Q. Describe the Size and Speed of Scanners?
Before actual scanning, a quick, low resolution scan known as pre-scan is made to preview the image and select scanning area. After this only does actual scan take place. Early colour scanners used to take 3 passes for a scan - one pass for every colour. Now Scanners use only one pass and use photodetectors to detect colours. Then, they operate as fast as monochrome Scanners. Though other issues are also included.
High resolution scans of large images outcomes in large file sizes. These can slow down processing because they require Hard Disk I/O for virtual memory. Hence forward for large scans it is essential to have higher RAM in your PC.