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In Reply to: RE: Late 2014 Mac Mini SD card slot compatibility questionÂ… posted by AbeCollins on November 28, 2015 at 10:47:55
Abe- Thank you so much for your reply and your input which has been so valuable in helping me solve problems with my Mac Mini in the past.
As you pointed out the Mac Mini's SD card slot does support all 3 generations of SD, SDHC and SDXC cards, but my inquiry pertains specifically to the cards which use the Ultra High Speed (UHS) bus which is available on some SDHC and SDXC cards that use 17 pins for access.
"The following ultra-high speeds are specified:
UHS-I-
Specified in SD version 3.01, supports a clock frequency of 100 MHz (a quadrupling of the original "Default Speed"), which in four-bit transfer mode could transfer 50 MB/s (SDR50). UHS-I cards declared as UHS104 (SDR104) also support a clock frequency of 208 MHz, which could transfer 104 MB/s. Double data rate operation at 50 MHz (DDR50) is also specified in Version 3.01, and is mandatory for microSDHC and microSDXC cards labeled as UHS-I. In this mode, four bits are transferred when the clock signal rises and another four bits when it falls, transferring an entire byte on each full clock cycle.
UHS-II-
Specified in version 4.0, further raises the data transfer rate to a theoretical maximum of 156 MB/s (half duplex) or 312 MB/s (full duplex) using additional row of pins (a total of 17 pins for full-size and 16 pins for micro-size cards).
Cards that comply with UHS show Roman numerals 'I' or 'II' next to the SD card logo, and report this capability to the host device.
Use of UHS-I requires that the host device command the card to drop from 3.3-volt to 1.8-volt operation and select the four-bit transfer mode, while UHS-II requires 0.4-volt operation."
My interest in the UHS-II class cards is not with respect to their higher speed capability, but rather the much lower voltage at which they operate thinking that this may in some way offer the potential for a lower noise data transfer? Any thoughts?
Follow Ups:
I know that the UHS-II class cards are 'compatible' with the Mac Mini and your newer Mini uses the PCIe bus as an interface to the card slot so it has the speed to accommodate the faster transfers from these UHS-II cards.
I couldn't tell you if there are any sonic benefits when these cards are operating at lower voltages. Personally, I wouldn't trust my music library to any SD card as they are not as reliable as an over provisioned SSD with wear leveling. But for experimenting, sure why not.
Sorry I couldn't be more specific as I rarely ever use the the SD slot in my Mini, and the few times that I have it was for moving a couple files.
Abe- Thank you for your admonition concerning the long term reliability of these SD Cards. In that I have taken the precaution of backing up my music library to several different locations I felt confident in loading a portion of it's contents onto a 32GB SanDisk SDHC UHS-I SD Card from one of the dual SD Card slots on my Nikon camera. A few days ago after comparing playback quality from a dedicated USB 3, Thunderbolt SSD and UHS-I SD Card sources using my Mac Mini with mixed results I began to wonder if the low voltage differential signaling used in the UHS-II SD Card spec might offer some sort of a more noticeable improvement and so after I had completed this free testing of the SDHC UHS-I card which I already owned I made this inquiry before deciding whether or not to buy a larger capacity SDXC UHS-II SD Card for use with my Mac Mini. Since the UHS-II SD Cards are only marginally more expensive than the UHS-I versions I just may get one and post back to this thread as to whether or not the Mac Mini can achieve the UHS-II 4.2 spec while using one.
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