An external hard disk drive is a type of hard disk drive which is connected to a computer 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, 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.