I have a JVC Camcorder, Model Everio GZ-MG37US, which uses a 30 GB hard drive.
On the hard drive, in the SD_VIDEO folder is another folder, PRG001.
Inside that folder, in addition to the .mod file, is a PRG001.PGI file and a .MOI file.
What are they? 
Well, according to the site bellow, the .pgi file is a management file. More specifically,
“[0051] Next, the structure of management files (e.g. PRG001.PGI) in the user area is described. A management file shows the correspondence between the content files in the content folders and the Key&Rule Entry areas. Specifically, a management file in a content folder stores data specifying the local number of a Key&Rule Entry area that corresponds to the plurality of contents stored in the content folder, this being achieved by corresponding the number (i.e. 001, 002, and so on) of the content folder with the local number of the Key&Rule Entry area."
http://72.14.205.104/search?q=cache:k7lC20h_a9QJ:www.freepatentsonline.com/EP1428214.html+%22PRG001.PGI%22&hl=en&ct=clnk&cd=3&gl=us
How do i play or open this files???
These files generally dont have any video content, just some weird codes for the camcorder and also used for successful burning on cds and dvds. So you need not worry about opening them.
i need to open pgi video from my jvc .. is that pgi format means that i lost video !!!
cant open the MOI files on my camcorder !! D:
the MOI files are other vids, because i can see them when i plug in my camcorder into my tv but when i plug it into my computer it wont show the vids because they’ve turned into MOI files !! HELP please.
test
MOI files just carry information about the relative MOD file with the same name.
I.E. MOV001.MOI carries information for the video file MOV001.MOD.
If your worried about which files do or don’t contain your video, just have a look at the size of the file. You should be able to see that all the MOD files are much larger in size them any other type of file.
If your struggling to do anything with your MOD files (like editing) as mentioned above, rename the extension to MPG or if you wish to do a whole bunch of them you can use a free program called SDcopy.