Electrical computers and digital processing systems: memory – Address formation – Address mapping
Reexamination Certificate
1997-05-22
2001-10-23
Chan, Eddie P. (Department: 2751)
Electrical computers and digital processing systems: memory
Address formation
Address mapping
C711S202000, C711S203000, C711S205000, C711S208000
Reexamination Certificate
active
06308247
ABSTRACT:
FIELD OF THE INVENTION
The invention disclosed broadly relates to data processing systems and more particularly relates to improvements in operating systems for data processing systems.
BACKGROUND OF THE INVENTION
The operating system is the most important software running on a computer. Every general purpose computer must have an operating system to run other programs. Operating systems typically perform basic tasks, such as recognizing input from the keyboard, sending output to the display screen, keeping track of files and directories on the disc, and controlling peripheral devices such as disc drives and printers. For more complex systems, the operating system has even greater responsibilities and powers. It makes sure that different programs and users running at the same time do not interfere with each other. The operating system is also typically responsible for security, ensuring that unauthorized users do not access the system.
Operating systems can be classified as multi-user operating systems, multi-processor operating systems, multi-tasking operating systems, and real-time operating systems. A multi-user operating system allows two or more users to run programs at the same time. Some operating systems permit hundreds or even thousands of concurrent users. A multi-processing program allows a single user to run two or more programs at the same time. Each program being executed is called a process. Most multi-processing systems support more than one user. A multi-tasking system allows a single process to run more than one task. In common terminology, the terms multi-tasking and multi-processing are often used interchangeably even though they have slightly different meanings. Multi-tasking is the ability to execute more than one task at the same time, a task being a program. In multi-tasking, only one central processing unit is involved, but it switches from one program to another so quickly that it gives the appearance of executing all of the programs at the same time. There are two basic types of multi-tasking, preemptive and cooperative. In preemptive multi-tasking, the operating system parcels out CPU time slices to each program. In cooperative multi-tasking, each program can control the CPU for as long as it needs it. If a program is not using the CPU however, it can allow another program to use it temporarily. For example, the OS/2 (TM) and UNIX (TM) operating systems use preemptive multi-tasking, whereas the Multi-Finder (TM) operating system for Macintosh (TM) computers uses cooperative multi-tasking. Multi-processing refers to a computer system's ability to support more than one process or program at the same time. Multi-processing operating systems enable several programs to run concurrently. Multi-processing systems are much more complicated than single-process systems because the operating system must allocate resources to competing processes in a reasonable manner. A real-time operating system responds to input instantaneously. General purpose operating systems such as DOS and UNIX are not real-time.
Operating systems provide a software platform on top of which application programs can run. The application programs must be specifically written to run on top of a particular operating system. The choice of the operating system therefore determines to a great extent the applications which can be run. For IBM compatible personal computers, example operating systems are DOS, OS/2 (TM), AIX (TM), and XENIX (TM).
A user normally interacts with the operating system through a set of commands. For example, the DOS operating system contains commands such as COPY and RENAME for copying files and changing the names of files, respectively. The commands are accepted and executed by a part of the operating system called the command processor or command line interpreter.
There are many different operating systems for personal computers such as CP/M (TM), DOS, OS/2 (TM), UNIX (TM), XENIX (TM), and AIX (TM). CP/M was one of the first operating systems for small computers. CP/M was initially used on a wide variety of personal computers, but it was eventually overshadowed by DOS. DOS runs on all IBM compatible personal computers and is a single user, single tasking operating system. OS/2, a successor to DOS, is a relatively powerful operating system that runs on IBM compatible personal computers that use the Intel 80286 or later microprocessor. OS/2 is generally compatible with DOS but contains many additional features, for example it is multi-tasking and supports virtual memory. UNIX and UNIX-based AIX run on a wide variety of personal computers and work stations. UNIX and AIX have become standard operating systems for work stations and are powerful multi-user, multi-processing operating systems.
In 1981 when the IBM personal computer was introduced in the United States, the DOS operating system occupied approximately 10 kilobytes of storage. Since that time, personal computers have become much more complex and require much larger operating systems. Today, for example, the OS/2 operating system for the IBM personal computers can occupy as much as 22 megabytes of storage. Personal computers become ever more complex and powerful as time goes by and it is apparent that the operating systems cannot continually increase in size and complexity without imposing a significant storage penalty on the storage devices associated with those systems.
It was because of this untenable growth rate in operating system size, that the MACH project was conducted at the Carnegie Mellon University in the 1980's. The goal of that research was to develop a new operating system that would allow computer programmers to exploit modern hardware architectures emerging and yet reduce the size and the number of features in the kernel operating system. The kernel is the part of an operating system that performs basic functions such as allocating hardware resources. In the case of the MACH kernel, five programming abstractions were established as the basic building blocks for the system. They were chosen as the minimum necessary to produce a useful system on top of which the typical complex operations could be built externally to the kernel. The Carnegie Mellon MACH kernel was reduced in size in its release 3.0, and is a fully functional operating system called the MACH microkernel. The MACH microkernel has the following primitives: the task, the thread, the port, the message, and the memory object.
The traditional UNIX process is divided into two separate components in the MACH microkernel. The first component is the task, which contains all of the resources for a group of cooperating entities. Examples of resources in a task are virtual memory and communications ports. A task is a passive collection of resources; it does not run on a processor.
The thread is the second component of the UNIX process, and is the active execution environment. Each task may support one or more concurrently executing computations called threads. For example, a multi-threaded program may use one thread to compute scientific calculations while another thread monitors the user interface. A MACH task may have many threads of execution, all running simultaneously. Much of the power of the MACH programming model comes from the fact that all threads in a task share the task's resources. For instance, they all have the same virtual memory (VM) address space. However, each thread in a task has its own private execution state. This state consists of a set of registers, such as general purpose registers, a stack pointer, a program counter, and a frame pointer.
A port is the communications channel through which threads communicate with each other. A port is a resource and is owned by a task. A thread gains access to a port by virtue of belonging to a task. Cooperating programs may allow threads from one task to gain access to ports in another task. An important feature is that they are location transparent. This capability facilitates the distribution of services over a network without program modification.
The message is use
Ackerman Dennis Frank
Desai Himanshu Harshadrai
Gupta Ram Kishor
Strinivasan Ravi Rengarajan
Chan Eddie P.
Hoel Joel
International Business Machines - Corporation
Nguyen Than V.
Walker Mark
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