MD5 takes a variable length message and creates a fixed length output of 128 bits digest
- Used to verify the integrity of a downloadable file.

SHA-1 also takes a variable length message and creates a fixed length 160 bit digest
- Used more widely (TLS, SSL, PGP, SSH, S/MIME & IPSEC)

SHA-0 was weak and not adopted.
SHA-2 is significantly different from SHA-1
NSA designed SHA-2 has a set of 4 hash with digests of 224, 256, 384 and 512.

Page 2-10 talks about it but not as in depth.