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Microsoft KB Archive/103825

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What Is Nonvolatile Random Access Memory (NVRAM)? PSS ID Number: Q103825 Article last modified on 11-11-1993 PSS database name: O_MSDOS

4.x 5.x 6.00 6.20


The information in this article applies to:
- Microsoft MS-DOS operating system versions 4.x, 5.x, 6.0, and 6.2

Nonvolatile random access memory (NVRAM) is a generic term for any read/write data storage system that does not lose data when the main system power is removed.

Other types of nonvolatile memory include FLASH memory, FLASH disk, electronic programmable read-only memory (EPROM), electrically erasable programmable read-only memory (EEPROM), and bubble memory.

Another form of nonvolatile memory is the combination of CMOS STATIC RAM and a battery. The battery provides the RAM chip with power while the main power supply is turned off. The battery should be strong enough to prevent the loss of data stored in the RAM chip.

In the personal computer environment, the nonvolatile RAM is implemented as CMOS RAM, which is generally contained in a chip that also contains the clock and/or calendar and the other system functions that need to continue operating even during periods without power.

When systems “lose their CMOS,” it may be caused by a weak battery, a bad battery connection, or a spurious write cycle. A well-designed NVRAM circuit has a write-protect circuit that prevents stored data loss when the CPU bus is being initialized during power up and power down.

Additional reference words: 4.00 4.01 4.01a 5.00 5.00a 6.00 n-vram nram non-volatile 6.20

Copyright Microsoft Corporation 1993.