Professional File System
Encyclopedia
The Professional File System is a filesystem originally developed commercially for the Amiga
Amiga
The Amiga is a family of personal computers that was sold by Commodore in the 1980s and 1990s. The first model was launched in 1985 as a high-end home computer and became popular for its graphical, audio and multi-tasking abilities...

, it is now distributed on Aminet with a 4-clause BSD license. PFS tends to perform very well, due to the simplicity of design. Compatible successor of Ami-FileSafe.

The device is split into two main areas. At the beginning of the device is the metadata section, which consists of a root block, and a generic array of blocks that can be allocated to store metadata. The rest of the device is another contiguous generic array of blocks that can be allocated to store data. The metadata section usually uses a few percent of the device, depending on the size of the device.

The metadata is stored as a tree of single blocks in the metadata section. The entire directory structure is recorded in the metadata, so the data section purely contains data from files. The metadata describes the location of data in files with extents of blocks, which makes the metadata quite compact.

When a metadata update occurs, the system looks at the block containing the metadata to be changed, and copies it to a newly-allocated block from the metadata section, with the change made, then it recursively changes the metadata in the block that points to that block in the same way. This way, eventually the root block needs to be changed, which causes the atomic metadata update.

The filesystem is reasonably good at keeping files unfragmented, although there is a defragmentation tool available which will work on an online filesystem.

It was the first filesystem to introduce the concept of the Recycle Bin
Recycle bin (computing)
In computing, the trash is temporary storage for files that have been deleted in a file manager by the user, but not yet permanently erased from the physical media...

 natively at filesystem-level to the Amiga, holding the last few deleted files in a hidden directory on the disk root.

As is common (and generally required) with Amiga filesystems, the filesystem does not need to be unmounted in order to be "cleanly" mounted afterwards.

PFS version 5.3 was developed in C and a small portion of assembly code by Michiel Pelt.

See also

  • Amiga Old File System
    Amiga Old File System
    On the Amiga, the Old File System was the filesystem for Amiga OS before the Amiga Fast File System. Even though it used 512-byte blocks, it reserved the first small portion of each block for metadata, leaving an actual data block capacity of 488 bytes per block...

     (OFS)
  • Amiga Fast File System
    Amiga Fast File System
    The Amiga Fast File System is a file system used on the Amiga personal computer. The previous Amiga filesystem upon the release of FFS became known as Amiga Old File System . OFS, while fine on floppy disk, soon proved too slow to keep up with era hard drives...

     (FFS)
  • Smart File System
    Smart File System
    The Smart File System is a journaling filesystem used on Amiga computers. It is designed for performance, scalability and integrity...

     (SFS)
  • File system
    File system
    A file system is a means to organize data expected to be retained after a program terminates by providing procedures to store, retrieve and update data, as well as manage the available space on the device which contain it. A file system organizes data in an efficient manner and is tuned to the...

  • List of file systems

External links

The source of this article is wikipedia, the free encyclopedia.  The text of this article is licensed under the GFDL.
 
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