What is the difference between a pin less and pin processor?

A pin processor have the pins at its bottom which merges in to the motherboard!
A pinless processor has no pins.pinless processor has a flat bottom with around an extra 297 connections to the motherboard. You cant fit one to a pinned socket. vote me if it is helpful

Differentiate between pinless and pin processor?

There are many reasons to why Intel moved from a pinned processor package, to pinless. The skeptics will say that Intel wanted to stem the flow of RMA's from processors with broken pins, but if you do a little digging, the real reasons are somewhat more complicated. The introduction of Socket 775 addressed a variety of issues with Socket 478; like excessive pressure from heatsinks which flexed the motherboard, not enough power-related pins to deal with high power consumption of emerging cores, and a few other points slightly more technical in nature.

If Intel had decided to introduce a higher pin density, it would have had to use a substantially larger substrate, which would have taken up more real estate on an already space deprived motherboard. Furthermore, if you divide the number of pins by the area of the processor you'll find that Socket 775 chips are among the most dense ever. A 775-pinned solution would have posed another problem; packing all those pins into the same small space would have meant even more fragile pins than used with the socket 478 design.

On the power front, next generation processors are drawing much more electricity and die shrinks aren't helping the situation as they once could. So the question arrises of how to feed future generation processors with the power requirements of yesterday's CPU socket architecture? According to Intel, Socket 478 Pentium 4's allocate 85 pins for power, 180 for ground. This is intended to power single core processors that chew up around 100W of power. Socket 775 on the other hand has a total of 523 power related contacts, 250 for power, 273 for ground! More contacts means more stable power for the processor, so you can bet that this form factor was designed with future generations in mind. If the roadmaps continue unchanged, socket 775 should be the defacto Intel desktop standard for the next two years.

One point not to be missed in all of this is that the socket 775 retention mechanism is a precision piece of engineering, and proper installation and care is important. To help alleviate potentially problems, MSI have included a small plastic installation tool to make inserting the socket 777 processor a little easier, and foolproof. It's a handy tool for people who avoid instructions manuals.