FreeBSD Glossary

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.

The programming language AML is written in.

A list of permissions attached to an object, usually either a file or a network device.

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.

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.

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 APM has been superseded by the much more generic and powerful ACPI specification for most applications.

A daemon that automatically mounts a filesystem when a file or directory within that filesystem is accessed.

The registers that determine which address range a PCI device will respond to.

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.

An implementation of the DNS protocols.

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®. FreeBSD is a descendant of the CSRG work.

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.

An RS232C signal indicating that a carrier has been detected.

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, Sun SPARC, PowerPC, and Alpha.

A method of authenticating a user, based on a secret shared between client and server.

An RS232C signal giving the remote system permission to send data.

See Also Request To Send.

A method of encrypting information, traditionally used as the method of encryption for UNIX® passwords and the crypt(3) function.

An RS232C signal sent from the modem to the computer or terminal indicating a readiness to send and receive data.

See Also Data Terminal Ready.

An RS232C signal sent from the computer or terminal to the modem indicating a readiness to send and receive data.

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.

An ACPI table, supplying basic configuration information about the base system.

The system that converts humanly readable hostnames (i.e., mail.example.net) to Internet addresses and vice versa.

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”.

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.

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. FreeBSD 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.

A system where the user and computer interact with graphics.

The markup language used to create web pages.

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.

See Also IP Version 6.

The new IP protocol. Invented because the address space in IPv4 is running out. Uses 128 bits for addressing.

Intel’s compiler for converting ASL into AML.

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.

See Also Post Office Protocol Version 3.

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.

A company that provides access to the Internet.

Japanese for “turtle”, the term KAME is used in computing circles to refer to the KAME Project, who work on an implementation of IPv6.

A method of dynamically loading functionality into a FreeBSD kernel without rebooting the system.

A kernel-supported threading system. See the project home page for further details.

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.

A network used on a local area, e.g. office, home, or so forth.

The FreeBSD kernel uses a number of resource locks to arbitrate contention for those resources. A run-time lock diagnostic system found in FreeBSD-CURRENT kernels (but removed for releases), called witness(4), detects the potential for deadlocks due to locking errors. (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 http://lists.FreeBSD.org/mailman/listinfo/freebsd-current and the LORs Seen page before posting to the mailing lists.

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.

An application used by users to display and write email.

To merge functionality or a patch from the -CURRENT branch to another, most often -STABLE.

To merge functionality or a patch from a repository HEAD to an earlier branch.

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.

See Also Merge From Current.

A message, usually shown on login, often used to distribute information to users of the system.

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.

A filesystem developed by Microsoft and available in its “New Technology” operating systems, such as Windows® 2000, Windows NT® and Windows® XP.

A means of synchronizing clocks over a network.

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.

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 FreeBSD, changes in networking standards, the affected hardware having since become obsolete, and so forth.

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).

A mythical piece of headgear, much like a dunce cap, awarded to any FreeBSD 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.

See Also Post Office Protocol Version 3.

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.

See Also Internet Message Access Protocol.

As FreeBSD 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.

A description of some kind of problem that has been found in either the FreeBSD source or documentation. See Writing FreeBSD Problem Reports.

A number, unique to a particular process on a system, which identifies it and allows actions to be taken against it.

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 FreeBSD/i386. This is usually the only way to use cards where the driver is closed-source. See src/sys/compat/ndis/subr_ndis.c.

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.

See Also Subversion.

An RS232C pin or wire that data is received on.

See Also Transmitted Data.

A standard for communications between serial devices.

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®.

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.

An RS232C signal requesting that the remote system commences transmission of data.

See Also Clear To Send.

An RS232 pin or wire that is the ground reference for the signal.

Subversion is a version control system currently used by the FreeBSD project.

A profiling counter internal to modern Pentium® processors that counts core frequency clock ticks.

A protocol that sits on top of (e.g.) the IP protocol and guarantees that packets are delivered in a reliable, ordered, fashion.

The term for the combination of the TCP protocol running over the IP protocol. Much of the Internet runs over TCP/IP.

An RS232C pin or wire that data is transmitted on.

See Also Received Data.

A method of locating a resource, such as a document on the Internet and a means to identify that resource.

The original UNIX® file system, sometimes called the Berkeley Fast File System.

An extension to UFS1, introduced in FreeBSD 5-CURRENT. UFS2 adds 64 bit block pointers (breaking the 1T barrier), support for extended file storage and other features.

A hardware standard used to connect a wide variety of computer peripherals to a universal interface.

A unique number assigned to each user of a computer, by which the resources and permissions assigned to that user can be identified.

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.

A method of using a public telecommunication such as the Internet, to provide remote access to a localized network, such as a corporate LAN.