mac mini (late 2014) sd card slot PCIe

Question

Level 1

8 points

mac mini (late 2014) sd card slot PCIe

So, when I was researching the sdcard reader for the macmini, I thought that they were all driven by the USB Bus. Because of that, I thought that the only advantage to using aSDcard for external flash storage over a USB flash drive was that it would keep a USB port free. I was looking into it because of speed, but in the end I didn't need much speed just to run backup and I went with aSDcard.

I ended up purchasing a Mac Mini (2014) and the SD Card reader is not listed under the USB bus. Additionally, the SD card reader in the systemprofilerlists the link speed as2.5 GT/s, making it a PCIe bus. I'm using a 32GB micro SDHC card from Silicon Power (cheap!), so the rate limiter could (theoretically?) be the adapter, but I tested speeds of 20.19MB/s write and 49.34 MB/s read (packaging lists "Up to 85 MB/s" read).

What is the fastest read/write that people have tested with the SD card reader in the 2014macmini?? Are these speeds still below USB3.0 flash drives?

Kind of a weak question, but I wanted to document the PCIe bus, since I had been confused/"in the dark" about it.

Mac mini, OS X Yosemite (10.10.5), Mac Mini (late 2014) 2.8GHz i5, 16G

Posted on Aug 29, 2015 10:26 AM

Reply

Answer 1

lllaass

Level 10

210,411 points

Aug 29, 2015 10:34 AM in response to one-hoop

My experience with SD cards is that they themselves are slower than USB 3

Reply

Answer 2

Aug 30, 2015 3:04 AM in response to one-hoop

SD cards are pretty slow. They are usually better than most USB memory sticks,

but not by much.

The speed numbers that all the vendors claim are very optimistic numbers and

in reality are for small data bursts. This is because of the way the technology works.

The actual memory contents are read in blocks from the nonvolatile storage into

the RAM buffer and then transferred. So, when that block is read, the speed can be

very fast. However, it then has to transfer the next block to the buffer which is slow

before sending the data.

I discovered this issue when working on an embedded project and found I was not getting

the claimed data throughput. The speed claim was true, but only for a 4KB block of data.

Reply