Wireless Hacks. 1917 IndustrialStrength Tips and Tools [Electronic resources] نسخه متنی

Hack 52 Compact Flash Hard Drive

Make your own tiny hard drive with no moving
parts and very low power consumption.

One challenge when
building your own embedded device is finding enough storage for the
operating system and any data you need to keep track of. While 2.5"
laptop hard drives probably have the highest ratio of storage space
to physical space, they introduce a couple of challenges for an
embedded system. A hard drive is a mechanical device, with fairly
strict environmental operating conditions (for both temperature and
humidity). They generate noise, draw a fair amount of power, and
above all, are quite fragile. In other words, you probably
wouldn't want to consider leaving one in a
relatively unprotected plastic box on your roof through the winter or
summer.

A very popular alternative to traditional hard drives is to use
flash RAM
instead. Flash memory uses only a tiny fraction of the power that a
hard drive uses, and can operate over a much wider range of
environmental conditions. It is very tiny, lightweight, and
noiseless. It can be rewritten many thousands of times, and can even
be dropped on the floor without fear of loss of data. While it
isn't nearly as cost effective in terms of price per
bit, the popularity of digital cameras has driven flash memory prices
down remarkably. If your application can fit in 32 to 512 MB of
space, then flash storage is a viable alternative to 2.5" hard
drives.

Many types of flash media can be used
as a standard IDE device by using a simple converter, shown
in Figure 4-15. One device I particularly like to
use is the CFADPT1 from Mesa Electronics. Their memory devices are
available online at http://www.mesanet.com/diskcardinfol. It
can be used on a standard IDE chain or on the SFF IDE found in
laptops. As the SFF IDE bus provides power on the data cable
(standard IDE doesn't), you need to connect a spare
floppy power connector to the adapter when using it with standard
IDE.

Once a CompactFlash card is inserted into the IDE adapter and
attached to your computer, no further configuration is necessary. CF
drives require no special drivers, and appear to be standard IDE
devices to the host computer. Partition and format them as you would
any other IDE device. Once an OS is installed, you can even boot from
them.

Mesa also carries hard-to-find SFF IDE ribbon cable with
connectors installed for a reasonable pricejust ask. A number
of suppliers carry CF-to-IDE adapters, and the going rate is about
$20. While SmartMedia and Memory Stick adapters are also available,
CF-to-IDE tends to be the cheapest way to go.

At the time of this writing, 512 MB compact flash cards are available
for under $100, 256 MB cards are available for around $50, and 128 MB
cards are going for an unbelievable $20. These are ideal for running
a micro Linux distribution, such as Pebble [Hack #53]. Note
that while you won't need one of these for use with
the Soekris [Hack #51] as it boots from CF
directly, these adapters will allow any computer with an IDE
interface to eliminate its most unreliable component: the hard
drive.