I am new to DCL. I am trying to write a script which will get the device information and then make a judgement on that information:
The following is what I have:

$ disk_loop:
$ p1 = f$device("*","disk")
$ if p1 .eqs. "" then goto done ! EXIT ON NO DISKS
$!
$ if f$locate(f$getdvi(''p1',"device_type_name"),"RZ") .nes. ""
$ then
$ write sys$output "''p1' is a disk"
$ else
$ endif
$ goto disk_loop
$ done:
$ exit

I believe the lexcial I am using is wrong. If someone has any thoughts please advise, thanks.

You're almost there. Biggest problem is in the line with f$locate.
- f$locate() returns an integer of the position where it finds the specified substring, or the length of the string when the substring isn't found.
- f$getdvi needs only the symbol p1, without quotes. You use the quotes only when the symbol has to be translated in a string like "''p1'"
It is best to split the specified line in two lines like :
$ thisdev = f$getdvi(p1,"device_type_name")
$ if f$locate("RZ",thisdev) .ne. f$length(thisdev)
Note that I also changed .nes. in .ne. because you do a comparison of integers, not strings.

One other remark :
P1 - P8 are special symbols (input parameters). I wouldn't
use them for 'normal' symbols. So I would change the line
$ p1 = f$device("*","disk")
in something more meaningful like
$ mydisk = f$device("*","disk")