I see that some flash drives advertise cd-rom like speeds: 200x or 150x,
for example. How do those speed translate to read and write speeds?
200 * 150KB/s, 150 * 150KB/s, as is also the case with CD
speeds.
There is a somewhat relevant (though now dated, not
including drive models you'd want today) article here:
http://www.anandtech.com/memory/showdoc.aspx?i=2549
Can their ratings be trusted?
Usually no, not directly relating to the real performance
you'll see in use, but if comparing two such flash drives
from manufacturers you trust, the higher speed will tend to
mean higher actual speed even though the actual is lower
than stated. Remember they may be optimistic, that 150X
actually means "up to" 150X.
I saw one advert that equated 200x to 32MB/s, but I don't know if that's
read or write, or one of those "up to" speeds.
It's always going to be "up to", the max read speed. Most
often to get nearest that you would be transferring few,
large files instead of small ones. For max write speeds
you'll need to dig deeper, contact the manufacturer, seek a
review of the product, or move on - buying from a different
manufacturer who will at least provide this important spec
instead of hiding it... though frankly I think they hide
specs when they have something to hide, as otherwise a
higher write speed indicates a more desirable product worth
more in the market.
Products with higher write speed tend to cost 70-100% more
for the same capacity in the 2GB to 8GB sizes, because
they're using SLC instead of MLC flash chips which cost
more, but also have roughly 10X higher write cycling which
could be important in certain high write cycle uses.
