The ASPI Layer
In the early days of CD-ROM, every manufacturer had his own interface and connections to the host. Standard interfaces, ASPI and CAM (which will operate ASPI devices and is functionally equivalent for Windows platforms) were devised and manufacturers of SCSI devices either conformed or wandered out of the market. The situation with IDE devices was similar, but the standard that was developed for them (ATAPI) made them look to the system like SCSI and allowed them to work through ASPI. For that reason, your computer's IDE adapter and devices may show up under the SCSI controls.
The ASPI layer is a collection of programs to realize the ASPI interface. Those components work together and must be consistent and complete to avoid problems in communicating and interpreting commands. Some vendors package a subset of the layer with their products - scanners are notorious for this.Often, they will grab an old file (one that's good enough for their needs) and package that with their own software - but with the then-current date. It will then install even though a later version is on your system and it will not be removed readily, again because the date is misleading. (Okay, it's a lie!)
Note that there is an approach to interfacing the components via miniport drivers which does not require the ASPI layer; there is none in Windows 2000, for example. In general, CD-R gets along fine without an ASPI layer if the code is written appropriately to use the "miniport driver". However, code which is not fully compliant may use an ASPI layer instead. That can work - if the layer is complete and consistent. Many support programs do rely on the ASPI layer, so one is needed for them even if not for programs such as Easy CD Creator 4.02 and above.