- 3d printer
- 3D printer is a computer-aided manufacturing (CAM) device that creates three-dimensional objects. Like a traditional printer, a 3D printer receives digital data from a computer as input. However, instead of printing the output on paper, a 3D printer builds a three-dimensional model out of a custom material.
3D printers use a process called additive manufacturing to form (or “print”) physical objects layer by layer until the model is complete. This is different than subtractive manufacturing, in which a machine reshapes or removes material from an existing mold. Since 3D printers create models from scratch, they are more efficient and produce less waste than subtractive manufacturing devices.
The process of printing a 3D model varies depending on the material used to create the object. For example, when building a plastic model, a 3D printer may heat and fuse the layers of plastic together using a process called fused deposition modeling (FDM). When creating a metallic object, a 3D printer may use a process called direct metal laser sintering (DMLS). This method forms thins layers of metal from metallic powder using a high powered laser.
While 3D printing has been possible since the 1980s, it has been primarily used for large scale industrial purposes. However, in recent years, 3D printers have become much cheaper and are now available to the consumer market. As the technology becomes more widespread, 3D printers may become a viable means for people to create their own home products and replacement parts.
- 3G is a collection of third generation cellular data technologies. The first generation (1G) was introduced in 1982, while the second generation of cellular data technologies (2G) became standardized in the early 1990s. 3G technologies were introduced as early as 2001, but did not gain widespread use until 2007.
In order to be labeled “3G,” a cellular data transfer standard must meet a set of specifications defined by the International Telecommunications Union, known as IMT-2000. For example, all 3G standards must provide a peak data transfer rate of at least 2 Mbps. Most 3G standards, however, provide much faster transfer rates of up to 14.4 Mbps.
While many cell phone companies market phones with “3G technology,” there is no single 3G standard. Rather, different companies use their own technologies to achieve similar data transfer rates. For example, AT&T uses a 3G technology based on GSM, while Verizon uses a technology based on CDMA. Additionally, cell phone networks outside the United States use different IMT-2000 compliant standards to achieve 3G data transfer speeds.
3G precedes 4G, the fourth generation of cellular data technologies.
- 403 error
- A 403 error is an HTTP error code that indicates access to a specific URL is forbidden. Websites often display 403 errors with a generic message such as, “You don’t have permission to access this resource.”
There are several reasons a web server may produce a 403 forbidden error. Some of the most common include:
A missing index page
An empty directory
Invalid folder permissions
Invalid file permissions
Invalid file ownership
When you access a website directory on an Apache web server (a URL ending with a forward slash “/”), the standard behavior is to display the contents of the index page (index.php, index.asp, etc). If no index page is available, the fallback option is to list the contents of the directory. However, for security purposes, many web servers are configured to disallow directory listings. Therefore, if you access an empty directory or a folder without an index page, you may receive a 403 error because the directory listing is forbidden.
Invalid file and folder permissions can also produce 403 errors. Generally, files and folders on web servers must have the following permissions enabled:
Owner: read, write
Owner: read, write, execute
Group: read, execute
Everyone: read, execute
If a specific file or the parent folder has incorrect permissions, the web server may be unable to access it, producing a 403 forbidden error. Similarly, if a file’s “owner” does not match the corresponding website user account, it may generate a 403 error. Ownership discrepancies can occur when files are transferred between accounts on a web server or when a file is uploaded by another user.
In some cases, access to a specific URL is intentionally forbidden for security reasons. In other cases, a forbidden error may be caused by an accidental website misconfiguration. If you unexpectedly receive a 403 error in your web browser, you can contact the webmaster of the corresponding website and provide the URL that produced the error.
- 404 error
- A 404 error is a common website error message that indicates a webpage cannot be found. It may be produced when a user clicks an outdated (or “broken”) link or when a URL is typed incorrectly in a Web browser’s address field. Some websites display custom 404 error pages, which may look similar to other pages on the site. Other websites simply display the Web server’s default error message text, which typically begins with “Not Found.” Regardless of the appearance, a 404 error means the server is up and running, but the webpage or path to the webpage is not valid.
So why call it a “404 error” instead of simply a “Missing Webpage Error?” The reason is that 404 is an error code produced by the Web server when it cannot find a webpage. This error code is recognized by search engines, which helps prevent search engine crawlers from indexing bad URLs. 404 errors can also be read by Web scripts and website monitoring tools, which can help webmasters locate and fix broken links.
Other common Web server codes are 200, which means a webpage has been found, and 301, which indicates a file has moved to a new location. Like 404 errors, these status messages are not seen directly by users, but they are used by search engines and website monitoring software.
- 4G is a collection of fourth generation cellular data technologies. It succeeds 3G and is also called “IMT-Advanced,” or “International Mobile Telecommunications Advanced.” 4G was made available as early as 2005 in South Korea under the name WiMAX and was rolled out in several European countries over the next few years. It became available in the United States in 2009, with Sprint being the first carrier to offer a 4G cellular network.
All 4G standards must conform to a set of specifications created by the International Telecommunications Union. For example, all 4G technologies are required to provide peak data transfer rates of at least 100 Mbps. While actual download and upload speeds may vary based on signal strength and wireless interference, 4G data transfer rates can actually surpass those of cable modem and DSL connections.
Like 3G, there is no single 4G standard. Instead, different cellular providers use different technologies that conform to the 4G requirements. For example, WiMAX is a popular 4G technology used in Asia and Eastern Europe, while LTE (Long Term Evolution) is more popular in Scandinavia and the United States.
- 4K is a display standard that includes televisions, monitors, and other video equipment that supports a horizontal resolution of roughly 4,000 pixels. The most common 4K standard is Ultra HD (or UHD), which has a resolution of 3840 x 2160 pixels (3,840 pixels wide by 2,160 pixels tall). It is exactly twice the resolution of HDTV (1920 x 1080) and has an identical 16 x 9 aspect ratio.
Mass production of 4K televisions began in 2013. Sony, Panasonic, Samsung, LG, Sharp, and other manufacturers now offer 4K televisions alongside their HDTV lineups. Several companies released high-resolution video capture devices prior to 2013 so that 4K video content would be available for the new TVs. For example, Canon, JVC, and other companies released 4K digital video cameras in 2012. RED released the RED ONE in 2007, which paved the way for the 4K devices that followed in the next few years.
While 4K is often used in reference to television, it can also refer to high-resolution computer monitors. For example, several hardware manufacturers now offer 4K displays, which may also be called Hi-DPI monitors or retina displays. The most popular Hi-DPI monitors resolution is 3840 x 2160, though some displays have a wider aspect ratio and a resolution of 4096 x 2160.
NOTE: 4K televisions may also be called UHDTVs (as opposed to HDTVs). However, the phrase “4K television” is more commonly used in marketing.
- 5G is the fifth generation of cellular data technology. It succeeds 4G and related technologies, including LTE. The first 5G cellular networks were constructed in 2018, while 5G devices became widespread in 2019 and 2020.
- 5G vs 4G
- Benefits of 5G include faster speeds, low latency, and greater capacity. The theoretical maximum data transfer rate of 5G is 20 Gbps (2.5 gigabytes per second). That is 20x faster than LTE-Advanced, which has a peak download speed of 1,000 Mbps. 5G latency (the time to establish a connection) is estimated to be 10 to 20 milliseconds, compared to 4G’s average latency of 40 ms. The maximum traffic capacity of 5G is roughly 100x greater than a typical 4G network.
4G smartphones and other devices are not compatible with 5G transmitters. Therefore, most 4G towers will be operational for several years after the rollout of 5G networks.
- 5G multiband
- Compared to previous cellular technologies, 5G uses a wider range of frequency bands. Instead of broadcasting all signals at a low frequency, 5G supports multiple frequencies that can be optimized for different areas. For example, low frequencies travel further but do not provide high data transfer rates. These are ideal for rural areas with a long distance between cellular towers. High frequencies have limited range and are highly impacted by physical barriers, but they support faster speeds. These are ideal for densely populated areas with large numbers of cell towers.
5G frequency bands are separated into three categories:
Low-band – broadcasts at low frequencies between 600 and 1,000 MHz, providing download speeds in the range of 30 to 250 Mbps. Both the frequency and range are similar to a 4G signal.
Mid-band – broadcasts between 1 and 6 GHz and provides speeds of 100 to 900 Mbps. The range of each cell tower is several miles radius. Mid-band is expected to be the most widely deployed.
High-band – broadcasts at ultra-high frequencies between 25 and 40 GHz. The short “millimeter waves” provide data transfer speeds above one gigabit per second. High-band 5G has a limited range of about one mile. It is ideal for city centers, sports stadiums, and other public gathering areas.
NOTE: While the maximum data transfer rates of 5G are much higher than 4G, actual speeds depend on the quality of the signal. The speed of high-band 5G signal, for instance, may drop by 50% if you step behind a building or walk a block away from the closest cell tower. With mid and high-band 5G, it is especially important to have a strong signal.
- 802.11a is an IEEE standard for transmitting data over a wireless network. It uses a 5 GHz frequency band and supports data transfer rates of 54 Mbps, or 6.75 megabytes per second.
The 802.11a standard was released in 1999, around the same time as 802.11b. While 802.11b only supported a data transfer rate of 11 Mbps, most routers and wireless cards at that time were manufactured using the 802.11b standard. Therefore, 802.11b remained more popular than 802.11a for several years. In 2003, 802.11g replaced both of the previous standards. 802.11g supports transfer rates of up to 54 Mbps (like 802.11a), but uses the same 2.4 GHz band as 802.11b.
NOTE: In order for an 802.11a connection to work, each device on the wireless network must support the 802.11a standard. For example, if a base station broadcasts an 802.11a signal, only computers with Wi-Fi cards that support 802.11a will be able to communicate with it. While many routers are backward-compatible with older standards, some must be manually configured to work with older 802.11a and 802.11b devices.
- 802.11ac (also called 5G Wi-Fi) is the fifth generation of Wi-Fi technology, standardized by the IEEE. It is an evolution of the previous standard, 802.11n, that provides greater bandwidth and more simultaneous spatial streams. This allows 802.11ac devices to support data transfer rates that are several times faster than those of 802.11n devices.
Unlike previous Wi-Fi standards, which operated at a 2.4 GHz frequency, 802.11ac operates exclusively on a 5 GHz frequency band. This prevents interference with common 2.4 GHz devices, such as cordless phones, baby monitors, and older wireless routers. Computers and mobile devices that support 802.11ac will benefit from the 5 GHz bandwidth, but older wireless devices can still communicate with with an 802.11ac router at a slower speed.
The initial draft of the 802.11ac standard was approved in 2012, but 802.11ac hardware was not released until 2013. The initial 802.11ac standard (wave 1) supports a maximum data transfer rate of 1300 Mbps, or 1.3 Gbps, using 3 spatial streams. This is significantly faster than 802.11n’s maximum speed of 450 Mbps. It also means 802.11ac is the first Wi-Fi standard that has the potential to be faster than Gigabit Ethernet. The second 802.11ac standard (wave 2) will support twice the bandwidth of wave 1 devices and offer data transfer rates of up to 3470 Mbps.
- 802.11b is one of several Wi-Fi standards developed by the Institute of Electrical and Electronics Engineers (IEEE). It was released in 1999 along with 802.11a as the first update to the initial 802.11 specification, published in 1997. Both 802.11a and 802.11b are wireless transmission standards for local area networks, but 802.11a uses a 5 GHz frequency, while 802.11b operates on a 2.4 GHz band.
The 802.11b Wi-Fi standard provides a wireless range of roughly 35 meters indoors and 140 meters outdoors. It supports transfer rates up to 11 Mbps, or 1.375 megabytes per second. In the late 1990s, this was significantly faster than Internet speeds available to most homes and businesses. Therefore, the speed was typically only a limitation for internal data transfers within a network. While 802.11b provided similar data transfer rates as 10Base-T Ethernet, it was slower than newer wired LAN standards, such as 100Base-T and Gigabit Ethernet.
In 2003, the IEEE published the 802.11g standard, which provides wireless transfer rates of up to 54 Mbps. 802.11g consolidated the previous 802.11 “a” and “b” specifications into a single standard that was backward-compatible with 802.11b devices. Most Wi-Fi devices used 802.11g throughout the 2000s until the 802.11n standard was published in 2009.
- 802.11g is a Wi-Fi standard developed by the IEEE for transmitting data over a wireless network. It operates on a 2.4 GHz bandwidth and supports data transfer rates up to 54 Mbps. 802.11g is backward compatible with 802.11b hardware, but if there are any 802.11b-based computers on the network, the entire network will have to run at 11 Mbps (the max speed that 802.11b supports). However, you can configure your 802.11g wireless router to only accept 802.11g devices, which will ensure your network runs at its top speed.
- 802.11n is a Wi-Fi standard that was introduced by the IEEE in 2007 and officially published in 2009. It supports a longer range and higher wireless transfer rates than the previous standard, 802.11g.
802.11n devices support MIMO (multiple in, multiple out) data transfers, which can transmit multiple streams of data at once. This technology effectively doubles the range of a wireless device. Therefore, a wireless router that uses 802.11n may have twice the radius of coverage as an 802.11g router. This means a single 802.11n router may cover an entire household, whereas an 802.11g router might require additional routers to bridge the signal.
The previous 802.11g standard supported transfer rates of up to 54 Mbps. Devices that use 802.11n can transfer data over 100 Mbps. With an optimized configuration, the 802.11n standard can theoretically support transfer rates of up to 500 Mbps. That is five times faster than a standard 100Base-T wired Ethernet network.
So if your residence is not wired with an Ethernet network, it’s not a big deal. Wireless technology can finally keep pace with the wired network. Of course, with the faster speeds and larger range that 802.11n provides, it is more important than ever to password protect your wireless network.
- Short for “Abnormal end.” An abend is an unexpected or abnormal end to a process. In computer software, it typically refers to a software crash when a program unexpectedly quits. For example, an error in a program’s code may cause it to freeze or crash while running a certain command. The result is an unexpected (and often inconvenient) end to the program.
The term “ABEND” was initially used by IBM OS/360 systems as an error message. It is now used by Novell Netware systems and also as a general programming term.
- Stands for “Network Address Translation.” NAT translates the IP addresses of computers in a local network to a single IP address. This address is often used by the router that connects the computers to the Internet. The router can be connected to a DSL modem, cable modem, T1 line, or even a dial-up modem. When other computers on the Internet attempt to access computers within the local network, they only see the IP address of the router. This adds an extra level of security, since the router can be configured as a firewall, only allowing authorized systems to access the computers within the network.
Once a system from outside the network has been allowed to access a computer within the network, the IP address is then translated from the router’s address to the computer’s unique address. The address is found in a “NAT table” that defines the internal IP addresses of computers on the network. The NAT table also defines the global address seen by computers outside the network. Even though each computer within the local network has a specific IP address, external systems can only see one IP address when connecting to any of the computers within the network.
To simplify, network address translation makes computers outside the local area network (LAN) see only one IP address, while computers within the network can see each system’s unique address. While this aids in network security, it also limits the number of IP addresses needed by companies and organizations. Using NAT, even large companies with thousands of computers can use a single IP address for connecting to the Internet. Now that’s efficient.