Secondary Storage Devices

Secondary Storage Device Any type of device that is external to the motherboard and can store data which can be processed by a computer. A secondary storage device's information can be easily edited and stays on even when there is no power source. Also, secondary storage devices are not directly accessible by the CPU. The 4 main secondary storage devices are: devices are: - Hard Drives - USB Drives - CDs/DVDs - SD/miniSD cards

Hard Drive (Disc) The hard drive is the most important secondary storage device The hard drive is the most important secondary storage device It's is the only external storage device that is directly inside the computer and cannot be taken out conveniently It's is the only external storage device that is directly inside the computer and cannot be taken out conveniently The computer stores digitally encoded data on rapidly spinning platters with magnetic surfaces The computer stores digitally encoded data on rapidly spinning platters with magnetic surfaces The seven main parts of a hard drive today are: the enclosure, the spindle, the spindle motor, the platter, the actuator arm, the interface and the logic board The seven main parts of a hard drive today are: the enclosure, the spindle, the spindle motor, the platter, the actuator arm, the interface and the logic board

Hard Drive Components Enclosure: The enclosure serves as the case for the internal components. for the internal components. Logic Board: The circuit board that contains the “instruction manual” for a computer accessing the hard drive. It “translates” the computer’s requests to manage data into commands that a hard drive can carry out. commands that a hard drive can carry out. The logic board also controls all internal functions.

Hard Drive Components Spindle Motor: The spindle motor is what rotates the platters; it is precisely controlled by rotates the platters; it is precisely controlled by the logic board. In an average computer hard drive, the spindle motor spins the platters at 7,200 or 10,000 RPM (revolutions per minute). The motor is attached to the spindle, which centers and fixes down the platters so that they can tolerate the spindle motor’s rapid rotations.

Hard Drive Components Platter: A thin glass or aluminium disc coated with an ultra-thin layer of cobalt alloy, which is naturally magnetic. Data is organized into outward rings from the spindle. Actuator Arm: Controlled by two very strong magnets, the actuator arm writes data onto the platter by aligning the magnetization of the cobalt alloy surface into patterns which the logic board can recognize. It is also able to read information by deciphering magnetization patterns on the platter.

Operation How It Works (Basics): 1. Information is requested from the hard drive 2. The Operating System tells the logic board that it wants a file 3. The logic board commands the spindle motor to spin the platter(s) 4. The actuator arm is moved into position 5. The logic board uses the actuator arm to decipher information from the magnetic patterns 6. The information is streamed through the interface into the computer’s RAM

Flash Memory A type of memory which does not need a power source to retain its contents. 1) As electrons flow through the flash memory device, the device physically traps electrons between gates 2) Trapped electrons between two gates are identified as a “one” 3) The electrons are kept between the gates indefinitely 4) Data is erased by releasing electrons from the gates; the cleared space between the gates is then identified as a “zero”

A USB (universal serial bus) is a device that can be used to transfer information between computers. They can be plugged into standard USB ports that are found on most modern computers. A typical USB mass storage device  USB Mass Storage Device

Information about USB Mass Storage Devices USB storage devices use flash memory, which is a common type of EEPROM memory (electrically erasable programmable read only memory), to store information Once plugged in to a USB port, the device can be installed quickly without any tools (provided the computer supports the device) Once plugged in to a USB port, the device can be installed quickly without any tools (provided the computer supports the device) USB 2.0 has a maximum transfer rate of 480MB/s USB 2.0 has a maximum transfer rate of 480MB/s USB devices can be unplugged or plugged in at any time USB devices can be unplugged or plugged in at any time A standard USB port 

Compatibility USB mass storage devices are compatible with any computer that has a USB port USB mass storage devices are compatible with any computer that has a USB port Virtually every computer made today has 1 or more USB ports Virtually every computer made today has 1 or more USB ports Up to 127 USB devices can be used simultaneously Up to 127 USB devices can be used simultaneously USB devices may have special cables to make them compatible with other types of slots, and vice-versa USB devices may have special cables to make them compatible with other types of slots, and vice-versa Examples of USB conversion cables 

SD Card The Secure Digital (SD) card is a form of flash memory used in modern digital devices to store data The Secure Digital (SD) card is a form of flash memory used in modern digital devices to store data Unlike the hard drive, the SD card has no moving parts and therefore has more resistance to shock damage Unlike the hard drive, the SD card has no moving parts and therefore has more resistance to shock damage SD cards have a locking switch which prevents data from being read, written, and deleted from the storage card SD cards have a locking switch which prevents data from being read, written, and deleted from the storage card The standard dimensions of an SD card are 32 mm long, 24 mm wide, and 2.1 mm thick The standard dimensions of an SD card are 32 mm long, 24 mm wide, and 2.1 mm thick

A size comparison of the MiniSD card to an index finger. MiniSD Card The MiniSD card is essentially a smaller version of the SD card The MiniSD card is essentially a smaller version of the SD card Its compactness is one of the reasons why it is used in many portable electronic devices Its compactness is one of the reasons why it is used in many portable electronic devices The standard dimensions of a MiniSD card are 21.5 mm x 20 mm x 1.4 mm The standard dimensions of a MiniSD card are 21.5 mm x 20 mm x 1.4 mm

Other Flash Memory Devices - CompactFlash Cards - Memory Sticks (Sony) - MultiMediaCards - SmartMedia Cards - xD-Picture Cards There are many other flash memory devices. These include:

Optical Discs Optical discs are flat circular discs that store readable information, typically in the form of tiny bumps layered in a track on one side of the disc. Since the majority of optical disks are not rewritable, they are commonly used as permanent storage for things like media files. Optical discs 

Information about Optical Discs There are 3 types of discs: ROM (read only memory), R (Recordable) and RW (ReWritable) There are 3 types of discs: ROM (read only memory), R (Recordable) and RW (ReWritable) A computer reads optical discs by using a laser beam to scan a tiny track on the disc A computer reads optical discs by using a laser beam to scan a tiny track on the disc Every time the beam is reflected off the disc, a sensor detects it and the computer reads a “one” Every time the beam is reflected off the disc, a sensor detects it and the computer reads a “one” ROM discs use bumps to reflect the laser beam; these discs are used for commercial purposes ROM discs use bumps to reflect the laser beam; these discs are used for commercial purposes Bumps on a ROM disc 

Recordable discs use dye to reflect the laser beam The optical properties of a recordable disc’s dye are permanently changed by the heat of the writing laser, resulting in varying reflectivity The optical properties of a recordable disc’s dye are permanently changed by the heat of the writing laser, resulting in varying reflectivity The computer uses two lasers for a recordable disc; a strong one for writing on the disc and a weaker one for reading the disc so that the disc’s dye is not further altered Information about Optical Discs

A rewritable disc reflects the reading laser with its phase-change alloy recording layer, which consists of silver, indium, antimony and tellurium The phase-change alloy material can switch between amorphous and crystalline states; therefore, it is rewritable Any area of a RW disc with information on it would be in a crystalline state; in order for the information to be deleted, the area would have to be changed into an amorphous state A computer must have an infra-red laser beam to be able to read and write on a RW disc; the laser uses heat to change between the alloy’s states (400°C for erasing information) Information about Optical Discs

Compatibility An optical disc drive is present in almost every computer manufactured nowadays An optical disc drive is present in almost every computer manufactured nowadays Due to having different formats, DVDs are not always compatible where CDs are Due to having different formats, DVDs are not always compatible where CDs are CDs have different sizes but most of them are compatible on regular computers CDs have different sizes but most of them are compatible on regular computers BluRay discs require a higher density laser, so they are not compatible with everything BluRay discs require a higher density laser, so they are not compatible with everything A BluRay disk

The Importance of Secondary Storage Secondary storage devices are important to us because we need some form of storage that can keep data indefinitely. Without secondary storage, you would lose all of your data every time you powered down your computer. External storage devices also provide us with portable forms of non-volatile memory outside of the computer, unlike primary storage.

References By Alex Patti and Robin Weng