If throughput is important to you then you will need to look at the times for preview and full scan images - using a representative sample of the material you intend to digitise and, as the computer system can effect transfer rates, on an identical or similar system to the one you intend to use. This is another area where the performance of scanners has dramatically improved over the past few years. If you intend to use an automatic sheet feeder for batch processing this may have an adverse effect on scan times. Passes Less important these days as most scanners are now single pass. Early scanners, especially the budget ones, were often triple pass when colour scanning.
Most current scanners have CCD arrays with three rows of sensors.
The resolution at which to scan your documents should be determined at the outset of the project probably during the feasibility study . New PCs come with the USB interface built in and the Windows operating system has supported it since 1996. USB eliminates the need to install SCSI cards and the setting of unique ID numbers for SCSI peripherals. SCSI was also a fragile technology in that circuitry could be damaged when SCSI devices where switched on or off when the attached computer was running. USB facilitates 'Hot-Plugging' where a device such as a scanner can be connected and recognised by a USB fitted computer while the computer is switched on.