# Memory Types

[Cisco OS (IOS)](https://app.gitbook.com/@mudassirs46/s/network-fundamentals/~/drafts/-MRZ8l67L5MHnaQIEh9W/cisco-os-ios) are stored in different Types of Memory installed in Cisco [Switches ](https://app.gitbook.com/@mudassirs46/s/network-fundamentals/~/drafts/-MRZ8l67L5MHnaQIEh9W/switch)& [Routers](https://app.gitbook.com/@mudassirs46/s/network-fundamentals/~/drafts/-MRZ8l67L5MHnaQIEh9W/router).

### Four types of Cisco Switch/Router Memory:

1. **FLASH Memory:**
   * FLASH Memory is a Removable/Non-Removable chip which stores the original but Compressed Cisco IOS image.&#x20;
   * Some part of FLASH memory can also be used to store the backup config files.
2. **ROM (Read Only Memory):**
   * Contains the POST & BOOTSTRAP program which finds the IOS image from FLASH Memory, decompresses & loads the compressed IOS from the Flash Memory to the RAM.
3. **NVRAM (NonVolatile RAM):**
   * Stores the Initial/Startup configuration file that is used when the Router/Switch is first powered on/Reloaded.
4. **RAM/DRAM (Dynamic Random Access Memory):**
   * Just like the computer's Random Access Memory (RAM) which is used to store the running configuration, Cisco's DRAM also does the same job.

## Reference:

CCNA 200-301 OCG, Volume 1, Pg. 99-100 - Wendell Odom.
