OT: Micro SD in adapter vs Micro SD native: Speed Diff?


P

(PeteCresswell)

Given two Class 10 SD cards: one micro and the other standard size,
should I expect a speed diff between the standard size and the micro in
a standard-size adapter?

One part of me thinks "No": it's just a pin-to-pin connection.

Another part thinks: "If you took everything you know about this stuff,
rolled it up into a ball, and set it on the edge of a razor blade; it
would look like a golf ball in the middle of the New Jersey Turnpike."
 
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P

Paul

(PeteCresswell) said:
Given two Class 10 SD cards: one micro and the other standard size,
should I expect a speed diff between the standard size and the micro in
a standard-size adapter?

One part of me thinks "No": it's just a pin-to-pin connection.

Another part thinks: "If you took everything you know about this stuff,
rolled it up into a ball, and set it on the edge of a razor blade; it
would look like a golf ball in the middle of the New Jersey Turnpike."
You have to watch the pinout table here. I got fooled when I
read it the first time.

http://en.wikipedia.org/wiki/Secure_digital

Initially, I saw 9 pins on SD, and 8 pins on microSD, and
assumed the worst.

The 8 pin interface on microSD, has one fewer ground signals,
so the transfer modes are the same. Both support a four bit
data bus (max).

This Toshiba spec, gives you some idea of the capabilities. And
in terms of development possibilities, I think they haven't built
the fastest interface mode yet (UHS-II ???).

https://www.toshiba.co.jp/p-media/wwsite/microsd.htm

Transfer Speed
for microSDHC UHS-I Card

New UHS-I Interface Conventional SD Interface
------------------------- -------------------------
Mode: SDR104 mode SDR50 mode High Speed mode
Max bus speed: 104 MB/s 50 MB/s 25 MB/s
Transfer rate: Read: 95 MB/s Read: 45 MB/s Read: 23 MB/s
Min transfer: UHS Class 1 (10MB/sec) [SD] Class 10 (10MB/sec)

And these are specs from a host controller site. The Toshiba doesn't
mention clock rates, and you can see the allowed clock rates here.
It's even possible the clock is turned off, when the bus is idle.

SD 1-bit / 4-bit
Identification Mode (up to 400 kHz)
SD/SDIO UHS-1 SDR12 mode (up to 25 MHz)
SD/SDIO UHS-1 SDR25 mode (up to 50 MHz)
SD/SDIO UHS-1 SDR50 mode (up to 100 MHz)
SD/SDIO UHS-1 SDR104 mode (up to 208 MHz)
SD/SDIO UHS-1 DDR50 mode (up to 50 MHz)

The 208MHz, times four bits at a time (nibble mode), gives 104MB/sec on bus.
And apparently available through just 8 pins.

Pin 1 DAT2
Pin 2 DAT3
Pin 3 CMD
Pin 4 Power
Pin 5 Clock
Pin 6 Ground
Pin 7 DAT0
Pin 8 DAT1

HTH,
Paul
 
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G

Gene E. Bloch

Given two Class 10 SD cards: one micro and the other standard size,
should I expect a speed diff between the standard size and the micro in
a standard-size adapter?

One part of me thinks "No": it's just a pin-to-pin connection.

Another part thinks: "If you took everything you know about this stuff,
rolled it up into a ball, and set it on the edge of a razor blade; it
would look like a golf ball in the middle of the New Jersey Turnpike."
My opinion is that different full size SD cards of the same class still
manage to operate at different speeds, and the same is true for
different micro-SD cards of the same class.

This could be the result of a reverse placebo effect, of course - and it
*is* just an opinion.

I have used HD Speed and similar software, but not recently.
 

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