CD-i programs are developed to run off of a compact disc on an optical disc drive. You cannot properly play back and test your programs from the hard disk of the computer you are using to develop the programs for your CD-i application. The data delivery system and CD interface, the data rate, and the (slow) access time of the CD drive need to be taken into account. Thus, it is necessary to emulate play of the application from optical disc. An emulator is an intelligent computer-peripheral device with a high-capacity hard disk. During CD-i development, a disc image is built onto the hard disk of the emulator and the disc image can be played as if it were on an optical disc. The emulator removes the need to burn new CD-i discs at various stages of development process to use for functional testing, and can, thus, save a lot of time and money.