Group A. Advantages of data spaces

Group B. Disadvantages of data spaces

Notes:

CLARIFICATION

· I'm afraid it's not quite clear what you mean by...

· I'm sorry I didn't quite follow what you said about...

· I'm afraid I don't understand what... mean(s).

· When you say..., do you mean that...?

ASKING QUESTIONS

· I'd like to know what/when/why/how/who/if...

· Could you tell me what/when/why/how/who/if...?

· I wonder what/when/why/how/who/if...

· Would you tell me what/when/why/how/who/if...?

· It's interesting to know (to find out) what/when/why/how/who/if...

TEST

1. Match the following words with the given definition:

1. processor, 2. keyboard, 3. mouse, 4. floppy disk 5. hard disk 6. modem 7. monitor 8. ROM 9. RAM.

a) Nonvolatile, no modifiable computer memory, used to hold programmed instructions to the system; b) The part of a television or computer on which a picture is formed or information is displayed; c) Rigid disk coated with magnetic material, for storing computer programs and relatively large amounts of data; d) An electronic device that makes possible the transmission of data to or from computer via telephone or other communication lines; e) A set of keys, usually arranged in tiers, for operating a typewriter, typesetting machine, computer terminal, or the like; f) Volatile computer memory, used for creating, loading, and running programs and for manipulating and temporarily storing data; main memory; g) Central processing unit: the key component of a computer system, containing the circuitry necessary to interpret and execute program instructions; h) A palm-sized device equipped with one or more buttons, used to point at and select items on a computer display screen and for controlling the cursor by means of analogous movement on a nearby surface; i) A thin, usually flexible plastic disk coated with magnetic material, for storing computer data and program.

2. Match the definitions from the table A with their equivalents in the Russian language from the table B:

Table A	Table B
1. DSSPs (Data Space Support Platforms)   2.DBMS (Database Management System)   3. Abstraction   4. Catalog and Browse   5. Search and Query   6. Local store and index   7. The Discovery Component   8. The Source Extension Component	a) Система управления базами данных   b) Абстракция   c) Компонент расширения источников   d) Каталог и просмотр   e) Компонентраскрытия   f) Платформы поддержки пространств данных   g) Локальное хранение и индексирование   h) Поиск и запрашивание

Unit 3. Real-Time Operating System

 

I. READING

1.1. Read and translate the text “Basic Kernel Services”[23]

Basic Kernel Services

 

Real-time and embedded systems operate in constrained environments in which computer memory and processing power are limited. They often need to provide their services within strict time deadlines to their users and to the surrounding world. It is these memory, speed and timing constraints that dictate the use of real-time operating systems in embedded software.

The kernel is the part of an operating system that provides the most basic services to application software running on a processor. The kernel of a real-time operating system (RTOS) provides an “abstraction layer” that hides from application software the hardware details of the processor (or set of processors) upon which the application software will run.

In providing this “abstraction layer” the RTOS kernel supplies five main categories of basic services to application software. The most basic category of kernel services, at the very center is Task Management. This set of services allows application software developers to design their software as a number of separate “chunks” of software – each handling a distinct topic, a distinct goal, and perhaps its own real-time deadline. Each separate “chunk” of software is called a “task”. Services in this category include the ability to launch tasks and assign priorities to them. The main RTOS service in this category is the scheduling of tasks as the embedded system is in operation.

The Task Scheduler controls the execution of application software tasks, and can make them run in a very timely and responsive fashion.

The second category of kernel services is Inter task Communication and Synchronization. These services make it possible for tasks to pass information from one to another, without danger of that information ever being damaged. They also make it possible for tasks to coordinate, so that they can productively cooperate with one another. Without the help of these RTOS services, tasks might well communicate corrupted information or otherwise interfere with each other.

Since many embedded systems have stringent timing requirements, most RTOS kernels also provide some basic Timer services, such as task delays and time-outs. Many (but not all) RTOS kernels provide Dynamic Memory Allocation services. This category of services allows tasks to “borrow” chunks of RAM memory for temporary use in application software. Often these chunks of memory are then passed from task to task, as a means of quickly communicating large amounts of data between tasks.

Many (but not all) RTOS kernels also provide a “Device I/O Supervisor” category of services. These services, if available, provide a uniform framework for organizing and accessing the many hardware device drivers that are typical of an embedded system.

In addition to kernel services, many RTOS’s offer a number of optional add on operating system components for such high-level services as file system organization, network communication, network management, database management, user-interface graphics, etc. Although many of these add-on components are much larger and much more complex than the RTOS kernel, they rely on the presence of the RTOS kernel and take advantage of its basic services. Each of these add-on components is included in an embedded system only if its services are needed for implementing the embedded application, in order to keep program memory consumption to a minimum.

Many non-real-time operating systems also provide similar kernel services. The key difference between general-computing operating systems and real-time operating systems is the need for “deterministic” timing behavior in the real-time operating systems. Formally, “deterministic” timing means that operating system services consume only known and expected amounts of time. Real-time and embedded systems are used in many applications such as airborne computers, medical instruments and communication systems. Embedded systems are characterized by limited processor memory, limited processing power, and unusual interfaces to the outside world. Real-time requirements impose stringent time deadlines for delivering the results of embedded processing.

 

Study the meaning of the following words and word combinations:

· real-time OS

· an embedded system

· a constraint

· a chunk

· to launch

· to assign

· priority

· scheduling

· corrupted

· stringent

· temporary

· an add-on component

· to implement

· consumption

· airborne computer

· to impose

 

1.2. Answer the following questions:

1. What are the constraints that dictate the use of real-time operating systems?

2. What is an “abstraction layer” in RTOS?

3. What are main categories of basic services in RTOS?

4. Inter task Communication and Synchronization controls the execution ofapplication software tasks, does it?

5. What does “deterministic” timing mean?

1.3. Find out in the text sentences logically connected with the following statements:

· Embedded systems as one kind of operating systems.

· Basic concepts of real-time operating systems.

· Development of real-time operating systems.

· Real-time and embedded systems in comparison.