This glossary contains terms and acronyms used within the &os; community and documentation. ACL ACPI AMD AML API APIC APM APOP ASL ATA ATM ACPI Machine Language AML Pseudocode, interpreted by a virtual machine within an ACPI-compliant operating system, providing a layer between the underlying hardware and the documented interface presented to the OS. ACPI Source Language ASL The programming language AML is written in. Access Control List ACL A list of permissions attached to an object, usually either a file or a network device. Advanced Configuration and Power Interface ACPI A specification which provides an abstraction of the interface the hardware presents to the operating system, so that the operating system should need to know nothing about the underlying hardware to make the most of it. ACPI evolves and supersedes the functionality provided previously by APM, PNPBIOS and other technologies, and provides facilities for controlling power consumption, machine suspension, device enabling and disabling, etc. Application Programming Interface API A set of procedures, protocols and tools that specify the canonical interaction of one or more program parts; how, when and why they do work together, and what data they share or operate on. Advanced Power Management APM An API enabling the operating system to work in conjunction with the BIOS in order to achieve power management. APM has been superseded by the much more generic and powerful ACPI specification for most applications. Advanced Programmable Interrupt Controller APIC Advanced Technology Attachment ATA Asynchronous Transfer Mode ATM Authenticated Post Office Protocol APOP Automatic Mount Daemon AMD A daemon that automatically mounts a filesystem when a file or directory within that filesystem is accessed. BAR BIND BIOS BSD Base Address Register BAR The registers that determine which address range a PCI device will respond to. Basic Input/Output System BIOS The definition of BIOS depends a bit on the context. Some people refer to it as the ROM chip with a basic set of routines to provide an interface between software and hardware. Others refer to it as the set of routines contained in the chip that help in bootstrapping the system. Some might also refer to it as the screen used to configure the bootstrapping process. The BIOS is PC-specific but other systems have something similar. Berkeley Internet Name Domain BIND An implementation of the DNS protocols. Berkeley Software Distribution BSD This is the name that the Computer Systems Research Group (CSRG) at The University of California at Berkeley gave to their improvements and modifications to AT&T's 32V &unix;. &os; is a descendant of the CSRG work. Bikeshed Building A phenomenon whereby many people will give an opinion on an uncomplicated topic, whilst a complex topic receives little or no discussion. See the FAQ for the origin of the term. CD CHAP CLIP COFF CPU CTS Carrier Detect CD An RS232C signal indicating that a carrier has been detected. Central Processing Unit CPU Also known as the processor. This is the brain of the computer where all calculations take place. There are a number of different architectures with different instruction sets. Among the more well-known are the Intel-x86 and derivatives, Arm, and PowerPC. Challenge Handshake Authentication Protocol CHAP A method of authenticating a user, based on a secret shared between client and server. Classical IP over ATM CLIP Clear To Send CTS An RS232C signal giving the remote system permission to send data. Common Object File Format COFF DAC DDB DES DHCP DNS DSDT DSR DTR DVMRP Discretionary Access Control DAC Data Encryption Standard DES A method of encrypting information, traditionally used as the method of encryption for &unix; passwords and the &man.crypt.3; function. Data Set Ready DSR An RS232C signal sent from the modem to the computer or terminal indicating a readiness to send and receive data. Data Terminal Ready DTR An RS232C signal sent from the computer or terminal to the modem indicating a readiness to send and receive data. Debugger DDB An interactive in-kernel facility for examining the status of a system, often used after a system has crashed to establish the events surrounding the failure. Differentiated System Description Table DSDT An ACPI table, supplying basic configuration information about the base system. Distance-Vector Multicast Routing Protocol DVMRP Domain Name System DNS The system that converts humanly readable hostnames (i.e., mail.example.net) to Internet addresses and vice versa. Dynamic Host Configuration Protocol DHCP A protocol that dynamically assigns IP addresses to a computer (host) when it requests one from the server. The address assignment is called a lease. ECOFF ELF ESP Encapsulated Security Payload ESP Executable and Linking Format ELF Extended COFF ECOFF FADT FAT FAT16 FTP File Allocation Table FAT File Allocation Table (16-bit) FAT16 File Transfer Protocol FTP A member of the family of high-level protocols implemented on top of TCP which can be used to transfer files over a TCP/IP network. Fixed ACPI Description Table FADT GUI Giant The name of a mutual exclusion mechanism (a sleep mutex) that protects a large set of kernel resources. Although a simple locking mechanism was adequate in the days where a machine might have only a few dozen processes, one networking card, and certainly only one processor, in current times it is an unacceptable performance bottleneck. &os; developers are actively working to replace it with locks that protect individual resources, which will allow a much greater degree of parallelism for both single-processor and multi-processor machines. Graphical User Interface GUI A system where the user and computer interact with graphics. HTML HUP HangUp HUP HyperText Markup Language HTML The markup language used to create web pages. I/O IASL IMAP IP IPFW IPP IPv4 IPv6 ISP IP Firewall IPFW IP Version 4 IPv4 The IP protocol version 4, which uses 32 bits for addressing. This version is still the most widely used, but it is slowly being replaced with IPv6. IP Version 6 IPv6 The new IP protocol. Invented because the address space in IPv4 is running out. Uses 128 bits for addressing. Input/Output I/O Intel’s ASL compiler IASL Intel’s compiler for converting ASL into AML. Internet Message Access Protocol IMAP A protocol for accessing email messages on a mail server, characterised by the messages usually being kept on the server as opposed to being downloaded to the mail reader client. Internet Printing Protocol IPP Internet Protocol IP The packet transmitting protocol that is the basic protocol on the Internet. Originally developed at the U.S. Department of Defense and an extremely important part of the TCP/IP stack. Without the Internet Protocol, the Internet would not have become what it is today. For more information, see RFC 791. Internet Service Provider ISP A company that provides access to the Internet. KAME Japanese for turtle, the term KAME is used in computing circles to refer to the KAME Project, who work on an implementation of IPv6. KDC KLD KSE KVA Kbps Kernel &man.ld.1; KLD A method of dynamically loading functionality into a &os; kernel without rebooting the system. Kernel Scheduler Entities KSE A kernel-supported threading system. See the project home page for further details. Kernel Virtual Address KVA Key Distribution Center KDC Kilo Bits Per Second Kbps Used to measure bandwidth (how much data can pass a given point at a specified amount of time). Alternates to the Kilo prefix include Mega, Giga, Tera, and so forth. LAN LOR LPD Line Printer Daemon LPD Local Area Network LAN A network used on a local area, e.g. office, home, or so forth. Lock Order Reversal LOR The &os; kernel uses a number of resource locks to arbitrate contention for those resources. A run-time lock diagnostic system found in &os.current; kernels (but removed for releases), called &man.witness.4;, detects the potential for deadlocks due to locking errors. (&man.witness.4; is actually slightly conservative, so it is possible to get false positives.) A true positive report indicates that if you were unlucky, a deadlock would have happened here. True positive LORs tend to get fixed quickly, so check &a.current.url; and the LORs Seen page before posting to the mailing lists. MAC MADT MFC MFH MFS MFV MIT MLS MOTD MTA MUA Mail Transfer Agent MTA An application used to transfer email. An MTA has traditionally been part of the BSD base system. Today Sendmail is included in the base system, but there are many other MTAs, such as postfix, qmail and Exim. Mail User Agent MUA An application used by users to display and write email. Mandatory Access Control MAC Massachusetts Institute of Technology MIT Merge From Current MFC To merge functionality or a patch from the -CURRENT branch to another, most often -STABLE. Merge From Head MFH To merge functionality or a patch from a repository HEAD to an earlier branch. Merge From Stable MFS In the normal course of FreeBSD development, a change will be committed to the -CURRENT branch for testing before being merged to -STABLE. On rare occasions, a change will go into -STABLE first and then be merged to -CURRENT. This term is also used when a patch is merged from -STABLE to a security branch. Merge From Vendor MFV Message Of The Day MOTD A message, usually shown on login, often used to distribute information to users of the system. Multi-Level Security MLS Multiple APIC Description Table MADT NAT NDISulator NFS NTFS NTP Network Address Translation NAT A technique where IP packets are rewritten on the way through a gateway, enabling many machines behind the gateway to effectively share a single IP address. Network File System NFS New Technology File System NTFS A filesystem developed by Microsoft and available in its New Technology operating systems, such as &windows2k;, &windowsnt; and &windowsxp;. Network Time Protocol NTP A means of synchronizing clocks over a network. OBE ODMR OS On-Demand Mail Relay ODMR Operating System OS A set of programs, libraries and tools that provide access to the hardware resources of a computer. Operating systems range today from simplistic designs that support only one program running at a time, accessing only one device to fully multi-user, multi-tasking and multi-process systems that can serve thousands of users simultaneously, each of them running dozens of different applications. Overtaken By Events OBE Indicates a suggested change (such as a Problem Report or a feature request) which is no longer relevant or applicable due to such things as later changes to &os;, changes in networking standards, the affected hardware having since become obsolete, and so forth. PAE PAM PAP PC PCNSFD PDF PID POLA POP POP3 PPD PPP PPPoA PPPoE PPP over ATM PPPoA PPP over Ethernet PPPoE PR PXE Password Authentication Protocol PAP Personal Computer PC Personal Computer Network File System Daemon PCNFSD Physical Address Extensions PAE A method of enabling access to up to 64 GB of RAM on systems which only physically have a 32-bit wide address space (and would therefore be limited to 4 GB without PAE). Pluggable Authentication Modules PAM Point-to-Point Protocol PPP Pointy Hat A mythical piece of headgear, much like a dunce cap, awarded to any &os; committer who breaks the build, makes revision numbers go backwards, or creates any other kind of havoc in the source base. Any committer worth his or her salt will soon accumulate a large collection. The usage is (almost always?) humorous. Portable Document Format PDF Post Office Protocol POP Post Office Protocol Version 3 POP3 A protocol for accessing email messages on a mail server, characterised by the messages usually being downloaded from the server to the client, as opposed to remaining on the server. PostScript Printer Description PPD Preboot eXecution Environment PXE Principle Of Least Astonishment POLA As &os; evolves, changes visible to the user should be kept as unsurprising as possible. For example, arbitrarily rearranging system startup variables in /etc/defaults/rc.conf violates POLA. Developers consider POLA when contemplating user-visible system changes. Problem Report PR A description of some kind of problem that has been found in either the &os; source or documentation. See Writing &os; Problem Reports. Process ID PID A number, unique to a particular process on a system, which identifies it and allows actions to be taken against it. Project Evil The working title for the NDISulator, written by Bill Paul, who named it referring to how awful it is (from a philosophical standpoint) to need to have something like this in the first place. The NDISulator is a special compatibility module to allow Microsoft Windows™ NDIS miniport network drivers to be used with &os;/i386. This is usually the only way to use cards where the driver is closed-source. See src/sys/compat/ndis/subr_ndis.c. RA RAID RAM RD RFC RISC RPC RS232C RTS Random Access Memory RAM Revision Control System RCS The Revision Control System (RCS) is one of the oldest software suites that implement revision control for plain files. It allows the storage, retrieval, archival, logging, identification and merging of multiple revisions for each file. RCS consists of many small tools that work together. It lacks some of the features found in more modern revision control systems, like Git, but it is very simple to install, configure, and start using for a small set of files. Received Data RD An RS232C pin or wire that data is received on. Recommended Standard 232C RS232C A standard for communications between serial devices. Reduced Instruction Set Computer RISC An approach to processor design where the operations the hardware can perform are simplified but made as general purpose as possible. This can lead to lower power consumption, fewer transistors and in some cases, better performance and increased code density. Examples of RISC processors include the Alpha, &sparc;, &arm; and &powerpc;. Redundant Array of Inexpensive Disks RAID Remote Procedure Call RPC Request For Comments RFC A set of documents defining Internet standards, protocols, and so forth. See www.rfc-editor.org. Also used as a general term when someone has a suggested change and wants feedback. Request To Send RTS An RS232C signal requesting that the remote system commences transmission of data. Router Advertisement RA SCI SCSI SG SMB SMP SMTP SMTP AUTH SSH STR SVN SMTP Authentication SMTP AUTH Server Message Block SMB Signal Ground SG An RS232 pin or wire that is the ground reference for the signal. Simple Mail Transfer Protocol SMTP Secure Shell SSH Small Computer System Interface SCSI Subversion SVN Subversion is a version control system currently used by the &os; project. Suspend To RAM STR Symmetric MultiProcessor SMP System Control Interrupt SCI TCP TCP/IP TD TFTP TGT TSC Ticket-Granting Ticket TGT Time Stamp Counter TSC A profiling counter internal to modern &pentium; processors that counts core frequency clock ticks. Transmission Control Protocol TCP A protocol that sits on top of (e.g.) the IP protocol and guarantees that packets are delivered in a reliable, ordered, fashion. Transmission Control Protocol/Internet Protocol TCP/IP The term for the combination of the TCP protocol running over the IP protocol. Much of the Internet runs over TCP/IP. Transmitted Data TD An RS232C pin or wire that data is transmitted on. Trivial FTP TFTP UDP UFS1 UFS2 UID URL USB Uniform Resource Locator URL A method of locating a resource, such as a document on the Internet and a means to identify that resource. Unix File System Version 1 UFS1 The original &unix; file system, sometimes called the Berkeley Fast File System. Unix File System Version 2 UFS2 An extension to UFS1, introduced in &os; 5-CURRENT. UFS2 adds 64 bit block pointers (breaking the 1T barrier), support for extended file storage and other features. Universal Serial Bus USB A hardware standard used to connect a wide variety of computer peripherals to a universal interface. User ID UID A unique number assigned to each user of a computer, by which the resources and permissions assigned to that user can be identified. User Datagram Protocol UDP A simple, unreliable datagram protocol which is used for exchanging data on a TCP/IP network. UDP does not provide error checking and correction like TCP. VPN Virtual Private Network VPN A method of using a public telecommunication such as the Internet, to provide remote access to a localized network, such as a corporate LAN.