Common Connection Interfaces

USB Power notes

Note: Devices supporting fast charging can supply 7.5 W if the port is in charging mode (no data transfer is possible in charging mode). Devices conforming to the USB Power Delivery version 2.0 specification are able to deliver up to 100 W of power.

USB On the Go (OTG)

USB On the Go (OTG) allows a port to function either as a host or as a device. For example, a port on a smartphone might operate as a device when connected to a PC but as a host when connected to a keyboard.

Storage Connector Types

USB and Thunderbolt are examples of multipurpose cables used to attach different kinds of external peripheral device (though it is also possible to use USB cabling within the system case). Internal storage devices use different types of interface, though.

Other Peripheral Connector Types

USB is the dominant interface for PC peripherals, but you may also come across cabled devices requiring different connections.

USB Connectors and Ports pt 2

A USB cable can feature Type A to Type A connectors but most convert from one type to another (Type A to Type B or Type A to Micro Type B for instance). In USB 3.0, there are 9-pin versions of the Type A, Type B, and Type B Micro connectors. USB 3.0 Type A connections are physically compatible with USB 1.1 and 2.0 connections, but the Type B/Type B Micro connections are not. So, for example, you could plug a USB 2.0 Type A cable into a USB 3.0 port, but you could not plug a USB 3.0 Type B cable into a USB 2.0 Type B port.As you can see, USB has historically featured a bewildering range of connector types. USB 3.1 defines a new USB-C 24-pin connector type. This should provide a single consistent hardware interface for the standard. The connector is reversible, meaning it can be inserted either way up. The connector design is also more secure and robust. USB-C can use the same type of connector at both ends or you can obtain USB-C to USB Type A or Type B converter cables

Molex connectors.

As well as a data connection, an internal hard drive needs to be connected to the computer power supply. A computer power supply will come with a number of peripheral power connectors. For older devices, this power connection is made using Molex connectors and ports. A Molex connector is usually white and has 4 pins plus red, yellow, and black wires.

RJ-45.

Most computers have a network adapter already installed as part of the motherboard chipset. The network adapter will have an RJ-45 port to connect the computer to the network, via another RJ-45 port in the network equipment. This port will be marked "LAN" (Local Area Network).An RJ-45 (Registered Jack) connector is used with twisted pair cable for Ethernet local area networking products. Twisted pair is a type of copper cabling where pairs of insulated conductors are twisted around one another, to minimize electrical interference.RJ-45 connectors are used with 4-pair (8-wire) cables. The connectors are also referred to as 8P8C, standing for 8-position/8-contact. This means that all eight "potential" wire positions are supplied with contacts, so that they can all carry signals if needed.

Molex connectors notes

Note: SATA drives are more likely to use the SATA power connector. Some devices might have both types of power connectors.

SATA and eSATA connectors

Note: The main drawback of eSATA compared to USB or Thunderbolt external drives is that power is not supplied over the cable. This is not so much of an issue for 3.5" drives, which require a separate power supply anyways, but it limits the usefulness of eSATA for 2.5" portable drives.

USB Connectors and Ports notes

Note: There were also a number of non-standard mini B connectors used on various digital camera models.

USB Standards notes

Note: USB 3 controllers actually feature two sub-controllers. One controller handles SuperSpeed-capable devices while the other supports legacy HighSpeed, FullSpeed, and LowSpeed USB v1.1 and v2.0 devices. Consequently legacy devices will not slow down SuperSpeed-capable devices. There are changes to the way the bus works to try to improve "real-world" bandwidth too.

USB Connectors notes

Note: USB has not historically been used as a display interface (to attach a monitor). That is changing as the USB-C connector (discussed later) is becoming more widely adopted.Note: To overcome the limitations of sharing bandwidth, most PC chipsets feature multiple USB controllers, each of which has only three or four ports

Serial Ports (RS-232 and DB-9) notes

Note: You might also come across the term PS/2. This was a serial interface used to attach mice and keyboards. PS/2 ports use a 6-pin mini-DIN format.

SCSI

SCSI could be used for both internal devices and external peripherals (such as scanners and printers) but you are very, very unlikely to find it used anywhere except for the connection of internal disk drives. While early SCSI types used 50-pin connectors, you are only likely to come across High Density (HD) 68-pin connectors or Single Connector Attachment (SCA) 80-pin connectors. SCA incorporates both a power connector and configuration wires, allowing for hot swappable drives.Also, you should note that while parallel SCSI as a physical interface has almost completely disappeared, the software interface and command set are used in many other storage technologies, including Serial Attached SCSI (SAS), Firewire, and Storage Area Networks (SAN).

SATA and eSATA connectors

Serial Advanced Technology Attachment (SATA) is the standard means of attaching internal storage drives to a desktop PC. Each SATA host adapter port supports a single device. Internal SATA cables can be up to 1 m (39"). The cables are terminated with compact 7-pin connectors.There is also an eSATA standard for the attachment of external drives, with a 2 m (78") cable. You must use an eSATA cable to connect to an external eSATA port; you cannot use an internal SATA cable. eSATAp is a non-standard powered port used by some vendors that is compatible with both USB and SATA (with an eSATAp cable). The USB interface dominates the external drive market, however.

RJ-11.

Smaller RJ-11 connectors are used with 2- or 3-pair UTP or with flat ribbon "silver satin" phone cables. Typically only one pair carries the dial tone and voice circuit (also called the Tip and Ring wires after the way older phono plugs were wired). The other pair is usually unused but can be deployed for a secondary circuit. RJ-11 connectors are used for telephone systems (for example, to connect a modem to a phone jack).Note: An RJ-11 connector only has two contacts (6P2C); to use more pairs, an RJ-14 (6P4C) connector is required. This is physically the same size as RJ-11 but has more wired contacts.

USB Connectors

The Universal Serial Bus (USB) has become the standard means of connecting peripheral devices to a computer. It is an example of a multipurpose cable that can be used to attach a wide range of peripherals and storage devices.A USB bus consists of a host controller and up to 127 devices. A device can be a hub (providing ports for additional devices) or function. Functions are divided into classes, such as human interface (keyboards and mice), mass storage (disk drives), printer, audio device, and so on.

Cable Length

The maximum cable length for LowSpeed devices is 3m while for FullSpeed and HighSpeed the limit is 5m. Vendors may provide longer cables however. SuperSpeed-capable cables do not have an official maximum length but up to about 3m is recommended.

USB Standards

There have been several iterations of the USB standard. Each new version introduces better data rates. A version update may also define new connector form factors and other improvements. The USB 2.0 (HighSpeed) standardspecifies a data rate of 480 Mbps. Note that this bandwidth is shared between all devices attached to the same host. The USB 3.0 standard introduces a SuperSpeed mode. SuperSpeed improves the bus bandwidth tenfold (to 5 Gbps or 5000 Mbps) and makes the link full duplex, so a device can send and receive at up to 5 Gbps simultaneously. USB 3.1 defines a SuperSpeed+ mode with a data rate of 10 Gbps. USB 3.2 promises 20 Gbps, but only over USB-C ports and cabling (discussed later)USB 3.x receptacles and connectors often have a blue connector tab or housing to distinguish them.

Lightning

Apple's iPhone and iPad mobile devices use a proprietary 8-pin Lightning port and connector. The Lightning connector is reversible (can be inserted either way up). The Lightning port is found only on Apple's mobile devices. To connect such a device to a PC, you need a suitable adapter cable, such as Lightning-to-USB A or Lightning-to-USB C.

Expansion Cards

Expansion cards (or add-on cards) can be installed on the motherboard to add functions or ports not provided as part of the chipset. An expansion card can be fitted to an appropriate slot (PCI or PCIe) on the motherboard.

SCSI

Modern connection interfaces use serial communications. These serial links can achieve Mbps and Gbps speeds because of improved signaling and encoding methods. Back when serial interfaces were much slower, PC vendors used parallel data transmission to support better transfer rates. While a serial interface essentially transfers 1 bit at a time, a parallel interface transfers 8 bits (1 byte) or more. This requires more wires in the cable and more pins in the connectors, meaning parallel interfaces are very bulky. Internal PC storage devices often used Parallel ATA (PATA)/Enhanced Integrated Drive Electronics (EIDE) connections. This supported transfer rates up to about 133 MBps. Workstations and servers requiring more speed would use the Small Computer Systems Interface (SCSI) bus instead. SCSI could support up to 320 MBps data rates. While you will not come across any new systems shipping with SCSI connections, you might need to support legacy systems that use SCSI.

I/O Adapters and Storage Cards.

Most Input/Output (I/O) bus functions are provided on the motherboard, which will typically have USB ports for external peripherals and SATA ports for internal storage drives. An adapter card can be installed to provide additional ports or a bus type that is not supported on the motherboard. Typical examples include an eSATA host adapter to make external storage ports available, a flash memory card reader, a card with extra USB ports, or a card supporting wireless peripherals, such as Bluetooth.

Network Interface Cards (NICs).

Most computers have a network adapter already installed as part of the motherboard chipset. However, there may be occasions when you need to install an add-on Network Interface Card (NIC) or need to upgrade an adapter to use a different type of network, bandwidth, or cabling. A Wi-Fi adapter can be added to connect to a wireless network. Wi-Fi adapters are developed to different 802.11 standards (802.11a/b/g/n/ac).

Network Connector Types

Network connections also use dedicated cable types, rather than multipurpose cabling such as USB and Thunderbolt

USB Power

Power is supplied by the host at 5V and a single device may draw up to 500 mA (milli-amps) or 2.5 W (increased to 4.5 W with the USB 3.0 specification). Devices that require more power than this, such as printers, must be connected to an external power supply.

Thunderbolt (TB)

The Thunderbolt (TB) interface was developed by Intel and is primarily used on Apple workstations and laptops. Thunderbolt can be used as a display interface (like DisplayPort or HDMI) and as a general peripheral interface (like USB). In its first two versions, Thunderbolt uses the same physical interface as MiniDP and is compatible with DisplayPort, so that displays with a MiniDP port can be connected to a host via Thunderbolt. Thunderbolt ports are distinguished from MiniDP by a lightning bolt icon. Version 2 of the standard supports links of up to 20 Gbps. Up to six devices can be connected to a single port by daisy-chaining the devices. You can also use a dock or hub device to channel a variety of ports (TB, USB, HDMI, and Ethernet, for instance) via a single Thunderbolt port on the host PC or laptop. Thunderbolt version 3 changes the physical interface to use the same port, connector, and cabling as USB-C. Converter cables are available to connect Thunderbolt 1 or 2 devices to Thunderbolt 3 ports. A USB device plugged into a Thunderbolt 3 port will function normally but Thunderbolt devices will not work if connected to a USB port that is not Thunderbolt-enabled. Thunderbolt 3 supports up to 40 Gbps over a short, high-quality cable (up to 0.5m/1.6ft).

Serial Ports (RS-232 and DB-9)

The serial port (or RS-232) is so called because data is transmitted over one wire one bit at a time. Start, stop, and parity bits are used to format and verify data transmission. While modern interfaces like USB are also serial, an RS-232 interface uses much less sophisticated signaling methods. Consequently, an RS-232 serial port supports data rates up to about 115 Kbps only.Serial ports are generally associated with connecting external modems, used to establish dial-up Internet connections, though even this function has largely been superseded by USB. You may also come across serial ports on network equipment, where a serial connection can be used to manage the device. RS-232 (Recommended Standard #232) specifies a 25-pin hardware interface, but in practice, PC manufacturers used the cheaper 9-pin D-subminiature (DB-9) male port shown above.

USB Connectors and Ports

USB connectors are always inserted with the USB symbol facing up. There have been several versions of the USB standard and these versions have often introduced new connector form factors. The main connectors for USB 2.0 are: Type A (4-pin)—for connection to the host. The connector and port are shaped like flat rectangles. Type B (4-pin)—for connection to a device. The connector and port are square, with a beveled top. There are also small form factor versions of the type B connector and port: Type B Mini (5-pin)—a smaller connector for connection to a device. This type of connector was seen on early digital cameras but is no longer widely used. The additional pin supports USB OTG. Type B Micro (5-pin)—an updated connector for smaller devices, such as smartphones and tablets. The micro connector is distinctively flatter than the older mini type connector.

Common Connection Interfaces OBJECTIVE COVERED Explain basic cable types, features, and their purposes.

You need to be able to identify how components are connected together to form a complete computer system. In this topic, you will compare PC and device connection interfaces and their characteristics. A PC is made up of many different components. All of these components need to be able to communicate with each other so that the computer can function properly. As PC designs have evolved over the years, several connection technologies have been implemented to provide communication among computer components. As a computer technician, identifying the methods used to connect devices to a computer will enable you to install, upgrade, and replace PC components quickly and effectively.