What is the difference betw SFC /scannow and ChkDSK/f?

I don't know if this should be posted under general discussion, but I began having problems, even a BSOD-twice, on my 150gig Raptor.
I cloned my 74gig Raptor to the 150, and everything seemed fine for a while. I don't recall what prompted the scan, but I ran sfc /scannow on the 74gig Raptor. I later got a message that said my installation on the 150gig was corrupted. This motherboard, an ASUS A8Ne, has the ability to interrupt the normal boot/post sequence by pressing F8. My 150gig Raptor would alternatively appear and disappear from the boot menu.
I tried running sfc on the 150gig and could not complete it. I then tried chkdsk, and it too failed, but it prompted me to run chkdsk/F. I did, and after reboot, it found a large number of corrupted, orphaned, and other files. It flew by on the screen too quickly for me to read. I suspect that even if I could read it, I wouldn't comprehend what it was. Anyway, after chkdsk/f the 150 Raptor appears to be running fine-so far, anyway. I did open the case and tried reseating every connector I could get my hands on. For the time being, I'm on needles and pins.

 

Chkdsk /f checks your hard drive for errors and fixes them.
Sfc /scannow checks your system files and replaces them if necessary.

 

SFC checks your system files and replaces certain ones if they are corrupt or missing by copying correct versions from either your install CD or some more current source, as is determined by the system version. It will not regress any file to an earlier version and therefore is not a dangerous tool under any circumstances.

Chkdsk /f checks your hard drive to verify that all files referenced by the files allocation table are intact and located where they are supposed to be. It cannot "Fix" any files that are corrupt or missing but can truncate any references to what is determined to be invalid file information. It saves such cropped file information to the root of your primary drive into text files (C:/FOUND.00, C:/FOUND.01, etc.) and allows you to review it to assess any value it may have. Most people have no idea of what to do with such files. The problem is, sometimes this is necessary information for the system to boot properly or perhaps information that is critical to your personal files. That means that under certain circumstances, chkdsk /f and chkdsk /r can render your drive unbootable or cause you to lose valuable personal files. For that reason, it is a good idea to have current backups before granting chkdkk /f or chkdsk /r to run. I recommend running it without any switches first to see what it finds. I don't mean to imply that it isn't a useful tool but just mean to warn the wise that things can go wrong, as my past experience has shown (twice).