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Nonvolatile flash memory is semiconductor memory that keeps its stored data when power is removed. It can be electronically programmed and erased, and it appears in both consumer storage products and embedded electronics. The two main flash architectures, NAND and NOR, are built for different jobs: NAND for dense data storage, NOR for fast reads and direct code access.
What “nonvolatile” means
A nonvolatile memory keeps its contents without a continuous power supply. Volatile memory does not. Samsung Semiconductor’s flash-memory glossary (page accessed 2026-10-07) contrasts flash with DRAM and SRAM, which lose saved data when power is switched off. Flash keeps the data, which is why it suits anything that must survive shutdown or removal from a device.
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The word describes retention without power. It does not promise that data lasts forever, and it does not mean the memory cannot wear out. Those limits are covered below.
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Flash is one type of nonvolatile semiconductor memory, not a synonym for the whole category. Altera’s Nios V Embedded Processor Design Handbook (version 25.3.1, dated 2026-04-09, section 2.3.2) lists flash, EPROM and EEPROM as examples of nonvolatile memory. The same section explains why the category matters to system designers:
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“Non-volatile memory retains its contents when the power switches off, making it a good choice for storing information that the system must retrieve after a system power cycle.”
What separates flash from its siblings is that it is electronically programmable and erasable, and it is commonly packaged in high-density arrays. Kingston’s Flash Memory Guide treats flash as a technology built on this electrical rewrite capability and names NAND and NOR as its two principal forms. That guide is older, so use it for background rather than for current product specifications.
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NAND and NOR: two flash architectures for different jobs
Both NAND and NOR are flash, but they are organized differently and tend to be chosen for different reasons. The comparison below reflects broad design tradeoffs stated by Samsung’s NAND glossary (accessed 2026-10-07) and Infineon’s NOR overview (accessed 2026-10-07). It is not a ranking that holds for every device.
| Attribute | NAND flash | NOR flash |
|---|---|---|
| Typical role | Mass data storage | Firmware and embedded code storage |
| Strength cited by sources | Dense storage in a small footprint | Fast random reads and direct code execution |
| Read behavior | Not stated in the consulted sources beyond the dense-storage role | Retains data without power; suited to direct access by the processor |
| Typical products named | Storage products such as USB drives | Embedded systems and firmware-holding devices |
The practical reading is simple. If the job is holding a large volume of user data, NAND is the usual choice. If a processor must fetch instructions directly from the memory, NOR is the usual choice. Avoid assuming one is faster overall: read speed, write speed, erase behavior, density, interface and the specific device all affect the outcome.
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Where nonvolatile flash appears
Samsung lists digital cameras, phones and USB drives among everyday products that use flash memory. In a USB drive, the flash is packaged with a controller and an interface, so the drive is a storage product, not a bare memory chip. The same principle applies to embedded electronics, where nonvolatile memory holds:
- Boot code that the device needs at startup.
- Persistent settings that must survive a power cycle.
- FPGA configuration data, which the device reloads when it powers up.
What nonvolatile does not guarantee
Three limits matter in practice, and none of them is captured by the one-word label.
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- Supports SPI interface.
- Capacity: 64M-bit / 8M-byte.
- Clock frequency: ≤104MHz.Work voltage: 2.7-3.6V.
Retention depends on conditions
“Nonvolatile” means power is not needed to maintain stored data under the device’s specified conditions. Those conditions, such as temperature and time since the data was written, vary by product and are set by the manufacturer. Check the datasheet for the retention figure that applies to your part rather than assuming a general duration.
Erase cycles are finite
Altera’s handbook notes that nonvolatile memory is usually erasable only a limited number of times. The page does not give a universal cycle count, and none should be assumed for all flash. Endurance is a property of the technology and the specific product.
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- 【Four Times Operating Efficiency】: The operating frequency of 104MHz is equal to 416MHz (50mbytes/sec), which is equivalent to four times the operating efficiency of ordinary single wire SPI
Retention figures are product-specific
Dell’s guidance on prolonged power-off retention for SSDs and NVMe drives (accessed 2026-10-07) gives a minimum retention duration under a stated standard and at maximum rated endurance. That is a conditional requirement for specified drive circumstances, not a general fact about flash memory. Use it as an example of how retention is qualified, not as a figure for other products.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.Common misreadings
- “All nonvolatile memory is flash.” EPROM and EEPROM are also nonvolatile, as the Altera handbook lists them.
- “A USB drive is a flash chip.” A USB drive is a packaged product that contains flash along with other electronics.
- “NOR is always faster.” NOR is cited for fast random reads and direct code access, not for superiority in every measure.
Checking a flash device’s specifications
When you need to confirm that a specific device will keep its data, look for these items in the datasheet or product documentation:
- The stated data retention period and the temperature condition attached to it.
- The rated endurance, usually expressed as program/erase cycles.
- Whether the part is NAND or NOR, since that determines whether it suits bulk storage or direct code execution.
- Whether the figures apply to the chip, the module or the complete product.
Those four checks answer most questions that the word “nonvolatile” leaves open.
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