Here is a quick pin-out list for 3.5" (PC) and 2.5" (Laptop) hard drives.

A regular full size hard drive has 40 pins or 39 if the key is blank.

A laptop hard drive has 44 pins... plus four more pins for setting the master / slave status... giving 48 pins with one, (number 20), blank as a key.

If you lay a 2.5" laptop hard drive down so that the center KEY pin (number 20) is on the bottom, then here is the configuration:

First two pins at the far right are called A & B. A is on top row. B is on lower row. Next two are C and D. These four pins allow you to install jumper pins so the computer knows whether the drive is master or slave.

If one of these is broken off, AND if the manufacturer uses those pins to designate Master and slave, then you could be in trouble. However, most leave them blank for master so if one is broken off, it will make no difference unless you have two drives installed... such as when you are copying data from one laptop drive to another... If you cannot put jumpers on the AB or CD pins when using two drives, your laptop will not select either drive. The jumper pins are followed by a blank space.

The next 44 pins and spaces are called the "standard 44 way mini IDE Hard Drive configuration pins" by most computer techies.

Again from the right, after a, b, c, d, space (top row as odd numbers and bottom row as even):

1. Reset Pin
2. Ground
3. DD7
4. DD8
5. DD6
6. DD9
7. DD5
8. DD10
9. DD4
10. DD11
11. DD3
12. DD12
13. DD2
14. DD13
15. DD1
16. DD14
17. DD0
18. DD15
19. Ground
20. Key, most always blank, and your cable has no socket for this space.
21. DMARQ
22. Ground
23. DI0W
24. Ground
25. DI0R
26. Ground
27. I0RDY
28. PSYNC:CSEL
29. DMACK
30. Ground
31. INTRQ
32. IOCS16
33. DA1
34. PDIAG
35. DA0
36. DA2
37. CS0
38. CS1
39. DASP
40. Ground


The above 40 pins are the same pin out as for a normal desktop 3.5" IDE/EIDE hard drive. But a laptop has four more pins as follows:

41. +5V (Logic)
42. +5V (Motor)
43. Ground
44. Type - (0-ATA)

Although these pin-outs are a worldwide standard different manufacturers will use their own version of pin-outs for the master / slave pins, please be sure to check with them if you are un-sure.