> (was Re: [linux-usb] usb-storage types (was: how do I do a port > > ... software ... for random-block flash access > > ... chokes over random-track disk access until/unless > > you put a fetch-around track cache in the middle.))) > If a device ... chokes on valid sequences ... Sorry to be unclear: the device doesn't choke, the [idiot] host chokes because it didn't cache appropriately. What I mean is that if you work where a late answer is a wrong answer then suddenly sequences valid for a flash drive may not be valid for a disk drive. Try accessing blocks in random orders, and measure time to read. I cannot say myself, but I hear that flash gives fairly constant time to read. Spinning media, by contrast, has to wait a revolution before it again sees the block it just saw. Spinning media performs like a hash table: you get constant time to the first block of a group, then you suffer linear search. Often, a strategy as simple as reading blocks in exactly reverse order will defeat any cache between you and the media, and you will see a block appear like clockwork once per rev. Even at 7200RPM once per rev is an infinity: 8,333,333ns. Down at 3600RPM, you get twice infinity. > > Where does flash memory fit? > Alan Cox <[EMAIL PROTECTED]> > ... San disk stuff claims to be a removable hard disk ... > Matthew Dharm <[EMAIL PROTECTED]> > ... Most flash memory devices call themselves direct-access ... x4402 Pat LaVarre of iOmega [EMAIL PROTECTED] http://members.aol.com/ppaatt/ --------------------------------------------------------------------- To unsubscribe, e-mail: [EMAIL PROTECTED] For additional commands, e-mail: [EMAIL PROTECTED]
