September 1999, Issue 110

Get Smart Media—(Part 1):
What's It All About?

FACE TO FACE

A closer look at the interface is necessary for those of you who want to become more intimate with these bite-sized storage devices (see Figure 1). The NAND flash array is set up in columns of 528 bytes called a "page."

Figure 1—Unlike conventional memory, each page of data has its own spare area associated with it.

Notice that this is a wee bit larger than an even 512 bytes. The 16 extra bytes in each page are not meant for data storage (more on this later).

A page is the smallest portion of memory that can be programmed (written to). To allow this to happen smoothly, a page buffer holds data to be written to or read from any flash page.

Stack up 32 pages and you have a block (512 × 32 + [16 × 32] = 16k + 512 bytes). A block is the smallest portion of memory that can be erased.

SmartMedia is not considered a byte-writable device. To change 1 byte (or all 528 bytes) within a page requires that a whole block be read or erased, and that the 32 pages of data be replaced with the updated data.

The smallest SmartMedia devices are 2 MB, which means that this device has 128 blocks. With 64 MB, SmartMedia is in development now, with larger devices planned. The 64-MB device requires 4096 blocks of flash memory.