Why are some scanners faster than others - what are the different scanning methods?

On my computer, Avast, full custom scan with PUP on and full rootkit etc., takes about 5 minutes, Malwarebytes full scan takes about 7 minutes. I tried F-Secure free scanner download and it took about 3-5 minutes.

But Trend Micro HouseCall takes about 45-60 minutes, and I assume there are some others that would take a long time also.

What different methods do antivirus software use that would make for such larger differences?

 

For your case it's definetly because of the cloud lookups. Trend micro checks file per file in the cloud which increase the scanning time.

Avast! gets its streaming updates so nothing is checked in the cloud during a scan.

 

Some use the traditional methods, some others not.

ie. see how works the super fast HitmanPro:

https://www.wilderssecurity.com/showpost.php?p=1787459&postcount=2665

 

Different vendor = different engine (mostly unless licensed), better coded, whitelists, and then heuristics, and advanced heuristics, behavior checking, reputation checking etc etc...it is different configurations in different engines. So it's almost impossible to say exactly why engine A is faster or slower than engine B or vice versa IMO. PC hardware may also play a role.

And usually the second scan is faster, sometimes a lot faster than the first scan.