SD Card - boot sector
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From: Maxim S. Shatskih on 11 Jan 2006 18:25 > That's the LBR. Removable flash media are formatted as hard disks. Usually. This depends upon its controller firmware, whether it reports itself as removable media or not. If not - then it will have MBR, and will have the "hard disk" icon in Windows. If yes - it will have no MBR (boot sector at sector 0) and will have the "diskette drive" icon in Windows. Windows does not support MBR and partitions on removable media, but requires the partition table (MBR, GPT or Dynamic Disk) on a non-removable media. -- Maxim Shatskih, Windows DDK MVP StorageCraft Corporation maxim(a)storagecraft.com http://www.storagecraft.com
From: larwe on 11 Jan 2006 20:18 Maxim S. Shatskih wrote: > Windows does not support MBR and partitions on removable media, but requires > the partition table (MBR, GPT or Dynamic Disk) on a non-removable media. In a practical sense: all embedded systems that I have seen (cameras, mainly) that use removable media will format it as a hard disk. I suspect that most media playback devices would not recognize a "big floppy" flash disk. Some flash media specifications explicitly require an MBR (SSFDC comes to mind). All the USB adapters I've used - which is many different types - cause Windows to format cards with an MBR. As a matter of interest, the units I have also report as removable to Windows. It's safe to say that anybody who doesn't format flash media with an MBR is being a maverick.
From: larwe on 11 Jan 2006 20:20 Maxim S. Shatskih wrote: > The card can have the MBR partition table. In this case, the boot sector is > usually sector 63. That's an amazingly broad generalization, broad to the point of being dangerously wrong. It depends entirely on the size of the card - because it's determined by the reported CHS geometry of the card, presumably for legacy FDISK reasons. The LBR is generally _one track_ away from the MBR. For the specific sizes of SD card you've used in recent times, maybe spt was always 63. The OP's post clearly shows that your generalization isn't even true for the cards he happens to have lying about.
From: larwe on 11 Jan 2006 20:23 Ross Marchant wrote: > Sometimes removeable media come with the MBR / partition table and so > formatting will retain will retain the MBR. However if the disk is > subsequently damaged then windows will totally reformat the disk, with no > MBR and the dos boot sector as sector 0. It is worthwhile checking for both > instances. I do this by checking if the first byte of sector 0 is 0xEB. What kind of interface were you using to access the drive? I just did the following: On a linux box: dd if=/dev/zero of=/dev/sda bs=512 count=100 then using the inbuilt O2Micro SD reader slot in my laptop, reformatted the card in Windows. The resulting card had an MBR with one partition (not marked active). So I don't think it's as consistent as this.
From: Beverly Howard [Ms-MVP/MobileDev] on 11 Jan 2006 21:24
While I can't speak to the structure of the card itself, it's been my observation that the card is only part of the equation... the reader plays a bigger part with respect to "booting" devices and it's ability to do so is dependant on both the computer's ability to boot from the connection method and that computer's current bios configuration has to be set to allow such a boot. Of about half a dozen different usb card readers, I have two that show up as usb boot devices on my system's boot selector menu and I have only two computers out of about seven which offer the capability to boot from usb devices... for example, my Sony Vaio Picturebook will boot via usb, but it will only recognize one specific usb floppy drive as a valid boot device. With those two bootable SD readers, I can then use different boot configurations stored on different SD cards to boot the pc. Tip... disconnect all usb devices except a card reader and follow your box's alternate boot steps... if the reader is bootable, it will show in the boot device menu under an interesting variety of device names. Beverly Howard [MS MVP-Mobile Devices] |