Comparison of filesystems

File system

Any computer file is stored on some kind of storage with a given capacity. Actually, each storage is a linear space to read or both read and write digital information. Each byte of information on the storage has its own offset from the storage start (address) and is referenced by this address. A storage can be presented as a grid with a set of numbered cells (each cell – single byte). Any file saved to the storage takes a number of these cells. Generally, computer storages use a pair of sector and in-sector offset to reference any byte of information on the storage.

Linux file systems

Open-source Linux OS always aimed to implement, test and use different concepts of file systems. Among huge amount of various file system types the most popular Linux file systems nowadays are:

Ext2, Ext3, Ext4 - 'native' Linux file system. This file system falls under active developments and improvements. Ext3 file system is just an extension to Ext2 that uses transactional file write operations with journal. Ext4 is a further development of Ext3, extended with support of optimized file allocation information (extents) and extended file attributes. This file system is frequently used as 'root' file system for most Linux installations.

Windows file systems

Microsoft Windows OS use two major file systems: FAT, inherited from old DOS with its later extension FAT32, and widely-used NTFS file systems.

FAT (File Allocation Table):

FAT file system is one of the most simple types of file systems. It consists of file system descriptor sector (boot sector or superblock), file system block allocation table (referenced as File Allocation Table) and plain storage space to store files and folders. Files on FAT are stored in directories. Each directory is an array of 32-byte records, each defines file or file extended attributes (e.g. long file name). File record references the first block of file. Any next block can be found through block allocation table by using it as linked-list.

NTFS (New Technology File System):

NTFS was introduced in Windows NT and at present is major file system for Windows. This is a default file system for disk partitions and the only file system that is supported for disk partitions over 32GB. The file system is quite extensible and supports many file properties, including access control, encryption etc. Each file on NTFS is stored as file descriptor in Master File Table and file content. Master file table contains all information about the file: size, allocation, name etc. The first and the last sectors of the file system contain file system settings (boot record or superblock). This file system uses 48 and 64 bit values to reference files, thus supporting quite large disk storages.

MacOS file systems

Apple Mac OS operating system applies HFS+ file system, an extension to their own HFS file system that was used on old Macintosh computers.

HFS+ file system is applied to Apple desktop products, including Mac computers, iPhone, iPod, as well as Apple X Server products. Advanced server products also use Apple Xsan file system, clustered file system derived from StorNext or CentraVision file systems.

This file system except files and folders also stores Finder information about directories view, window positions etc.

Swap Space

Swap space in Linux is used when the amount of physical memory (RAM) is full. If the system needs more memory resources and the RAM is full, inactive pages in memory are moved to the swap space. While swap space can help machines with a small amount of RAM, it should not be considered a replacement for more RAM. Swap space is located on hard drives, which have a slower access time than physical memory.

So, if:

M = Amount of RAM in GB, and S = Amount of swap in GB, then

If M < 2

       S = M *2

Else

       S = M + 2