Memory Card Standards Migrate Toward High Speed PCI Express

June 11, 2019 Gibson Ming-Dar Chen, UD Info

Due to high-speed applications, for example, high-resolution, such as 4K and 8K, video recording demand, both CompactFlash and SecureDigital (SD) card associations promote PCI Express with low latency NVM Express® protocol.

CompactFlash card standard started with CF with PATA interface in 1990, which was the most popular interface for Digital Camera and handheld Personal Digital Assistant (PDA) in early 2000.  The second generation standard for CF card is CFast. It features SATA III with up to 500MB/s read/write performance. However, it is not successful in the handheld device due to its bulky size. Then the CF association announced a new standard with PCI Express interface named CFexpress (or CFX). CFX leverages the PCIE Gen 3 interface to have theoretical transfer rate up to 2GB/s. Its height increases from 3.3 mm to 3.8 mm to accommodate more NAND units for higher capacity. Based on the 3D NAND, CFX with 1TB is available now. Its plug-and-play feature widens its applications. The following figure shows the trend of three standards of CompactFlash.

Compared to CompactFlash, the SecureDigital (SD) card has been widely used in digital cameras, cellular phones and other storage devices.

To meet the demand of high-resolution camera recording, gaming and mobile applications, SD association promoted a new standard, SD 7.0 named SD Express, which has up to 985MB/s bandwidth and supports PCIE Gen3 x 1 and NVMe 1.3 mode, (see figure below). This new standard is backward compatible with High Speed and Ultra-high Speed I (UHS I), but not UHS II standard.

These standards with PCI Express interfaces give the two memory card standards a new life and opportunity in the future digital mass storage world. It might change the video recording, mobile application and computing ecosystem. However, if the biggest application, the cellular phone, does not implement these standards, the growth of these standards will be still limited.  Also, the fast data upload through 5G or other channels to the cloud is also an issue for the applications with these standards. We will see what will happen then.

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