An external hard disk drive is basically a type of hard disk drive that can be connected to a computer either by a USB cable or other means. Modern entries into the market consist of standard SATA, IDE, or SCSI hard drives in portable disk enclosures with USB, eSATAp, eSATA, SCSI, and IEEE 1394 Firewire client interfaces to connect to the host computer. The first commercial hard disks were large and cumbersome, were not stored within the computer itself, and therefore fit within the definition of an external hard disk. The hard disk platters were stored within protective covers or memory units, which sat outside. These hard disks soon evolved to be compact enough that the disks were able to be mounted into bays inside a computer. Early Apple Macintosh computers did not have easily accessible hard drive bays or, in the case of the Mac Plus, any hard drive bay at all, so on those models, external SCSI disks such as the Apple ProFile were the only reasonable option. Early external drives were not as compact or portable as their modern descendents. Right now, western digital external hard drive is probably one of the best, if not the best, brand that we have in the market today.