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What is a USB Hub

by:ShunXinda      2020-06-12
A USB Hub can be used to provide direct communications between a number of USB enabled devices, or more commonly to expand the capabilities of a single USB port on a computer and allow multiple devices to use a single connection. This can be useful when a computer has a shortage of USB ports and a mouse, keyboard and printer could all be connected via single USB hub. A number of computers could share the services of a hub to connect to a printer, but this is not recommended and a networked printer via an Ethernet switch is a much better solution. USB (Universal Serial Bus) was originally devised around 1996 with data rates of 1.5Mbps and 12Mbps defined. The 1.5Mbps standard was referred to as Low Speed, whilst the 12Mbps standard was described as Full Speed. Version 1.1 was very popular and many devices such as computers and printers soon adopted this standard. In 2000 the USB 2.0 standard was developed by a group of vendors including HP and Intel and this resulted in a data rate of 480Mbps. Finally in 2008 the USB 3.0 specification was drafted and increased the potential data rates up to a whopping 5Gbs whilst ensuring backwards compatibility with the USB 2.0 standard. A USB Hub will usually have a single Upstream port to connect a PC to a hub or indeed another PC, whilst downstream ports are used to connect a number of peripherals to a PC. Effectively you are building a network of devices that can then access a single PC, with 127 ports being the maximum number of ports allowed on a USB network. PC vendors quickly adopted the standards because it simplified the way peripherals could be connected to a single PC. Printers no longer needed to connect to a PC by means of a cumbersome parallel cable, and Mice, Keyboards and external devices such as CD drives, DVD drives and Flash drives could all use simple USB connections to the PC. Small hubs with few ports often have the ports in a horizontal formation, and often anything over 3 or 4 ports with have a configuration with multiple vertical rows of ports. There are practical limits on the maximum length of cable to be used with the USB Specifications, with 3 Metres being suggested for USB 1.1 and 3.0 and 5 metres for the USB 2.0 specification. USB Hubs are often powered from a mains supply, but a bus-powered hub will derive its power from a Host computer over the same cable. The maximum power that can be drawn from a host device is 500mA so a bus-powered hub can therefore only support 4 downstream ports as the hub itself will require 100mA, leaving 100mA for each of the downstream peripherals. A hub that is powered from a mains supply can provide the full power of 500mA to each individually connected device. Although a lot of hubs will have a power rating of around 1A, they can often supply power for up to 7 devices due to the fact that many devices actually draw less then 100mA of power. If you are using a 7 port hub for example and you have power problems, check the ratings of connected devices, although you should rarely find that your devices are collectively drawing too much power. Some vendors are manufacturing hubs with a bigger power supply in response to demand. Downstream ports on a USB Hub will typically require a flat A-Type connector, as will ports built-in to a PC. Cables with A-Type connectors will carry power to the attached device as well as the data. In contrast a B-Type connector is almost square in shape and is used to connect to the upstream port on the hub, and will carry power and data, although in some cases is only used as a power cable to draw power from its upstream host. Memory sticks and Flash Drives usually have a Type-A connector although there is often no cable involved. There are two other main type of USB connectors know as Mini and Micro, but these are normally used for portable devices such as phones, cameras and PDAs, and are not normally associated directly with USB Hubs. So, if you have a shortage of USB ports on your PC, consider a low cost USB Hub which are often compact Plug & Play devices, therefore there is no technical knowledge needed to configure one.
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