Terry said:
much slower?
How you would compare it's speed to a hard drive?
I know that most flash memory has a USB interface. How much faster
would flash memory be if it were plugged into the computer bus?
The flash design is divided into two parts. The flash memory chip
is one part. A controller is the second part. The controller converts
the USB packets, into a format suitable for driving the memory
chip.
(Works for me in IE...)
http://www.toshiba.com/taec/adinfo/mlcnand/popup_nand_nor.html
NAND flash is divided into two types. SLC is single level.
MLC is multi level (2 bits per cell). MLC gives higher
density, but has a reduced number of write cycles. And if
you look at the charts for "program" or write rate, SLC
has the better write performance.
SLC is rated at 8MB/sec write and 24MB/sec read. A hard drive
is 60MB/sec speed near the start of the disk, and 40MB/sec
near the end of the disk. So flash is not even close,
when it comes to write speed.
The USB bus is 60MB/sec theoretical cable speed, but around
57MB/sec using real packets, and a lot less than that, when
real time overheads are taken into account. But using USB2 for
flash, in the example cited above, should not be the limiting
factor.
And flash is constantly being improved, so there could well
be designs that go faster than the chart above. More companies
than just Toshiba, make flash.
DRAM is a lot faster. If we take just one chip off a DDR2-800
DIMM, a chip that has an 8 bit interface, then it would
transfer 800MB/sec. The whole DIMM would be PC2-6400 or 6400MB/sec.
http://en.wikipedia.org/wiki/DDR2
If you operate the flash chips in parallel, then any speed you
want is possible (assumes min transfer size is huge). It just
takes a large enough number of chips. Sort of like a RAID 0
array, only using flash chips. For example, a PCI Express x16
card, filled with flash chips, would make a dandy ReadyBoost.
This is an older card, holding a number of flash chips. This
whole board is only twice as fast as a USB stick
http://www.cetia.com/graphics/products/flash.jpg
Paul
