Information Technology Reference
In-Depth Information
Removable Media and Devices
A device can have removable media, and an entire device can be removable
from the computer that communicates with the device.
Removable Media
In a drive with removable media, users can easily insert and remove media in
the drive. CD and DVD drives have removable media because you can easily
swap discs. A memory-card reader with a card slot has removable media.
Hard drives and flash drives have non-removable media because you can't
easily remove the hard disk from its drive or the flash memory from its cir-
cuit board. A device reports whether it has removable media in the response
to a SCSI INQUIRY command. Some flash drives with non-removable
media report that they have removable media. Chapter 6 has more about the
INQUIRY command.
Removable Devices
An entire storage device can also be removable or non-removable from the
computer that accesses the drive. USB drives are removable. An internal
drive is considered non-removable because removing the drive requires more
work than detaching a cable.
Managing Removal
A user can detach a USB device or remove a flash-memory card at any time.
If a device or card is removed while the host is writing to the media, the
device and host should detect the removal and handle it as gracefully as pos-
sible.
Hardware Interfaces
A storage device can support one or more interfaces to its storage media. In
most cases, the device's CPU doesn't access the media directly. Instead, the
CPU communicates with an intelligent controller embedded in a drive or
flash-memory card. In devices that support USB, the CPU also interfaces to
a USB device controller.
Search WWH ::
Custom Search