FD
Fidei Defensor, abbreviated as FD and translated from Latin as "Defender of the Faith," is a hereditary title held by the sovereigns of England and, subsequently, the United Kingdom, originating from a papal honor granted to King Henry VIII in recognition of his theological defense of Roman Catholic sacraments against Martin Luther's Reformation critiques.[1][2] The title was conferred via a papal bull issued by Pope Leo X on October 11, 1521, rewarding Henry's authorship of Assertio Septem Sacramentorum (Defense of the Seven Sacraments), a treatise asserting papal supremacy and transubstantiation.[3][4] Following Henry VIII's schism with Rome over his divorce from Catherine of Aragon and the establishment of the Church of England in the 1530s, Pope Paul III revoked the title in 1538 as part of broader excommunications.[5] English Parliament reinstated it through statutes in 1543 and 1544, detaching it from papal authority and aligning it with the monarch's role as Supreme Head (later Governor) of the Church of England, a position emphasizing protection of Anglican doctrine amid ongoing religious conflicts.[6] The abbreviation FD appears on British coinage alongside regal inscriptions, symbolizing the crown's enduring ecclesiastical stewardship, though its original Catholic intent has evolved into a marker of national religious independence.[3] This shift highlights a defining irony: a papally awarded honor repurposed by the very schism it opposed, underscoring causal tensions between monarchical prerogative and doctrinal fidelity in Tudor England.Computing and Technology
File Descriptor
A file descriptor is a non-negative integer that serves as an index into a process-specific table maintained by the operating system kernel, identifying an open file or other input/output resource such as a pipe, socket, or device.[7] This abstraction enables uniform handling of diverse resources under the Unix philosophy that "everything is a file," allowing system calls likeread() and write() to operate on files, terminals, and network connections alike.[8] File descriptors are process-unique, meaning each process maintains its own table, and they are typically small integers starting from 0, with higher values allocated sequentially upon opening new resources.
In Unix-like systems, three standard file descriptors are predefined for every process at startup: descriptor 0 for standard input (stdin), used for reading input from the keyboard or redirected sources; descriptor 1 for standard output (stdout), for writing normal program output; and descriptor 2 for standard error (stderr), for diagnostic messages independent of output redirection.[9] These conventions originated in early Unix implementations from the 1970s and are standardized in POSIX, ensuring portability across compliant systems.[7] The POSIX standard specifies that functions such as open() return the lowest unused descriptor number, and operations like [dup](/page/DUP)() or [dup2](/page/DUP)() duplicate descriptors to share access to the underlying file description, which includes attributes like file offset, access mode, and reference count.
File descriptors facilitate low-level I/O control via system calls, contrasting with higher-level buffered streams in C libraries (e.g., FILE* pointers), which wrap descriptors but add buffering and formatting. The kernel enforces limits on the number of open descriptors per process (e.g., via ulimit -n in shells, often defaulting to 1024 on Linux systems as of kernel versions post-2.6), to prevent resource exhaustion from errors like file handle leaks. Closing a descriptor with close() decrements the reference count on the associated file description, freeing the entry when it reaches zero, while errors such as exceeding limits return -1 with errno set to EMFILE or ENFILE. This mechanism supports efficient multiplexing, as seen in select() or poll() for handling multiple descriptors concurrently in network servers.