How Flash Memory Works – Advantages & Disadvantages

What is Flash Memory?

Flash memory is a type of erasable read-only memory (EEPROM) that clears and rewrites data in chunks for fast, energy-efficient access and rewriting. Flash memory, or flash storage, is non-volatile, which means it remains viable even without an active power source. Although technically a type of read-only memory (ROM), flash memory is distinct from conventional ROM in that you can edit it as well as read it.

How Does Flash Memory Work?

Flash memory comes built into solid-state chips, and each chip houses an array of flash memory cells. Rather than use the traditional electromechanical method, flash memory uses electrical circuits to log data. Here’s the process:

1. Current flows through the transistor between each cell’s source (electric input) and drain (electric output).

2. The transistor controls the current’s path of by acting as an on-off switch, or a gate.

3. An “on” transistor allows the flow of electrons across the cell, which stores a 1 in binary code.

4. An “off” transistor blocks electrons and stores a 0.

Volatile memory like random access memory (RAM) returns all the gates to the 0 state when the power source turns off, thus erasing all stored data. But ROM, including flash memory, works by adding a second gate, known as the “floating gate,” to each cell. As electrons pass through a transistor in the “on” state, some get stuck to the floating gate and remain there to store a 1 indefinitely, with or without power. All types of programmable ROM (PROM) experience this partial loss of electrons. In electrically erasable PROM (EEPROM), the gate will only stop electrons when a user applies a specific negative voltage to the gate to return the transistor to 0.

Types of Flash Memory: NOR and NAND

Flash memory comes in two basic types: NOR and NAND. The names reflect the types of logic gates each type utilizes. Logic gates are groups of transistors that work together to carry out an “if-then” operation to produce the desired output. The logic gate’s structure determines which output will result from any possible input.

-NOR flash memory. NOR has a faster read speed than NAND and can read and edit more precisely, but it comes at a higher price point per byte. Users choose NOR flash memory mostly for executing code.

-NAND flash memory. NAND has a slower read speed and can only access memory in blocks rather than bytes, but it is cheaper than NOR. It works well for storing large and frequently-updated files.

Pros and Cons of Flash Memory

1. Disadvantage: Editing Ability. The main drawback of most EEPROM is that editing memory byte by byte can take an unacceptably long amount of time. Flash memory addresses this issue by grouping bytes into chunks, or “blocks,” which cuts down the editing time significantly. Grouping the bytes into blocks speeds up the process, but it also means you lose the ability to edit specific bytes. A computer can read a specific byte from any address on the flash chip, but it can only erase and rewrite in block units.

2. Disadvantage: Lifetime. Flash memory does not have an infinite lifetime. Applying high voltage fields eventually degrades the transistors, which means the floating gates will take longer to work. However, most types of flash don’t start to slow down until at least 10,000 rewrites, and you can distribute those edits over the entire chip to limit the functional impact of the wear and maintain utility for much longer.

3. Advantage: Efficiency. Because flash memory stores data without the use of moving mechanical parts, its operation requires less energy than older systems. Flash memory also stores data much more compactly than a hard drive can.

New developments in flash technology continue to decrease the cost per byte of flash memory. Flash chips are also sturdier and more drop-resistant than their predecessors, which makes them great for mobile devices, including digital cameras and camcorders, cell phones, MP3 players, and notebook computers.