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Understanding Flash and Dram to IOS

Hello guys

 

I am finding a new IOS to a Router 3925 and almost all the IOS needs 1024 Dram and 256 Mb Flash.

 

But I am wondering why they need 256 Mb flash if the weight of IOS I am interesting  is 107 Mb...??? Is there something else that the flash does aside the weight of IOS?

 

And also why so much dram?

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VIP Expert

Re: Understanding Flash and Dram to IOS

Sometimes Cisco requirements are beyond what's actually required for a specific instance of an IOS version and feature set, but they often set these requirements to support other (more space consuming) feature sets and/or later IOS versions (which tend to grow in size) that are on their road map.

BTW, I have, in the past, run IOS images that actually fit which don't meet the minimum DRAM or flash requirements. The latter (flash) is generally simple, it fits or it doesn't. The former (DRAM) depends on how much your IOS expands when decompressed and/or the actual running config.

If your IOS image fits in flash, you'll likely be fine, however, if you have a support need issue, TAC might also not support you if you don't meet their minimum resource requirements.
1 REPLY 1
VIP Expert

Re: Understanding Flash and Dram to IOS

Sometimes Cisco requirements are beyond what's actually required for a specific instance of an IOS version and feature set, but they often set these requirements to support other (more space consuming) feature sets and/or later IOS versions (which tend to grow in size) that are on their road map.

BTW, I have, in the past, run IOS images that actually fit which don't meet the minimum DRAM or flash requirements. The latter (flash) is generally simple, it fits or it doesn't. The former (DRAM) depends on how much your IOS expands when decompressed and/or the actual running config.

If your IOS image fits in flash, you'll likely be fine, however, if you have a support need issue, TAC might also not support you if you don't meet their minimum resource requirements.
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