SD card
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The SD card is a proprietary, non-volatile, flash memory card format developed by the SD Association. They come in three physical forms: the full-size SD, the smaller miniSD, and the smallest, microSD
This microSDHC card holds 8 billion bytes. Beneath it is a section of a magnetic-core memory (used until the 1970s) that holds eight bytes using 64 cores. The card covers approximately 20 bits (2+1⁄2 bytes).
Back side of a microSD card, showing its eight electrical contacts
Back side of a UHS-II microSD card, showing the additional row of contacts
Front and back of an SD Express card
MultiMediaCard
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MultiMediaCard is a memory card standard used for solid-state storage, originally introduced in 1997 by SanDisk, Siemens, and Nokia. Designed as a compact, low-pin-count, postage‑stamp‑sized card alte
SD card
…August 1999 as Secure Digital by SanDisk, Panasonic (then known as Matsushita), and Kioxia (then part of Toshiba). It was designed as a successor to the MultiMediaCard (MMC) format, introducing several enhancements including a digital rights management (DRM) feature, a more durable physical casing, and a mechanical…
Undersides of an MMC (left) and SD card (right) showing the differences between the two formats
Top of four types of MMC cards (clockwise from left): MMC, RS-MMC, MMCplus, MMCmobile, metal extender
Bottom of the same four cards