Memory and Flash on CISCO router
Before you install a new Cisco IOS Software image on your router, check if your router meets the memory requirements for that image. For this, issue theshow version command on your router, and look for these lines:
...
cisco RSP4 (R5000) processor with 65536K/2072K bytes of memory
...
16384K bytes of processor board System flash (Read ONLY)
The first line tells you how much Dynamic RAM (DRAM) and Packet memory are installed in your router. Some platforms use a fraction of their DRAM as Packet memory. The memory requirements take this into account, so you have to add both numbers to find the amount of DRAM available on your router (from a memory requirement point of view).
Example 1: Separate DRAM and Packet Memory
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cisco RSP4 (R5000) processor with 65536K/2072K bytes of memory
...
The 4000, 4500, 4700, and 7500 routers have separate DRAM and Packet memory, so you only need to look at the first number. This shows that the router has 65536 K (or 64 M) of DRAM.
Example 2: Combined DRAM and Packet Memory
... cisco 2611 (MPC860) processor (revision 0x202) with 29696K/3072K bytes of memory ...
The 1000, 1600, 2500, 2600, 3600, and 7200 routers use a fraction of DRAM as Packet memory, so you need to add both numbers to find out the real amount of DRAM. In this example, the router has 2969 K + 3072 K = 32768 K (or 32 M) of DRAM.
Example 3: Available Flash Memory
...
cisco RSP4 (R5000) processor with 65536K/2072K bytes of memory
...
16384K bytes of processor board System flash (Read ONLY)
The bottom line tells you how much Flash memory is available. Some of it might already be in use. In order to find out the amount of free Flash memory, issue a show flash command:
Router#show flash
System flash directory:
File Length Name/status
1 8407884 c2600-io3s56i-mz.121-6
[8407948 bytes used, 8369268 available, 16777216 total]
16384K bytes of processor board System flash (Read/Write)
Variants of the show flash command can be used to inspect different specific Flash devices on the platform. Refer to the show flash command definitionfor information on how to use these variants.
You need to satisfy both the DRAM and the Flash requirements to be able to use the software you choose. If you do not meet the requirements, you can either add more Flash or more DRAM in the router, or choose another Cisco IOS Software release. You may also consider a reduced feature set or an older release, since they have less features, and therefore fewer requirements.
(Courtesy : http://www.cisco.com/en/US/products/sw/iosswrel/ps1834/products_tech_note09186a00800fb9d9.shtml)