View Full Version : dpc-ud1 usb drive

26-01-2004, 12:13 AM
i have a dpc-ud1 xd picture card usb drive and in the instructions it says that on a system with win me you have to tell it to eject the drive before i can un plug the drive
what would happen if i just unplugged it from the usb without ejecting it first ?
on my other comp with win 98se it doesn't need to be ejected

26-01-2004, 11:49 AM

Graham L
26-01-2004, 04:42 PM
It is a"disk" with a directory. Most "modern" OSs buffer the directories of disks. The buffers are written out periodically.

But if a disk is removed before the buffered directory is written out, the contents and directory might not match. :_|

This is a good way to lose files. ;-)

I would tend to "eject" such devices (whatever the OS). It doesn't take long to make sure that the directory has been written out.

26-01-2004, 05:29 PM
ok so this is were i show how little i know :-)
what do you mean by The buffers are written out periodically.?

Graham L
26-01-2004, 05:41 PM
The directory is an area of the "disk". It is a list of the files,and where they are stored. For speed, the OS might keep a copy in memory, rather than read and write the actual disk each time it is used. The disk copy is called a "buffer". If you tell the OS to eject the disk, it will write the directory to the disk. That is "writing (or "flushing") out the buffer". (Sometimes files are not written immediately they are produced by the computer --- they also need to be written before the disk is removed).

Usually, the OS will check every so often -- 5 secs or so-- whether there are any buffers which have not been written out, and do so.

26-01-2004, 06:00 PM
Plugging another memory card in without "stopping" or "ejecting" the old one does get some card readers upset I have found.
Corrupt files on the second card one result.

Probably as a result of the buffer getting re-written to the wrong card?

This is where significant time has elapsed since last accessing the first card as well, so its not a 5 second issue.

I now use an embedded card reader, which does not suffer from the problem. It does not require stopping and I cannot make it fault by changing cards.

Graham L
26-01-2004, 06:13 PM
That was a problem with CP/M floppies, too. :D That's what Ctrl/C was for ... and it happened in some MSDOS versions too. Then floppy drives were given a "media change" line in the interface. Then a few generation of hardware and software later the problems recur.

A "single-drive" USB device such as this one will probably risk having its directory corrupted. The OS would recognise the device being unplugged (and unregistered by the USB controller) as a medium change.

"There is nothing new under the sun." The worst "bugs"are those which are continually reinvented.