When CD Recorders were first developed, creating a CD was a two step process. A physical or real image was created on the hard drive and then this data was streamed to the recorder. The physical image is a single file that is the exact same size as the final CD. As computers increased in speed, this two step process was shortened and the physical
image was never actually created, but was replaced by a virtual image. The `virtual' image is created in RAM, and the CD file layout is created `on-the-fly' as the host computer streams data out to the CD Recorder. Most software allows you to create a CD from either a physical or virtual image. While a physical image requires additional hard disk space (for the file), it is still a useful method. Physical images are necessary when the source data is on a remote device,
when the files are very small, or when recording at high speeds.