Quick Tips: How Much RAM Do I Have?

• By Joe Astorino
• December 16, 2011
• 1 Comment

So there you are in the datacenter troubleshooting some mind numbing issue that should probably never be happening in the first place according to the documentation on CCO.  After 2 days of pulling your hair out, you finally realize the only other thing you can do is try a different IOS.  Anxiously, you fly over to the Cisco login page, authenticate yourself and find that fresh shiny IOS image you need to fix your life today. Looking at the requirements, you see it has a minimum flash and DRAM requirement and start to wonder “Does my box meet the requirement”?

One of the common questions that people new to working on Cisco stuff always ask is “How do I see the amount of RAM in my router”?  This blog will answer that question.

The simple answer is to just run show version and piece things together.  Let’s take a look at an example.

Router#sh version
Cisco IOS Software, 3800 Software (C3825-ADVIPSERVICESK9-M), Version 15.0(1)M3, RELEASE SOFTWARE (fc2)
Technical Support: http://www.cisco.com/techsupport
Copyright (c) 1986-2010 by Cisco Systems, Inc.
Compiled Sun 18-Jul-10 05:11 by prod_rel_team

ROM: System Bootstrap, Version 12.4(13r)T15, RELEASE SOFTWARE (fc1)

Router uptime is 16 weeks, 5 days, 10 hours, 15 minutes
System returned to ROM by power-on
System restarted at 06:24:03 GMT Sun Aug 21 2011
System image file is "flash:c3825-advipservicesk9-mz.150-1.M3.bin"
Last reload type: Normal Reload

This product contains cryptographic features and is subject to United
States and local country laws governing import, export, transfer and
use. Delivery of Cisco cryptographic products does not imply
third-party authority to import, export, distribute or use encryption.
Importers, exporters, distributors and users are responsible for
compliance with U.S. and local country laws. By using this product you
agree to comply with applicable laws and regulations. If you are unable
to comply with U.S. and local laws, return this product immediately.

A summary of U.S. laws governing Cisco cryptographic products may be found at:
http://www.cisco.com/wwl/export/crypto/tool/stqrg.html

If you require further assistance please contact us by sending email to
export@cisco.com.

Cisco 3825 (revision 1.2) with 487423K/36864K bytes of memory.
Processor board ID FTX1446A0BT
2 Gigabit Ethernet interfaces
2 Virtual Private Network (VPN) Modules
DRAM configuration is 64 bits wide with parity enabled.
447K bytes of NVRAM.
511056K bytes of ATA System CompactFlash (Read/Write)

Configuration register is 0x2102

So there you have it, pretty simple.  Or is it?  It says we have “487423/36864” KB of memory.  Great…how does that help us?  Well, you need to understand how memory is allocated by IOS to really get it.  Basically, IOS takes the full amount of DRAM you have, and it divides it into two chunks.  It is sort of like a PC that has video RAM built into the motherboard instead of a dedicated video card.  For example, your PC might have 2GB of RAM but in reality, 256MB is used by the operating system as video memory. In IOS it works like this:

– A very large chunk is allocated for system memory

– A small chunk is allocated for packet memory.  In other words, we need SOME small amount of RAM to actually temporarily store packets in

Add these two values together to get your total amount of RAM.  So let’s see here…

487423 + 36864 gives me 524,287 KB of memory.  There are 1024KB in 1MB of memory so basic math tells me I have 524,287 / 1024 or 512MB of RAM.

Hopefully this has been useful for you guys.  Thanks for reading!