Flash Memory

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First, the technical stuff:

Invented by Dr. Fujio Masuoka in 1984, flash memory was named when one of one of his co-workers mentioned that the process of erasing this new type of memory reminded him of a camera flash.

Like RAM, flash memory can be read and written one byte at a time. There is a limitation, however, in the way flash memory must be erased in larger blocks. So for example, if you wanted to write 1 bit of data to a flash memory unit, you may have to erase 4096 kilobytes of data first. Once the target block is cleared out, all subsequent writes to that area are fairly quick.

There are two types of flash memory: NOR and NAND. Following is a brief explanation of each type:

NOR memory can be read like any normal ROM once it has been written to. In other words, a system can map NOR flash to its own address space and access it with normal memory interfaces.

NAND flash memory cannot be directly mapped to the host system’s address space. This means that to easily work with NAND memory, it must first be copied to RAM, and then copied back to the flash device when all writes are done. These restrictions and added complexity are offset by faster erase and write times, making the trade off with NOR flash worthwhile for many systems that don’t need random access to data. (For example, memory cards for digital cameras or MP3 players)

Flash memory is less long-lived than DRAM, in that you can only erase a block of data half a million times or so before the integrated circuits inside begin to break down. DRAM, on the other hand, doesn’t degrade over time.

One method of offsetting the erase limit on flash is to randomly relocate data blocks regularly, to provide even wear and tear across the chip.

Now, let’s get a little less technical!

We’ve already learned that flash memory is used in digital cameras. Different camera manufacturers design around different types of flash. Secure Digital (SD), Memory Stick, and xD Picture Cards are all popular forms of flash memory for digital cameras. Another popular form of flash memory is the thumb drive (also known as a pen drive or key drive). These handy devices are about the size of a pack of gum, and can store anywhere from 16 megabytes to 64 gigabytes of data. Since there are no moving parts, they are much more durable than floppies, compact disks, or hard drives.

There is a trend towards making certain applications re-locatable, in the sense that you can install them to (and run them from) a pen drive. All configuration settings and files are associated with the pen drive, so when you take it with you, all your important documents, bookmarks, etc, come along as well. As an added bonus, you are now completely secure if anyone were to steal your computer; your personal information can’t be stolen from your PC if it was never saved there!

Another cool use of a flash drive is using it to boot your computer. Similar to the way a LiveCD can start your computer into an operating system like Linux, it is possible to put a bootable operating system on a flash drive. If your computer supports it, this gives you the ability to debug problems with an ailing windows installation or an extra safe way to run a virus scan.

Another way to use a pen drive is by making it a music player! Some digital music players double as a USB flash drive to make the process of adding and removing songs a snap. In addition to that, it’s not uncommon to find a flash drive that plays MP3s and includes a radio tuner!

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