Query on large database much slower on HDD
There are two problems
PROBLEM #1 : MyISAM
MyISAM does not cache data (stored in the .MYD) which means data must be read for disk every time. Indexes may be cached (read once from .MYI), but not data.
See my old post in What are the main differences between InnoDB and MyISAM? under the MyISAM subheading
PROBLEM #2 : HDD vs SSD
An HDD must use spindles to move its read/write heads across a disk
An SSD is a random read/write device. It zeros in on blocks to disk faster than HDD.