These are chunk files. The original file was split into 645 MB chunks so they fit on a CD. They don't make any sense alone. You have to concatenate them in correct order (by ascending extension) to get the original file.
In the *NIX world the splitting could be performed using the
split tool (
split -b 645M original.file) and original file could be recreated with
cat and output redirection (
cat original.file.* > original.file).
There's not much one can say about the original file just with the knowledge that it was split, but your folder looks like you're dealing with some kind of disk images created using Linux-based tool (
sda = first disk supported with the
sda2 are its first two partitions).
What I think 7-Zip is doing here is it recognizes your chunk files and tries to interpret them concatenated as a whole. Apparently the format is supported (or partially supported) and indeed there's a disk image inside containing a NTFS filesystem.
The "HDD_Look" file has quite a distinctive name, so I've googled it and found this forum thread. Apparently it's a disk image created by PING software, which is an obscure Linux-based disk imaging tool. It's probably using some specialized imaging software under the hood, like
ntfsclone or possibly simply
dd. Your file are slightly over 8 GB total and
dd would produce an exact byte-for-byte copy of the partition, so I'd expect the image to either be significantly larger or be a multiple of 1 GB +/- 1 MB, so I'd rather guess it's one of the former ones. The
file utility on Linux may be able to tell you more.