Networks

Network Interface Controllers (NICs) can connect a computer to different physical mediums, such as Ethernet and Wi-Fi. Every NIC in the world has a unique MAC (media access control) address. It consists of 48 bits. Therefore, there are 28 trillion possible MAC addresses. Some devices randomly change their MAC address for privacy.

You can use command ifconfig to check you network interface controller and its corresponding MAC address. There exists virtual interfaces as well. For example, lo, the loopback device, is a virtual interface. It connects your computer to a mini network containing just your computer.

Virtualization

Virtualization is the illusion of private resources, provided by the software. We have virtual memory, virtual machine (hardware), virtual machine (languages), virtual operating system (container).

• Each process using a virtual address space is not aware of other processes using memory (illusion of private memory).
• Virtualized resources include CPU, RAM, disks, network devices, etc. VMs rarely use all their allocated resources, so overbooking is possible. If each program is deployed to a different VM, operating system overheads dominate.
• JVM or PVM runs Java Bytecode and Python Bytecode. Programs written in Java and Python are compiled to their corresponding byte code instead of a specific machine code.
• Virtual operating systems, or a containers, are run on a some flavor of Linux. You can have a container of Ubuntu and a container on Debian (but not Windows, since they are running on top of Linux). Containers are more efficient than virtual machines, but less flexible.

Containers and Virtual Machines are Sandboxes.