Wikipedia:Reference desk/Archives/Computing/2018 August 4

= August 4 =

Difference between pen drive and SD cards
If I understand correctly, they are deep inside exactly the same, a NAND memory chip, but have different controllers that connect to different interfaces.

But why do SDs have more points of contact?

Are SDs and micro SD packaged in another way and that's it?

Could you just package an SD as a pen drive?

Which is more reliable for backups?

And how can SDs be much smaller, even if you don't count the pen drive box?


 * I assume that by "Pen Drive", you mean a USB flash drive? Overly simplified; the USB flash drive have the controller chips on the drive, while the SD card relies on controller chips in the PC / camera / media player you plug it into. That is one reason the SD cards can be smaller - another reason is that the USB stick needs a USB connector, which is physically large. WegianWarrior (talk) 15:40, 4 August 2018 (UTC)
 * Note that as per the article on SD linked below, the middle part isn't correct. Both SD and USB require controllers. SD is designed primarily for one purpose and so is I'm pretty sure simpler than USB (although remember SDIO and DRM are part of the SD standard) and the controller likewise but I don't think in the modern age this is actually significant in terms of chip size required. In both cases the design can be monolithic [//rusolut.com/monolithic-sd-card-pinout-monosd1/]  . I imagine pretty much all microSDs are monolithic but USB flash drives may not be. (If you look at the photo in our article, you can see examples of SD cards with separate controller chips and flash chips but I'm not sure how common they are even for SD cards nowadays.) I'm not sure if there are other component required for a USB device, but I'm fairly sure the USB connector is really the biggest part required. For example I have a USB flash device very similar to this sort  and they are actually very common nowadays as mine was one of the cheapies from China (but one with a real capacity). You can actually even get flatter ones if you don't mind not having the whole USB plug although I suspect these aren't compliant with the USB standard. Take a look at the Pico series here for example  (e.g.   . With USB type C, you can get sticks which I'm sure are fully compliant and small e.g. [//mashable.com/2016/02/21/sandisk-usb-c-flash-drive/]. As per Comparison of memory cards, SmartMedia and xD are the two formats without a controller. The first died before memory cards were even really significant. The later at least lasted long enough that I suspect you can find people who've used it easily. Nil Einne (talk) 19:19, 4 August 2018 (UTC)


 * On the last USB drive that I bought, the USB connector appears to take up 80% of the volume and the remaining 20% is a miniature handle. The actual chip must be micro SD size and inside the USB connector.  The pin configurations for SD cards are given in our article Secure Digital.  Dbfirs  15:56, 4 August 2018 (UTC)


 * Are there any that make the handle as small as possible to show off? Like a needle sticking out of the USB connector with a very miniature handle at the end to hold? Sagittarian Milky Way (talk) 04:29, 10 August 2018 (UTC)


 * I haven't seen any quite like that. Are you going to register the design and manufacture them?   Db<i style="color: #4fc;">f</i><i style="color: #6f6;">i</i><i style="color: #4e4;">r</i><i style="color: #4a4">s</i>  05:53, 11 August 2018 (UTC)


 * A card reader interfaces to PC by USB. At its front end it interfaces several card types. The most variations can be found at SD cards and successors. Old card readers fail on compatibility to newer SD cards. All the flash memory itself is able to get read out very fast (often reaching the USB 2.0 bottle neck), but fast writing is where fake manufacturers are cheating causing the customer a lost of data. Sometimes just a ½ or ¼ of real memory is sold. Inside an old SD card, there is a PCB, a controller an the flash memory device(s). Mass demands and expired patents allow a single package production. -- Hans Haase (有问题吗) 11:01, 11 August 2018 (UTC)