The development of a hobbyist operating system is one of the more involved and technical options for a computer hobbyist. The definition of a hobby operating system can sometimes be vague. It can be from the developer's view, where the developers do it just for fun or learning; it can also be seen from the user's view, where the users are only using it as a toy; or it can be defined as an operating system which doesn't have a very big user base. [1] [2]
Development can begin from existing resources like a kernel, an operating system, or a bootloader, or it can also be made completely from scratch. The development platform could be a bare hardware machine, which is the nature of an operating system, but it could also be developed and tested on a virtual machine. Since the hobbyist must claim more ownership for adapting a complex system to the ever-changing needs of the technical terrain, much enthusiasm is common amongst the different groups attracted to operating system development.
Elements of operating system development include:
The C programming language is frequently used for hobby operating system programming, as well as assembly language, though other languages can be used as well.
The use of assembly language is common with small systems, especially those based on eight bit microprocessors such as the MOS Technology 6502 family or the Zilog Z80, or in systems with a lack of available resources because of its small output size and low-level efficiency. [3]
Most hobby operating systems use a command-line interface or a simple text user interface due to ease of development. More advanced hobby operating systems may have a graphical user interface. For example, AtheOS was a hobby operating system with a graphical interface written entirely by one programmer.
This section is predominantly x86 oriented.
The term BIOS (Basic Input/Output System) refers to firmware that initialises computer hardware and has provisions to load an operating system. [4] The BIOS also sets up a standard interface for several low-level device drivers at boot time. BIOS resources are often used by hobbyist operating systems, especially those written on 16-bit x86 machines, as many hobby operating systems developers lack the time to write complex low level drivers themselves or they simply want to get into writing software for the system as soon as possible.
The most commonly used BIOS functions are VideoBIOS and Disk services. These are used because video cards and disk drives vary significantly on different machines and specialised drivers are often difficult to write.
The use of the BIOS is uncommon in operating systems that operate in Protected mode or Long mode, because the system must switch back to real mode which BIOS drivers run in. [5]
In the context of an operating system, a device driver is a computer program that operates or controls a particular type of device that is attached to a computer or automaton. A driver provides a software interface to hardware devices, enabling operating systems and other computer programs to access hardware functions without needing to know precise details about the hardware being used.
An operating system (OS) is system software that manages computer hardware and software resources, and provides common services for computer programs.
Computer operating systems (OSes) provide a set of functions needed and used by most application programs on a computer, and the links needed to control and synchronize computer hardware. On the first computers, with no operating system, every program needed the full hardware specification to run correctly and perform standard tasks, and its own drivers for peripheral devices like printers and punched paper card readers. The growing complexity of hardware and application programs eventually made operating systems a necessity for everyday use.
In computer software, an application binary interface (ABI) is an interface between two binary program modules. Often, one of these modules is a library or operating system facility, and the other is a program that is being run by a user.
Real mode, also called real address mode, is an operating mode of all x86-compatible CPUs. The mode gets its name from the fact that addresses in real mode always correspond to real locations in memory. Real mode is characterized by a 20-bit segmented memory address space and unlimited direct software access to all addressable memory, I/O addresses and peripheral hardware. Real mode provides no support for memory protection, multitasking, or code privilege levels.
In computing, a system call is the programmatic way in which a computer program requests a service from the operating system on which it is executed. This may include hardware-related services, creation and execution of new processes, and communication with integral kernel services such as process scheduling. System calls provide an essential interface between a process and the operating system.
System software is software designed to provide a platform for other software. Examples of system software include operating systems (OS).
An object-oriented operating system is an operating system that is designed, structured, and operated using object-oriented programming principles.
Hardware abstractions are sets of routines in software that provide programs with access to hardware resources through programming interfaces. The programming interface allows all devices in a particular class C of hardware devices to be accessed through identical interfaces even though C may contain different subclasses of devices that each provide a different hardware interface.
In the 80386 microprocessor and later, virtual 8086 mode allows the execution of real mode applications that are incapable of running directly in protected mode while the processor is running a protected mode operating system. It is a hardware virtualization technique that allowed multiple 8086 processors to be emulated by the 386 chip. It emerged from the painful experiences with the 80286 protected mode, which by itself was not suitable to run concurrent real-mode applications well. John Crawford developed the Virtual Mode bit at the register set, paving the way to this environment.
Unified Extensible Firmware Interface is a specification that defines an architecture for the platform firmware used for booting a computer's hardware and its interface for interaction with the operating system. Examples of firmware that implement the specification are AMI Aptio, Phoenix SecureCore, TianoCore EDK II, InsydeH2O.
The Advanced Host Controller Interface (AHCI) is a technical standard defined by Intel that specifies the register-level interface of Serial ATA (SATA) host controllers in a non-implementation-specific manner in its motherboard chipsets.
Computer operating systems based on the Linux kernel are used in embedded systems such as consumer electronics, in-vehicle infotainment (IVI), networking equipment, machine control, industrial automation, navigation equipment, spacecraft flight software, and medical instruments in general.
BIOS implementations provide interrupts that can be invoked by operating systems and application programs to use the facilities of the firmware on IBM PC compatible computers. Traditionally, BIOS calls are mainly used by DOS programs and some other software such as boot loaders. BIOS runs in the real address mode of the x86 CPU, so programs that call BIOS either must also run in real mode or must switch from protected mode to real mode before calling BIOS and then switching back again. For this reason, modern operating systems that use the CPU in Protected mode or Long mode generally do not use the BIOS interrupt calls to support system functions, although they use the BIOS interrupt calls to probe and initialize hardware during booting. Real mode has the 1MB memory limitation, modern boot loaders use the unreal mode or protected mode to access up to 4GB memory.
QEMU is a free and open-source emulator. It emulates a computer's processor through dynamic binary translation and provides a set of different hardware and device models for the machine, enabling it to run a variety of guest operating systems. It can interoperate with Kernel-based Virtual Machine (KVM) to run virtual machines at near-native speed. QEMU can also do emulation for user-level processes, allowing applications compiled for one processor architecture to run on another.
System Management Mode is an operating mode of x86 central processor units (CPUs) in which all normal execution, including the operating system, is suspended. An alternate software system which usually resides in the computer's firmware, or a hardware-assisted debugger, is then executed with high privileges.
In computer science, hierarchical protection domains, often called protection rings, are mechanisms to protect data and functionality from faults and malicious behavior.
The interrupt descriptor table (IDT) is a data structure used by the x86 architecture to implement an interrupt vector table. The IDT is used by the processor to determine the memory addresses of the handlers to be executed on interrupts and exceptions.
In computing, virtualization (v12n) is a series of technologies that allows dividing of physical computing resources into a series of virtual machines, operating systems, processes or containers.
The kernel is a computer program at the core of a computer's operating system and generally has complete control over everything in the system. The kernel is also responsible for preventing and mitigating conflicts between different processes. It is the portion of the operating system code that is always resident in memory and facilitates interactions between hardware and software components. A full kernel controls all hardware resources via device drivers, arbitrates conflicts between processes concerning such resources, and optimizes the utilization of common resources e.g. CPU & cache usage, file systems, and network sockets. On most systems, the kernel is one of the first programs loaded on startup. It handles the rest of startup as well as memory, peripherals, and input/output (I/O) requests from software, translating them into data-processing instructions for the central processing unit.
