The USB (universal serial bus) is a relatively recent way to connect instruments and devices to the PC. Most new computers have one or two USB ports, in addition to the familiar RS232 (COM) and parallel ports. You can use the USB ports for many peripherals, including digital cameras, printers and data acquisition and control units like the Microlink 751.
The USB is extremely convenient for data acquisition for several reasons.
If your PC does not have a USB port you can buy a PCI-based card which provides one. However, you need to be running Windows 98SE or Windows 2000. (Early releases of Windows 95 do not support USB, later releases have some support but it's better to use Windows 98SE or 2000.) You can test whether your PC is USB compatible by visiting www.usb.org and downloading their evaluation utility program.
If you don't wish to upgrade your machine there are many other ways to connect data acquisition equipment to computers, such as Ethernet, RS232, RS485 or GPIB.
The USB cable should have an "A" plug at one end (for the computer) and a "B" plug at the other: no sockets. Any other arrangement doesn't conform to the standard. The cable comprises four wires: two carry your signal data and two supply voltage. The bus can operate at two different speeds, depending on the attached device. The device itself tells the bus what its speed is through the voltage cables. The cable should not be longer than 5 metres for fast devices, or 3 metres for slow devices. However, you can use up to 5 USB hubs to connect cables, giving a maximum distance of 30 m.