Jan 15, 2014

Understanding Flash Memory Cards

Removable Flash Memory Cards

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.


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