SCSI an acronym for Small Computer System Interface had it's core foundation developed by Shugart Associates in 1978 as a descendent of a prior system called SASI. Designed for small computers and their peripherals, SCSI as a whole is a set of hardware and software standards. The set of SCSI standards included such topics as physical, device to device, inner connection methods and the software protocol used to negotiated data between the host computer and the peripheral devices.
SCSI also has the added capability of simultaneously operating multiple peripheral devices, and depending on the particular version of SCSI that is being utilized can function with upwards of 8-16 peripheral devices attached to the host computer. The list of SCSI compatible peripherals is dynamic but primarily consists of hard drives, tape drives, optical drives and scanners.
Sequential logic is a form of binary circuit design that employs one or more inputs and one or more outputs, whose states are related by defined rules that depend, in part, on previous states. Each of the inputs and output(s) can attain either of two states: logic 0 (low) or logic 1 (high).
A common example of a circuit employing sequential logic is the flip-flop, also called a bistable gate. A simple flip-flop has two stable states. The flip-flop maintains its states indefinitely until an input pulse called a trigger is received. If a trigger is received, the flip-flop outputs change their states according to defined rules, and remain in those states until another trigger is received.
There are several different kinds of flip-flop circuits, with designators such as D, T, J-K, and R-S. Flip-flop circuits are interconnected to form the logic gates that comprise digital integrated circuits (ICs) such as memory chips and microprocessors.
Sequential logic differs from combinatorial logic (also called combinational logic). In the latter scheme, the output states depend only on the input states at a specific moment in time, and not on previous states.
SMTP is an acronym for Simple Mail Transfer Protocol. From the start, SMTP was a broadly collaborative and informal effort starting in the early 1970's. The impetus for SMTP grew from the need for a standard email protocol for the then fairly new US Government ARPANET. By the 1980's, with the general acceptance of UNIX, SMTP became widely accepted as a means for sending and receiving email.
Currently, much of the send and receive functions are handled with competing protocols called Post Office Protocol (POP) or Internet Message Access Protocol (IMAP). For that reason, SMTP today is generally relegated for relaying messages from email servers.
SONET is the American National Standards Institute standard for synchronous data transmission on optical media. The international equivalent of SONET is synchronous digital hierarchy (SDH). Together, they ensure standards so that digital networks can interconnect internationally and that existing conventional transmission systems can take advantage of optical media through tributary attachments.
SONET provides standards for a number of line rates up to the maximum line rate of 9.953 gigabits per second (Gbps ). Actual line rates approaching 20 gigabits per second are possible. SONET is considered to be the foundation for the physical layer of the broadband ISDN (BISDN).
Asynchronous transfer mode runs as a layer on top of SONET as well as on top of other technologies. SONET defines a base rate of 51.84 Mbps and a set of multiples of the base rate known as "Optical Carrier levels (OCx)."
A spider is a program that visits Web sites and reads their pages and other information in order to create entries for a search engine index. The major search engines on the Web all have such a program, which is also known as a "crawler" or a "bot." Spiders are typically programmed to visit sites that have been submitted by their owners as new or updated. Entire sites or specific pages can be selectively visited and indexed. Spiders are called spiders because they usually visit many sites in parallel at the same time, their "legs" spanning a large area of the "web." Spiders can crawl through a site's pages in several ways. One way is to follow all the hypertext links in each page until all the pages have been read.
The spider for the AltaVista search engine and its Web site is called Scooter . Scooter adheres to the rules of politeness for Web spiders that are specified in the Standard for Robot Exclusion (SRE). It asks each server which files should be excluded from being indexed. It does not (or can not) go through firewall. And it uses a special algorithm for waiting between successive server requests so that it doesn't affect response time for other users.
Storage Area Network - SAN:
A storage area network (SAN) is a high-speed special-purpose network (or subnetwork) that interconnects different kinds of data storage devices with associated data server s on behalf of a larger network of users. Typically, a storage area network is part of the overall network of computing resources for an enterprise. A storage area network is usually clustered in close proximity to other computing resources such as IBM S/390 mainframes but may also extend to remote locations for backup and archival storage, using wide area network carrier technologies such as asynchronous transfer mode or Synchronous Optical Networks.
A storage area network can use existing communication technology such as IBM's optical fiber ESCON or it may use the newer Fibre Channel technology. Some SAN system integrators liken it to the common storage bus (flow of data) in a personal computer that is shared by different kinds of storage devices such as a hard disk or a CD-ROM player.
SANs support disk mirroring, backup and restore, archival and retrieval of archived data, data migration from one storage device to another, and the sharing of data among different servers in a network. SANs can incorporate subnetworks with network-attached storage (NAS) systems.