Flash memory is often used in embedded systems as a means to store data and information, providing the system with the needed instructions to operate. Two of the most widely used types of Flash memory include NOR and NAND Flash. In this article, we’ll discuss the key differences between NOR and NAND Flash, as well as some advantages and disadvantages of each.
What is Flash Memory?
Flash memory is a non-volatile memory storage device that can be electrically erased and reprogrammed. Non-volatile memory means that the memory device will retain the stored data even when the system is powered off. One of the reasons that Flash memory is often used in embedded systems is its ability to erase data in blocks rather than by individual bytes. Because Flash memory needs to be erased before it can be programmed, this helps expedite the process and allows for faster programming.
There are several different types of Flash memory, but the most commonly used include NOR and NAND Flash. Both of these types of Flash memory store data in memory cells made from floating gate transistors. NOR and NAND Flash get their names from the type of logic gate used in the cell and differ through their architecture and purpose.
NAND and NOR Flash Architecture and Purpose
NOR flash is optimized for random access capabilities, which means it is capable of accessing data in any order and does not require following a sequence of storage locations. In its internal circuit configuration, each of NOR Flash’s memory cells are connected in parallel; one end of the memory cell is connected to the source line and the other end is connected to the bit line. Because of this, the system is able to access individual memory cells.
NAND Flash, on the other hand, is optimized for high-density data storage and gives up the ability for random access capabilities. Unlike NOR Flash, NAND Flash cells are connected, usually eight memory transistors at time, in a series to the bit line called a string. Here, the source of one cell is connected to the drain of the next one. This series connection reduces the number of ground wires and bit lines, and as a result of this configuration, NAND has a smaller cell size. This does not however allow for direct access to individual cells.
Advantages and Disadvantages of NOR and NAND Flash
Memory Capacity and Size
Because NAND Flash offers higher densities, it is capable of much higher memory capacities. This gives it an advantage for data storage applications such as Flash drives, digital cameras, and USB drives. Because of its higher densities, NAND has a smaller memory cell size and is able to scale.
Image by Conversely, NOR Flash offers a lower density and therefore has a lower memory capacity compared to NAND. This makes NOR Flash more appropriate for low-capacity and high-reliability applications, such as storing code in devices including cell phones or medical devices. Additionally, NOR has a larger memory cell size which limits its scaling capabilities compared to NAND.
Write/Erase/Read Performance
The architecture of NOR and NAND Flash affect how each perform when writing, erasing, and reading data. Because NOR Flash memory cells are connected in parallel and can be accessed directly, this enables short read times. However, due to NOR Flash having a larger cell size and its more complicated erasure process, this affects its ability to write and erase as quickly compared to NAND.
On the other hand, NAND’s memory cells are connected in a series which are organized into pages which are then sub-organized into blocks. NAND reads are slower since it supports page and block access, not random access where it can read each byte individually. However, NAND writes and erases are quicker than with NOR.
Power Consumption
In terms of power consumption, NOR requires more current when it is first powered on, but requires less power for standby. Conversely, NAND requires less power to start up, but more for standby power. However, both NOR and NAND both are comparable in its instantaneous active power, but this can vary depending on how the memory is used. For instance, NOR is typically slow on writes and consumes more power than NAND. NOR is typically fast on reads, which consume less power.
Cost
Due to its smaller size and high-density configuration, NAND has a lower cost per bit compared to NOR Flash.
Summary
In summary, NAND Flash offers high storage density and a smaller cell size. With its low-cost, high-density, high-speed program/erase applications, NAND is often preferred for file storage in consumer applications. NOR Flash offers a much faster read speed and random-access capabilities, making it suitable for storing and executing code in devices such as cell phones.
Support for Flash Memory Programming
Total Phase offers various host adapters that can be used to program I2C- and SPI-based NOR Flash memory devices. Our host adapters are fit for a variety of different project requirements.
The Aardvark I2C/SPI Host Adapter is a general-purpose I2C or SPI host adapter that can be used to transfer serial messages using the I2C or SPI protocols.
The Cheetah SPI Host Adapter is a high-speed host adapter that is specialized to communicate with high-speed, SPI-based Flash memory. It is capable of communicating over SPI at up to 40+ MHz.
The Promira Serial Platform is our advanced FPGA-based platform that can perform high-speed I2C or SPI programming. Depending on the application, this tool supports up to 80 MHz as an SPI master and up to 3.4 MHz as an I2C master.
The Flash Center Software is a software package that allows engineers to quickly erase, program, and verify I2C- and SPI-based EEPROM and Flash memory chips that are interfaced through the Aardvark I2C/SPI Host Adapter, Cheetah SPI Host Adapter, and Promira Serial Platform.
The software natively supports over 500 memory chips from major chip manufacturers that can be found within the parts library. The software provides expansive support for NOR SPI Flash memories, including Micron N25Q Serial NOR Flash memories and Spansion Serial NOR Flash memories, just to name a few.
If users don’t see their part listed, it’s possible to easily add the part by following these steps: How to Create and Add a Custom Flash Part to Flash Center Software
For more information on how our tools can support your Flash programming requirements, please email us at sales@totalphase.com.