Computers are not just purely electrical devices.They also have moving components in them. These moving components take time to find themselves in the proper place to retrieve data. Some such components include DVD Drives, Hard Drives, CD drives,Floppy drives, and Zip Drives. There are varying cabling formats to each of these components including SCSI SATA IDE or a Floppy Ribbon some are even external like USB or IEEE but the point is that these devices require some time to retrieve data more so then say a USB flash drive or an SD micro Chip.
