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Hardware Installation Guide for the Cisco 4000 Series  Integrated Services Router
OL-32185-02
Chapter 1      Overview of Cisco 4000 Series ISRs
  Hardware Features of Cisco 4000 Series ISRs
System Flash
Depending on the model that you have purchased, the routers use a CompactFlash or an eUSB flash for 
the internal bootflash memory. The CompactFlash and eUSB flash stores the operating system software 
image. 
The CompactFlash is applicable only to Cisco 4451-X ISR. Each model supports 1 internal 
CompactFlash 8-GB, 16-GB, or 32-GB memory card. The CompactFlash is located behind the fan tray 
on the router chassis. 
Cisco 4431 ISRs have a eMMC flash device. The device supports 8GB, 16GB, or 32 GB.
Cisco 4300 Series ISRs have an onboard flash device or a eMMC flash device. It supports 8GB or 16GB.
Note For Cisco  4451-X ISR, you must use Cisco-qualified CompactFlash cards. Use of any other cards during 
normal network operation can affect system performance or reliability.
Note Do not run the router without a CompactFlash card installed. Cisco IOS XE software does not boot 
without a flash card in the router.
Solid State Drives
The NIM slots in the router support a field-replaceable solid state drive module with a dual-SSD SATA 
slot. The NIM can be installed in any bay slot 0. The SSDs are hot-swappable as part of normal 
operation. See the “Locate Internal and External Slots for Modules on Cisco 4331 ISR” section on 
page 6-9 section for more information.
Cisco 4300 ISR platforms support optional internal SSD mSATA. This device is not hot-swappable and 
requires opening the chassis to service or upgrade.
Packet Voice Digital Signal Processor Modules
The Packet Voice Digital Signal Processor Modules (PVDM4s) add additional voice capabilities to the 
routers. The PVDM4 is installed inside the chassis of the router. See the “Install PVDM4 on the 
Motherboard of Cisco 4400 Series ISRs” section on page 6-33 for installation instructions.