Why not just store startup configuration file in Flash Memory?

[169.254.X.Y]

I do definitely know the differences between NVRAM and Flash memory. I did googled for past few days, but I was not able to find the 100% satisfying answer. Some people said that nowadays, people can actually store the startup configuration file in Flash. Others said no because of booting process plus because of the speed(NVRAM is faster than Flash). I am just wondering why smart people invented NVRAM. + Why can't the router just load IOS from flash and then get the startup configuration file from flash, and skip the NVRAM?    

P.S. After pondering, I figure out why we should not save the startup configuration file in FLASH Memory. I am not 100% sure, but I am 99% sure. It is because of configuration register value :) If you carefully look at these two register value [0x2102 and 0x2142], you would agree with me. If you don't agree with me, please share with me your thoughts :) 

[Julio E. Moisa]

Hi

The following link can be useful. And Actually the IOS image is loaded from the flash: (compact flash:), now the idea with the configuration file is be saved into nonvolatil drive. 

https://supportforums.cisco.com/t5/lan-switching-and-routing/where-is-the-startup-config-stored/td-p/1336554

[Joseph W. Doherty · Accepted solution]

Let's take a trip down memory lane.  (Pun intended - laugh).

Returning to yesteryear, NVRAM (or PROM) was very expensive, and so often devices only had small quantities.  So, only what critically was needed, and would fit, was placed into such a hardware resource.  The startup config file, which often was changed, and wasn't too larger, was well servered by NVRAM.  Of course, on some systems, a large startup config (or multiple different copies) wouldn't fit in NVRAM, and so, Cisco provided an option to compress the startup config.

Also recall, on some of the earlier Cisco devices, IOS came on ROM.  If you wanted to upgrade the IOS, ROM chips had to be physically swapped.

[169.254.X.Y]

Thank you very much :)

[wambenarcisse@yahoo.fr]

This answer is not satisfying. When you change any configurations, confs are applied directly on RAM (and the relevant programs are configured directly) but that doesn't tell us why confs should be in NVRAM to persist between boots. In fact I don't see any reason for this. Boot is the heaviest process it takes sometimes to finalize and you got NVRAM's content at startup or when you copy nvram's content to the RAM but for a little file it is very very quick to do a copy from say a HDD to a RAM and more quick from a Flash to a RAM and vis-versa. So what is the critical reason which oblige us to use something as quick as a NVRAM? to do an off-load copy so tat CPU is no busy?   

[Joseph W. Doherty]

Sorry, are you not satisfied with the information I provided, or are you not satisfied with Cisco's approach?

[wambenarcisse@yahoo.fr]

Both are not satisfiying. it takes very few times to save a little block of KBytes even in a HDD it is very quick.

So I don't understand the criticality of saving startup inside a NVRAM instead of a Flash memory (saving all datas inside a flash).

[Joseph W. Doherty]

You've mentioned HDD twice. Perhaps you've overlooked the state of HDD technology in the 80s? I remember when some of the first HDDs, also in the 80s, became available for microcomputers. There were just a "tad" larger then they are today; not inexpensive, either. Also, I suspect, Cisco's NVRAM probably has more robust operational specification than HDD, even today's. Perhaps you don't appreciate how easy it is to deal with device that's already mapped into the CPU's memory address space vs. accessing a HDD's contents; and, it appears you believe you don't need NVRAM's speed compared to HDD. On the last, HDDs were also a "tad" slower back then, then they are today. (Heck, even today, there's a reason solid-state disk drives, effectively huge "flash" devices, are becoming so popular - it's for their increased speed.)

I don't recall writing it was critical for startup to be saved to NVRAM, rather than Flash. Further, I'm unsure, by your statement, if you realize both NVRAM and Flash are, more-or-less, generic terms for CPU addressable memory that keeps in contents without power and can be changed. The underlying technology, back when Cisco first used "NVRAM", was most likely EEPROM, but many more choices exist today.

You may also not realize, 3 to 4 decades ago, devices using flash weren't that common. Remember early PC's didn't have flashable BIOS, often you needed to replace the ROM chips. PCs startup parameters were also stored in battery backed-up CMOS RAM.

So, having started with computers four decades ago, I believe Cisco's design approach was reasonable. Of course, you need not agree, but you might try designing your own network router, using technology from back then, and see what you come up with. If it differs from Cisco's approach, and other hardware vendors of the time, please post it. I would enjoy reading of it (seriously). Of course, hindsight is often 20/20, but still, how else something "then" could have been done, can be very educational.