The Universal Serial Bus (USB), developed by Apple, IBM and Microsoft, was first introduced with the Apple iMac computer. It’s now fitted on all modern Macs and PCs, and is also supported by Windows 98 and later systems.

Connections are made via a special 4-way modular plug and socket.

USB 1.0/1.1

The original USB 1.0 interface runs at between 1.5 and 12 Mbit/s, slower than the SCSI ports on older computers and not fast enough for a hard disk drive, although adequate for a modest device such as a floppy disk or Zip drive.

Early Mac OS machines have two USB 1.0 ports wired together, with a total speed of 12 Mbit/s, although later models have two independent USB 1.0 ports, giving 24 Mbit/s. The latter arrangement lets you use one port for a demanding disk drive or CD-ROM drive whilst employing the other connection for a simple device such as a mouse or keyboard.

USB 2.0

The USB 2.0 interface runs at higher rates of 60, 120, 240 or 480 Mbit/s, uses the same connector and is compatible with USB 1.0, although it doesn’t speed up your existing USB 1.0 devices. Unfortunately, USB 2.0 isn’t supported by older Mac OS computers, although you can accommodate it by fitting an appropriate PCI card or PC Card.

USB Products

A wide range of USB devices are now available, many of which are suitable for both PCs and Mac OS computers. Unfortunately, some don’t accommodate daisy-chaining, which means you may have to buy a USB hub.

USB products, as well as devices connected to them, may require specific driver software, although class compliant USB devices work with the drivers built into modern versions of Mac OS X and Windows. If you have problems with a special driver you may find your device works better without it. Alternatively, try third-party software such as USB Overdrive.

Interface Adaptors

A range of different adaptors can be used to connect devices that use older ports or special interfaces. Common USB devices of this kind are listed below.

Games Controller Adaptor

If you like games you’ll want to have a games controller as well as a standard mouse: fortunately, USB lets you connect both at once. Most controllers, including those designed for PCs, can be used on a Mac OS machine without special software.

To control your machine’s functions remotely you can use a USB-equipped infrared receiver and matching infrared controller. In some instances this kind of receiver can also be operated from any universal remote control that runs at 33 kHz.

Keyboard or Mouse Adaptor

You can replace or supplement your existing keyboard or mouse by alternative USB devices. However, you should note that there are three versions of Apple’s USB keyboard, so you should check that you have the correct variety for your computer.

ADB Adaptor

This lets you connect an older Apple ADB device, such as a keyboard or mouse, to your computer. Two ADB ports are often provided, although sometimes you can only use one at a time. Such an adaptor is also suitable for controlling an ADB-equipped monitor, assuming your monitor’s software can be persuaded to work with it. You can even use this gadget to connect an ADB keyboard or other device to a USB-equipped PC, allowing a Mac OS keyboard to control a Windows machine.

Parallel Adaptor

This lets you connect a printer or other device with a Centronics parallel port. So, you can get out that old PC printer and use it with a modern computer. However, once it’s connected, you’ll need suitable printer driver software. Unfortunately, some drivers are difficult to find, although Keyspan’s adaptor works with the original printer drivers in the Classic Mac OS.

SCSI Adaptor

This can connect older SCSI devices, such as hard disk drives or scanners, to your computer. Most have a 25-way D connector, as used for SCSI on ‘classic’ Macs, or a 50-way Amphenol connector, as found on many standard SCSI devices.

Serial Adaptor (mini-DIN)

This lets you use devices designed for use with a serial port, such as the Modem or Printer ports fitted on a ‘classic’ Mac OS machines. Such adaptors usually have two ports, each of which are connected via an 8-way mini-DIN socket, although sometimes you can’t use both ports at once. Unfortunately, these ports don’t usually accept a device that feeds an external clock back into the port. This means that you can’t use such an adaptor for the following devices:-

  1. Some types of printer or scanner
  2. Any serial-connected MIDI interface
  3. Devices that require a GeoPort serial connection
  4. Printers or other devices that operate via LocalTalk

You must also ensure that you have the software for running your device via USB, Remember, software designed for ‘classic’ serial ports may not work via USB, although some adaptors support Apple’s StyleWriter printers in the Classic Mac OS.

Serial Adaptor (DB25)

Similar to the above, this usually provides a single port via a 25-way D connector, also known as a DB25. This kind of adaptor is ideal for connecting a device that was originally designed for an older PC. Unfortunately, some devices won’t work or may require an extra RS-232 adaptor. As with the above, there can be numerous hardware and software complications.

Serial Adaptor (DB9)

Similar to the above, but primarily designed for connecting a sub-notebook computer or a personal organiser, also known as a portable digital assistant (PDA). The most common device of this kind is of course the Palm personal organiser. Note that adaptors of this type often run the serial port only 57.6 kbit/s, instead of the usual Mac maximum of 230 kbit/s.

Communications Adaptors

The following adaptors allow you to communicate with other devices:-

Bluetooth Adaptor

A simple adaptor that lets your machine use the Bluetooth wireless-based communications system. This kind of device may contain firmware that can be updated by using appropriate software on your computer.

GSM Mobile Phone Adaptor

Lets you use the Internet in conjunction with special software and a suitable GSM mobile phone.

ISDN Adaptor

This lets you reach the outside world via the Integrated Services Digital Network (ISDN), providing a faster and more reliable connection than a modem, typically running at 64 kbit/s over a single channel or 128 kbit/s over two channels.

LocalTalk Adaptor

Allows you to use network printers and other devices that are fitted with Apple’s outdated LocalTalk connection system. Some adaptors provide the LocalTalk circuit via a 4-way modular connector, also known as a RJ11, as used for the PhoneNet wiring system. If you don’t use PhoneNet, or you only want to connect a one device, you should install a RJ11 to LocalTalk adaptor.

Phone Adaptor

Connects a phone line to your computer, allowing you to use the latter for managing voice mail, caller ID or fax data.

USB Server

This allows one or more USB-connected devices, usually in the form of printers, to be shared over a local network by means of a common Ethernet connection. Note that the USB connection on the server is connected to a device, not a computer.

Wi-Fi Adaptor

A simple adaptor that lets your machine work in a Wi-Fi wireless-network. This kind of device may contain firmware that can be updated by using appropriate software on your computer.

Multimedia Devices and Adaptors

Various devices can be used to connect audio equipment and video equipment to your computer. These can supplement the existing hardware or provide additional connections or features that aren’t available on your machine. Examples include:-

Analogue Audio Adaptor

Lets you connect the analogue audio inputs and/or outputs of audio devices to your computer. This kind of device is particularly necessary if your machine doesn’t have an analogue audio input.

Analogue Audio Devices

A USB headset, incorporating a microphone and headphones, with an inline volume control, can be plugged directly into a standard USB port. Alternatively, you can connect a stand-alone USB microphone or a pair of USB loudspeakers.

Digital Audio Adaptor

This lets you connect digital audio equipment that has S/PDIF ‘digital in’ (DI) or ‘digital out’ (DO) circuits, usually via RCA phono jacks, also known as PIN jacks. Some adaptors work at both 16-bit and 24-bit audio resolution.

MIDI Adaptor

A MIDI adaptor, also known as a MIDI interface, lets you send musical performances to external MIDI instruments. Sadly, older devices with ‘classic’ serial ports don’t work via a serial adaptor (see above), so a USB-based MIDI adaptor may be required.

MP3 Player

Any sound files that have been encoded in MP3 format can be downloaded via USB to a portable MP3 player, allowing you to carry part or all of your music collection around with you. Apple’s iPod is a very popular example of such a device. Some players can also operate as a sound recorder, typically creating WAV or MP3 files for each recording session.

Video and Audio Adaptor

The cheapest device of this kind provides a analogue video input for your computer, often with built-in MPEG compression. More advanced adaptors accommodate inputs and outputs for both video and audio, and some even incorporate a TV tuner. In addition, you can obtain a TV camera that can be plugged into a USB port. The speed of USB normally limits such devices to a half-size picture of 384 × 288 or 352 × 288 pixels, scanned at 30 or 25 frames per second (frm/s).

Video Output Adaptor

This gives a video output for an external monitor, which may be required if you computer doesn’t incorporate a monitor output socket. Such devices usually produce a full-size picture of 768 × 576 pixels, at a scanning rate of 30 or 25 frm/s.

Other USB Devices

The following USB devices can also be encountered:-

Barcode Reader

This device lets you read barcodes, usually without needing special driver software.

Card Reader

This reads data from a storage card, as found in digital cameras or MP3 players, such as a CompactFlash (CF) or SmartMedia (SM) card. Note that each kind of card requires a matching reader. Alternatively, you can use a USB-enabled card (see below).

Disk Drive

Generally speaking, USB 1.0 isn’t fast enough for a CD or disk drive, although adequate for an old-style floppy disc drive. USB 2.0 is sufficient for many drives, although it can only be used at full speed if your computer has matching USB 2.0 ports.

CompactFlash Card (USB-enabled)

This is identical in all other respects to a standard CompactFlash card but incorporates its own USB interface, avoiding the need for a separate card reader. To connect such a card to your computer you’ll need a Jumpshot USB cable.

Musical Keyboard

Together with a suitable application, such as Apple’s GarageBand, you can use this to create music on your computer. However, for more advanced musical work, where connections to external MIDI-equipped devices are required, a suitable MIDI keyboard and a matching USB MIDI adaptor (see above) may be the preferred option.

Hardware Key

A hardware key, also known as a USB dongle, prevents unauthorised use of software. It plugs into your USB bus, sadly using a valuable connection. One common variety of dongle is the MacHASP by Aladdin Systems, containing 100 bytes of memory.

VoIP Telephone

This kind of telephone handset is used in conjunction with a Voice over Internet Protocol (VoIP) application, such as Skype, allowing you to communicate with other VoIP users at no charge. However, you’ll have to pay a regular fee to communicate with standard non-VoIP telephones.

USB Connections and Cables

USB devices commonly have a Type A or Type B connector, or both, as shown in the diagram below. The ‘wide’ Type A variety appears on computers (or at the output of a hub, see below) whilst the ‘square’ Type B version is fitted to peripheral devices (or to the input of a hub).

Devices are often connected via an A-B cable, with a Type A plug at one end and a Type B at the other, as shown below.

Up to 127 USB devices can be connected to a single port. Although most computers only have two ports, some devices accommodate daisy-chaining. If you don’t have enough sockets, you must get a USB hub, although some USB-controlled monitors have a built-in hub. Apple’s USB keyboard also works as a hub: this has two Type A sockets, one for the mouse and another that for extra devices, as well as a Type B connector for the circuit to the computer.

USB Power

Unlike some older interfaces, USB provides a + 5-volt power supply for peripheral equipment, typically with a maximum current capacity of 500 mA per port. This enables a small device, such as a keyboard, miniature hard disk or scanner, to be connected to a port without any further power connection, making USB equipment both small and lightweight. Some USB devices accept power from the USB bus or an external supply unit, depending on the situation. Alternatively, if you have several power-hungry USB devices, you may have to use a self-powered USB hub.

Connections in Detail

The following diagram shows the pin connections for standard Type A and Type B connectors:-

whilst the next shows mini-USB sockets. These are only in Type B form and are supplied in 5-way and 4-way versions.


Help Center, Mac OS 9.1, Apple Computer Inc, 2001

MacWorld magazine (UK), IDG Communications, 2002-2004

©Ray White 2006.