FastCopy does not use the operating system's cache for copying, so you can specify the amount of memory to use for the “Buffer." The default is 32 MB, but if you need to copy large files and have commodious memory installed, you can increase this.
The slider right below the buffer setting allows you to specify the speed control from “Suspend," to a percentage, to Auto Slow, which makes it adjust speed based on other activity on the PC such as mouse movement or a change in the active window, and, of course, Full Speed ahead.
“Nonstop" means continue despite any read/write errors. “Verify" means verify the destination file after writing. “Estimate" means give an estimation of when the operation will finish before starting the copy.
“ACL" means copy the Access Control List attributes of the files. This would be normal for Vista’s file system, and you should select it, but if you were copying to FAT, you may want to turn this off. Likewise, “AltStream," or alternate stream is a feature of Vista’s NTFS. Alternate streams are used to contain things like thumbnails for an image or formatting data for a document. Alternate streams are fine to include when writing to NTFS volumes, but Vista will ignore them when writing to a flash drive, CD-R, or FAT file system drive. Thus it‘s safe to select this in Vista.