Flash vs NVRAM

[wardp100]

I'm sure I'll get panned for this but can someone please clarify the distinction between Flash and NVRAM?

What has me confused is the line "By default, the configuration register is set to load the Cisco IOS from flash memory and to look for and load the startup-config file from NVRAM." (CCNA Study Guide Sixth Edition - Lammle pg. 254).

What is the difference between flash and NVRAM? Strictly speaking isn't flash NVRAM (non-volatile RAM)? My 7200 has a 16Meg flash card and 4Meg of internal flash DIMM according to a sh ver. Is the 4Meg of internal flash the NVRAM? What has me even more confused is that a dir flash:, dir slot0: (the flash card) and dir NVRAM: all show 16Meg of memory and exactly the same amount of memory left but different files, ie the IOS in dir flash: (or dir slot0: which are the same thing) and the startup- and running-config in dir NVRAM:. It looks almost as if NVRAM is a 'partition' on the flash card?

I'm sure it's a silly question and I've probably missed something, but I hope someone can please clear this up for me?

Thank you
Peter

[dbeare]

I believe the information that you are looking for is on p.175 under the Bringing Up A Router section. Hope this helps.

[darenmatthews]

Hope this helps (from http://www.cisco.com/warp/public/473/switchMEM_FLASHsizes_24050.html )

These memory devices are included in the matrix:

DRAM/SDRAM—Memory used to perform the CatOS or IOS system images.
NVRAM—Memory used to store start-up configuration file (nvram:).
OnBoard Flash—Memory used to hold system images for booting (bootdisk: or bootflash: or flash:).
Removable Flash—Memory which can be removed from the system which typically holds system images (slot0: or disk0: or disk1:).
- Daren

[laser]

just so I'm clear

Flash contains the IOS image.
The router uncompresses the IOS image from flash and loads it into DRAM/RAM?

Thx

[darenmatthews]

Yes, that is correct. Spot on.

[zoltron30]

just so I'm clear

Flash contains the IOS image.
The router uncompresses the IOS image from flash and loads it into DRAM/RAM?

Thx


yup, those pound symbols you see when the router boots indicate that the ios is being decompressed into ram. ram is much quicker than flash memory.... nvram is usually small as it really just holds a small starup file....

[FrankHenry]

The below link cleared up the confusion for me. NVRAM is on the board.

hope it helps

http://www.cisco.com/en/US/products/hw/routers/ps214/products_tech_note09186a0080094eb4.shtml

[lammle]

Be careful.
They are showing a brief explanation here.

NVRAM is a partition of Flash memory in all Cisco devices. They are not seperate chips.

Although this picture may show that, it's only for discussion to make sure that you know that NVRAM and FLASH are used for completely different reasons.

Todd Lammle

[crissa]

Hello,
if you have enough memory for an IOS but not enough enough flash you could load the IOS (at boot time) from a tftp server. If you don't have enough memory you have to use another IOS!
Bye, Tore

[HermeszData]

Be careful.
They are showing a brief explanation here.

NVRAM is a partition of Flash memory in all Cisco devices. They are not seperate chips.

Todd Lammle

Is this accurate????

The reason I ask is because I remember seeing a topic where someone had purchased a router from ebay. They did a basic power on test when the receive it to make sure it booted properly then set it aside for a while.

Later, when they were ready to put it into service in their Lab Rack, they found it would not allow them to save the config to NVRAM. Attempts at copy run start or wr received a ""NVRAM Verification Failed" error.

According the the link below, there were actually 2 2650XM routers. According to this thread, it appears that someone harvested the nvram chips at some point prior to the vendor shipping the routers to this person. Once they addressesd this with the vendor, replacement chips we sent and installed and problems solved.

http://www.techexams.net/forums/ccna-ccent/50540-fried-nvram.html

I have not looked into this further, but I suspect that all the 2600/2600XM series are the same. I also know that I can remove the CF (Flash Card) from my 2811 and 2821 and still be able to write config changes to nvram without throwing an error. When I reboot, with the flash card re-installed, it reloads with the config saved just prior to reboot (confirmed while writing this post).

As I think back about the various flash memory upgrades I have done with routers I own or purchased and sold, 2600 series, 3600 series, and 1760s, I never lost an existing config when changing flash memory modules. If, as you say, "NVRAM is a partition of Flash memory in all Cisco devices. They are not seperate chips." then any configurations stored on that partition on the flash module would move with the module (much the same as removing a HD containing partitions from a PC and replacing it with a HD with completely different partitions) and not remain on the router!

From this, I think you may understand my confusion and thus my question.

Respectfully questioning (and continully seeking knowledge)

[ddarwactor]

John and Todd, I'm wondering the same thing. While upgrading my internal flash for a subsequent IOS upgrade, I removed both sticks of existing flash and after loading the new IOS was surprised to see the same config come up that I was using prior to the upgrade. Meaning...the config wasn't on those sticks of internal flash memory (now tucked safely away in an anti-static bag). Am I missing something?
I realize this is an old post but didn't see a final response so thought to get an update. Thanks!

[Big Evil]

This may help.


http://www.cisco.com/en/US/docs/ios/12_0/configfun/configuration/guide/fcmemory.html

[ddarwactor]

It sure did, thanks!