W25Qxx
The W25Qxx is a common series of serial EEPROM chips.
Naming
These EEPROM chips are typically named "x25qxxx" where the first x indicates the manufacturer ("W" indicates Winbond) and the xxx after the Q indicates the size (in Mbits). A "W25Q128" is therefore 128 Mbits = 16 mB EEPROM manufactured by Winbond.
Connections
W25Qxx devices are available in a number of different packages, but the most common is a SOIC-8 package. These will typically have the following pinout:
It is worth noticing that many (if not all) of these devices can operate in two different "modes". Regular SPI with a MOSI/MISO pair of signals, and Quad-SPI where 4 data lines are being used.
Memory Layout
The memory in these devices are divided into blocks, sectors and pages.
Blocks
At the highest level is the "block". Blocks will typically be chunks of 64kB. In the case of the W25Q128 it will look like this:
