There are two options available to connect external devices to your PC or laptop:
- USB connects a range of low speed (keyboard, mouse, printer, scanner), medium speed (TV tuner, Web cam, DVD drive), and slightly crippled high speed disk devices. This provides a high degree of flexibility and generality, but at a performance cost.
- eSATA connects external disks to a computer. The eSATA cable is a thicker more robust version of the internal SATA cable. It runs at the same speed as in the internal cable, so an external eSATA disk has the same performance as an internal disk, and maybe better performance when you are using a laptop.
Every modern computer mainboard has four or six USB 2 ports on the back. Typically the mainboard will have two additional “headers” onto which you can plug a cable that feeds two additional pairs of USB ports. A case will have one pair of USB ports on the front, and mainboards often come with a bracket that you can screw onto the end of an unoccupied card slot to generate two more USB ports in the back.
All the devices (except video) that used to have individual ports on the back of the computer can now be connected to a USB port. The keyboard and mouse can connect to either USB or the round “PS/2” port. Printers now connect directly to USB instead of the massive obsolete “parallel port”. If anyone needs a modem any more, an external serial port can also be connected through USB.
If you have an old computer without USB 2, you can buy a PCI card with 4 or 5 USB ports for $27.
The modern USB 2.0 port supports three specific transfer speeds:
- A “low speed” USB device transfers data at 1.5 megabits per second.
- A “full speed” USB device transfers data at 12 megabits per second.
- A “high speed” USB device transfers data at 480 megabits (60 megabytes) per second.
USB 3.0 adds an additional speed:
- A “super speed” USB device transfers data at 3200 megabits (400 megabytes) per second
Unfortunately, a buyer has to be careful of the terminology. Technically, USB 2.0 is a specification of the physical and electrical interface specification. A few vendors claim to have USB 2.0 ports but do not support high speed devices. So make sure that a device claims “high speed” or 480 Mbs before buying it.
It is possible to get cables that have a USB connection to the PC and then convert the USB protocol into one of the old legacy standards that support old devices. One cable produces the old printer “parallel” port connector. Another cable produces a serial port connection to a dial up modem or to specialized devices. There are wireless and wired Ethernet connectors. A few devices connect to a USB port and then (with an internal software device driver) connect to a monitor to add an additional screen to your laptop.
One USB port on your computer can be connected to a hub device. The hub then distributes the signal to (typically) eight external ports that can support eight devices. However, all the devices share the same USB connection and must share the same bandwidth.
So if you are looking for a simple and inexpensive way to connect external disks to your computer, the current best technology is eSATA. This is a slightly more rugged version of the simple SATA cables that connect hard disks inside the computer.
Like the internal SATA, it is available in 150 and 300 Megabyte per second speeds. Since desktop disks typically transfer at a maximum of 40 megabytes/sec, and the very fastest Raptor disks only do 80 megabytes/sec, 150 is a perfectly fine speed. In fact, since the slower 150 MB/s is slightly more robust against connection problems, the author forces all his own SATA external disks to run at 150 even when they are nominally rated at 300.
eSATA allows you to run external disks at the same speed and with the same performance as internal disks. If you have a small case, then external disks may be a requirement. Even with a large case they can be useful for backup or archival. While USB will continue to be useful for the wide range of slower speed devices, eSATA is establishing itself as the preferred external disk connection.