Almost all advanced Cisco routers and switches are equipped with the Cisco proprietary operating systems called the IOS (Internetwork Operating System). Cisco PIX firewalls have a special operating system, the PIX Finesse OS.
In some versions of the IOS, there is a MIB (Management Information Base) module integrated into the IOS operating system. The MIB is an operating system component included with all recent IOS distributions that allows network administrators to view and manage device memory over the network. MIB is prerequisite software for other applications that deal with Cisco memory management, reporting data to RME (Resource Manager Essentials) and during installation of other additional software to a given device.
Before discussing the reasons to upgrade your router's memory, the following is description of the different types of memory that used in a Cisco product.
Processor Memory
This memory acts similar to the CPU cache in a computer, controlling all basic computing operations of your switch or router. Regardless of any other memory being used, the processor memory is always the first memory that is accessed and used. All the files needed for booting and essential system files required for functioning for any Cisco device are stored in the processor memory. If you are using a product that has IOS before 11.1, then the total of all types of memory is reported as the processor memory.
Flash Memory Card/Disk or Cisco Memory Card
The flash memory is a special type of programmable memory that is used to store images of the IOS software on it, in addition the flash memory is used to upgrade versions of the router or switch being used. The term 'flashing a product' means upgrading the version of IOS stored on the flash memory card.
Shared Memory/RAM (Random Access Memory)
The reason this is often referred to as the shared memory, is that it is erased every time the router is restarted or when the memory is deliberately cleared. This memory is usually the easiest to upgrade. The RAM stores all data that is temporary in nature, and upgrading the RAM usually helps improve the speed and the computing power of the Cisco product. It is generally cheaper than Flash memory, and manufactured both OEM by Cisco and by third party manufacturers, such as PC Wholesale.
While PIX firewalls and the routers that IOS runs on ultimately have finite processing power, this is often not the bottleneck that first limits their ability to grow. More often, IOS is hampered by having allocated as much (or more) dynamic Random Access Memory (DRAM) than it has available. Older firewalls and routers, which shipped with very small Cisco memory (Flash) cards, the factor limiting the usefulness of the hardware may be the Operating System installed on it.
IOS and PIX OS each have vastly larger memory footprints than they did as recently as a few years ago, and the current versions of these operating systems require more memory than many devices are equipped with. Both the RAM and Flash memory of a Cisco router can be upgraded. Such an upgrade may significantly extend the longevity of a network operating with older equipment. Two of the principal reasons to upgrade your devices memory to increase its speed and to run the most current version of Cisco IOS.
Increasing speed
Just like conventional computers, increasing the memory of a Cisco product increases its speed. If the product is a Cisco router or switch that handles large amounts of data over the network, increasing the RAM of the product can improve both the processing speed and the device's performance.
Upgrading the IOS
For devices with Cisco IOS 11.1 or older the only way to improve its performance is to upgrade the IOS. However, older Cisco hardware is usually not equipped with sufficient flash memory to store a newer version of the IOS. In this case, the only option is to upgrade the flash memory of the Cisco product. All versions of the Cisco IOS after version 11.1, used by most Cisco routers and non-firewall hardware around the world, has functionality to report MIB values over the network via SNMP (Simple Network Management Protocol), allowing network administrators and other authorized device managers to make queries to the database from across the network. Obsolete versions of the IOS, without the MIB module, do not have this functionality and can only report the size of processor memory.
