<P> USB flash drives use the USB mass storage device class standard, supported natively by modern operating systems such as Windows, Linux, macOS and other Unix - like systems, as well as many BIOS boot ROMs . USB drives with USB 2.0 support can store more data and transfer faster than much larger optical disc drives like CD - RW or DVD - RW drives and can be read by many other systems such as the Xbox One, PlayStation 4, DVD players, automobile entertainment systems, and in a number of handheld devices such as smartphones and tablet computers, though the electronically similar SD card is better suited for those devices . </P> <P> A flash drive consists of a small printed circuit board carrying the circuit elements and a USB connector, insulated electrically and protected inside a plastic, metal, or rubberized case, which can be carried in a pocket or on a key chain, for example . The USB connector may be protected by a removable cap or by retracting into the body of the drive, although it is not likely to be damaged if unprotected . Most flash drives use a standard type - A USB connection allowing connection with a port on a personal computer, but drives for other interfaces also exist . USB flash drives draw power from the computer via the USB connection . Some devices combine the functionality of a portable media player with USB flash storage; they require a battery only when used to play music on the go . </P> <P> M - Systems, an Israeli company later acquired by SanDisk, filed the first patent for a USB flash drive in April 1999, known as a DiskOnKey . Later in 1999, IBM filed an invention disclosure by one of its employees . Flash drives were sold initially by Trek 2000 International, a company in Singapore, which began selling in early 2000 . IBM became the first to sell USB flash drives in the United States in 2000 . The initial storage capacity of a flash drive was 8 MB . Another version of the flash drive, described as a pen drive, was also developed . Pua Khein - Seng from Malaysia has been credited with this invention . Patent disputes have arisen over the years, with competing companies including Singaporean company Trek Technology and Chinese company Netac Technology, attempting to enforce their patents . Trek won a suit in Singapore, but has lost battles in other countries . Netac Technology has brought lawsuits against PNY Technologies, Lenovo, aigo, Sony, and Taiwan's Acer and Tai Guen Enterprise Co . </P> <P> Flash drives are often measured by the rate at which they transfer data . Transfer rates may be given in megabytes per second (MB / s), megabits per second (Mbit / s), or in optical drive multipliers such as "180X" (180 times 150 KiB / s). File transfer rates vary considerably among devices . Second generation flash drives have claimed to read at up to 30 MB / s and write at about half that rate, which was about 20 times faster than the theoretical transfer rate achievable by the previous model, USB 1.1, which is limited to 12 Mbit / s (1.5 MB / s) with accounted overhead . The effective transfer rate of a device is significantly affected by the data access pattern . </P>

When did the first usb flash drive appear on the retail market