Keith Nuttle wrote:
I have recently had a Windows XP computer that I replaced with a Windows
8.1 computer. I scrubbed the disk with a disk eraser.

Question: If I were to scrub a thumb drive or flash card, does it need
the multipass cleaning that a hard drive would require?

Thumb drive/flashcard stores in is chip memory, "and/or" gates. It
seems like once the gate was change there would be no residual
properties to remove.

A hard drive stores by changing the surface properties of the disk.

The flash device does not use magnetism and doesn't have
a fringing field to worry about. A single pass
should take care of it.

Using Guttman erasure for that, would be a waste of
write life on the storage device.

If blocks of flash memory get spared out, those
old blocks may not get erased. And while an
SSD has "Enhanced Secure Erase" as a means to
try to erase them, I don't think the USB flash
drive has a mechanism for that. Just ordinary writes
are available to erase a USB flash key. You would
use a USB flash key with encryption, if you want
all data at rest to be encrypted (even data locked
into a spared out block).

Paul