type of adapters as a conventional motherboard and power supply would use. The exterior of the caddy typically has two female sockets, used for data transfer and power. Variants of caddy: some larger caddies can support several devices at once and can feature either separate outputs to connect each device to a different computer, or a single output to connect both over the same data cable some caddies do not require an external power supply, and instead obtain power from the device to which they are connected some caddies have integrated fans with which to keep the drives within at a cool temperature caddies for all major standards exist, supporting for example ATA, SCSI and SATA drives and USB, SCSI and FireWire outputs Advantages: relatively high transfer speed; typically faster than other common portable media such as CDs, DVDs and USB flash drives, slower than drives connected using solely ATA, SCSI and SATA connectors storage; typically larger than CDs, DVDs and USB flash drives price-to-storage ratio; typically better than CDs, DVDs and USB flash drives Disadvantages: power; most variants require a supply, unlike CDs, DVDs and USB flash drives... size; typically larger than CDs, DVDs and USB flash drives Form factors Multiple drives: RAID-enabled enclosures and iSCSI enclosures commonly hold multiple drives. High-end and server-oriented chassis are often built around 3.5-in drives in hot-swappable drive caddies. "5.25-inch" drive: (5.75 in × 8 in × 1.63 in = 146.1 mm × 203 mm × 41.4 mm)Most desktop models of drives for optical 120-mm discs (DVD-ROM or CD-ROM drives, CD or DVD burners), are designed to be mounted into a so-called "5.25-inch slot", which obtained its nickname because this slot size was initially used by drives for floppy disks in the IBM PC AT. (The original "5.25-inch slot" in the IBM PC was with 3.25 in (82.6 mm) twice as high as the one commonly used today; in fact, the PC's drive size was called "5.25-inch full-height", and the size used in the PC AT and commonly used today is "5.25-inch half-height".) "3.5-inch" drive: (4 in × 5.75 in × 1 in = 101.6 mm × 146.05 mm × 25.4 mm) This smaller, disk-drive form factor was introduced with the Apple Macintosh series in 1984, and later adopted throughout the industry beginning widely with the IBM PS/2 series in 1987, which included drives of this size for 90-mm ("3.5-inch") floppy disks. This