Those specs are usually in regards to scanners, and flatbed scanners in particular, especially when they give you two different numbers. On your 4800x1200, it means that the scanner has an optical resolution of 1200 pixels per inch, but the stepper motor, which is what moves the sensor underneath the glass, actually moves in smaller increments, or steps, in this case 4800 "steps" per inch. It's mostly theoretical marketing hype, as it makes little if any visible difference, but it sounds great. All things being equal, the 4800x1200 scan *should* be better, as it's lowest res is double that of the 600x600, but very often 600 ppi on one scanner is sharper than 1200 on another. There's only one way to find out.
