Understanding Flash Memory and associated concept

Flash storage a definition:

Flash storage systems are composed of a memory unit and an access controller. The memory unit is used to store data.

The access controller manages and controls access to the storage space on the memory unit.

Types of flash memory:

1.   NOR flash

-       This has every cell connected to ground and interns it resemble the way NOR gate behaves,

and due to same reason this can be programmed randomly. And it byte addressable  

2.   NAND flash

-       Nand flash connects several cell connected in series, interns resembles with the Nand gate.

Due to the reason it can be programmed, only in blocks/pages not bytewise( Randomly)

Note: Both the flash memories uses field effect MOSFET-Metal oxide filed effect transistor- FET is  voltage controlled device while BJT- Bi polar junction transistors is voltage controlled device.  

What causes flash to store data permanently ?

Flash is a transistor-based silicon memory technology that can store information permanently by trapping electrons into,

floating-gate transistors( Field effect MOSFET)

Flash memory advantage and limitations

NOR Flash:

 Pros

-          Offers random access and hence Byte can read and written like in RAM.

-          Board can be booted directly from this type of flash memory,  as it offers random access.

-          NOR offers faster read speed.

Cons:

-          However, with NOR technology, write and erase functions are slow compared to NAND

-          NOR also has a larger memory cell size than NAND, limiting scaling capabilities and therefore achievable bit density compared to NAND

Usage: PDA, mobile phone( usually internal memory)

NAND flash:

Pros:

-          Cost effective, cheaper than NOR,

-          Size is smaller than NOR

-          Erase is cycle is faster than that of NOR.

-          can be used where big memory size is needed ideally, uses NAND gate.  

Cons:

-          No random access

-          Board can never be directly booted from this  kind of flash.

Usage: Device in which larger permanent storage is required. I.e. Digital camera, SD cards