Which type of memory is erased on a Cisco device when rebooted?

Dynamic Random-Access Memory (DRAM) is volatile memory used by a Cisco device to store the running configuration, the active Cisco IOS software image, routing tables, and packet buffers. Because DRAM is volatile, its contents are lost when the device loses power or is rebooted. Upon startup, the device copies the Cisco IOS from flash memory and the startup configuration from NVRAM into DRAM to begin operation.

B. PVDM: A Packet Voice Digital Signal Processor Module (PVDM) is a hardware component for voice features, not a primary memory type for storing the device's configuration or operating system.
C. flash: Flash memory is non-volatile and is used to store the Cisco IOS software image(s). Its contents are preserved during a reboot to allow the device to load the operating system.
D. NVRAM: Non-Volatile Random-Access Memory (NVRAM) is used to store the startup configuration file. Its contents are retained through reboots, ensuring the device's saved configuration is loaded upon startup. ---

1. Cisco Systems, "Internetworking Technology Handbook," Chapter: Router Components.

Section: Main Memory (DRAM): "DRAM is volatile; information is lost when the router is powered down or restarted."

Section: Nonvolatile RAM (NVRAM): "NVRAM is nonvolatile... NVRAM stores the router's backup/startup configuration file."

Section: Flash Memory: "Flash is nonvolatile... Flash memory stores the Cisco IOS software images."

This official Cisco handbook explicitly defines the volatility and function of each memory type.

2. Cisco Systems, "Cisco IOS Configuration Fundamentals Command Reference," Document ID: 13610.

Section: Memory, Processors, and Interfaces: "The running configuration is stored in RAM; the startup configuration is stored in NVRAM... If the router is powered off before you save the running configuration, the running configuration is lost."

This document clarifies that the running configuration resides in volatile memory (DRAM/RAM) and is lost on power-off unless saved to NVRAM.

3. Kurose, J. F., & Ross, K. W. (2017). Computer Networking: A Top-Down Approach (7th ed.). Pearson.

Chapter 5, Section 5.2: The Control Plane: Per-Router Control: In discussions of router architecture, the text distinguishes between the forwarding plane and the control plane. The control plane software and data structures (like routing tables derived from protocols) are executed and stored in the router's main processor and memory (DRAM), which are volatile. The startup configuration and OS image are stored in non-volatile memory (NVRAM, flash).

This is a standard university-level textbook that corroborates the fundamental principles of router memory architecture.