A Disk Image is a copy of the drive saved in file. Disk Image can be useful for backup/restore purposes or, even for the analysis by other utilities. Using Active@ UNERASER you can create Disk Image for the whole HDD (Hard Disk Drive) as well as for the particular logical drive.
Another way (available in Professional version only) is to run software with parameter -image, for example:
Created Disk Image is set of files: Drive_80h.hdd, Drive_80h.001, Drive_80h.002...
Each file (except the last one) has size 1GB. Reason for files separation is that MS-DOS does not support files having size more than 2GB. If you need disk image of the whole drive in one file - you can merge them later on manually.