Sorry yes the HD stands for Hard drive storage which is used for live pause and record other channels and also allows you to view any channel that you have not recorded up to half hour before you turned your telly on, in other words if the satlite receiver is in the normal ON mode (not the standby mode) and you had it on say the Doccumentary Channel, then as you came home from outside and turned your telly on and saw an intersting Doccumentary programme and you wished you had seen it from the begining, but luckily you can if you had preselected that rewind feature from the menue when you first bought it, so you could rewind back up to 1/2 hr before the current showing , so this measn the HD is always busy running 24hrs, and this packs them up in less than a year, mine did, so i got a replacement one which now does not do the 1/2hr rewind so when you turn it on, the HD is not running, but it would run if you were recording or watching previously recored programme.
My advice is do not select 1/2 rewind setting otherwise in less than a year you will need a new HD.