Ihave a DSR4639 are they still avail or is the4921 the replacement model
Yes, the Altech 4639 boxes were discontinued 3-4 years ago and have been replaced by the Altech 4921 model.
What are the dimensions of the vast decoder 4921 with the inbuilt 500 gig hard drive.
The 4921 500gig are 225mm wide, 42mm high and 135mm deep. They are the smallest VAST boxes available.