Olly or IDA are the way to go. If you want fairly strong analysis, use IDA, but it's not good for debugging and making patches like OllyDbg is. IDA may be too heavy for some purposes, and handles way more processor architectures than you'll ever need d: Also, there is hypothetically MS-DOS source code which may be available via certain unspeakable means if you want to look at the source for some of the CL tools like fdisk, copy, etc.. But, I'm not suggesting that you download it or anything, at all, ever.
gniripsni ewa si rehte eht morf cisum siht