CFexpress – the next generation memory cards for digital imaging
As technology progresses, we see that the memory cards are getting faster and with bigger capacity. For many years, CompacFlash was “the standard” of the imaging industry and was widely adopted by most companies desiring the highest capacity and performance available. SD cards, long perceived as non-professional media, fought their way to still be dominant on the market today. Nowadays very few cameras use cards different than SD. Nikon use XQD cards in their D5, D500 and D850, while Canon use CFast cards in their 1D X Mark II and dual CFexpress Type B in 1D X Mark III. Several older models use Compact Flash cards and this is it. All other cameras use some variation of SD cards – SD, SDHC, SDXC. Will a new standard (CFexpress) raise from the ashes of XQD ad CFast?
CompactFlash (CF) card
CompactFlash (CF) is a flash memory mass storage device used mainly in portable electronic devices. The format was specified and the devices were first manufactured by SanDisk in 1994. CompactFlash became the most successful of the early memory card formats, surpassing Miniature Card and SmartMedia. Subsequent formats, such as MMC/SD, various Memory Stick formats, and xD-Picture Card offered stiff competition. Most of these cards are smaller than CompactFlash while offering comparable capacity and speed. CompactFlash remains popular and is supported by many professional devices and high-end consumer devices. As of 2017, both Canon and Nikon use CompactFlash for their flagship digital still cameras. Traditional CompactFlash cards use the Parallel ATA interface, but in 2008, a variant of CompactFlash, CFast was announced. CFast (also known as CompactFast) is based on the Serial ATA interface.
Secure Digital (SD) card
Secure Digital (SD) is a non-volatile memory card format developed by the SD Card Association (SDA). The standard was introduced in August 1999 by joint efforts between SanDisk, Panasonic (Matsushita Electric) and Toshiba as an improvement over MultiMediaCards (MMC), and has become the industry standard. The three companies formed SD-3C, LLC, a company that licenses and enforces intellectual property rights associated with SD memory cards and SD host and ancillary products. In January 2000 the companies also formed the SD Association (SDA), a non-profit organization, to promote and create SD Card standards.
The Ultra High Speed (UHS)
The Ultra High Speed (UHS) is a bus available on some SDHC and SDXC cards – up to version 6. UHS-I cards support a clock frequency of 208 MHz, which could transfer 104 MB/s. UHS-II further raises the data transfer rate to a theoretical maximum of 156 MB/s (full duplex) or 312 MB/s (half duplex) using an additional row of pins. UHS-III, released in February 2017, added two new data rates to the standard. FD312 provides 312 MB/s while FD624 doubles that. Both are full-duplex. The physical interface and pin-layout are the same as with UHS-II, retaining backward compatibility.
The Secure Digital Ultra Capacity (SDUC)
The Secure Digital Ultra Capacity (SDUC) format, described in the SD 7.0 specification was announced in June 2018. SD Express adds the popular PCI Express and NVMe interfaces to the legacy SD interface. The PCIe interface delivers a 985 megabytes per second (MB/s) maximum data transfer rate and the NVMe upper layer protocol enables advanced memory access mechanism, enabling a new world of opportunities for the popular SD memory card. In addition, the maximum storage capacity in SD memory cards grows from 2TB with SDXC to 128 TB with the new SD Ultra Capacity (SDUC) card.
In November 2010, SanDisk, Sony and Nikon presented a next generation card format to the CompactFlash Association – the XQD card format, which was officially announced with the final specifications by the CompactFlash Association in December 2011.
XQD card is a memory card format primarily developed for flash memory cards. It uses PCI Express as a data transfer interface instead of Parallel ATA or Serial ATA. The format is targeted at high-definition camcorders and high-resolution digital cameras. It offers target read and write speeds from 1 Gbit/s (125 MB/s) to about 4 Gbit/s (500 MB/s) and storage capabilities beyond 2 TB.
The cards are not backward compatible with CompactFlash or CFast cards. XQD and CFast were both designed as a replacement of the then-16-year-old (in 2010) CompactFlash standard.
XQD version 2.0 was announced in June 2012, featuring support for PCI Express 3.0 with transfer rates up to 8 Gbit/s (1000 MB/s).
To try and bring the top-tier manufacturers using CFast and XQD together around a common standard, the CompactFlash Association (CFA) has promoted an evolution of the XQD standard known as CFexpress. CFexpress (or CFx) is a standard for removable media cards, designed to allow high resolution files, and high speed recording with low latency, be achieved in a small rugged form factor. CFexpress is the same size and connector as the XQD card format, and is aimed at various applications within industrial, imaging, compute and enterprise markets.
CFexpress is the merging of two standards: XQD® 2.0 and CFAST® 2.0, into a new standard that uses the popular PCIe® interface, and the NVM Express® protocol. The standard will use PCIe 3.0 interface with 1 to 8 lanes where 1 GB/s data can be provided per lane. NVM Express is also supported to provide low overhead and latency. There will be multiple form factors that feature different PCIe lane counts. One of the goals is to unify the ecosystem of removable storage by being compatible with standards already widely adopted, such as PCIe and NVMe. There already is a wide range of controllers, software and devices that uses these standards, accelerating adoption.
Advantages of CFexpress
The benefits of a CFx Type B card for use in digital imaging applications are several:
- Form Factor ideally suited for higher capacities needed in imaging applications – up-to 1TB with current NAND flash memory technology
- Physical size that is easy to handle – slightly larger than SD and slightly smaller than CFast or CompactFlash (29.6 x 38.5 x 3.8 mm)
- Performance capability capable of >1GB/sec transfer rates, through the use of two PCIe data lanes.
- NVMe protocol support for optimized performance with flash memory in newer computing architectures
- Backward compatibility possible to XQD host platforms through upgrade of host operating system (firmware)
CFexpress will allow many hardware manufactures to use the established high performance benefits of PCIe® and NVM Express® in a compact, removable form factor. Performance of CFexpress will start out PCIe® 3.0×2 (two-lanes) with the possibility to scale to x8 (eight-lanes) in the future. CFexpress can also be customized when required.
CF Express raises from the ashes of XQD ad CFast
DPReview posted a letter from ProGrade Digital CEO Wes Brewer, who says that “ProGrade Digital is not planning to manufacture XQD cards at this time. We are however strongly promoting the future standard of CFexpress through our efforts in the Compact Flash Association. The CFexpress Type B form factor of this new standard is the successor to XQD, and allows existing cameras that utilize XQD cards to be upgraded to operate with the new CFexpress Type B cards if the original equipment manufacturer (OEM) chooses to update firmware in those devices. In addition to the option of backward compatibility to XQD cameras, the new CFexpress cards utilize two lanes of PCIe (vs. one lane on XQD) and support the NVMe (Non Volatile Memory express) protocol, which provides more than twice the interface speed of XQD. Look for ProGrade Digital to make announcements in this area throughout 2018.”
Wes Brewer further said that “the CFexpress standard has been evolving for several years within the CompactFlash Association as a successor to both CFast and XQD formats. We are pleased to be working within the CFA and alongside device manufacturers to bring to market this next generation removable storage standard. Industry adoption of CFexpress will allow for much higher resolution and higher bit rate image capture than ever before in many still image and video capture devices. Faster offload speeds will also greatly benefit the post-capture workflow through the extremely high read speeds it provides.”
The company was founded by former Lexar executives who are aiming to offer the highest quality memory cards on the market. The founders of ProGrade Digital are industry veterans in the removable storage and digital photography industries. Each, having spent time at leading companies such as Lexar and SanDisk, brings extensive expertise in the design, development and manufacture of digital storage products, ProGrade has benchmarked their new CFexpress card to hit greater than 1400 MB/s read speeds and over a 1000 BMB/s burst write speeds. This would be over well over double current speeds found on the highest-end CFast cards, matching speeds found on computer SSDs. On a memory card. That fits in the center of the palm of your hand. That has the same form factor as XQD.
The new CFexpress 1.0 format is the future of digital storage for high-end photography and video applications. With a theoretical limit of up to 8 GB/s thanks to support for eight channels that each run at 1GB/s, these cards have a lot of room to grow. But that doesn’t mean they’re slow today. In fact, as the first public demonstration of CFexpress 1.0, these are some of the fastest cards to date.
While XQD is a format that may well die out with the advent of CFexpress (it may seem nearly dead already with Sony as the format’s sole manufacturer), it is possible that with the right firmware, CFexpress cards could be used in XQD-accepting cameras, as the formats are potentially interchangeable. You will still be limited to the speed of the card being used, but it’s possible that the transition from XQD to CFexpress could be painless. Moreover, this could easily be what other manufacturers have been waiting for before making the switch to a smaller, more capable, longer-term solution. CFexpress seems to be just that.
ProGrade’s CFexpress cards will be available in 256 GB, 512 GB, and 1TB capacities when they are released later this year around September.
PS: Image credit: https://progradedigital.com/2018/04/08/cfexpress-white-paper/