Loading screens let the player know that their device is still working as well as sometimes providing alternate entertainment to tide them over while data loads. Loading screens became more prevalent as consoles switched from chip-based storage such as cartridges to optical solutions such as CD-ROM. However, this is not to say that load times began with CD-ROMS; many early PC games, in addition to some cartridge based games (Out of this World, Mickey Mania), had notable load times. While the capacity and price of optical media is much less expensive than chip-based storage, optical media suffers from much slower read speeds, requiring a break to load resources to RAM so that gameplay is not interrupted at a critical moment. Increasing resource size (games nowadays are typically several gigabytes) compared to device speed is also a factor, as the maximum attainable transfer rates with mechanical storage such as optical drives and hard disks become a limiting factor.
Because loading screens are an interruption, an attempt is made to make them either as entertaining or seamless as possible. In Call of Duty 4, single-player loading screens run video to explain the situation that players are about to enter into, turning the loading screen into a supplement rather than a barrier to gameplay. Others may use minigames during loading screens, although Namco maintains a US patent (#5,718,632) for this and therefore is typically unseen from any other company.