Computers, Laptops & Tablets Accessories & Hardware 45 45 people found this article helpful Evaluating and Using Various SD Cards By Fred Zahradnik Freelance Contributor Former Lifewire writer Fred Zahradnik has a long history as a writer and is considered an expert on all things related to GPS products and software. our editorial process Fred Zahradnik Updated June 01, 2019 Tim Grist Photography / Getty Images Accessories & Hardware Cards Keyboards & Mice Monitors HDD & SSD Printers & Scanners Raspberry Pi Tweet Share Email Secure digital or SD cards are small 24 mm by 32 mm cards that hold rows of memory chips within pins. They plug into compatible SD slots on consumer electronics devices and hold flash memory that is retained even when the device is turned off. SD cards can hold additional memory ranging from 64 to 128 gigabytes, but your device may be limited to working with 32GB or 64GB cards. SD cards for GPS devices often come loaded with supplemental maps or charts to enhance map detail and supply supplemental travel information. SD cards can also be used for media storage and are often used with smartphones. How SD Cards Work SD cards require a dedicated port on your electronic device. Many computers are manufactured with these slots, but you can connect a reader to many devices that don't come equipped with one. The card’s pins match with and connect to the port. When you insert the card, your device effectively begins communicating with it through the card’s microcontroller. Your electronic device automatically scans your SD card and imports data from it, or you can manually move files, pictures, and apps to the card. Durability SD cards are remarkably tough. A card is not likely to break apart or suffer internal damage if you drop it because it’s a solid piece with no moving parts. Samsung claims that its microSD card can endure the crushing weight of 1.6 metric tons without suffering damage and that even an MRI scanner won’t delete the card’s data. SD cards are said to be impervious to water damage as well. MiniSD and MicroSD Cards In addition to the standard size SD card, you'll find two other sizes of SD cards on the market suitable for use with electronic devices: MiniSD cards and MicroSD cards. The MiniSD card is smaller than the standard SD cards. It measures just 21 mm by 20 mm. It is the least common of the three sizes of SD cards. It was originally designed for mobile phones, but with the invention of the microSD card, is lost market share. A microSD card performs the same functions as a full-size card or MiniSD, but it's much smaller — just 15 mm by 11 mm. It's designed for small handheld GPS devices, smartphones, and MP3 players. Digital cameras, recorders, and game systems usually require full-size SD cards. Your electronic device will likely only accommodate one of these three sizes, so you need to know the correct size before you purchase a card. If you want to use either a MiniSD or MicroSD card with a device that uses standard size SD cards, you can purchase an adapter that allows you to plug the smaller cards into the standard SD slot.