Operating System Flashcards
Networking
0 - To understand Networking, you need to understand all of the components involved.
1 - the Physical Layer represents the physical devices that interconnect computers. Includes specifications for networking cables and connectors that join devices and how signals are sent over these connections.
2 - the Data Link Layer introduces the first protocols. It is responsible for defining a common way of interpreting these signals. Most common protocol is the Ethernet. It is also responsible for getting data across a single link.
3 - The network/Internet Layer allows different networks to communicate with each other through devices called routers. it is responsible for getting data delivered across a collection of networks (multiple links). Most common version is the IP(Internet Protocol). Network Software is divided into Client(application initiate a requests for data) and the Server software (answers the request across the network). A single node may be running multiple client or server applications. Delivers data between two individual does.
4 - Transport Layer determines which client and server program are supposed to get that data. TCP IP (Transmission Control Protocol) is the most common one; the two are different protocol performing different tasks.
5 - The Application Layer has a lot of protocols (application -specific) that allows you to browse the web or send/receive email.
Remote(1)
1 - remote connections makes it easy to manage multiple machines from across the world.
2 -SSH or secure shell (Software) is a protocol implemented by other programs (uses secure Shell protocol) to securely access one computer from another. To use SSH, you need to have an SSH client installed on the computer you’re connecting from along with an SSH server on the computer you’re trying to connect to.
3 - It constantly checks if a client is trying to connect to it, then will authenticate its requests. The most popular program to use SSH within Linux is the OpenSSH program.
Remote(2)
4 - SSH keys come in a set of two keys called private and public keys.
5 - You can lock something with the public key, but you can only unlock it with a private key and vice versa. This ensures that whatever is in the safe is available to only those with the public and private keys.
Remote Connections on Windows(1)
1 - PuTTY is a free, open source software that you can use to make remote connections through several network protocols including SSH. You download it and launched, a window will appear showing you the basic options for your connection. Make a note of the hostname, port ( set to 22, default for SSH), and connection type options. Then, click Open to start up a new SSH session,
2 - PuTTY also comes with a tool called Plink or PuTTY Link, which is built into the command line after PuTTY is installed. You can use Plink to make remote SSH connections too.
Remote Connections on Windows(2)
3 - Another method is the Remote Desktop Protocol or RDP. RDP provides users with a graphical user interface to remote computers provided the remote computer has enabled incoming RDP connections(through computer settings).
4 - RDP should be used for those who you trust.
5 - You can launch the RDP client in a few ways. You can type mstsc at the run box or lookup Remote Desktop connections in the Start Menu.
Components of an Operating System(1)
1 - PC means personal computer, , But in today’s world, PC is more commonly referred to as a Windows computer.
2 - the two components that make up an operating system, the kernel space and the user space.
- The kernel does file storage in file management. You can compare it to a physical office file where we store data in paper form. A file system is how we manage these files just like in an office, we use a system to store our files.
- Another important function of the kernel is process management. We have many programs that we want to run on our system. To run them, we manage the order they run in, how many resources they take up, how long they run, etcetera.
Components of an Operating System(2)
- Next up is memory management. Our kernel optimizes memory usage and make sure our applications have enough memory to run.
- The last important function that a kernel performs is input/output or I/O management. This is how our kernel talks to external devices like disks, keyboards, networks, connections, audio devices, and more. I/O management is anything that can give us input or that we can use for output of data.
3 - The user space is everything outside the kernel. These are the things that we interact with directly like programs, such as text editors, music players, system settings, user interfaces, etcetera.
Files and File System(1)
1 - Let’s start with the file system. When we have a brand new hard disk that we want to store data on, we need to erase and configure the disk. This way our operating system can read and write data to it.
2 - here are lot of file systems, and they’re used for different purposes. Some file systems support the storage of large amounts of data, others only support small amounts. They can operate at different speeds, and have varying resiliency towards file corruption, and so on.
3 - For Windows, the major file system that’s used is NTFS. It was introduced in the previous version of Windows OS, Windows NT. And it includes many features, like encryption, faster access speeds, security, and more.
4 - For Mac OS, the default file system is HFS+. It’s journaled, which means it does a better job at saving your disk state in case of a failure. This is a feature on other types of file systems, like NTFS.
5 - For Linux, different distributions will use different file system types. A standard for file systems for Linux is ext4, which is compatible with older ext file systems.
Linux is ext4, which is compatible with older ext file systems.
Files and File System(2)
6 - In general, different file system types don’t play nicely with each other. A good guideline to use is just to use the file system that your operating system recommends.
7 - Another important part of file management is the storage of actual file data. We write data to our hard drive in the form of data blocks. When we save something to our hard disks, it doesn’t always sit in one piece. It can be broken down into many pieces and written to different parts of the disk. Block storage improves faster handling of data because the data isn’t stored on one long piece and it can be accessed quicker. It’s also better for utilizing storage space.
8 - Lastly, we need to keep the metadata that contains the information about our file. There’s a lot of information about our file that we want to know, like who created it, when it was last modified, who has access to it, and so on. The file metadata tells us everything we need to know about our file. It also tells us what type of file it is. A file extension is the appended part of a filename that tells us what type of file it is in certain operating systems.
Process Management
1 - A program is an application that we can run, like Chrome.
2 - We can have many processes of the same program running at the same time. Think of how many Chrome windows you can open .
3 - The kernel creates processes, efficiently schedules them (time slice and allocates a certain amount of RAM and CPU), and manages how processes are terminated(CPU execute each program one by one for 1 millisecond).
Memory Management
1 - When processes are run, they have to take up space in memory, so that the computer can read and load them quickly. However, compared to our hard disk drives, memory comes in smaller quantities. So to give us more memory than we physically have, we use something called virtual memory.
2 - Virtual memory is a combination of hard drive space and RAM that acts like memory that our processes can use. When we execute a process, we take the data of the program in chunks we call pages. We store these pages in virtual memory. If we want to read and execute these pages, they have to be sent to physical memory or RAM.
3 - The kernel handles the process of taking pages of data and swapping them between RAM and virtual memory.
I/O Management
1 - Another important task that our kernel handles, is managing input and output.
2 - These include our monitors, keyboards, mice, hard disk drives, speakers, bluetooth headsets, webcams, and network adapters.
3 - These I/O devices are all managed by our kernel, the kernel needs to be able to load up drivers that are used, so that we can recognize and speak to these different types of hardware. When the kernel is able to start the drivers to communicate with hardware, it also manages the transfer of data in, and out of the devices.
4 - the devices also need to be able to talk to each other. Our kernel handles all the intercommunication between devices. It also figures out what the most efficient method of transfer is, and it tries its best to make sure our data doesn’t have errors during process.
5 - When you’re troubleshooting or solving a problem with a slow machine, it’s usually some sort of hardware resource deficiency. (ex: not enough RAM means you cant load up as many processes).
Interacting with the OS: User Space
1 - The final major aspect of an operating system, how humans interact with it. This is what we call, the user space.
2 - There are two ways that we can interact with our OS, with a shell or a graphical user interface (ex: create files).
3 - A graphical user interface or GUI, is a visual way to interact with a computer.
4 - A shell (most common is BASH or Bourne Again Shell) is basically a program that interprets text commands and sends them to the OS to execute. Before we had fancy visual interfaces, commands like create a file had to be typed out. While we have GUIs today, the shell is still commonly used to run commands, especially by power users.
5 - Power users are above average computer users. In Linux especially, it’s essential that you actually know commands, not just a GUI. This is because most of the Linux machines you interact with in IT support, will be accessed remotely.
Logs
1 - computers speak to us in the form of logs, which are that record system events on our computer.
2 - Just like a systems diary our computer will record events like when it was turned on, when a driver was loaded and even when something isn’t working in the form of error messages. In all operating systems, logs are kept so we can refer back to them when we need to find out something that happened. But logs can be hard to navigate because our computer will essentially record everything.
The Boot Process
1 - When we start up a computer, we use the term boot. For most operating systems, the boot process follows a general pattern:
- First, the computer is powered on.
- So next, the BIOS/UEFI runs a process called the Power On Self Test or POST.
- Next, depending on the BIOS/UEFI configuration, a boot device will be selected. Devices that are attached to our system, like hard drives, USB drives, CD drives, et cetera are configured in a certain boot order.
- the computer will search for what's known as a bootloader. The bootloader is a small program that loads the operating system.
- Once our computer finds a bootloader on a device in the listed order, it will start to execute this program. This will then start to load a larger and more complex program and eventually loads our operating system. Once the bootloader loads up our operating system, our kernel gets loaded.
- The kernel controls access to our computers resources. It also loads up drivers and more, so that our hardware can talk to our software.
- Next, essential system processes and user space items are launched. These include processes like user log in, spinning up a desktop environment, and more which basically allows us to interact with our system.
