SCSI to SD/IDE
csquared3 at tx.rr.com
Mon Dec 6 10:29:30 CST 2010
On 12/5/2010 1:10 PM, Chuck Guzis wrote:
> Okay, a faintly related question to this thing with SD cards.
> Are USB pen drives any better at leveling wear than SDHCs? The
> reason I ask is that there's a USB 2.0 flash driver available for the
> inexpensive AVR90USB162 chip that might also work as a SCSI-emulated
> device. Any sort of buffering isn't possible, as the chip only has
> 512 bytes of SRAM. But there are many other inexpensive USB-capable
> microcontrollers as well.
I had been wondering the same thing. I did a bit of internet searching
and found that it appears that the controller inside the USB stick does
do some degree of wear leveling. I thought the following URLs were
I had not thought of the fact that wear leveling has security
implications as indicated here. Surely this is not an issue with
vintage systems though.
Then I wondered about CF and SD, and found that they appear to be wear
leveled internally as well.
I must say that all this makes me feel much better about their potential
use as hard drive substitutes in vintage systems. I also learned that
some of the USB drives have a RAM buffer (512 bytes or so), so one might
not even need to worry much about buffering data in a bridge device. I
do wonder what algorithm they use to decide when to write the RAM to
flash - probably varies some by manufacturer. I do think the bridge
should provide a "flash drive busy" indicator to discourage removal of
the flash device while a write is in progress. The built in LED in most
USB drives might suffice for them, but I don't believe I've ever seen
that in a CF or SD card.
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