Explanation:

A laptop is specifically designed to be portable and lightweight, making it ideal for travelers and mobile users. It integrates all essential components, including the display, keyboard, and pointing device, into a single, compact unit that can be easily carried. Option (a) Super computer is a large, powerful, and non-portable machine. Option (c) Mini computer is a mid-range computer, larger than a microcomputer and not typically designed for easy portability. Option (d) File servers are dedicated computers that store and manage data for other computers on a network, and are generally not portable. Thus, a Laptop ($ \text{b} $) perfectly fits the description.