Computer Terminology: Ports, Network Media, and Drives
As biomedS become more involved with computers and device networks, many of us use computer terminology on a regular basis but are not exactly sure what those terms mean.
For instance, we often have to contend with numerous connectors or ports on devices. Unfortunately, the wiring conventions are not always the same, so we have to use exact replacement cables. Some of the ports that biomeds commonly deal with are:
- Serial: Generally a nine-pin port used to connect external modems or mice.
- Parallel: Used to connect external devices such as scanners and printers. The 25-pin port is sometimes called a printer port.
- USB: Stands for universal serial bus. This port is used to connect all kinds of external devices, such as external hard drives, printers, mice, and scanners. You can connect as many as 127 devices to a USB port.
- PS/2: Used to connect a computer mouse or keyboard to a PC. Most PCs come with two PS/2 ports.
- FireWire: Also called IEEE 1394. This port is used to transfer large amounts of data very quickly. Usually, camcorders and other video equipment use this port to get data onto a computer.
Commonly referred to as printer ports, 25-pin parallel ports like those pictured at left typically connect printers to PCs.
Network Media Types
Network media types vary widely, from the simple twisted pair to fiber with many in between.
- Unshielded twisted pair: A commonly used cable, consisting of two unshielded copper wires twisted around each other, that connects home computers and many business computers to phone lines.
- Shielded twisted pair: A higher grade of twisted pair that is often used for horizontal wiring in local area network (LAN) installations. An outer covering, or shield, is added to the ordinary twisted pair telephone wires; the shield functions as a ground.
- Coaxial cable: Used by cable TV companies between the community antenna and user homes and businesses. It is called coaxial because it includes one physical channel that carries the signal surrounded (after a layer of insulation) by another concentric physical channel, both running along the same axis.
- Optical fiber (or fiber optic): Fiber optic refers to the medium and the technology associated with the transmission of information as light pulses along glass or plastic fibers. Optical fiber carries much more information than conventional copper wire, and it is generally not subject to electromagnetic interference and the need to retransmit signals.
In many imaging devices, when we contend with scuzzy drives, we know we are dealing with memory units. Scuzzy is a colloquialism for SCSI, or small computer system interface, a set of American National Standards Institute (ANSI) standard electronic interfaces that allow personal computers to communicate with peripheral hardware such as disk drives, tape drives, CD-ROM drives, printers, and scanners more quickly and flexibly than previous interfaces.
On other devices, hard disksoften called disk drives, hard drives, or hard disk drivesboth store and provide relatively quick access to large amounts of data on an electromagnetically charged surface or set of surfaces called a hard disk. Hard-drive storage capacity is measured in megabytes or gigabytes. As a measure of computer storage, a megabyte (MB) is 2 to the 20th power bytes, or 1,048,576 bytes in decimal notation. A gigabyte (GB) is 1,024 megabytes, or two to the 30th power bytes, or 1,073,741,824 bytes in decimal notation. While the gigabyte is most common, there is also the terabyte (1 thousand gigabytes) and an exabyte (1 billion gigabytes). Despite what some manufacturers tell us, hard drives are commercially available devices; but they may have some proprietary software or interface.
Other devices may use memory chips instead of drives. These units are generally a little faster but may not have the capacity of a drive. Sometimes, devices will have both static memory (such as read-only memory, or ROM, which is built-in computer memory containing data that normally cannot be written to) and dynamic memory (such as random access memory, or RAM, which keeps the operating system, application programs, and data in current so that they can be quickly reached by the computer). Becoming more common is the memory stick, which is basically an expanded RAM that plugs into a USB port and is portable. We are starting to see diagnostic and troubleshooting programs on memory sticks instead of on floppy disks. The trick is to determine which one is the problem when troubleshooting. Defragging the memory is always a good first step in any troubleshooting procedure.
Having multiple hard drives in a device is not uncommon; a common problem with multi-drive systems is that information gets routed to the wrong drive. This is a program or user error and not a hardware one, so start troubleshooting from the nonhardware viewpoint.
Multi-hard-drive devices can be set up in one of two ways: multiple physical drives acting independently, or a redundant array of independent disks (RAID, originally redundant array of inexpensive disks). RAID is a way of storing the same data in different places (thus, redundantly) on multiple hard disks. By placing data on multiple disks, input/output operations can overlap in a balanced way, improving performance. Since multiple disks increase the mean time between failure (MTBF), storing data redundantly also increases fault-tolerance.
Optical discs and drives are generally found in very high-end imaging and archiving systems. DVDs (digital versatile discs, formerly digital video discs) are becoming the media of choice in many applications. DVDs are an optical disc technology with a 4.7-gigabyte storage capacity on a single-sided, one-layered disk, which is enough for a 133-minute movie. DVDs can be single- or double-sided and can have two layers on each side; a double-sided, two-layered DVD will hold up to 17 gigabytes of video, audio, or other information. This compares to 650 megabytes (.65 gigabyte) of storage for a CD-ROM.
1) The maximum number of devices that can be connected to a USB port is ________.
2) RAM stands for __________________________.
3) A DVD can be ___________________________.
4) A PS/2 port is used for ________________________.
Answers: 1-d, 2-b, 3-d, 4-b
Bryan Harrington is a senior development engineer with Revenue Enhancement Strategies and maintains www.psacake.com, which contains programming and development tips.