Today's Technical Term: SDN

Stands for "Software-Defined Networking."

SDN is a networking architecture that separates the responsibilities for routing and forwarding network data packets. A central server takes over all routing decisions for the network, instead of leaving those decisions up to each individual node. An administrator can configure and manage a network through software running on the server, instead of managing each device separately. Data centers, enterprise networks, and campuses often use SDN to manage large, complex networks.

Each function of a router or switch is conceptually part of one of three planes:

In a traditional network infrastructure, each device is responsible for all three planes. In a software-defined network, each switch or node is only responsible for the data plane; the central server takes over the control and management planes.

An administrator of a traditional network must configure each switch (or other type of node) on that network separately. A large network may have dozens or even hundreds of switches, which leads to a lot of duplicate work when updating configuration settings on each one. Software-defined networking centralizes the control and management of the entire network into a single dedicated device. An SDN server instructs the switches and other nodes how to forward data packets using a network protocol like OpenFlow.

In addition to being easier to manage, software-defined networks can move data more efficiently. Individual switches making routing decisions on their own may not choose the most efficient route, since they have limited knowledge of the conditions across the entire network. An SDN server, however, can monitor and control the entire network to optimize traffic for specific applications while bypassing congestion.

Today's Technical Term: SD

Stands for "Secure Digital." SD is a type of memory card used to store data in portable electronic devices. Examples include digital cameras, video recorders, smartphones, and portable music players. SD cards are considered removable storage (instead of internal or external storage), since they can be inserted and removed from a compatible device.

The first SD cards were introduced in 1999. They used almost the same form factor as the existing MultiMediaCard (MMC) format, but were slightly thicker (2.1 mm vs 1.4 mm). The dimensions of a standard SD card are:

Each SD card has a slanted upper-right corner to ensure the card can only be inserted one way. The left side of a card has a physical slider that prevents the card from being written (read-only) when moved to the LOCK position. The "secure" part of "Secure Digital" refers to its built-in DRM protection technology. The SD format supports Content Protection for Recordable Media (CPRM), which prevents protected content from being read from another storage device.

Since its introduction in 1999, the SD card format has gone through several iterations. Below are different versions of SD, listed with their storage capacity and maximum data transfer rate.

Another version of SD, called microSD, was introduced in 2005. microSD cards are much smaller than SD cards, with dimensions of 11 mm x 15 mm x 1mm. Small devices like GoPros and smartphones have microSD slots to reduce the overall device size as much as possible. microSD cards can be used in standard SD card slots using a microSD-to-SD adapter.

Today's Technical Term: Script

A script is a list of programmatically-written instructions that can be carried out on command. Scripts can automate batch processes on a local computer or server, and are often used to generate dynamic webpages on a web server. Scripts are like small programs, written in a scripting language like VBScript, AppleScript, or PowerShell; unlike programs, they do not need to be compiled before running.

The commands in a script may be interpreted by an individual program or an interpreter. For example, a Photoshop script can only contain actions for Photoshop to apply to an image, while a Visual Basic or AppleScript file instead can send commands to multiple separate programs. Web servers run scripts written in ASP, JSP, and PHP to generate dynamic webpage content.

Writing a script in a scripting language is similar to writing a program in a programming language. Scripting languages and programming languages share many common elements and syntax. The commands in a scripting language are often simple and human-readable, allowing you to open and edit scripts in a plain text editor.

NOTE: Do not run unfamiliar or unknown scripts on your computer. Some scripting languages, like Visual Basic Script, can access and modify local files to potentially damage the contents of your computer and introduce malware.

Today's Technical Term: Screen Burn

Screen burn or "screen burn-in" is a residual image left on a screen after displaying the same image for a long time. It is a faded version of the image or "ghost image" that covers part or all of the screen.

Screen burn is usually caused by video or graphics with content that does not move or change for an extended period of time. Examples include the menu bar on a Mac or the task bar on a Windows computer. On a TV, it may be the logo of a specific channel or the information panel of a video game. On a smartphone, it may be the status bar at the top of the screen. If certain pixels consistently display the same image while other pixels display changing graphics, the unchanging pixels may leave behind a ghost image.

Screen burn affects several types of screens, including CRTs, plasma displays, and OLED screens. In older displays, such as CRT monitors, leaving a single image displayed for a long time could physically damage the screen. This type of burn-in could produce dark spots that were noticeable even when the display was turned off. In modern displays, screen burn typically occurs when the electronics that produce light lose their luminance. When specific pixels display a single image for a long time, they may lose their red, green, or blue (RGB) brightness relative to other pixels. This may produce a ghost image that is the inverse of the image that was consistently displayed.

Screen burn is rare with LCD panels because liquid crystals are less susceptible to burn-in. OLED displays, on the other hand, are susceptible to screen burn since individual LEDs may lose their luminance relative to other LEDs if overused. This may happen when certain pixels display the same color over a long period of time.

Screen burn is rare on modern displays with normal use. For noticeable screen burn to take place, you would have to run the same program or tune to the same channel every day for several weeks or months. However, if you consistently play the same video game or watch the same channel, screen burn can happen over time. You can limit and possibly avoid screen burn by varying the content you watch on your screen. You should also turn off your display when you're not using it. Finally, it is wise to enable sleep mode or a screensaver that automatically runs when the screen has not changed for awhile.

Today's Technical Term: SATA

Stands for "Serial Advanced Technology Attachment," or "Serial ATA."

SATA is a standard bus interface for connecting storage devices like hard drives, solid-state drives, and optical drives to a computer's motherboard. It replaced the previous standard, parallel ATA, and provides much faster transfer speeds using smaller and simpler cables.

The SATA standard has received several updates since its introduction in 2003. SATA 3, the third and most recent revision, supports a maximum data transfer speed of 6 Gbps (4.8 Gbps, or 600 MB/s, after accounting for data encoding overhead). The specification also allows the hot-swapping of devices so users can connect and disconnect drives without shutting down their computers.

Both SATA drives and parallel ATA drives are IDE devices, which means they integrate the storage controller chip into the drives themselves. This adds more physical size and complexity to the drives but simplifies the connection to the motherboard. SATA cables are significantly thinner than parallel ATA cables, making them easier to organize inside a computer's case. SATA devices each have their own independent bus, unlike parallel ATA devices that share a single bus between two devices (requiring two drives to share one cable, and for the drives to have primary and secondary roles assigned using jumpers).

NOTE: A variant of SATA, called eSATA, exists for external hard drive connections.

Today's Technical Term: SAN

Stands for "Storage Area Network."

A SAN is a specialized network of storage devices accessible by multiple servers or workstations. A SAN is a separate network from a LAN, with access between the two typically managed by file servers that connect to both networks and create a bridge. A file server sees the SAN storage pool as if it were a local disk connected directly to the server, and it can share that storage with the rest of the LAN. SANs are used by enterprises and other large organizations that need large pools of high-speed, low-latency network data storage.

A file server can only connect to as many drives as it has physical interfaces for, so a SAN can provide more data storage capacity than a single file server could provide. Storage devices in a SAN are connected using high-speed Fibre Channel connections and managed by SAN switches. A file server equipped with a Fibre Channel interface can connect to a SAN switch and access its storage pool. Multiple file servers can independently connect to the same SAN to provide network administrators with more options for managing data access.

Unlike a NAS or traditional network storage drive, a SAN stores data using block-level storage that manages and organizes data in fixed-sized blocks instead of by entire files. Block-level storage can provide higher data access speeds and lower latency by spreading files out across multiple physical drives. For example, if a SAN saves a 5 GB data file in blocks on five separate drives, each one only needs to read 1 GB of data — providing much quicker access than if one drive had to read all 5 GB by itself.

In most cases, access to a SAN storage pool is provided by a file server acting as a bridge. However, sometimes it may be beneficial for a workstation to connect to a SAN directly and bypass any overhead from a file server. For example, a video editing workstation that requires high-speed access to large 8K video files can use a Fibre Channel interface to connect directly to a SAN storage pool for the fastest possible access speed.

Today's Technical Term: S/PDIF

Stands for "Sony/Philips Digital Interface" (and is pronounced "spid-if"). S/PDIF is a digital audio transmission standard for transferring audio between two devices. It is uni-directional (one-way) and supports uncompressed stereo audio and compressed surround sound audio.

A S/PDIF audio signal may be transmitted over coaxial or fiber optic cable. Coax transmissions use RCA connectors, while optical transmissions use Toslink connectors. Regardless of the transfer medium, a S/PDIF signal is always digital, not analog.

S/PDIF supports uncompressed 2-channel (stereo) audio, making it an ideal interface for CD players, turntables, and other stereo audio devices. While S/PDIF supports surround sound signals, it does not have enough bandwidth to transmit more than two channels of uncompressed digital audio. Therefore, S/PDIF must transfer 5.1 and 7.2 surround sound audio in a compressed format, such as Dolby Digital. Specifically:

Uncompressed surround sound audio requires a high-bandwidth digital connection, such as HDMI or ADAT.

Today's Technical Term: Runtime

Runtime refers to the time a program runs on a computer or device. During runtime, the computer's CPU executes the commands in the program's machine code. It starts when you first open a program and the operating system loads it into RAM, along with any extra libraries or external frameworks the program calls for. The runtime ends when you close or quit the program, and the memory allocated to it becomes available for other programs.

In a software development context, the word "runtime" also refers to the environment a software developer designs a program to run within. The runtime environment consists of the operating system and linked code libraries. For example, programs that run in Windows make calls to dynamically linked library files (DLLs) to execute various standard functions. The runtime environment may also include virtual machines or interpreter programs necessary for the program to run.

A runtime error is an error, or bug, that happens while the program is running. The term differentiates these errors from errors that occur while the program is compiling, like syntax errors and other compilation errors.

Today's Technical Term: RTF

Stands for "Rich Text Format."

RTF is a file format for rich text documents that may include styled text and images. It is a widely-supported document format that most text editors and word processors can open and edit. Microsoft first developed the RTF format as an interchange format, allowing users to save Word documents in a format that maintained most of Word's features but could be opened in other applications.

The RTF format supports most rich text formatting, including font styling (like bold, italics, and underline), custom typefaces, and multiple font sizes. It also includes page layout options allowing you to customize page margins, line spacing, tab width, and text alignment. You can add annotations and comments, insert tables, and create automatically-numbered and bulleted lists. You can also embed images inside an RTF file, including bitmap images, PNGs, GIFs, and JPEGs.

Most word processors and text editors supporting rich text can open and edit RTF files. However, not every application that can open the RTF format supports every available feature. Some formatting options, image types, tables, annotations, and comments are often not supported by basic text editors like Windows WordPad and macOS TextEdit. If you don't need to share a text document with other people using other word processors, you'll have more features available using a word processor's default file format.

File Extension: .RTF

Today's Technical Term: NAND

NAND is the most common type of flash memory. It is used in several types of storage devices, including SSDs, USB flash drives, and SD cards. NAND memory is non-volatile, meaning it retains stored data even when the power is turned off.

Surprisingly, NAND is not an acronym. Instead, the term is short for "NOT AND," a boolean operator and logic gate. The NAND operator produces a FALSE value only if both values of its two inputs are TRUE. It may be contrasted with the NOR operator, which only produces a TRUE value if both inputs are FALSE.

NAND flash memory contains an integrated circuit that uses NAND gates to store data in memory cells. NOR flash memory stores data using NOR gates. While NOR devices read data faster, they are slower at writing data and do not store data as efficiently. NAND devices write and erase data faster and store significantly more data than NOR devices of the same physical size.

Overall, NAND storage is more efficient than NOR, which is why NAND is the most popular type of flash memory. As read and write speeds have improved, NAND devices have become faster than traditional hard drives. Therefore, SSDs and integrated flash memory have replaced HDDs in most computers.