SD_Cards.md

A Summary of SD Card Specifications:

The following is derived from a video on the channel Explaining Computers. A channel with videos so awesomely good and useful that I felt compelled to take notes for future reference. This document is one such case where the best explanation of SD cards ever is summarized.

Card Form Factors:

Over the years, different SD card form factors have been introduced:

Year	Type	Status
2000	Standard SD cards	Older, less common
2003	Mini SD cards	Extinct
2005	Micro SD cards	Ubiquitous

Card Storage Capacity:

Memory capacities keep on increasing:

Type	Maximum Capacity
SD	2G
SD HC (High Capacity)	32G
SD XC (Extended Capacity)	2T
SD UC (Ultra Capacity)	128T

Card Write Speed:

Since SD cards are often associated with cameras, the device's write speed is the most important specification in that application.

MB/s	Speed Class	UHS Speed	Video Speed
90			V90
60			V60
30		U3	V30
10	C10	U1	V10
6	C6		V6
4	C4
2	C2

Application Rating:

As SD cards are moving into applications beyond cameras, other aspects of performance beyond brute write speed become important. This results in an application rating which focuses on the card's ability to handle many I/O operations and large numbers of files.

Rating	Read IOPS	Write IOPS	Write Speed
A1	1500	500	>10
A2	4000	1000	>10

Bus Interface Ratings:

Finally, the interface between the host system and the SD device has undergone a few revisions.

Interface	Bus Speed MB/s	Connection	Status
High Speed	25	Standard	OK
UHS-I	104	Standard	OK
UHS-II	312	2 Rows	OK
UHS-III	624	2 Rows	Not adopted?
SD Express	985	2 Rows	Leading edge

Note: It very much looks like the UHS-III interface is being skipped over in favor of SD Express.