Removable Flash Memory Cards

While your computer's BIOS chip is the most common form of
Flash memory, removable solid-state storage devices are also
popular. SmartMedia and CompactFlash cards are both
well-known, especially as "electronic film" for digital
cameras. Other removable flash-memory products include Sony's
Memory Stick, PCMCIA memory cards, and memory cards for video
game systems. We'll focus on SmartMedia and CompactFlash, but
the essential idea is the same for all of these products --
every one of them is simply a form of flash memory.

There are a few reasons to use flash memory instead of a hard
disk:

* It has no moving parts, so it's noiseless.
* It allows faster access.
* It's smaller in size and lighter.

So why don't we just use flash memory for everything? Because
the cost per megabyte for a hard disk is drastically cheaper,
and the capacity is substantially more.

The solid-state floppy-disk card (SSFDC), better known as
SmartMedia, was originally developed by Toshiba. SmartMedia
cards are available in capacities ranging from 2 MB to 128 MB.
The card itself is quite small, approximately 45 mm long, 37
mm wide and less than 1 mm thick.

As shown below, SmartMedia cards are extremely simple.
A plane electrode is connected to the flash-memory chip by
bonding wires. The flash-memory chip, plane electrode and
bonding wires are embedded in a resin using a technique
called over-molded thin package (OMTP). This allows
everything to be integrated into a single package without the
need for soldering.

The OMTP module is glued to a base card to create the actual
card. Power and data is carried by the electrode to the
Flash-memory chip when the card is inserted into a device.
A notched corner indicates the power requirements of the
SmartMedia card. Looking at the card with the electrode
facing up, if the notch is on the left side, the card needs
5 volts. If the notch is on the right side, it requires 3.3
volts.

SmartMedia cards erase, write and read memory in small blocks
(256- or 512-byte increments). This approach means that they
are capable of fast, reliable performance while allowing you
to specify which data you wish to keep.They are less rugged
than other forms of removable solid-state storage, so you
should be very careful when handling and storing them.
Because of newer, smaller cards with bigger storage
capacities, such as xD-Picture Cards and Secure Digital
cards, Toshiba has essentially discontinued the production of
SmartMedia cards, so they're now difficult to find.

CompactFlash cards were developed by Sandisk in 1994, and
they're different from SmartMedia cards in two important
ways:

* They're thicker.
* They utilize a controller chip.

CompactFlash consists of a small circuit board with
flash-memory chips and a dedicated controller chip, all
encased in a rugged shell that is thicker than a SmartMedia
card. CompactFlash cards are 43 mm wide and 36 mm long, and
come in two thicknesses: Type I cards are 3.3 mm thick, and
Type II cards are 5.5 mm thick.

CompactFlash cards support dual voltage and will operate at
either 3.3 volts or 5 volts.

The increased thickness of the card allows for greater
storage capacity than SmartMedia cards. CompactFlash sizes
range from 8 MB to as much as 100GB. The onboard controller
can increase performance, particularly in devices that have
slow processors. The case and controller chip add size,
weight and complexity to the CompactFlash card when compared
to the SmartMedia card.