S

SAN

See Storage Area Network (SAN).

SCCS

See Source Code Control System (SCCS).

screened twisted pair (ScTP)

A cable where the twisted pair is screened from electromagnetic interference by a thin aluminum screen. Not as effective as shielding the cable. See also shielded twisted pair (STP), unshielded twisted pair (UTP).

SCSI

See Small Computer Systems Interface (SCSI).

ScTP

See screened twisted pair (ScTP).

SDLC

See Synchronous Data Link Control (SDLC).

SDSL

See Symmetric Digital Subscriber Line (SDSL).

secondary

A DNS server without local files (receiving information from the primary server via the named.xfer process); like an NIS slave server.

sector

The smallest unit of physical space on a disk. Typically the smallest unit of data that is read from or written to the disk.

security group

Provide a way to organize objects so that an administrator who has an appropriate role in the group can operate on objects in the group.

sentry

A process that monitors a variety of system activities, such as the amount of disk space available, and that can generate events or alarms based on thresholds.

sequence

The CORBA data type for implementing lists.

Serial Line Internet Protocol (SLIP)

A protocol (RFC 1055) for connecting a host (such as a microcomputer) to an internet via a modem.

server

A process that fulfills a request issued by a client process and transmits a response back to the client.

server skeleton

Unmarshals the data associated with a request for presentation to a method, and marshals the data returned.

service level agreement (SLA)

An agreement from one party to provide a specified level of service, typically involving a maximum-allowed response time or guarantee of service being available for a minimum time, to another party. Service level agreements are part of any vendor maintenance contract.

SGML

See Standardized General Markup Language (SGML).

shielded twisted pair (STP)

A cable where the twisted pair is shielded from electromagnetic interference. See also unshielded twisted pair (UTP).

SIMM

See Single In-line Memory Module (SIMM).

Simple Mail Transfer Protocol (SMTP)

The base protocol (RFC 821) for exchanging electronic mail over a network. See also Extended Simple Mail Transfer Protocol (ESMTP), Multipurpose Internet Mail Extensions (MIME), NeXTMail.

Simple Network Management Protocol (SNMP)

A base protocol (RFC 1157) for monitoring and managing hosts on a network. See also Management Information Base (MIB).

Single In-line Memory Module (SIMM)

A small plug-in card containing memory chips for a workstation or personal computer.

skeleton

The ORB component which assists an object adapter in passing requests to particular methods. It is specific to an object and an interface.

SLA

See service level agreement (SLA).

slave

The secondary NIS servers in an NIS domain.

SLIP

See Serial Line Internet Protocol (SLIP).

Small Computer Systems Interface (SCSI)

Pronounced "scuzzy," SCSI is a parallel interface standard used by Apple Macintosh computers, PCs, and many Unix systems for attaching peripheral devices to computers. SCSI interfaces provide for faster data transmission rates (up to 80 megabytes per second) than standard serial and parallel ports. In addition, you can attach many devices to a single SCSI port, so that SCSI is really an I/O bus rather than simply an interface.

SMTP

See Simple Mail Transfer Protocol (SMTP).

SNA

See Synchronous Network Architecture (SNA).

SNADS

See Synchronous Network Architecture Distribution Services (SNADS).

SNMP

See Simple Network Management Protocol (SNMP).

SONET

See Synchronous Optical Network (SONET).

Source Code Control System (SCCS)

A suite of utilities to administrate source code such that only one person can change any given file at any given instant. Provides audit trails.

spam

The historical term for electronic junk mail, or unwanted messages in email or USENET News. See also Unsolicited Commercial Email (UCE).

speed

The speed of various technologies can best be shown by the following table:

Name	Bandwidth	bps	Highway analogy
POTS, DS0	-	64,000	3-foot garden path
ISDN	2 POTS	128,000	6-foot sidewalk
T1, DS1	24 POTS 12 ISDNs	1,544,000	4-lane highway
Ethernet	~6.5 T1s	10,000,000	26-lane highway
T3, DS3	28 T1s	43,232,000	112-lane highway
OC1	32 T1s	51,840,000	80-lane highway
Fast Ethernet	~65 T1s	100,000,000	160-lane highway
OC3	3.6 x T3	155,000,000	~1-mile wide highway
OC12	4 x OC3	622,000,000	~4-mile wide highway
OC48 (Internet2)	4 x OC12	2,075,136,000 (2.4 Gb/s)	~16-mile wide highway
OC192	4 x OC48	8,300,544,000 (9.6 Gb/s)	~64-mile wide highway

Portions of this table taken from the Keane (New Hampshire) Public Library database.

SQL

See Structured Query Language (SQL).

stack

A last in, first out data structure. See also queue.

staging

The process of configuring a host to a known state (for example, from tape or a preconfigured host), to speed up the configuration process.

Standardized General Markup Language (SGML)

A generalized format for marking up documents, originally created by the United States government. One of the more common subsets of SGML is HyperText Markup Language (HTML).

state database

A database containing the state of each metadevice, stored in a dedicated (and non-metadevice) disk partition. See also Disk Suite.

Storage Area Network (SAN)

A network where a small number of computers share a large amount of data, usually within a single server room, where performance is critical. Examples of SAN protocols include Fiber Channel and the Small Computer Systems Interface (SCSI).

STP

See shielded twisted pair (STP).

stripe

A method of writing data to multiple disks, interleaving blocks on different disks to increase performance. (Performance increases generally require multiple disk controllers.) A logical grouping of multiple physical disk partitions. See also concatenated stripe, Disk Suite.

stripe width

The width of, or number of partitions in, a stripe.

Structured Query Language (SQL)

An industry-standard language for performing queries against a database.

stub

A local procedure corresponding to a single operation that invokes that operation when called.

submirror

A metadevice attached to a mirror.

subnet

A group of machines that share information and resources. A subsection of a network.

subscription

Registering resources to a group, so that operations on a group are applied to all subscribers.

Sun Remote Procedure Call (SUNRPC)

The Remote Procedure Call (RPC) structure developed by Sun for communication between clients and servers. For example, NetInfo uses RPC to communicate.

SUNRPC

See Sun Remote Procedure Call (SUNRPC).

superblock

A special reserved block on disk that contains the detailed structure of the file system, including the block size, frag size, and inode tables.

SVC

See Switched Virtual Circuit (SVC).

swap

Swap space is a place on your disk(s) where your processes go if you run out of physical memory. It is part of the virtual memory system of all Unixes, allowing you to have more process memory than phsyical memory, if you need it. If you run out of swap space, you will be unable to create more processes. Solaris uses an "eager" swap algorithm - it reserves space when it creates a process, so even if you never ever use it, you have to have "enough" in your system, just in case. So, what is enough?

At the least, swap space should be as large as the RAM in the system. In an ideal world, all of our machines have plenty of memory and this never happens. In reality, something as simple as a page-compile, which launches a whole new JVM process, can put you over the edge. Thus, it should probably be set at ~1.5x the physical memory. A good rule of thumb from the 1990s was that swap should be twice physical memory.

Here are some tools you can use to see what's up with your swap space:

swap -s

This will show you what's available, and what is used.

vmstat -S 5

This will print out system stats every 5 seconds. If you are moving things in and out of swap you will see non-zero numbers in the "so" and "si" in the "page" stats and you'll probably also see "free" in the "memory" stats going very low.

switch

Network hardware that routes packets or cells (either ATM or voice) based on the address of the virtual circuit.

Switched Virtual Circuit (SVC)

A virtual circuit in an ATM network established dynamically via software.

Symmetric Digital Subscriber Line (SDSL)

A symmetric high-speed digital network connection, usually between a home or small business and a telecommunications vendor, providing an always-up direct connection to an Internet Service Provider (ISP). The upstream (from the user to the ISP) and downstream (from the ISP to the user) speeds are identical. See also Asymmetric Digital Subscriber Line (ADSL), Digital Subscriber Line (DSL).

Synchronous Data Link Control (SDLC)

A data protocol spoken between the DISOSS mail system on the IBM 3090 mainframe and the Enterprise Mail Exchange (EMX) unit.

Synchronous Network Architecture (SNA)

IBM's network architecture.

Synchronous Network Architecture Distribution Services (SNADS)

The distribution protocol, handling delivery and verification, for Synchronous Network Architecture (SNA).

Synchronous Optical Network (SONET)

An ANSI standard to connect telephone switches at 155 Mb/s speeds (OC3).

sysadmin

See system administrator.

system administrator

The godlike being who keeps your system running. Responsible for everything involving your system and the network it's on, including but not limited to managing your account (creation, modification, closure, deletion), your workstation, your subnet, your routers, the system-wide hosts table, the mail subsystem, all mail aliases and groups, keeping time synchronized across the network, the news subsystem, the printer subsystem, any applications you use--basically, the person who keeps everything working smoothly and seamlessly.