HDD

HDD stands for Hard Disk Drive, a conventional magnetic data-storage device. In Digital Cinema, the term commonly refers to a physical storage medium used to deliver and transport Digital Cinema Packages (DCPs). Large DCPs in particular have traditionally been supplied to cinemas, festivals and technical service providers on removable hard drives. A DCP stored on an HDD is not a single movie file. The drive carries the complete DCP structure, including picture and sound track files, CPLs, PKLs, the Asset Map and, where applicable, subtitle or other assets. The HDD itself is therefore only the storage and transport medium. A DCP can equally be transferred via network delivery, SFTP, satellite or other digital distribution methods. ISDCF documentation explicitly describes hard-disk transfer as one of the established methods of transporting DCPs between facilities. For physical DCP delivery, an arbitrary externally formatted hard drive is not necessarily sufficient. To ensure that a drive can be read reliably by Digital Cinema equipment from different manufacturers, industry recommendations exist for the partition layout and file system. The ISDCF publishes these recommendations under its documentation for distribution-device and hard-disk formats. Traditionally, DCP delivery drives have often used a Linux file system such as EXT2, and later also EXT3. This does not mean that the DCP itself requires Linux. The purpose is to provide a common file-system format that Digital Cinema servers from different manufacturers can read. Historical ISDCF recommendations specify a single Linux partition using EXT2 or EXT3. A particularly common form of physical DCP delivery is the CRU drive. In this system, a SATA hard drive is installed in a robust removable cartridge. Many professional DCP servers and Theatre Management Systems have compatible CRU bays, allowing the delivery drive to be inserted directly into the system. The widely deployed DX115 system was designed for this purpose and has long been an industry standard for physical DCP distribution. In normal cinema operation, the DCP is generally not played directly from the delivery HDD. Instead, the content is first ingested onto the local storage of the cinema server, Integrated Media Server or Theatre Management System. During ingest, the content is copied and identified by the cinema system before being prepared for playback. The HDD itself does not determine whether a DCP is Interop or SMPTE. A single drive can contain multiple DCPs and different DCP packaging types. In one ISDCF interoperability test, for example, SMPTE and Interop DCPs were distributed together on a standard EXT2-formatted CRU drive. Encrypted DCPs can also be transported on an HDD. The encryption belongs to the DCP and is independent of the physical storage medium. Playback additionally requires a valid KDM for the intended cinema server or media block and the appropriate validity period. In modern Digital Cinema workflows, conventional HDDs are increasingly complemented or replaced by SSDs and network-based delivery systems. HDDs, SSDs and other suitable storage devices can all be used for physical DCP delivery, provided that the storage device and its file system are compatible with the receiving Digital Cinema system. ISDCF recommendations therefore now address physical distribution devices more generally, including HDDs, SSDs and USB-based media. DCP distribution drives should also be handled carefully when connected to ordinary desktop computers. In particular, unsuitable third-party EXT file-system drivers on Windows or macOS may risk unintended changes or file-system corruption. ISDCF therefore recommends that DCP distribution media be connected primarily to DCP-aware systems such as cinema servers, SMSs or TMSs. Short definition: In Digital Cinema, an HDD is a hard disk used primarily as a physical transport medium for DCPs. DCP delivery drives are partitioned and formatted according to industry recommendations so that cinema servers and TMS systems can reliably recognize the medium and ingest the DCPs stored on it.