Solid state memory retains data even when it is not powered on. It can accept only a limited number of writes in its lifetime, however, and eventually wears out.

Wear leveling and garbage collection, which are discussed in detail in upcoming slides, are techniques used to extend the life of the memory and increase storage efficiency.

There are two types of solid-state memory used in smartphones, including NAND and NOR. NOR is commonly used for firmware, while NAND is generally used for storage of user data.

NAND versus NOR flash

•  NOR commonly used for firmware

•  NAND commonly used for user data

•  NAND blocks are subdivided into pages

•  NAND is more commonly used today

Smartphones store data on one or more chips within the phone that use flash memory technology. They may also store additional data on removable storage cards (microSD) and/or SIM cards, which are discussed later in this section.

For solid state memory, data is written to flash memory in units called pages. Pages are made up of multiple cells. Blocks are made up of multiple pages.¹

Flash memory can only be erased in larger units called blocks.

An empty unit of flash memory is filled with 1s rather than with 0s as with traditional hard disk drive type media. Erased blocks are overwritten with 0x1111111.

Reference:

[1] https://for585.com/9ahez (Image)