C as D , or vice versa. Hit the Enter key after naming the file. A box will pop up asking about compression . I always use Fast . If you re hurting for disk space, select High , which applies more aggressive compression.
More compression makes smaller images, but take longer to create.
Some people see higher compression as a bad thing. But most agree that less compression is safer than more. This is it, hoss. Double check both source and destination selections. Don t continue if you have any questions, or if something doesn't look right.