6.3.21 HDD technologies  There are four main methods of connecting HDDs and other peripheral devices to computers, USB (Universal Serial Bus), IEEE 1394 (Firewire), SCSI (Small Computer System Interface) and SATA/ATA (Serial Advanced Technology Attachment/AT Attachment). They each have particular advantages in certain situations. USB and Firewire are planned to be all-purpose buses that can be used to connect to personal computer a HDD as well as digital video camera or MP3 player. SCSI and SATA/ATA are mainly used to connect hard disk drives to a computer or disk storage system.  SCSI and its successor SAS (Serial Attached SCSI) interface allows faster writing and reading speeds, and facilitates access to larger numbers of drives than the SATA/ATA drives. SCSI disks can accept multiple commands at once on a SCSI bus and does not suffer from request queues like SATA/ATA. The SATA/ATA drives are comparatively cheaper. The read access speed is largely the same and in an audio context neither interface will limit the operation of the digital audio workstation (DAW) more than the other. The performance difference of SCSI/SAS and SATA drives can have meaning in heavily utilised centralised hard disk storage system.  Fibre Channel (FC) SCSI/SAS drives are mainly used in demanding use in enterprise or business systems while the cheaper SATA drives are more used in the personal market, but they are also increasingly used in enterprise and business systems to offer more cost-effective storage capacity e.g. in archival storage. In archival storage, the actual decision between (FC) SCSI/SAS and SATA technology is dependent on the actual load of the system. If a system is used to archive small or medium amounts of content that is not accessed intensively a SATA based solution might well be enough. The actual decision must be based on clearly identified demands and negotiations with one’s storage provider.  USB and Firewire connected disk can be used to transfer content from one environment to another, but since they are rather unreliable, difficult to monitor and easy to loose they should not be used for archiving even though their pricing may seem very attractive.  The interface is not a completely consistent indication of the reliability and performance of a given drive or storage system and the purchaser should be more aware of other operating and configuration parameters of a storage system. It seems to be the case that more reliable drives are associated with the FC SCSI/SAS interface. Nonetheless, HDDs are not in themselves permanently reliable, and all audio data should be backed up on suitable tape (see 6.3.5 Data Tape Performance). (For further discussion see Anderson, Dykes and Riedel 2003).  There is one emerging storage technology which may have a prominent position in the near future. Solid- state storage in form of flash memory is developing as a alternative to moving disks and has already become an alternative to a HDD in laptop PCs. Some storage manufacturers have also introduced flash drives in their low cost or midrange storage systems and are planning to introduce flash drives in their high end systems too. Even though flash storage still has some challenges in storage reliability to overcome it might become a viable solution to storage needs of archival community; its price per gigabyte is becoming competitive, it is more environmentally friendly due to lower demand for power, and it does not have moving parts, which could mean longer life time of storage units. A life time of ten years instead of five years for a storage unit could mean lower investment and management costs for an archivist since every other migration to the next storage technology could be skipped. In terms of read and write performance flash storage is already comparable with HDD technology.