Installation guide

Upgrading Memory in Cisco 4000 Series Routers 5
Memory Systems
Memory Systems
Cisco 4000 series routers contain the following memory systems:
• Main memory consists of dynamic random-access memory (DRAM) single in-line memory
modules (SIMMs). It is reserved for the CPU to execute Cisco Internetwork Operating System
(Cisco IOS) software and to hold the running configuration and routing tables.
• Shared memory also consists of DRAM SIMMs, and buffers data transmitted or received by the
router’s network interfaces.
• Flash memory stores the Cisco IOS software image. Flash memory is provided as erasable
programmable read-only memory (EPROM) on the original Cisco 4000 daughter card and as
Flash SIMMs on the replacement Cisco 4000 daughter card and in all other Cisco 4000 series
routers. In the Cisco 4500, Cisco 4500-M, Cisco 4700, and Cisco 4700-M routers, Flash
memory also stores the boot helper, a subset of Cisco IOS software that allows the router to boot
when Flash memory does not contain a valid Cisco IOS image.
Because Flash memory holds the Cisco IOS image, upgrading it causes the image to be lost. To
restore it, you need a Trivial File Transfer Protocol (TFTP) file server that holds the desired
image. You can then download the Cisco IOS files into the upgraded Flash memory using TFTP.
Consult your network administrator about the availability of TFTP file servers and Cisco IOS
software on your network. Refer to the Cisco IOS configuration guides and command references
for TFTP procedures. For information about Cisco publications, refer to the section “Cisco
Documentation” later in this document.
Note One upgraded router can serve as a TFTP server to upgrade other routers.
• EPROM stores the ROM monitor and the boot helper in the Cisco 4000 and the Cisco 4000-M.
In the Cisco 4500, Cisco 4500-M, Cisco 4700, and Cisco 4700-M routers, EPROM stores only
the ROM monitor; the boot helper is stored in Flash memory.
• Nonvolatile random-access memory (NVRAM) stores the configuration file and virtual
configuration register. This memory cannot be upgraded.
Figure 1 shows a block diagram of EPROM-based and Flash-based memory systems in Cisco 4000
series routers.