Monday, January 7, 2008
Flash Memory Basics
What's the anatomy of a memory card?
Have you ever wondered what's inside your memory card? How can they keep cramming more storage in the same space, or how much further can the prices fall? It seems like, only yesterday, we needed to take out a second mortgage to buy a 256 MB CF card. Now you can find 2 GB cards for as little as $15.
The mass adoption of digital photography in recent years has fueled the growth for flash memory cards, as capacities increase and average selling prices continue to decline. This article, the first in a two-part series, attempts to explain the core components of memory cards, the technology differences and the basic economics of these products as they play an increasingly critical role in our digital workflow.
Most modern memory cards contain two main components, a NAND flash memory controller chip and one or more flash memory chips (Figure 1). NAND stands for “Not AND” vs. AND or NOR, i.e. “Not OR,” and it's the type of flash memory most commonly used in memory cards today. It's all based on Boolean logic, and while there are technical differences, they really aren't worth dwelling on here. The most important aspect of any flash memory is that, unlike a computer's DRAM, it has the ability to store data for long periods of time without requiring a power source.
The controller chip functions like a traffic cop and translator between the “host device,” usually a camera or reader, and the NAND flash memory (Figure 2). Controller chips are critical because they provide an industry-standard interface, such as SD or CompactFlash, on the host side to which cameras can be designed, thus insulating the host from changes in flash technology, densities or speeds. In most cases, you can plug old CF cards into new cameras, and they still work.