The Universal Serial Bus (USB) is the standard technology for connecting peripherals to computers. However, the current version of USB 3.0 looks to confront competitors like Thunderbolt.
What are the core functions of USB 3.0?
The Universal Serial Bus (USB) is a serial, host-oriented bus technology for connecting different peripherals to computers. It allows data rates of 480 MBit / s (USB 2.0) or 4.8 GBit / s (USB 3.0). USB uses a master / slave architecture: The master is equipped with a host controller, which controls the connected slaves (terminals). Up to 127 devices can be connected to a USB bus. The maximum cable length for USB 3.0 is now 5 meters
How does USB 2.0 differ from USB 3.0 (USB 2 vs 3)?
The USB 3.0 specification (“SuperSpeed USB/USB 3 0 Speed”) was adopted in autumn 2008 by the USB Implementers Forum (USB-IF). Compared to 2.0 (“Hi-Speed USB/USB 2 0 Speed”), it includes the following changes:
A gross data rate of 4.8 GB / s instead of 0.48 GBit / s.
The omission of “device polling”, ie the regular check of the bus, whether new devices have been added. USB 3.0 uses an asynchronous interrupt-controlled method. Connected devices are only then aroused from a “virtual sleep mode” when they do something, for example transfer data. This reduces the power requirement.
Power supply for external devices with up to 900 mA (instead of 500 mA for USB 2.0): This allows systems with higher power consumption, such as external hard disks or IP cameras, to be connected. A minimum of 150 mA is available per device (USB 2.0: 100 mA).
Full-duplex data transfer instead of half-duplex as with USB 2.0.
Sync-N-Go technology reduces the waiting time for data transfer between USB hosts / slaves.
USB 3.0 uses a shielded differential pair cable (SDP) with eight wires instead of an unshielded twisted pair cable (UTP). Two of the wires ensure SDP’s backward compatibility to USB 2.0.
USB devices at USB 3.0 can tell the host which maximum latencies they “bear”. This also reduces energy requirements.
Which external systems can be powered by USB 3.0?
USB 3.0 supplies external devices such as hard disks and SSDs with up to 900 mA via the USB cable. For USB 2.0 it was 500 mA. The 900 mA usually suffice for external 2.5-inch hard drives. For larger and more current models, either an external power supply must be used, or the manufacturer must supply a Y cable that is connected to a second USB port for power supply. Mobile mass storage devices with eSATA port also access USB to ensure power supply. Unconfigured USB devices and those which are not active, USB 3.0 150 mA (100 for USB 2.0) are available.
By mid-July 2012, the USB 3.0 Promoter Group approved the USB Power Delivery specification. It provides end devices with USB cable up to 100 watts. This makes it possible, among other things, to recharge the batteries of notebooks via USB or to supply external storage systems with power.
What is the compatibility of USB 2.0 and USB 3.0?
In general, USB 3.0 hosts and slaves (end devices) are backwards compatible with version 2.0. This means: USB 2.0 systems like sticks, external drives or WLAN adapters can be connected to a USB 3.0 port and vice versa: USB 3.0 systems also work on USB 2.0 ports. The situation with the USB cables looks different. USB 3.0 type A plug (flat, blue connector) are also compatible with USB 2.0 ports on the host side, such as a PC. This is different for end devices that are connected via a cable with Type B connectors (square shape): USB 3.0 terminals such as a printer can also be connected to the host with old Type B cables. However, a Type B USB 3.0 cable does not fit with a USB 2.0 hard disk. The reason for this is the changes that USB 3.0 has brought with regard to the power supply of devices. This requires other cables and for type B connectors a differently shaped connector.
What other techniques besides USB 3.0 are available for connecting peripherals to computers?
In addition to USB 3.0, the following techniques are relevant:
ESATA: The Serial AT Attachment Bus (SATA) was originally only intended for use inside computers, especially for the connection of hard disks. It is a serial bus interface that couples a host bus controller to point-to-point connections to hard drives and optical drives. With eSATA, a specification has been available since 2004, which is used to connect external drives and hard disks. The maximum cable length is 2 meters, the data throughput is 3.2 GBit / s (SATA 2G) or 6 GB / s for SATA-6G interfaces. This means that the gross data rate of eSATA is higher than that of USB 3.0 and Firewire 800.
Firewire / IEEE 1394: Firewire / IEEE 1394 is a serial peer-to-peer / full duplex transmission with low protocol overhead. Apple began 1986 with the development of Firewire. The IEEE (Institute of Electrical and Electronics Engineers) placed Firewire 1995 under the designation IEEE 1394 in the rank of a standard. By the year 2000 the maximum data rate was 400 MBit / s. In 2002, IEEE 1394b adopted an extended specification (Firewire 800, S800) that provides a data rate of 800 Mbps. Other additions are Firewire S1600 (1.6 GBit / s) and Firewire S3200 (3.2 GBit / s), which are available since 2007.
A Firewire cable has a maximum length of 4.5 meters. In IEEE 1394b, further types of connections have been defined, including network cables and optical fibers. This allows distances of up to 72 meters to be bridged. A drawback, however, is that Firewire S3200 was not able to penetrate the market. It is currently being considered to develop a FireWire version with 6.4 GBit / s.
Thunderbolt: Thunderbolt is a high-speed I / O technology, which Intel developed together with Apple originally under the name “Light Peak” and presented in February 2011. It supports two protocols: PCI Express (PCIe) and Display Port (DP). Thunderbolt is technically a PCI Express interface, which is led over a cable to the outside. The data transfer rate for the first version of Thunderbolt is 10 GBit / s, simultaneously in both directions (sending and receiving, full duplex).
Data and video information is transmitted at Thunderbolt at the same time. Therefore, external screens such as Apple’s Thunderbolt display or even TV devices can be connected to a computer via this interface. This is done in a daisy chain. Similar to USB, Thunderbolt devices can be powered by copper data cables. With the maximum cable length of 3 meters, 10 W is the maximum. Originally, Thunderbolt should use optical fibers (LWL). This was, however, set aside for reasons of cost. With fiber optics, distances of up to 50 m can be bridged.
What are the advantages and disadvantages of USB 3.0 and Firewire?
For USB 3.0, the simple structure and low cost speak. This has led to a high level of acceptance, reflecting the large number and low price of USB products. For example, a USB 3.0 cable of 3 meters in length costs between 6 and 8 euros in online trading. For a similar Thunderbolt cable is almost 50 euros due.
A disadvantage of USB 3.0 is the limited compatibility with USB 2.0 and USB 1.1. For USB 2.0, however, this only applies to the connection of USB 2.0 devices using Type B cables, which have been developed for USB 3.0. Another weak point is the Bulk-Only Transport Protocol (BOT), which limits the data throughput. With the USB Attached SCSI Protocol (UASP), an alternative is available, which should help.
An advantage of Firewire is the high data throughput thanks to the use of a slim communication protocol with a low overhead. In addition to USB 2.0, a bidirectional data transfer is possible, so simultaneous transmission and reception. However, these functions also include USB 3.0 and Thunderbolt. In addition, Firewire comes out without a host, such as a PC, Mac computer or a QacQoc USB hub. This is reflected in lower component costs.
The biggest drawback of Firewire is that the development is stagnating. Although many providers of external devices such as hard drives and DVD drives as well as notebooks and PCs still equip their computers with Firewire 800 interfaces. However, products are missing for Firewire S1600 and S3200. With Apple, which is based on Thunderbolt and USB 3.0, Firewire has also lost its strongest ally.