320GB 5400RPM Hard Disk Drive with Hard Drive Heater for Toughbook 53 MK1 Genuine Panasonic Replacement Hard Drive with Caddy Case CF-K53HD3213.

The hard drive heater allows the hard drive to heat up much faster making it able to be used in harsher, colder environments.

This hard drive comes already built into the caddy case made by Panasonic.  This allows you to simply remove your old hard drive and replace it with this hard drive.