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Router Processor memory different from RAM memory on show version

I have a Cisco 3845 router having with monitoring tool reporting high processor utilization. From what I know, RAM specs should also reflect in show memory. However I am observing that RAM indicated at the show version 256MB is different from the one seen in show memory 87MB. Based from the used Total and Used processor memory it yields 95% utilization with only 4MB free space. Can anyone help me further understand this situation.


sh platf | i dim
Size of dimm = 256 Megabytes


sh ver | i memory
Cisco 3845 (revision 1.0) with 211968K/50176K bytes of memory.

sh mem
                    Head           Total(b)    Used(b)    Free(b) Lowest(b) Largest(b)
Processor 67BF8B80 87061632 82986848 4074784 2820800 2532336
I/O            2CF00000 51379712 22521732 28857980 28782640 28788604



Cisco IOS Software, 3800 Software (C3845-ADVIPSERVICESK9-M), Version 12.4(24)T5, RELEASE SOFTWARE (fc3)
Technical Support:
Copyright (c) 1986-2011 by Cisco Systems, Inc.
Compiled Fri 04-Mar-11 06:12 by prod_rel_team

ROM: System Bootstrap, Version 12.4(13r)T11, RELEASE SOFTWARE (fc1)

WGDCA3845RTR1 uptime is 7 years, 24 weeks, 4 hours, 44 minutes
System returned to ROM by power-on
System restarted at 21:29:40 EDT Thu Jul 28 2011
System image file is "flash:c3845-advipservicesk9-mz.124-24.T5.bin"

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Cisco 3845 (revision 1.0) with 211968K/50176K bytes of memory.
Processor board ID FTX1331AHU5
1 FastEthernet interface
3 Gigabit Ethernet interfaces
1 Serial interface
1 Virtual Private Network (VPN) Module
1 Subrate T3/E3 port
DRAM configuration is 64 bits wide with parity enabled.
479K bytes of NVRAM.
62720K bytes of ATA System CompactFlash (Read/Write)

Configuration register is 0x2102


NAME: "3845 chassis", DESCR: "3845 chassis"
PID: CISCO3845 , VID: V03 , SN: FTX1331AHU5

NAME: "c3845 Motherboard with Gigabit Ethernet on Slot 0", DESCR: "c3845 Motherboard with Gigabit Ethernet"
PID: CISCO3845-MB , VID: V07 , SN: FOC132862Q1

NAME: "One-Port Fast Ethernet High Speed WAN Interface Card on Slot 0 SubSlot 0", DESCR: "One-Port Fast Ethernet High Speed WAN Interface Card"
PID: HWIC-1FE , VID: V01 , SN: FOC14494U8C

NAME: "PVDMII DSP SIMM with four DSPs on Slot 0 SubSlot 4", DESCR: "PVDMII DSP SIMM with four DSPs"
PID: PVDM2-64 , VID: V01 , SN: FOC13353RKP

NAME: "PVDMII DSP SIMM with four DSPs on Slot 0 SubSlot 5", DESCR: "PVDMII DSP SIMM with four DSPs"
PID: PVDM2-64 , VID: V01 , SN: FOC13353RN1

NAME: "PVDMII DSP SIMM with four DSPs on Slot 0 SubSlot 6", DESCR: "PVDMII DSP SIMM with four DSPs"
PID: PVDM2-64 , VID: V01 , SN: FOC13353RMP

NAME: "PVDMII DSP SIMM with four DSPs on Slot 0 SubSlot 7", DESCR: "PVDMII DSP SIMM with four DSPs"
PID: PVDM2-64 , VID: V01 , SN: FOC13311D22

NAME: "Clear/Subrate T3/E3 WAN on Slot 1", DESCR: "Clear/Subrate T3/E3 WAN"
PID: NM-1T3/E3= , VID: V01 , SN: FOC13316VKD

NAME: "Gigabit Ethernet Controller on Slot 2", DESCR: "Gigabit Ethernet Controller"
PID: NM-1GE , VID: V01 , SN: FOC13301F49

NAME: "High Density Voice2 Network module with no board interface on Slot 4", DESCR: "High Density Voice2 Network module with no board interface "
PID: NM-HDV2 , VID: V02 , SN: FOC133061TW

Hall of Fame Cisco Employee

Hello Carlson,

Indeed, your show memory output suggests that the processor memory is around 83 MiB (MiB = 1024 KiB = 1024 * 1024 B), and if we add it together with the memory set aside for the I/O packet buffers, the total memory apparently available to the system is around 132 MiB. The rest of your 256 MiB RAM module is occupied by the unpacked IOS image itself, and obviously, this part of RAM is not available for any other purposes since writing data there would overwrite the IOS code.

It would appear that your router would truly benefit from more RAM. However, if extending the RAM in the router is not an option, then looking at your I/O memory utilization, it looks like we could try allocating less memory to the I/O region, leaving more memory for the processor usage.

You are currently allocating 49 MiB out of 256 MiB for I/O which is around 20% (somewhat less). We can try changing this percentage to 15% (around 38,4 MiB) to give your processor memory some more breathing space. To do this, you would need to configure this command in the global configuration mode:

memory-size iomem 15

then save the configuration and reload the router.

Please feel welcome to ask further!

Best regards,

VIP Expert

As you mention high processor utilization, do you believe having additional memory would decrease that? If so, likely not.

In addition to what Peter suggests, there are other things you migth consider or do to free of processor RAM. For starters, expecially in the older IOS versions, there are often many different IOS images, differing in feature set support. Those with less features have a smaller memory footprint.

Second, some configuration features can use a lot of RAM, such as the memory console buffer and/or NetFlow and/or IP SLA stats, etc.

Lastly, sometime you can run out of RAM by not having enough in a large enough free memory block. This is more likely to happen if your overall available RAM is low, but sometimes just running for a long time will lead to it too. A temporary cure for that is a reboot.
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