I am looking at buying a chip holder for a chip that comes in the form of DIP28S according to different datasheets on it. However when I searched for DIP28S chip holders I could only find SOP28 chip holders, and the measurements of them would allow the DIP28S chip to fit in those chip holders. So my assumption would be that DIP28S is the same or very similar package form to SOP28. Am I correct?
DIP28S could be a "shrink DIP" through-hole package, that is basically a standard DIP x 0.7.
It used to be quite popular in the Asian market (eg. Fujitsu).
Also "DIP28S" has also been used to refer to the "skinny" 300-mil wide 28-pin DIP package to distinguish it from the 600-mil wide package.
In no way is it the same as an SOP-28 SMT package.
DIP28 is usually 600 mils wide, with a 300 mil width also very common; the "S" in this package name refers to the fact that it is 400 mils wide as per the mechanical drawing. You will need to find a socket that fits appropriately, rather than the normal 300 mil or 600 mil sockets used for DIP28.