What you never knew you didn't know
While researching a few upcoming SD / microSD product reviews here at PC Perspective, I quickly found myself swimming in a sea of ratings and specifications. This write up was initially meant to explain and clarify these items, but it quickly grew into a reference too large to include in every SD card article, so I have spun it off here as a standalone reference. We hope it is as useful to you as it will be to our upcoming SD card reviews.
SD card speed ratings are a bit of a mess, so I'm going to do my best to clear things up here. I'll start with classes and grades. These are specs that define the *minimum* speed a given SD card should meet when reading or writing (both directions are used for the test). As with all flash devices, the write speed tends to be the more limiting factor. Without getting into gory detail, the tests used assume mostly sequential large writes and random reads occurring at no smaller than the minimum memory unit of the card (typically 512KB). The tests match the typical use case of an SD card, which is typically writing larger files (or sequential video streams), with minimal small writes (file table updates, etc).
In the above chart, we see speed 'Class' 2, 4, 6, and 10. The SD card spec calls out very specific requirements for these specs, but the gist of it is that an unfragmented SD card will be able to write at a minimum MB/s corresponding to its rated class (e.g. Class 6 = 6 MB/s minimum transfer speed). The workload specified is meant to represent a typical media device writing to an SD card, with buffering to account for slower FAT table updates (small writes). With higher bus speed modes (more on that later), we also get higher classes. Older cards that are not rated under this spec are referred to as 'Class 0'.
As we move higher than Class 10, we get to U1 and U3, which are referred to as UHS Speed Grades (contrary to the above table which states 'Class') in the SD card specification. The changeover from Class to Grade has something to do with speed modes, which also relates with the standard capacity of the card being used:
U1 and U3 correspond to 10 and 30 MB/s minimums, but the test conditions are slightly different for these specs (so Class 10 is not *exactly* the same as a U1 rating, even though they both equate to 10 MB/sec). Cards not performing to U1 are classified as 'Speed Grade 0'. One final note here is that a U rating also implies a UHS speed mode (see the next section).
Subject: General Tech, Storage | September 12, 2014 - 08:08 PM | Scott Michaud
Tagged: sandisk, sdxc, sdhc, sd card, 512GB
Assuming your camera, card reader, or other device fully conforms to the SDXC standard, Sandisk has developed a half-terabyte (512GB) memory card. Beyond being gigantic, it can be read at up to 95 MB/s and written at up to 90 MB/s, which should be enough to stream 4K video. Sandisk claims that it is temperature proof, shock proof, water proof, and x-ray proof. It also comes with a lifetime warranty and "RescuePRO Deluxe" recovery software but, honestly, I expect people would just use PhotoRec or something.
It should be noted that the SDXC standard covers memory cards up to 2TB so it will probably not be too long before we see another standard get ratified. What is next? SDUC? SDYC? SDALLTHEC? Blah! This is why IEEE assigns names sequentially.
The SanDisk Extreme PRO UHS-I SDHC/SDXC 512GB memory card should be available now, although I cannot yet find them online, for $799.99 MSRP.
Subject: Storage | January 20, 2014 - 10:46 PM | Jeremy Hellstrom
Tagged: sdhc, FlashAir Wi-Fi, toshiba, sd card
Toshiba's FlashAir Class10 is a Wi-Fi enabled SD Card which thankfully supports a number of security protocols which should make it easy for you to get pictures from your camera without sharing them with the world. Madshrimps like the bundled FlashAir software which allows you to tweak functionality up to and including setting up Internet Pass Thru Mode. Check out the surprisingly fast transfer rates in their full review.
"The FlashAir Wi-Fi SDHC from Toshiba is available in different capacities of 8GB, 16GB or 32GB, features a well-developed interface for easy access from both our PC and mobile devices without the need of using an extra app and is also built with the Internet Pass Thru functionality for being able to browse the web while being connected to the newly connected network."
Here are some more Storage reviews from around the web:
- Corsair Flash Voyager GO 32GB micro-USB Flash Drive Review @ Legit Reviews
- Patriot Spark 32GB USB 3.0 Flash Drive @ NikKTech
- Icy Dock ToughArmor MB992SK-B 3.5" SATA Mobile Rack Review @HiTech Legion
- RaidSonic ICY BOX IB-121CL-U3 HDD Docking & Clone Station @ NikKTech
- Thecus N2310 NAS Server Network Storage @ Benchmark Reviews
- Western Digital Red (WD40EFRX) 4 TB NAS Hard Disk Drive @ TechARP
- Plextor M6e PCI Express 512GB SSD @ Kitguru