This table provides summary of comparison of various flashmemory cards, as of 2025[update]. Of memory cards (i.e. intended as such, to use e.g. internally), SD cards allow for largest capacity by far (with SDUC variant up to 4 TB max. currently available, and the spec allocs up to 128 max.), though the much bulkier CFexpress cards can also match the capacity. The relatively large (external) USB flash drives allow for more capacity, and are available with 8 TB.
Common information
Unless otherwise indicated, all images are to scale.
Subcompact (15 mm × 11 mm × 1 mm), DRM, up to 2 GB.[5] (2 GB cards use larger block sizes and may not be compatible with some host devices. See Article)
Same build as microSD/microSDHC, but greater capacity and transfer speed, 32 GB and higher. Standard goes up to 2 TB (not compatible with older host devices).
Very slim (45.0 mm × 37.0 mm × 0.76 mm), no wear leveling controller, up to 128 MB. This particular example shows the write protect sticker (the silver disc).
Packages the flash memory, currently soldered in shipping smartphones, into a removable card form factor. Uses the SCSI command set including queuing. The electrical interface makes use of differential signaling, which enables high bus speeds and robustness under noisy conditions and reduced pin count (compared to parallel bus alternatives such as UHS-I).
Universally compatible across most non-mobile computer platforms, their greater size suits them better to file transfer/storage instead of use in portable devices
Physical details
Note that a memory card's dimensions are determined while holding the card with contact pins upwards. The length of cards is often greater than their width. Most cards show a directional arrow to aid insertion; such an arrow should be upward.
The following chart gives details on availability of adapters to put a given card (horizontal) in a given slot or device (vertical). This table does not take into account protocol issues in communicating with the device.
Following labels are used:
+ (native) – A slot is native for such card.
D (Directly compatible) – A card may be used in such a slot directly, without any adapters. Best possible compatibility.
M (requires a Mechanical adapter) – Such adapter is only a physical enclosure to fit one card sized into another; all electrical pins are exactly the same.
EM (requires an Electro-Mechanical adapter) – Such adapter features both physical enclosure and pins re-routing as terminals are sufficiently different. No powered elements in such adapter exists, thus they're very cheap and easy to manufacture and may be supplied as a bonus for every such card.
E (requires an Electronic adapter enclosure) – These adapters must have components—potentially requiring external power—that transform signals, as well as physical enclosure and pin routing.
X (requires an eXternal adapter) – Technically the same as E, but such adapter usually consists of 2 parts: a pseudo-card with pin routing and physical enclosure size that perfectly match the target slot and a break-out box (a card reader) that holds a real card. Such adapter is the least comfortable to use.
XM (requires an eXternal electro-mechanical adapter) – Technically the same as EM, but such adapter usually consists of 2 parts: a pseudo-card with pin routing and physical enclosure size that perfectly match the target slot and a break-out box (a card reader) that holds a real card. Such adapter is the least comfortable to use.
Empty cell – Card cannot be used in such slot, no single adapter is known to exist. Sometimes a chain of adapters can help (for example, miniSD→CF as miniSD→SD→CF).
^In March 2008, Olympus started shipping the MASD-1 microSD-to-xD adapter along with its latest compact digital cameras, with a shape designed to fit only in those latest camerasArchived 2011-06-25 at the Wayback Machine. The physical adapter is in fact purely electromechanical, although the xD and SD protocols are completely incompatible. This demonstrates that the cameras themselves must understand the SD protocol, and thus the adapter is more properly termed an electronic adapter, with the electronic logic contained in the camera rather than the physical accessory.
^SD cards are usually thicker than MMC ones, and although it uses perfectly compatible pins, not every MMC slot may allow thick SD card to be inserted