The Raspberry Pi

The Raspberry Pi is a credit-card sized computer with Broadcom BCM2835 System on a Chip (SoC) which includes an ARM1176JZF-S (ARM11 family, ARMv6 architecture) processor at 700 MHz.
The Revision B Board has 512 MB of RAM shared with the GPU. More info about the Raspberry Pi can be found on the Raspberry Pi Official website and on Wikipedia.
As Operating System I use Raspbian (A Debian wheezy port, optimised for the Raspberry Pi).
A new version of Raspberry Pi, the Raspberry Pi 2 Model B, was released on 2 February 2015. It has a 900MHz quad-core ARM Cortex-A7 CPU (ARMv7-A architecture) and 1 GB of RAM.

Whats services are running on my two Raspberry Pi?

On Raspberry Pi 2:
SSH Server
DX Cluster Node (DXSpider)
Nginx Web Server
Unbound DNS Server

On Raspberry Pi:
SSH Server
OpenVPN Server
LoTW QSL Notifications System (LQNS) Server
VNC Server
RRDtool Round Robin Database
Digital sensors
SDM120C for energy monitoring
and more....

To understand how to configure Raspberry for install and configure a Web Server, PHP and MySQL database see this page.
To understand how to configure Raspberry Pi to connect an I²C chip see the I²C page, for a 1-Wire chip see the 1-Wire page.

My Linux Server system informations:

OS: Linux Ubuntu 24.04.1
Kernel version: 6.8.1-1014-realtime
CPU utilization: 1.8%
Total Memory: 7941 MB
Used Memory: 2993 MB
Web Server: nginx/1.25.1 (with HTTP/3, HTTP/2 and TLS 1.3 support)
MySQL version (MariaDB): 10.11.8