A Tethered or "Corded" Barcode Scanner is connected to your computer by a cable. Usually this is a cable connected to the USB port of your computer. In older computers the barcode scanner can be connected to the keyboard or to the serial port of your computer. Most barcode scanners send a beam of light at the barcode and read the reflection. There are four main types of barcode scanner readers:

1) CCD (or contact) - This type of barcode scanner requires the scanner to be very near the barcode. 
This is the oldest technology and hence these are the least expensive type of barcode scanner.

2) Laser - This type of barcode scanner creates a a laser line across the barcode. Laser barcode readers
can read barcodes from a much greater distance and are much faster readers than CCD barcode readers.

3) Linear Imagers - This type of barcode scanner reads barcodes by taking a "picture" of the barcode and
then reading it. Linear Imagers are most commonly used in Warehouses and Outdoors settings.

4) Omni-directional - These type of barcode scanners can read barcodes from any direction. They are most commonly used in retail situations or when a large number of items needs to be scanned in a short time.