PATCH_SD.COM Version 5.0 of Microsoft's SmartDrive disk cache utility, provided with MS-DOS 6.2, is capable of caching CD-ROM drives. The program is designed to work exclusively with MSCDEX CD-ROM driver. Corel's PATCH_SD.COM program can modify the SMARTDRV.EXE to recognize Corel CORELCDX as a valid CD-ROM driver and cache CD data. The SMARTDRV cache uses memory more efficiently than Corel CDXCACHE - the same block of memory will be used simultaneously for hard disk and CD disk caches. On the other hand, the CDXCACHE program has smaller overhead and operates faster then SMARTDRV. Also, the CORELCDX /UNLOAD option will not work with SmartDrive, as the cache program needs to be loaded after CorelCDX. The PATCH_SD.COM program is designed to modify version 5.0 of SMARTDRV.EXE, (45145 bytes in size only). If the binary image does not match, the patch will not be installed. The patching program scans memory to locate the active SmartDrive cache program and from there locates the original disk image of SMARTDRV.EXE. If the SmartDrive cache is not currently installed, the program will ask you to enter the full path and name of the disk file to patch. The original Microsoft SMARTDRV.EXE is saved in the same directory as SMARTDRV.MSC. In order for the patch to work, you need to reboot the system (to reinstall SMARTDRV.EXE). Also, for SmartDrive to recognize a CD device, the CorelCDX driver needs to be installed before SMARTDRV.EXE (e.g. by changing sequence of entries in AUTOEXEC.BAT).