(edited 9-Jul-91, Chapter 1) (RT--11 System Components\int_rsc_chap)

A computer system is a collection of components that works together to process data. This chapter describes the following components of the RT--11 computer system: (unnumbered) (Hardware\bold)

The hardware components are the mechanical devices in the system, the machinery and the electronics that perform physical functions. (Software\bold)

The software components are the programs written for the system. These programs perform logical and mathematical operations, provide the basic tools for manipulating information, and provide a means for you to control the system. (Documentation\bold)

Documentation includes the manuals and listings that tell you how to use the hardware and software.

Collectively, these components provide a complete computer system that lets both novice and expert use a computer. (System Hardware)

The hardware components of the RT--11 computer system consist of the computer and its peripheral devices --- machinery external to the computer that supplements the computer by providing resources for operations the computer cannot handle alone. (Computer)

The computer has two basic components: (unnumbered) (Processor\bold)

The (processor) or the (central processing unit) (CPU) is the control center of the computer. It performs all data processing, such as comparing information, calculating a value, and printing, displaying, or storing information. The RT--11 computer system is constructed around a Digital PDP--11 processor. Any PDP--11 model can be used in an RT--11 system. (Memory\bold)

(Memory) or (main memory) is a series of storage locations within the computer where the computer processes your data. The amount of memory contained in a PDP--11 computer varies depending on the computer: the smallest memory size is 32K bytes; the largest possible size is 4096K bytes. The minimum memory distributed with a MicroPDP--11 computer is 512K bytes. (Peripheral Devices)

The RT--11 computer system requires a minimum of two peripheral devices: a terminal and a disk storage device with its medium. (Terminal)

Your interaction with the computer system occurs through the terminal. You enter information --- operating commands, for example --- from the terminal's keyboard, which you use much like a typewriter keyboard. The computer, in turn, displays information and messages on the terminal's printer or screen.

Generally, an RT--11 computer system has one terminal through which all interaction between the system and the user takes place. This is called the (console terminal). If the system has more than one terminal, one of them is still designated the console terminal and the system is still considered a single-user operating system. However, the other terminals can be controlled by one or more application programs. (Storage Devices)

Although you should have more than one storage device, one disk may be adequate. Depending on your computer system, you can have any combination of disk drives, diskette drives, and magnetic tape drives.

With two storage devices you can use one to hold your operating system files, and the other to back up (make a copy of) the operating system files. This way, you have a means of replacing your RT--11 files if they are damaged or accidentally deleted.

Some disk drives contain (fixed) disks; that is, they come with a hard disk permanently installed in them. For example, the MicroPDP--11 computer is configured with a fixed hard disk.

Other storage devices are not distributed with a medium permanently installed in them. You insert the storage medium or volume (disk, diskette, magtape) in these drives when you want to store or retrieve information.

Each drive has a device name (2-letter mnemonic) and a unit number (0, 1, 2, n). The mnemonic identifies the type of hardware interface to which the device is connected; and the unit number identifies the specific drive, since you can have more than one drive for each type of hardware interface.

Once the storage volume is in the drive, you access it by the device name and unit number. Then, the storage medium becomes an area apart from the computer's main memory to hold your information. This is further explained in (int_start_chap).

Storage devices and volumes are classified in three ways according to their use: (unnumbered) (System (SY)\bold)

The system device and volume contains the operating system files. The system boots (starts up) from this volume when you turn on the computer. The system volume can be identified by its physical device mnemonic and unit number or by the logical (symbolic) name SY. (Default storage (DK)\bold)

The default storage volume stores files you create when you do not specify a device in which to store them. This volume can be identified by its physical device memnonic and unit number or by the logical (symbolic) name DK.

When you first install the operating system, the system device logical name (SY) and the default storage device logical name (DK) represent the same device. However, after you install the system files, you can reassign the logical name DK to a different device. See (int_start_chap) for an explanation of why you would want to do this and the commands that enable you to do this. (Backup\bold)

You use the backup device to create backup copies of your own or of the system files. You do this by copying the files from the volume on the system device to the volume on the backup device. If your operating system does not come with a backup copy of the system files, then you should make one when you install the system.

The backup device should have a removable volume (rather than a fixed one). This device has no logical name automatically assigned to it by the operating system. (Optional Devices)

You can add optional peripheral devices to your computer system according to your needs. For example, if your computer system is used primarily for program development, it may have extra storage devices and a high-speed printing device. Computer systems used in a laboratory environment may have graphics display hardware and an analog-to-digital converter. Computer systems that provide (or use) information in conjunction with another kind of computer system often have a magtape device and an auxiliary communication port.

The hardware configuration of your RT--11 computer system includes the computer, the terminal, storage devices, and any other devices you choose to add. (System Software)

System software is a collection of programs that effectively transforms the system hardware components into usable tools. These programs include operations, functions, and routines that make it easier for you to use the hardware to solve problems and produce results. For example, some system programs store and retrieve data among the peripheral devices. Others perform difficult or lengthy mathematical calculations. Some programs let you create, edit, and process application programs of your own. Still others handle entire applications for you.

As shown in (sf_fig), system software always includes an operating system, which is the (intelligence) of the computer system. In addition, the system software usually includes one or several language processors and it sometimes includes specific applications. These components make the whole called system software. However, they vary in size depending on what each component includes in a specific software system.

(System Software\sf_fig) (nofloat\keep) (POSTSCRIPT\mlo-003558.PS\12) (The RT--11 Operating System)

The operating system is a collection of programs that organizes all the hardware and software resources of the computer system into a working unit and gives you control. It lets you create, store, and manage files and create and run programs of your own.

The RT--11 operating system consists of the four types of programs shown in (ros_fig). The size of each of these components varies depending on what each includes in a specific operating system.

(RT--11 Operating System\ros_fig) (nofloat\keep) (POSTSCRIPT\mlo-003559.PS\12.5) (unnumbered) (Monitor\bold)

The monitor (executive) program is the link between the system hardware, the system software, and you. You operate the computer through the monitor. Its major functions are to: (#) (unnumbered\#) Accept, acknowledge, and process commands that you or a program give the system Control all input to and output from the system Time or schedule when jobs (programs) are run Maintain the file system Check for abnormal conditions in the system and issue clear, informative messages Control the way the system uses memory

(Monitor Components\bold)

The monitor consists of three major components: (unnumbered\-) (Resident monitor (RMON)\bold)

The resident monitor provides the console terminal service and central program code necessary for both system and user programs. It always remains in computer's main memory, regardless of system operations, and is the basic source of control in the computer. (Keyboard monitor (KMON)\bold)

The keyboard monitor, the most visible part of the monitor, interprets the command language you use to communicate with the computer. When you see the system prompt (a period), KMON is waiting for you to give it a command.

Because you need KMON only when you issue commands, KMON sometimes does not stay in memory but is replaced, or (overlaid), by other programs if they need the space. However, KMON returns as soon as the other program terminates. (User service routines (USR)\bold)

The user service routines access information stored on disks and tapes; for example, routines in the USR open and close files. Depending on how your system is set up, the USR can be swapped in and out of main memory in the same way as KMON.

(Monitor Types\BOLD)

RT--11 has three types of monitors, each with its own RMON, KMON, and USR components. Which monitor type you choose is dictated by the hardware and the application.

When you install your operating system, you choose one of the following monitors to run the system: (unnumbered\-) (Unmapped (SB and FB)\bold)

RT--11 distributes two unmapped monitors; the single job (SB) and foreground/background (FB). The SB monitor is the simplest and smallest monitor and can support only one utility or user program at a time. This monitor could be ideal for small systems being used for one specific application with little system overhead.

The FB monitor includes all the features of the SB monitor as well as its foreground/background feature. This feature lets one job run at high priority in the (foreground), while KMON or a user-written program runs at low priority in the (background). For example, with the FB monitor, you can be editing a file in the background while a time-critical program is collecting, storing, and analyzing data in the foreground. (Single-mapped (XM)\bold)

The XM monitor gives you all the features of the unmapped monitors and extends the amount of memory normally available on a PDP--11 computer.

The XM monitor also gives you the system job feature, which means you can run programs as system jobs to keep the background free for entering commands and running other jobs and the foreground free for a time-critical job. (int_sysjob_chap) further explains the system job feature.

The XM monitor lets you run up to eight programs at the same time. You are limited only by the size of the programs and the amount of memory in your computer.

(A single-job single-mapped monitor can be built through the system generation process. Look for the XB entry in the (mas_book) for references throughout the documentation.) (Fully-mapped (ZM)\bold)

The ZM monitor gives you all the features of the XM monitor and also supports separated Instruction and Data address space and Supervisor Mode. The ZM monitor lets you take advantage of all the features in the current PDP--11 processors.

(A single-job fully-mapped monitor can be built through the system generation process. Look for the ZB entry in the (mas_book) for references throughout the documentation.)

You can tell which monitor your system has from the first line the system displays on your terminal screen when you boot (start) your system. That line identifies the operating system, the monitor, and the version number of the operating system. For example, the following line says that you are running Version 5.6 of the RT--11 operating system with the XM monitor controlling system operations: RT-11XM V05.6

Once you have booted your system, you can identify your monitor by issuing the following command at the period (.) prompt: (.)(SHOW CONFIGURATION (RET))

The first line of the configuration display identifies the operating system, the monitor, and the version number of the operating system. See Chapters (int_fb_chap\value ) and (int_xm_chap\value) for more complete descriptions of the RT--11 monitors. (Device handlers\bold)

Device handlers provide the interface to the hardware devices that are part of the computer system. Device handlers transmit control signals and data to and from your system's peripheral hardware devices (printer, terminal, and so on). A device handler exists for every type of peripheral device that the system supports. (Utilities\bold)

Utilities are programs that cover a wide range of resources; such programs let you create and edit text files, manage programs and files, and locate user-programming errors. Some of the utility programs in the RT--11 operating system are as follows: (unnumbered\-) (Editors), which let you create and modify programs, memos, or any text file you wish to create. (File management programs), which let you manipulate and maintain your programs and data --- to transfer them between devices, to update them, and to delete them when you are done with them. (Communication programs), which let you communicate with other computers and operating systems and to transfer files between RT--11 and another operating system. (Debugging programs), which help you find and correct errors in your programs. (HELP) and (INDEX), which are designed to help you find information about RT--11: HELP gives on-line KMON command descriptions; INDEX, gives on-line references to topics described in the RT--11 manuals. A (librarian), which lets you to store and retrieve often-used programming routines. A (linking program), which converts programs into a format suitable for loading and execution. A (macro assemble), which converts assembly language source code into object modules. (Support for language processors\bold)

The RT--11 operating system supports programming languages. This support is in the form of the libraries SYSMAC and SYSLIB provided with the operating system. The macro library SYSMAC contains operating system macros and calls used in MACRO--11 programs, and the System Subroutine Library (SYSLIB) allows access to those macros by high-level languages such as FORTRAN. (Language Processors)

You use a language processor to translate the programs you create with a text editor into a series of binary codes the computer can understand. A language processor exists for every programming language supported by the system, whether it is a low-level language or a high-level language. (unnumbered) (Low-Level (Assembler)\bold)

RT--11 distributes one low-level assembler language, MACRO--11. The assembler translates assembly code (low-level language) into binary code (machine-level language) in the form of an object file. Assemblers are usually one-for-one translators; that is, each instruction in the language usually becomes one instruction to the computer.

An advantage of programming in assembly language is that it gives you control over such factors as program size and execution speed. A disadvantage is that it is a more intricate language than a higher level one, and low-level languages require much more knowledge of the computer and its devices than a higher level language requires. (High-Level (Compilers and Interpreters)\bold)

High-level languages can be divided into compiled and interpreted languages. Compilers and interpreters are the respective language processors for these languages. These processors usually translate each high-level language instruction into a series of assembly-language or machine-level instructions. This means high-level languages require you to write less code for a computer operation than assembly languages require, which makes programming in a high-level language easier.

Usually a compiler makes more than one pass through an entire program before translating it. In this way, the compiler checks for errors at many levels and optimizes (eliminates) code when possible. The compiler-translated language is called the object code, while the high-level language text file is called the source code.

PDP--11 C, FORTRAN IV, FORTRAN--77, and DIBOL are languages that use a compiler. RT--11 support for FORTRAN IV and FORTRAN--77 is described in (INT_FORT_CHAP).

Like compilers, intrepreters also translate instructions written in a high-level language. However, while compilers translate an entire program before letting you run the program, interpreters translate and run a program at the same time, on an instruction-by-instruction basis. The interpreter does not produce an object file. This is a slower way to run a program than first compiling it and then running it. But one advantage of an interpreter is that you do not have to compile and link files. Another advantage is that you can interactively debug errors in a program as they appear.

BASIC--PLUS is a high-level language that uses an interpreter. Also, optionally, BASIC--PLUS lets you preserve the intermediate translated program and thereby lessen the waiting period before a BASIC program is ready to run. RT--11 support for BASIC--PLUS is described in (int_bas_chap). (Application Programs)

Digital and several other companies sell application programs that run on the RT--11 operating system. Application programs cover many categories, such as marketing, purchasing, inventory management, manufacturing, and engineering. Some general application programs include: (unnumbered) Word processing Spreadsheet analysis Communications Accounting Database management Graphics

Other specialized application programs are geared to particular businesses such as law, medicine, dentistry, real estate, and municipal administration.

To help keep you up to date on what application programs from Digital and other companies are available for the PDP--11, Digital publishes the (PDP--11 Software Source Book). The source book describes more than 2000 application programs, many of which run on the RT--11 operating system. If you want to order the source book, contact your local Digital sales office. (System Documentation)

System documentation can include manuals telling you how to use the hardware and software and also source listings of programs that make up the operating system. Source listings, however, have to be purchased separately and are not included in the software documentation set. (unnumbered) (Hardware manuals\BOLD)

Hardware manuals describe the devices in the computer system. RT--11 hardware documentation includes a processor handbook or technical manual that describes the PDP--11 computer you are using, and an owner's manual or user's guide for each peripheral device in your computer system. These manuals tell you how to operate the devices and give you special programming information that you may need if you intend to write device drivers or special system software involving the devices. (Software manuals\BOLD)

Software manuals describe the operating system and the language processors.

All RT--11-related software manuals are listed and described in the (gui_book). Many of these manuals are provided with your system; others can be ordered through your local Digital sales office. (Source listings\bold)

Source listings are listings of the commented assembly language code that makes up the RT--11 operating system. These detailed listings are generally needed only if you intend to modify the system software. They can be ordered in microfiche form through your local Digital sales office, which also sells the source kits for the operating system. (Chapter Summary)

The RT--11 computer system consists of the following components. (multipage) (3\23\29) (Hardware\ Software \ Documentation) ( Basic components (simple) Computer Terminal 1 disk storage devices

Optional components (simple) Extra terminals Extra storage devices Printer(s) Other devices \ RT--11 Operating system (simple) Monitor Device handlers Utilities Support for language processors

Language processors Application programs \ Hardware manuals Software manuals Source listings) (#)

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