Hard Disk Direct provides the latest delivery information as provided to them by their suppliers. Most items will show an ETA (Estimated Time of Arrival) for each product that is back-ordered. However, some of their suppliers do not offer ETAs and hence they bring their customers the best delivery estimates in those certain conditions.
In addition to this, you can keep track of the out-of-stock items from the list before actually purchasing the product. You can also request to receive email notifications when items are back in stock so that you may purchase them at your convenience.