Bare machine

Last updated June 23, 2024

In computer science, bare machine (or bare metal) refers to a computer executing instructions directly on logic hardware without an intervening operating system. Modern operating systems evolved through various stages, from elementary to the present day complex, highly sensitive systems incorporating many services. After the development of programmable computers (which did not require physical changes to run different programs) but prior to the development of operating systems, sequential instructions were executed on the computer hardware directly using machine language without any system software layer. This approach is termed the "bare machine" precursor to modern operating systems. Today it is mostly applicable to embedded systems and firmware with time-critical latency requirements, while conventional programs are run by a runtime system overlaid on an operating system.

Advantages

For a given application, in most of the cases, a bare-metal implementation will run faster, using less memory and so being more power efficient. This is because operating systems, as any program, need some execution time and memory space to run, and these are no longer needed on bare-metal. For instance, any hardware feature that includes inputs and outputs are directly accessible on bare-metal, whereas the same feature using an OS must route the call to a subroutine, consuming running time and memory.^[1]

Disadvantages

For a given application, bare-metal programming requires more effort to work properly and is more complex because the services provided by the operating system and used by the application have to be re-implemented regarding the needs. These services can be:

System boot (mandatory)
Memory management: Storing location of the code and the data regarding the hardware resources and peripherals (mandatory)
Interruptions handling (if any)
Task scheduling, if the application can perform more than one task
Peripherals management (if any)
Error management, if wanted or needed

Debugging a bare-metal program is difficult since:

There are no software error notifications nor faults management, unless they have been implemented and validated.
There is no standard output, unless it has been implemented and validated.
The machine where the program is written cannot be the same where the program is executed, so the target hardware is either an emulator / simulator or an external device. This forces to set up a way to load the bare-metal program onto the target (flashing), start the program execution and access the target resources.

Bare-metal programming is generally done using a close-to-hardware language, such as Rust, C++, C, assembly language, or even for small amounts of code or very new processors machine code directly.^[2] All the previous issues inevitably mean that bare-metal programs are very rarely portable.

Examples

Early computers

Early computers, such as the PDP-11, allowed programmers to load a program, supplied in machine code, to RAM. The resulting operation of the program could be monitored by lights, and output derived from magnetic tape, print devices, or storage.

Embedded systems

Bare machine programming remains common practice in embedded systems, where microcontrollers or microprocessors often boot directly into monolithic, single-purpose software, without loading a separate operating system. Such embedded software can vary in structure, but the simplest form may consist of an infinite main loop, or "superloop", calling subroutines responsible for checking for inputs, performing actions, and writing outputs.

Development

The approach of using bare machines paved the way for new ideas which accelerated the evolution of operating system development.

This approach highlighted a need for the following:

Input/output (I/O) devices to enter both code and data conveniently:
- Input devices, such as keyboards, were created. These were necessary, as earlier computers often had unique, obtuse, and convoluted input devices.

For example, programs were loaded into the PDP-11 by hand, using a series of toggle switches on the front panel of the device. Keyboards are far superior to these vintage input devices, as it would be much faster to type code or data than to use toggle switches to input this into the machine. Keyboards would later become standard across almost every computer, regardless of brand or price.

Output devices such as computer monitors would later be widely used, and still are to this day. They proved themselves to be a huge convenience over earlier output devices, such as an array of lights on the Altair 8800, which would indicate the status of the computer.

Computer monitors can also easily display the output of a program in a user friendly manner. For example, one would have to be intimately knowledgeable about a specific early computer and its display system, consisting of an array of lights, to even begin to make sense of the status of the computer's hardware. In contrast, anybody who can read should be able to understand a well-designed user interface on a modern system, without having to know anything about the hardware of the computer on which the program is being run.

Faster, cheaper, more widely available secondary storage devices to store programs to non-volatile memory. This was needed, as it was cumbersome to have to type code in by hand in order to use the computer in a useful way, which would be lost upon every reboot due to the system saving it to volatile memory.
The requirement for a convenient high-level language and a translator for such a high-level language to the corresponding machine code.
Linkers to link library modules, which may be written by the user or already available on the system.
Loaders to load executables into RAM from the secondary storage.
Suitable I/O devices, such as printers for producing a hard copy of the output generated by programs.

Related Research Articles

Forth is a stack-oriented programming language and interactive integrated development environment designed by Charles H. "Chuck" Moore and first used by other programmers in 1970. Although not an acronym, the language's name in its early years was often spelled in all capital letters as FORTH. The FORTH-79 and FORTH-83 implementations, which were not written by Moore, became de facto standards, and an official technical standard of the language was published in 1994 as ANS Forth. A wide range of Forth derivatives existed before and after ANS Forth. The free and open-source software Gforth implementation is actively maintained, as are several commercially supported systems.

An operating system (OS) is system software that manages computer hardware and software resources, and provides common services for computer programs.

The PDP-8 is a family of 12-bit minicomputers that was produced by Digital Equipment Corporation (DEC). It was the first commercially successful minicomputer, with over 50,000 units being sold over the model's lifetime. Its basic design follows the pioneering LINC but has a smaller instruction set, which is an expanded version of the PDP-5 instruction set. Similar machines from DEC are the PDP-12 which is a modernized version of the PDP-8 and LINC concepts, and the PDP-14 industrial controller system.

<span class="mw-page-title-main">Booting</span> Process of starting a computer

In computing, booting is the process of starting a computer as initiated via hardware such as a button on the computer or by a software command. After it is switched on, a computer's central processing unit (CPU) has no software in its main memory, so some process must load software into memory before it can be executed. This may be done by hardware or firmware in the CPU, or by a separate processor in the computer system.

In computing, a process is the instance of a computer program that is being executed by one or many threads. There are many different process models, some of which are light weight, but almost all processes are rooted in an operating system (OS) process which comprises the program code, assigned system resources, physical and logical access permissions, and data structures to initiate, control and coordinate execution activity. Depending on the OS, a process may be made up of multiple threads of execution that execute instructions concurrently.

An embedded system is a computer system—a combination of a computer processor, computer memory, and input/output peripheral devices—that has a dedicated function within a larger mechanical or electronic system. It is embedded as part of a complete device often including electrical or electronic hardware and mechanical parts. Because an embedded system typically controls physical operations of the machine that it is embedded within, it often has real-time computing constraints. Embedded systems control many devices in common use. In 2009, it was estimated that ninety-eight percent of all microprocessors manufactured were used in embedded systems.

In computer science, an instruction set architecture (ISA) is an abstract model that generally defines how software controls the CPU in a computer or a family of computers. A device or program that executes instructions described by that ISA, such as a central processing unit (CPU), is called an implementation of that ISA.

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.

Ladder logic was originally a written method to document the design and construction of relay racks as used in manufacturing and process control. Each device in the relay rack would be represented by a symbol on the ladder diagram with connections between those devices shown. In addition, other items external to the relay rack such as pumps, heaters, and so forth would also be shown on the ladder diagram.

KERNAL is Commodore's name for the ROM-resident operating system core in its 8-bit home computers; from the original PET of 1977, followed by the extended but related versions used in its successors: the VIC-20, Commodore 64, Plus/4, Commodore 16, and Commodore 128.

Execution in computer and software engineering is the process by which a computer or virtual machine interprets and acts on the instructions of a computer program. Each instruction of a program is a description of a particular action which must be carried out, in order for a specific problem to be solved. Execution involves repeatedly following a "fetch–decode–execute" cycle for each instruction done by control unit. As the executing machine follows the instructions, specific effects are produced in accordance with the semantics of those instructions.

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.

Embedded software is computer software, written to control machines or devices that are not typically thought of as computers, commonly known as embedded systems. It is typically specialized for the particular hardware that it runs on and has time and memory constraints. This term is sometimes used interchangeably with firmware.

MBASIC is the Microsoft BASIC implementation of BASIC for the CP/M operating system. MBASIC is a descendant of the original Altair BASIC interpreters that were among Microsoft's first products. MBASIC was one of the two versions of BASIC bundled with the Osborne 1 computer. The name "MBASIC" is derived from the disk file name MBASIC.COM of the BASIC interpreter.

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.

A hypervisor, also known as a virtual machine monitor (VMM) or virtualizer, is a type of computer software, firmware or hardware that creates and runs virtual machines. A computer on which a hypervisor runs one or more virtual machines is called a host machine, and each virtual machine is called a guest machine. The hypervisor presents the guest operating systems with a virtual operating platform and manages the execution of the guest operating systems. Unlike an emulator, the guest executes most instructions on the native hardware. Multiple instances of a variety of operating systems may share the virtualized hardware resources: for example, Linux, Windows, and macOS instances can all run on a single physical x86 machine. This contrasts with operating-system–level virtualization, where all instances must share a single kernel, though the guest operating systems can differ in user space, such as different Linux distributions with the same kernel.

The Parallax P8X32A Propeller is a multi-core processor parallel computer architecture microcontroller chip with eight 32-bit reduced instruction set computer (RISC) central processing unit (CPU) cores. Introduced in 2006, it is designed and sold by Parallax, Inc.

In computing, an emulator is hardware or software that enables one computer system to behave like another computer system. An emulator typically enables the host system to run software or use peripheral devices designed for the guest system. Emulation refers to the ability of a computer program in an electronic device to emulate another program or device.

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.

MikroSim is an educational computer program for hardware-non-specific explanation of the general functioning and behaviour of a virtual processor, running on the Microsoft Windows operating system. Devices like miniaturized calculators, microcontroller, microprocessors, and computer can be explained on custom-developed instruction code on a register transfer level controlled by sequences of micro instructions (microcode). Based on this it is possible to develop an instruction set to control a virtual application board at higher level of abstraction.

References

↑ Gordon, Abel; Amit, Nadav; Har'El, Nadav; Ben-Yehuda, Muli; Landau, Alex; Schuster, Assaf; Tsafrir, Dan (2012). "ELI" . ACM SIGPLAN Notices. 47 (4): 411–422. doi:10.1145/2248487.2151020.
↑ "Practical Guide to Bare Metal C++" . Retrieved December 16, 2022.