I'm still confused about NVRAM (Non Volatile RAM) physical implementation. Does it always works like the CMOS in our PC mainboard, I mean always backed-up with a lithium battery or it can be implemented without the battery and in the latter case is it working like a flash ROM ? And what the term's exact meaning ?
Posted on 2003-04-25 03:48:43 by Pinczakko
humm, I don't know whether NVRAM is a specific type of ram, or a category. I am rather certain that the nonvolatile ram used in eg USB memory devices (some sort of flash ram?) isn't battery backed, and it would seem weird & unlikely for the various flash memory cards to be battery backed, too.

Also, battery backing for solid state harddrives? Humm.
Posted on 2003-04-25 03:54:22 by f0dder
nvram is a non-volatile ram, aka its data not disappear when the power is off. so, its like a rom. dont know how the exact implementation, but maybe its like flash.
Posted on 2003-04-25 07:57:08 by dion
I don't remember how nvram works or the difference between it and flash. I do recall working for a vending machine company and we used these huge capacitors to store a charge for memory and, I think, the mcu so it could run even when the power was off. The caps were 1 or 2 whole farad! I think they were made by Sony and were slightly smaller than a hockey puck.
Posted on 2003-04-25 08:12:57 by drhowarddrfine
IMHO you are wrong. NVRAN (As far as I know) is combination of two types of memory - there is a RAM bank and EEPROM bank. When the chip is powered, the RAM bank works and this gives the high speed operation (EEPROM and FLASH are very slow and allows very little write cycles - about 10^5..10^6 for eeprom and less for FLASH). When the power goes down, the chip backups the RAM bank to the EEPROM. (And of course when the power comes -> the RAM is loaded from EEPROM).
Posted on 2003-04-25 08:45:56 by JohnFound
RAM is RAM, EPROM is EPROM, EEPROM is EEPROM.

Basically, they are all advertising logos, but they do accurately describe the products.

I am most familiar with Dallas Semi's NVRAM. They use CMOS for low/no power when idle, and actually include a small battery cell inside the package to provide the hold-on voltage during power off.

For a bulkier package, you get the advantage of EEPROM with the speed of RAM.
Posted on 2003-04-25 17:46:32 by Ernie
Ernie's right. NVRAM (aka Battery Backed RAM) is just low power RAM combined with a battery and bus isolation circuity.

EEPROM, Flash, etc. are all non volatile.

Flash is a version of EEPROM. It's called Flash because you program sectors instead of bytes at a time. Sectors vary in size from one chip to another (SST 29C010 has 128 byte sectors while Winbond 29C040 uses 256 byte sectors)
Posted on 2003-04-26 02:24:19 by eet_1024