USB flash drive (Universal Serial Bus)

Introduction:

                      A USB flash drive is a data storage device that includes flash memory with an integrated Universal Serial Bus (USB) interface. USB flash drives are typically removable and rewritable, and physically much smaller than a floppy disk. Most weigh less than 30 g. As of September 2011 drives of up to 256 gigabytes (GB) are available. Storage capacities as large as 2 terabytes are planned, with steady improvements in size and price per capacity expected. Some allow up to 100,000 write/erase cycles, depending on the exact type of memory chip used, and a 10 year shelf storage time.

Parts:

1. USB Standard, Male A-plug
2. USB mass controller device
3. Test points
4. Flash Memory Chip
5. Crystal oscillator
6. LED (Optional)
7. Write-protect switch (Optional)
8. Space for second memory chip

USB Connector

                      The USB connector is the small, silver extension that extends from the main USB device. The connector is what inserts into the USB port of the computer. Because this part of the USB flash drive is easily damaged, newer USB flash drives come with a switch that pulls the connector into the main compartment. This avoids the problem of the connector melting, accumulating dust or being crushed. The USB connector inserts into any USB port in a computer, or the user can insert it into a hub for devices on a machine.

Memory Chip

                      The flash memory chip, a black chip placed on the main circuit board of the USB drive, is what stores the information. This chip is protected by an outer case. These cases are sometimes clear, so the user can see the flash memory chip on the USB drive's circuit board. The flash memory chip contains different amounts of memory, depending on the device purchased. Flash drives started with a capacity of a few megabytes, but they continue to increase in capacity. Flash drives can hold gigabytes of information of flash memory chips.

LED and Crystal Oscillator

                      USB flash drives contain light-emitting diodes (LEDs). LEDs are lighted components that indicate processing or connection for the user. A green LED is used to mean "Ready." It indicates that the USB drive is connected and ready to save information. Some flash drives have a red LED light to indicate that an issue exists with the connection. A crystal oscillator is a small component on the flash drive's circuit board that sends a frequency signal. These oscillators are used in watches and other devices that keep time. Oscillators are used to control the output of the flash drive.

Advantages / Disadvantages:

Advantages

                      Compared to hard drives, flash drives use little power, have no fragile moving parts, and for most capacities are small and light. Data stored on flash drives is impervious to mechanical shock, magnetic fields, scratches and dust. These properties make them suitable for transporting data from place to place and keeping the data readily at hand.

Flash drives also store data densely compared to many removable media. In mid-2009, 256 GB drives became available, with the ability to hold many times more data than a DVD or even a Blu-ray disc.

Disadvantages

                      Like all flash memory devices, flash drives can sustain only a limited number of write and erase cycles before the drive fails. This should be a consideration when using a flash drive to run application software or an operating system. To address this, as well as space limitations, some developers have produced special versions of operating systems or commonplace applications (such as Mozilla Firefox) designed to run from flash drives. These are typically optimized for size and configured to place temporary or intermediate files in the computer's main RAM rather than store them temporarily on the flash drive.