort of preallocation, which involves reserving blocks for a file before they are actually needed - making sure the file won't get fragmented if it gets bigger over time. The number of the preallocated blocks is defined in the length field of the file's extent of its inode object.
The idea is instead of writing to data blocks one at a time during a write, the allocation requests are accumulated in a buffer and are written to the disk at once. Not having to call the file system's block allocator on every write request helps the file system make better choices with distributing the available space. For instance, by placing large files apart from smaller files.
Imagine that a small file is located between two large files. Now, if the small file is deleted, it leaves a small space between the two files. Spreading the files out in this manner leaves enough gaps between data blocks, which helps the filesystem manage and avoid fragmentation more easily.
A Directory Folder in Windows is a special file used as a logical container to group files and directories within a file system. The inode or MFT entry of a directory contains information about that directory, as well as a collection of entries pointing to the files "under" that directory.
The files aren't literally contained within the directory, but they are associated with the directory in a way that they appear as directory's children at a higher level, such as in a file explorer program. These entries are called directory entries. In addition to the directory entries, there are two more entries.
On Linux, you can use the ls in a directory to see the directory entries with their associated inode numbers:. The limitation can be in the length of the filename or filename case sensitivity. The web page contains your company logo, which is a PNG file, like this:.
If the actual file name is Logo. Because in Linux ext4 file system logo. This makes exFAT an ideal option for storing massive data objects, such as video files. As you know, the logical layer of the file system provides an API to enable user applications to perform file operations, such as read , write , delete , and execute operations.
That said, operating systems provide convenient file management utilities out of the box for your day-to-day file management. These text-based interfaces help users do all sorts of file operations as text commands - Like how we did in the previous examples. This feature is also available in the CLI Command prompt or Terminal , where a user can change file ownerships or limit permissions of each file right from the command line interface. For instance, a file owner on Linux or Mac can configure a file to be available to the public, like so:.
Please note this is just an example, and you should not set a file's permission to One day, you open the file, make some changes and save it. But what if the system crashes while the older version of the file is being replaced with the new version? In older file systems like FAT32 or ext2 the data would be corrupted because it was partially written to the disk. This is less likely to happen with modern file systems as they use a technique called journaling.
The main purpose is to keep track of the changes that haven't yet been committed to the file system physically. The journal is a special allocation on the disk where each writing attempt is first stored as a transaction. Once the data is physically placed on the storage device, the change is committed to the filesystem. In case of a system failure, the file system will detect the incomplete transaction and roll it back as if it never happened.
That said, the new content that was being written may still be lost, but the existing data would remain intact.
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