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

MS-DOS


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The information in this article applies to:

 - Microsoft MS-DOS operating system versions 4.x, 5.x, 6.0, and 6.2
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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.