Inside every Intellivision is 4K of ROM containing the Exec software. It provides two benefits: reusable code that can effectively make a 4K cartridge an 8K game, and a software framework for new programmers to develop games more easily and quickly. It also allows other programmers to more easily review and continue another's project. Under the supervision of David Rolfe (APh) and graphics supplied by Mattel artist Dave James, APh was able to quickly create the Intellivision launch title library using mostly summer students. The drawback is that to be flexible and handle many different types of games the Exec runs less efficiently than a dedicated program. Intellivision games that leverage the Exec run at a 20 Hz frame rate instead of the 60 Hz frame rate for which the Intellivision was designed. Using the Exec framework is optional, but almost all Intellivision games released by Mattel Electronics used it, and thus run at 20 Hz. The limited ROM space in the early years of Intellivision game releases also meant there was no room for computer artificial intelligence and many early games required two players.