Summary of Commonly Used Storage Media

Traditional photography uses film to sensitize and record images, while digital photography uses image sensor to sensitize and record on storage medium after processing by digital signal processor. There are many kinds of storage media, and new products are constantly developed and old products are eliminated. Common storage media include SD card, CF card, CFAST card, xqd card, cfexpress card, memory stick, XD card, micro hard disk, MMC card and SM card, among which SD card is the most commonly used. CFAST card, xqd card and cfexpress card take into account the application of SLR and micro single high-speed camera.

SD memory card (secure digital memory card) is a high-speed storage device based on semiconductor flash memory. It was jointly developed by Panasonic, Toshiba and SanDisk in August 1999. While launching SD memory card, Secure Digital Card Association (SDA) was established to formulate relevant specifications and be responsible for the promotion of SD memory card. The data transmission and physical specifications of SD card are developed from MMC (multimedia card), which is about the same size as MMC card. The size is 32mmx24mmx2.1mm, the length and width are the same as MMC card, but it is 0.7mm thicker than MMC card to accommodate larger capacity storage units.

1. Dimensions

SD card family has three members: SD, miniSD and microSD, and the size decreases in turn. The standard SD card is used for most cameras and cameras. The body is equipped with a write protection switch - but it does not affect the interior of the memory card, but the identification of the card reading device. MiniSD card has withdrawn from the historical stage. MicroSD card, also known as TF card, is mainly used in mobile phones, motion cameras, UAVs and other products.

Different SD card sizes

2. Capacity

The SD card we collectively refer to has many versions in terms of maximum capacity. The original SD card used FAT16 file system, and the maximum capacity can only reach 2GB. Now it has exited the mainstream application. The most common SDHC (sdhigh capacity) memory card and SDXC (sdextended capacity) memory card use FAT32 file system and exFAT file system respectively, with maximum capacity of 32GB and 2TB respectively. The new sduc memory card has a theoretical capacity of 128tb. It is worth mentioning that SD cards above 64GB (SDXC and sduc) adopt exFAT format, and the size of a single file can be greater than 4GB. It is the user's choice to continuously record 4K high bit rate video shooting for a long time.

SD cards of different capacities

3. Speed class

Speed level is the performance specification specified by SD Card Alliance, and it is also the sign that SD card manufacturers need to print on the product body and outer packaging. The speed level usually only reflects the minimum performance level of the SD card and does not represent the actual performance.

No UHS: single row contact, the highest standard C10 (continuous writing speed not less than 10MB / s), and the theoretical speed not more than 25mb / S (usually refers to the reading speed, and the writing speed will be slightly lower). This kind of card has basically withdrawn from the market.

Uhs-i: single row contact, highest standard C10, U3, V30 (continuous write speed 30MB / s), theoretical speed 104mb / s. This is the main product in the current market.

Uhs-ii: double row contact, highest standard C10, U3, V90 (continuous write speed 90MB / s). The theoretical speed of full duplex mode is 156mb / S (most cameras), and the theoretical speed of half duplex mode is 312mb / S (card reader, etc.).

Uhs-iii: double row contact, highest standard C10, U3, V90, full duplex mode can reach 624mb / s. However, there is no actual product yet.

Sdexpress: double row contacts, pcie3.0 bus and nvme support, which can reach the ultra-high speed of 985mb / s. At present, Shandi (Western data) has launched a prototype product. It should be noted that sdexpress can only be downward compatible with uhs-i and does not support uhs-ii or uhs-iii - that is, when one of the memory cards and devices does not support sdexpress, the maximum speed that the system can achieve is 104mb / s.

SD card speed level and corresponding video format

CF card (CompactFlash) was originally a data storage device for portable electronic devices. As a storage device, it revolutionized the use of flash memory, which was first produced by SanDisk in 1994 and formulated relevant specifications. The internal controller of the CF card is designed to fully simulate the hard disk, using the standard parallel ATA / IDE (Integrated Drive Electronics) interface, the latest specification cf6.0 of the international CFA Association, and the bus speed can be up to 167MB / s.

CFAST card is a standard and specification formulated by CFA (compact flash Association, CFA) in 2008. It is a new upgraded standard of CF specification developed by CF camp. The transmission protocol used is SATA. SATA2 was used in the early stage, and sata3 is now widely used. At the same time, like the CF card, it is known as the world's smallest SATA solid state drive. Cfast2.0 specification supports SATA - , and the bus speed can reach 600MB / s. CFAST card based on CFAST 2.0 specification is suitable for industrial and professional imaging and video markets.

With the continuous evolution of flash memory products, the association has released the cfexpress * 1.0 specification of PCIe transmission signal in 2017. CFAST card and CF card are two different levels of products. It can be said that CFAST card is the advanced evolution and "variation and upgrading" of CF card, but it can not be taken for granted that CF card is CFAST card, or that the two are the relationship of renewal. CF card and CFAST card cannot be used in common.

CFAST card identification

Pin of CFAST card

The xqd card specification was originally published by Sony, SanDisk and Nikon in November 2010 and was immediately extracted as a development goal by CompactFlash Association. On December 8, 2011, the compact flash Association announced the newly developed xqd memory card format, and then the first batch of samples were displayed at the "CP 2012" exhibition in Japan in February 2012. Xqd is a memory card format using flash memory. It is designed for the shortcomings of CF card. It has the advantages of smaller volume, faster writing, larger capacity, better reliability and stability. Based on the PCI Express specification, the initial continuous write speed is only 125mb / s and the maximum capacity is 32GB; The new generation xqd card has a reading speed of 440mb / s and a writing speed of 400MB / s, with a maximum capacity of 240gb. High speed writing can continuously shoot up to 200 raw pictures. In terms of video recording, it can achieve stable high frame 4K recording while avoiding the decline of speed.

SD card and xqd card

On CP 2019, the CF Card Association (CFA) published the cfexpress2.0 specification. Cfexpress card is a new generation of memory card standard. At present, Nikon's z-series micro single, Panasonic's s S-Series and Canon's R-Series micro single support this standard, which divides cfexpress cards into three types.

Type A: size 20mm * 28mm * 2.8mm, slightly smaller than SD card, 1 PCIe channel, theoretical transmission speed 1GB / s, mainly designed for ordinary digital cameras;

TypeB: the size is 38.5mm * 29.8mm * 2.8mm, which is the same as the xqd card. It has two PCIe channels and a theoretical transmission speed of 2GB / s. It is mainly designed for high-end digital cameras;

Typec: the size is 54mm * 74mm * 4.8mm, the shape is similar to 2.5-inch SSD, 4 PCIe channels, and the theoretical transmission speed is 4GB / s. It is mainly designed for desktops, laptops and tablets to replace solid state drives.