Scanners are devices that scan an image (or text) optically and then convert them into a digital image. Current scanners normally use one of a contact image sensor (CIS) or a charge-coupled device (CCD) to function whereas older drum style scanners utilised a photomultiplier tube to sense the images. Rotary scanners are another type of drum scanner with the difference that it uses a CCD instead of a photomultiplier.
But scanning the image is only one small component of the whole process and for it to be of any use at all, it has to find its way to the computer and then to the application that’s actually using it. In other words, the process of transferring of the image from the scanner through to the eventual software application that requires whatever has been scanned. This will depend on a couple of things. The first is how the scanner is actually connected to the said computer, and second, how the relevant software application obtains the information from the connected scanner.
Scanners actually generate large amounts of data during the scanning process. If you consider that an average A4 size of paper scanned at 600 dpi which is an uncompressed 24-bit image can be approximately one hundred megabytes of data, which has to be transferred and then consequently stored. Modern day scanners have no issue at all in generating this data volume, often in mere seconds. They are only held back by the physical interface that connects them to a computer. Below we list these connection types for you.
Parallel connections are the slowest type of transfer method and they use the parallel port of the computer. Their only conceivable benefit of a parallel connection is a financial one.
The general purpose interface bus (GPIB) is another type of connection and was only adopted by a very small number of manufacturers. It usually served a DOS/Windows environment.
The small computer system interface (SCSI) is typically only supported via a SCSI interface card and although some scanners with this connection method come supplied with their own dedicated card, any SCSI controller is a viable option. SCSI connections can transfer data at the highest speeds that both the device and the controller can support. SCSI connections have for the most part now been replaced by Firewire and USB.
Universal serial bus (USB) connected scanners are simple to use and can transfer data very quickly. They are also cheaper than the SCSI connected devices. Theoretically, USB 2.0 devices can transfer data at sixty megabytes per second.
Finally there is the Firewire scanner connection that is comparable to the USB 2.0 connections. Firewire speeds can vary from 25 to 800 MB/s but a particular device may not be able to support all of these speeds.