Glossary

S

In Windows, what are StickyKeys, and how do I enable them?

The StickyKeys feature allows you to use key combinations involving the Ctrl, Alt, or Shift key by pressing only one key at a time. StickyKeys is available in Windows 95, 98, Millennium Edition (Me), NT, and 2000.

To enable StickyKeys, follow the steps below:

1. Click the Start button and select Settings, then Control Panel.
2. Double-click Accessibility Options.
3. Select the Keyboard tab if it isn't already selected.
4. Click the Use Sticky Keys checkbox. Then, next to this checkbox, click the Settings... button.
5. Click OK twice.

To turn StickyKeys on, press the Shift key five times. To turn the feature off again, press Shift five times.

What are SCSI standards, interfaces, and connectors?

SCSI (Small Computer Systems Interface) is a smart bus, controlled with a microprocessor, that allows you to add up to 15 peripheral devices to the computer. These devices can include hard drives, scanners, printers, and other peripherals. High-end single SCSI boards have two controllers and support up to 30 peripherals on a single expansion card. An advantage of SCSI is that you can connect several peripherals to one host adapter, using only one slot in the bus.

Uses for SCSI

SCSI is widely used in workstations, servers, and mainframes; it is less commonly used in desktop PCs. The advantage of SCSI in a desktop PC is that you can add a scanner and several other drives (for example, CD-Rs, DVD-RAM, Zip drives), as well as hard drives, to one SCSI cable chain. This has become less important as alternate interfaces such as USB and FireWire have become popular.

SCSI is useful in network servers, where several hard drives can be easily set up as a RAID configuration. If one drive fails, it can be removed and a new one inserted, without loss of data, while the system is still operational. This feature of RAID hardware is called hot-swapping.

You can install SCSI hard drives in a PC that already contains one or more IDE disk drives. The IDE drive will still be the boot drive, and the SCSI drives will provide additional storage. An IDE device is always the default boot device even if a SCSI hard drive is installed and configured as SCSI device number 0. For example, if a SCSI hard drive is on the same computer with an IDE CD-ROM drive, the computer will always boot to the CD-ROM drive; the only way around this is to replace the IDE CD-ROM with a SCSI one.

Connecting SCSI devices

SCSI devices are daisy-chained together. External devices have two ports, one for the incoming cable and another for the outgoing cable to the next device. An internal device has a single port that attaches to a ribbon cable with multiple connectors. Some higher-end SCSI cards may have multiple internal ports that allow you to attach multiple ribbon cables.

Each SCSI device must have a unique ID number; normally you can set these numbers by flipping rotary switches on external devices or by setting jumpers on internal ones. The SCSI ID determines the device order, which runs from 7 to 0 and then from 15 to 8. The host adapter defaults to the highest priority, which is 7.

You must terminate the device at the end of a SCSI chain by either setting a switch or plugging a resistor module into the open port. Usually, host adapters default to terminated. If devices are connected both internally and externally, you must remove the host adapter termination and apply termination to the ends of both chains.

There are adapters that allow SCSI peripherals to be connected via the parallel port. The parallel port's transfer rate is considerably less than that of the SCSI host adapter, but it does provide a means to hook up SCSI devices to laptops. Not all SCSI devices will work on a parallel adapter, and some SCSI devices have their own parallel port adapters. In general, expect transfer rates of around 1MBps when using a SCSI-to-parallel-port adapter.

SCSI support

Windows 95, 98, NT, Me, and 2000 and most older Macintosh computers provide internal support for SCSI, but Windows 3.1 and DOS do not. Newer Macintosh computers support FireWire rather than SCSI for high-performance interfaces. To install SCSI in a Windows 3.1 or DOS computer, you must add the appropriate SCSI driver.

More information

This information was adapted from TechEncyclopedia at:

  http://www.techweb.com/encyclopedia/defineterm?term=scsi

You can find more information on SCSI at:

  http://www.pcguide.com/ref/hdd/if/scsi/index.htm

  http://www.adaptec.com/

  http://www.faqs.org/faqs/scsi-faq/

SCSI standards

• SCSI-1: Uses an 8-bit bus and a 25-pin Centronics-style connector. Supports data rates of 4-5MBps and can support up to 7 devices.
• SCSI-2: Same as SCSI-1, but uses a 50-pin connector instead of a 25-pin connector, and supports multiple devices. This is what is most commonly meant as plain SCSI. Can support up to 7 devices.
• Fast SCSI: Uses an 8-bit bus, but doubles the clock rate to support data rates of 10MBps. Uses a 50-pin connector and can support up to 7 devices.
• Wide SCSI or Fast Wide SCSI: Uses a wider cable (168 cable lines to 68 pins) to support 16-bit transfers. Supports data rates of 20MBps and can support up to 15 devices
  
  Note: The term "wide" refers to the number of cable lines, not to the physical width of the cable, which is actually smaller than a 50-pin "narrow" SCSI cable.
• 8-bit Ultra SCSI-3: Uses an 8-bit bus, and supports data rates of 20MBps.
• 16-bit Ultra SCSI-3: Uses a 16-bit bus. Supports data rates of 40MBps and can support up to 15 devices. Also called Ultra Wide SCSI.
• 8-bit Ultra2 SCSI-3: Uses an 8-bit bus. Supports data rates of 40MBps and can support up to 8 devices.
• Wide Ultra2 SCSI: Uses a 16-bit bus. Supports data rates of 80MBps and can support up to 15 devices.
• Ultra3 SCSI: Not a specific protocol, but rather a label that the SCSI Trade Association created to apply to any SCSI technology that combines Ultra2 SCSI with one or more of six new features as defined by the ANSI SCSI-3 Parallel Interface - 3 (SPI-3) specification. Since Ultra3 does not restrict which features must be included, there could be as many as 63 variations that could qualify as Ultra3 SCSI. It would also be possible that two Ultra3 SCSI devices might not communicate at 160MBsec because they would not include the same set of features.
• Ultra 160 SCSI: This is Adaptec's proprietary implementation of a subset of the Ultra3 specification. It includes Double Transition Clocking (sending info on both the rise and decay of a clock cycle, which speeds data transfer without increasing the controller's clock speed), Cyclical Redundancy Checking (CRC), and Domain Validation (optimum speed negotiation). This has become the de facto standard.

SCSI connectors and interfaces

• Centronics 50-pin connector: The Centronics 50-pin connector was once the most widely used SCSI connector. An external connector only, the Centronics is a SCSI-1 connector that looks the same as the Centronics cable that attaches to a parallel port printer. The Centronics 50-pin cable comes in male and female styles, and gender changers and cable converters are commonly available. Although used on older SCSI devices and external drive enclosures, this interface is no longer heavily used, due to its slow speed and short cable lengths.
• High-density 50-pin connector: The high-density 50-pin connector is used on scanners and Jaz drives. It is one of the more common SCSI connectors and is usually used to connect SCSI-2 devices. Both ends of the cable are usually 50-pin male, while the sockets on the host adapter and external devices are 50-pin female.
• DB 25-pin connector: The DB 25-pin or D Sub 25 is by far the most widely used connector. This connector is used for parallel and serial printers in addition to the many other devices available. Both ends of the cable are usually 25-pin male, while the sockets on the host adapter and external devices are 25-pin female. This cable is almost always an external connector.

Note: DB-25 SCSI cables are not compatible with and should not be used as serial or printer cables; serial cables and printer cables should not be used or attached to DB-25 SCSI adapters. You can short out the SCSI host adapter or the motherboard by using the wrong cable. Marking cables is the best way to avoid this.

• IDC50 connector: The IDC50 is the most common internal SCSI connector. It is very similar to the standard IDE internal ribbon cable. The IDC50 SCSI cable is considerably wider then an IDE ribbon cable; in fact, it is usually the widest standard internal cable in use. This is a standard SCSI-2 10MBps internal SCSI cable. Many low-end cables have only two or three connectors, allowing for one or two devices to be attached to the cable. Seven-device cables are available, though they are often expensive and require a large case, as the cables may be four or five feet long.
• High-density 68-pin connector: The high-density 68-pin connector is the SCSI connector of choice for SCSI-3 host adapters and peripherals. There is an internal ribbon cable version that looks very similar to the IDC50 connector. Many low-end cables have only two or three connectors, allowing for one or two devices to be attached to the cable. Seven-device cables are available, though they are often very expensive and require a large case, as the cables may be three or more feet long. Both ends of the external cable are usually 68-pin male, while the sockets on the host adapter and external devices are 68-pin female.
• SCA 80-pin Micro-Centronics connector: SCA stands for Single Connector Attachment, a type of disk drive connector that includes connection pins for the power cables as well as the data wires. A SCA connector uses an 80-pin plug and socket to connect peripherals. This connector combines power, data channel, and ID configuration for fast installation and removal. SCA connectors are typically found only on high-end SCSI hard disks. The SCA interface was designed to provide a standard connection for systems using drives that can be hot-swapped. SCA makes swapping SCSI hard drives much easier than with traditional SCSI cables, plugs, and sockets. An adapter enables SCA drives to fit into standard SCSI enclosures.

You can find more information about SCA connectors at:

  http://www.seagate.com/support/kb/disc/sca.html

You can find more information about SCSI interfaces and connectors at:

  http://www.cablemakers.com/newconn.html

Also see:

• For the PC, what are the differences between MFM, RLL, IDE, EIDE, ATA, ESDI, and SCSI hard drives?

What is a stripe set disk?

A stripe set disk is at least 2, and at most 32, physical disks that are bound together to form one logical disk. Data is written evenly across all physical disks, one row at a time. The partitions in a stripe set are all approximately the same size so that the data can be written in stripes across each partition, which increases the transfer and request rates.

Some benefits of a stripe set disk are:

• Stripe sets improve read and write performance because each stripe of information can be accessed in parallel.
• Disk activity is balanced across all disks.
• Several small disks can be combined into one large logical disk to provide increased storage capacity.

The major drawback of a stripe set disk occurs when any single disk in the set fails. This failure causes the loss of the entire stripe set.

For a visual representation of a stripe set disk (also known as a striped disk array) see:

  http://www.acnc.com/raid.html

Also see:

• Using Windows NT, how do I change where print jobs are spooled?
• What is a RAID array?

What is an SMTP server?

An SMTP server is a computer that receives outgoing mail messages from users and routes them to their intended recipients. All SMTP servers implement some version of the Simple Mail Transport Protocol (SMTP), and most that run Unix use the sendmail program. Messages often must pass through several servers to reach their destinations, and SMTP facilitates this.

The SMTP server address for Indiana University Bloomington is:

  mail-relay.indiana.edu

The SMTP server address for IUPUI is:

  mail-relay.iupui.edu

For security reasons, these servers are accessible only from computers connected directly to the IUB or IUPUI networks via Ethernet or modem, or to outside connections routed through the IUB or IUPUI VPN servers.

Also see:

• What is DNS?
• What is POP mail?
• What is IMAP (Internet Message Access Protocol)?

What is ScanDisk?

ScanDisk is a disk analysis and repair tool, first released in Microsoft DOS 6.2, that checks a drive for errors and corrects any problems that it finds. An updated, 32-bit ScanDisk is included with Windows 95, 98, Me, 2000, and XP. Although you can run it from the command line, it is easier to run it as follows:

1. Double-click My Computer.
2. Right-click the hard drive you want to scan and select Properties.
3. Select the Tools tab. In the "Error Checking" section, click the Check Now button (this button appears in the "Error Checking Status" section in Windows 95, 98, and Me).

To check the current drive for errors at the command prompt in DOS 6.2 or Windows 3.x, 95, 98, or Me, use the following syntax:

  scandisk

In Windows NT 4.0, 2000, and XP, use a different command:

  chkdsk

Note: Do not confuse the Windows NT, 2000, and XP CheckDisk utility with the Windows 95, 98, and Me version. In Windows 95, 98, and Me, CheckDisk is missing certain features that ScanDisk has, such as the ability to do a surface scan. But in Windows NT, 2000, and XP, CheckDisk is a full replacement for ScanDisk, and is missing none of those features. In fact, Microsoft's support site uses the term ScanDisk for the CheckDisk feature in Windows NT, 2000, and XP, except in cases where the term chkdsk needs to be entered explicitly.

You can use options and additional features at the command prompt. To view a listing of these options for ScanDisk, enter:

  scandisk /?

To view a listing of these options for CheckDisk, enter:

  chkdsk /?

Also see:

• In Windows 95, 98, Me, NT, and 2000, how can I check a disk for errors?
• What is a lost cluster?
• Why does my computer run Scandisk every time I start it?
• In DOS, what does the CHKDSK (check disk) command actually do?
• In DOS, what is the procedure for installing or upgrading DOS on a hard drive?
• What are some examples of common DOS commands?

What is SLIP?

SLIP stands for Serial Line Internet Protocol. It runs the standard TCP and IP protocols over a serial link instead of over the Ethernet port on the back of your workstation. Basically, it means using a serial port as a slow network interface port.

UITS does not provide SLIP service due to an incompatibility with our dialin servers. IUB and IUPUI users should instead use PPP, which is the preferred protocol for the Bloomington and Indianapolis campuses. For more information about PPP, see the references listed below.

Also see:

• Does IUPUI support PPP dialup connections?
• For dialin access at Indiana University, what are the minimum hardware and software requirements?

What is SQL?

SQL is an abbreviation for "Structured Query Language". It is a specialized language for updating and requesting information from databases. SQL is an ANSI and ISO standard, and is the de facto standard database query language. SQL works with a variety of established database products such as those from Oracle and Sybase. It is widely used in both industry and academia, often for enormous, complex databases.

In a distributed database system, a program often referred to as the database's "back end" runs constantly on a server, interpreting data files on the server as a standard relational database. Programs on client computers allow users to manipulate that data, using tables, columns, rows, and fields. To do this, client programs send SQL statements to the server. The server then processes these statements and returns replies to the client program.

To illustrate, consider a simple SQL command, SELECT. SELECT retrieves a set of data from the database according to some criteria. For example, to retrieve from a table called Customers all records that have a value of Smith for the column Last_Name, a client program would prepare and send this SQL statement to the server back end:

  SELECT * FROM Customers WHERE Last_Name='Smith';

The server back end may then reply with data such as this:

  +---------+-----------+------------+

  | Cust_No | Last_Name | First_Name |

  +---------+-----------+------------+

  | 1001    | Smith     | John       |

  | 2039    | Smith     | David      |

  | 2098    | Smith     | Matthew    |

  +---------+-----------+------------+

  3 rows in set (0.05 sec)

Also see:

• If I have Open Client, why do I also need Sybase ODBC?
• What are flat file and relational databases?
• In Paradox for Windows, what wildcards can I use in SQL programs?