MS-DOS 4
MS-DOS 4.0 was a multitasking release of MS-DOS developed by Microsoft based on MS-DOS 2.0. Lack of interest from OEMs, particularly IBM (who previously gave Microsoft multitasking code on IBM PC DOS included with TopView), led to it being released only in a scaled-back form. It is sometimes referred to as European MS-DOS 4.0, as it was primarily used there. It should not be confused with PC DOS 4.00 or MS-DOS 4.01 and later, which did not contain the multi-tasking features. History Apricot Computers pre-announced "MS-DOS 4.0" in early 1986, and Microsoft demonstrated it in September of that year at a Paris trade show. However, only a few European OEMs, such as SMT Goupil and International Computers Limited (ICL), actually licensed releases of the software. In particular, IBM declined the product, concentrating instead on improvements to MS-DOS 3.x and their new joint development with Microsoft to produce OS/2. As a result, the project was scaled back, and only those ...
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Multitasking MS-DOS 4
Multitasking may refer to: * Computer multitasking, the concurrent execution of multiple tasks (also known as processes) over a certain period of time ** Cooperative multitasking ** Pre-emptive multitasking * Human multitasking, the apparent performance by an individual of handling more than one task at the same time * Media multitasking Media multitasking is the concurrent use of multiple digital media streams. Media multitasking has been associated with depressive symptoms and social anxiety by a single study involving 318 participants. A 2018 review found that while the liter ...

International Computers Limited
International Computers Limited (ICL) was a British computer hardware, computer software and computer services company that operated from 1968 until 2002. It was formed through a merger of International Computers and Tabulators (ICT), English Electric Computers (EEC) and Elliott Automation in 1968. The company's most successful product line was the ICL 2900 Series range of mainframe computers. In later years, ICL diversified its product line but the bulk of its profits always came from its mainframe customers. New ventures included marketing a range of powerful IBM clones made by Fujitsu, various minicomputer and personal computer ranges and (more successfully) a range of retail point-of-sale equipment and back-office software. Although it had significant sales overseas, ICL's mainframe business was dominated by large contracts from the UK public sector, including Post Office Ltd, the Inland Revenue, the Department for Work and Pensions and the Ministry of Defence. It also had ...
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INT 21h
The DOS API is an API which originated with 86-DOS and is used in MS-DOS/ PC DOS and other DOS-compatible operating systems. Most calls to the DOS API are invoked using software interrupt 21h ( INT 21h). By calling INT 21h with a subfunction number in the AH processor register and other parameters in other registers, various DOS services can be invoked. These include handling keyboard input, video output, disk file access, program execution, memory allocation, and various other activities. In the late 1980s, DOS extenders along with the DOS Protected Mode Interface (DPMI) allow the programs to run in either 16-bit or 32-bit protected mode and still have access to the DOS API. History of the DOS API The original DOS API in 86-DOS and MS-DOS 1.0 was designed to be functionally compatible with CP/M. Files were accessed using file control blocks (FCBs). The DOS API was greatly extended in MS-DOS 2.0 with several Unix concepts, including file access using file handles, hiera ...
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MS-Net
MS-Net, sometimes stylized as MS-NET, was an early network operating system sold by Microsoft during the earliest days of local area networking (LANs). Overview MS-Net was not a complete networking system of its own; Microsoft licensed it to vendors who used it as the basis for server programs that ran on MS-DOS, porting it to their own underlying networking hardware and adding services on top. Version 1.0 was announced on 14 August 1984 and released along with the PC/AT on 2 April 1985. A number of MS-Net products were sold during the late 1980s, before it was replaced by LAN Manager in 1990. MS-Net's network interface was based on IBM's NetBIOS protocol definition, which allowed it to be ported to different networking systems with relative ease. It did not implement the entire NetBIOS protocol, however, only the small number of features required for the server role. One key feature that was not implemented was NetBIOS's name management routines, a feature 3rd parties often added ...
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Shared Memory (interprocess Communication)
In computer science, shared memory is memory that may be simultaneously accessed by multiple programs with an intent to provide communication among them or avoid redundant copies. Shared memory is an efficient means of passing data between programs. Depending on context, programs may run on a single processor or on multiple separate processors. Using memory for communication inside a single program, e.g. among its multiple threads, is also referred to as shared memory. In hardware In computer hardware, ''shared memory'' refers to a (typically large) block of random access memory (RAM) that can be accessed by several different central processing units (CPUs) in a multiprocessor computer system. Shared memory systems may use: * uniform memory access (UMA): all the processors share the physical memory uniformly; * non-uniform memory access (NUMA): memory access time depends on the memory location relative to a processor; * cache-only memory architecture (COMA): the local memor ...
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Pipeline (Unix)
In Unix-like computer operating systems, a pipeline is a mechanism for inter-process communication using message passing. A pipeline is a set of processes chained together by their standard streams, so that the output text of each process (''stdout'') is passed directly as input (''stdin'') to the next one. The second process is started as the first process is still executing, and they are executed concurrently. The concept of pipelines was championed by Douglas McIlroy at Unix's ancestral home of Bell Labs, during the development of Unix, shaping its toolbox philosophy. It is named by analogy to a physical pipeline. A key feature of these pipelines is their "hiding of internals" (Ritchie & Thompson, 1974). This in turn allows for more clarity and simplicity in the system. This article is about anonymous pipes, where data written by one process is buffered by the operating system until it is read by the next process, and this uni-directional channel disappears when the processes ...
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Interprocess Communication
In computer science, inter-process communication or interprocess communication (IPC) refers specifically to the mechanisms an operating system provides to allow the processes to manage shared data. Typically, applications can use IPC, categorized as clients and servers, where the client requests data and the server responds to client requests. Many applications are both clients and servers, as commonly seen in distributed computing. IPC is very important to the design process for microkernels and nanokernels, which reduce the number of functionalities provided by the kernel. Those functionalities are then obtained by communicating with servers via IPC, leading to a large increase in communication when compared to a regular monolithic kernel. IPC interfaces generally encompass variable analytic framework structures. These processes ensure compatibility between the multi-vector protocols upon which IPC models rely. An IPC mechanism is either synchronous or asynchronous. Synchr ...
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Intel 80386
The Intel 386, originally released as 80386 and later renamed i386, is a 32-bit microprocessor introduced in 1985. The first versions had 275,000 transistorsmit.edu—The Future of FPGAs
(Cornell) October 11, 2012 and were the CPU of many s and high-end s of the time. As the original implementation of the

Protected Mode
In computing, protected mode, also called protected virtual address mode, is an operational mode of x86-compatible central processing units (CPUs). It allows system software to use features such as virtual memory, paging and safe multi-tasking designed to increase an operating system's control over application software. When a processor that supports x86 protected mode is powered on, it begins executing instructions in real mode, in order to maintain backward compatibility with earlier x86 processors. Protected mode may only be entered after the system software sets up one descriptor table and enables the Protection Enable (PE) bit in the control register 0 (CR0). Protected mode was first added to the x86 architecture in 1982, with the release of Intel's 80286 (286) processor, and later extended with the release of the 80386 (386) in 1985. Due to the enhancements added by protected mode, it has become widely adopted and has become the foundation for all subsequent enhancements ...
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Preemptive Multitasking
In computing, preemption is the act of temporarily interrupting an executing task, with the intention of resuming it at a later time. This interrupt is done by an external scheduler with no assistance or cooperation from the task. This preemptive scheduler usually runs in the most privileged protection ring, meaning that interruption and resuming are considered highly secure actions. Such a change in the currently executing task of a processor is known as context switching. User mode and kernel mode In any given system design, some operations performed by the system may not be preemptable. This usually applies to kernel functions and service interrupts which, if not permitted to run to completion, would tend to produce race conditions resulting in deadlock. Barring the scheduler from preempting tasks while they are processing kernel functions simplifies the kernel design at the expense of system responsiveness. The distinction between user mode and kernel mode, which det ...
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New Executable
The New Executable (abbreviated NE or NewEXE) is a 16-bit .exe file format, a successor to the DOS MZ executable format. It was used in Windows 1.0–3.x, Windows 9x, multitasking MS-DOS 4.0, OS/2 1.x, and the OS/2 subset of Windows NT up to version 5.0 (Windows 2000). A NE is also called a segmented executable. History The first product to be released using the New Executable format was Windows 1.0 in 1985, followed by the 1986 multitasking MS-DOS 4.0, which was a separate branch of MS-DOS development, released between mainstream MS-DOS versions 3.2 and 3.3, and sometimes referred to as "European MS-DOS 4.0". OS/2 1.0 was not released until 1987, but the "target operating system" field in the file header reserves value 01 for OS/2, and 02 for Windows, suggesting that the format was designed with OS/2 already in mind, the Joint Development Agreement between IBM and Microsoft for OS/2 having been signed in August 1985, a few months before Windows 1.0 was released in November ...
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