Prototype DCBs
Many of the constants and variables contained within a DCB may be left blank (i.e., these default to zero).
The OPEN process results in a merge of the constants and variables specified in the DD JCL statement, and the dataset label for existing magnetic tape and direct-access datasets, into the DCB, replacing the zero values with actual, non-zero values.
A control block called the JFCB (Job File Control Block) initially holds the information extracted from the DD statement for the dataset. The results of the merge are stored in the JFCB which may also be written into the DSCB during the CLOSE process, thereby making the dataset definition permanent.
An example is the BLKSIZE= variable, which may be (and usually is) specified in the DCB as zero. In the DD statement, the BLKSIZE is specified as a non-zero value and this, then, results in a program-specified LRECL (logical record length) and a JCL-specified BLKSIZE (physical block size), with the merge of the two becoming the permanent definition of the dataset.
Fortran is a general-purpose, compiled imperative programming language that is especially suited to numeric computation and scientific computing.
Virtual Storage Access Method (VSAM) is an IBM DASD file storage access method, first used in the OS/VS1, OS/VS2 Release 1 (SVS) and Release 2 (MVS) operating systems, later used throughout the Multiple Virtual Storage (MVS) architecture and now in z/OS. Originally a record-oriented filesystem, VSAM comprises four data set organizations: key-sequenced (KSDS), relative record (RRDS), entry-sequenced (ESDS) and linear (LDS). The KSDS, RRDS and ESDS organizations contain records, while the LDS organization simply contains a sequence of pages with no intrinsic record structure, for use as a memory-mapped file.
Job Control Language (JCL) is a name for scripting languages used on IBM mainframe operating systems to instruct the system on how to run a batch job or start a subsystem. The purpose of JCL is to say which programs to run, using which files or devices for input or output, and at times to also indicate under what conditions to skip a step. Parameters in the JCL can also provide accounting information for tracking the resources used by a job as well as which machine the job should run on.
dd is a command-line utility for Unix, Plan 9, Inferno, and Unix-like operating systems and beyond, the primary purpose of which is to convert and copy files. On Unix, device drivers for hardware and special device files appear in the file system just like normal files; dd can also read and/or write from/to these files, provided that function is implemented in their respective driver. As a result, dd can be used for tasks such as backing up the boot sector of a hard drive, and obtaining a fixed amount of random data. The dd program can also perform conversions on the data as it is copied, including byte order swapping and conversion to and from the ASCII and EBCDIC text encodings.
Disk Operating System/360, also DOS/360, or simply DOS, is the discontinued first member of a sequence of operating systems for IBM System/360, System/370 and later mainframes. It was announced by IBM on the last day of 1964, and it was first delivered in June 1966. In its time, DOS/360 was the most widely used operating system in the world.
In the context of IBM mainframe computers in the S/360 line, a data set or dataset is a computer file having a record organization. Use of this term began with, e.g., DOS/360, OS/360, and is still used by their successors, including the current z/OS. Documentation for these systems historically preferred this term rather than file.
IEFBR14 is an IBM mainframe utility program. It runs in all IBM mainframe environments derived from OS/360, including z/OS. It is a placeholder that returns the exit status zero, similar to the true command on UNIX-like systems.
This article discusses support programs included in or available for OS/360 and successors. IBM categorizes some of these programs as utilities and others as service aids; the boundaries are not always consistent or obvious. Many, but not all, of these programs match the types in utility software.
In the IBM System/360 storage architecture, the Volume Table of Contents (VTOC), is a data structure that provides a way of locating the data sets that reside on a particular DASD volume. With the exception of the IBM Z compatible disk layout in Linux on Z, it is the functional equivalent of the MS/PC DOS File Allocation Table (FAT), the NTFS Master File Table (MFT), and an inode table in a file system for a Unix-like system. The VTOC is not used to contain any IPLTEXT and does not have any role in the IPL process, therefore does not have any data used by or functionally equivalent to the MBR. It lists the names of each data set on the volume as well as size, location, and permissions. Additionally, it contains an entry for every area of contiguous free space on the volume. The third record on the first track of the first cylinder of any DASD volume is known as the volume label and must contain a pointer to the location of the VTOC. The location of the VTOC may be specified when the volume is initialized. For performance reasons it may be located as close to the center of the volume as possible, since it is referenced frequently. A VTOC is added to a DASD volume when it is initialized using the Device Support Facilities program, ICKDSF, in current systems.
Basic Assembly Language (BAL) is the commonly used term for a low-level programming language used on IBM System/360 and successor mainframes. Originally, "Basic Assembly Language" applied only to an extremely restricted dialect designed to run under control of IBM Basic Programming Support (BPS/360) on systems with only 8 KB of main memory, and only a card reader, a card punch, and a printer for input/output — thus the word "Basic". However, the full name and the initialism "BAL" almost immediately attached themselves in popular use to all assembly-language dialects on the System/360 and its descendants. BAL for BPS/360 was introduced with the System/360 in 1964.
This is an overview of Fortran 95 language features. Included are the additional features of TR-15581:Enhanced Data Type Facilities, which have been universally implemented. Old features that have been superseded by new ones are not described – few of those historic features are used in modern programs although most have been retained in the language to maintain backward compatibility. The current standard is Fortran 2018; many of its new features are still being implemented in compilers. The additional features of Fortran 2003, Fortran 2008 and Fortran 2018 are described by Metcalf, Reid and Cohen.
A user exit is a subroutine invoked by a software package for a predefined event in the execution of the package. In some cases the exit is specified by the installation when configuring the package while in other cases the users of the package can substitute their own subroutines in place of the default ones provided by the package vendor to provide customized functionality. In some cases security controls restrict exits to authorized users, e.g., EXCP appendages in MVS.
In IBM mainframe operating systems, basic partitioned access method (BPAM) is an access method for libraries, called partitioned datasets (PDSes) in IBM terminology. BPAM is used in OS/360, OS/VS2, MVS, z/OS, and others.
In IBM mainframe operating systems, Basic sequential access method (BSAM) is an access method to read and write datasets sequentially. BSAM is available on OS/360, OS/VS2, MVS, z/OS, and related operating systems.
In IBM mainframe operating systems, Execute Channel Program (EXCP) is a macro generating a system call, implemented as a Supervisor Call instruction, for low-level device access, where the programmer is responsible for providing a channel program—a list of device-specific commands (CCWs)—to be executed by I/O channels, control units and devices. EXCP for OS/360 and successors is more specifically described in the OS System Programmer's Guide.; EXCP for DOS/360 and successors is more specifically described in DOS Supervisor and I/O Macros. This article mostly reflects OS/360 through z/OS; some details are different for TOS/360 and DOS/360 through z/VSE.
OS/360, officially known as IBM System/360 Operating System, is a discontinued batch processing operating system developed by IBM for their then-new System/360 mainframe computer, announced in 1964; it was influenced by the earlier IBSYS/IBJOB and Input/Output Control System (IOCS) packages for the IBM 7090/7094 and even more so by the PR155 Operating System for the IBM 1410/7010 processors. It was one of the earliest operating systems to require the computer hardware to include at least one direct access storage device.
Basic Direct Access Method, or BDAM is an access method for IBM's OS/360 and successors computer operating systems on System/360 and later mainframes. BDAM "consists of routines used in retrieving data from, and storing data onto, direct access devices." BDAM is available on OS/360, OS/VS2, MVS, z/OS, and related high-end operating systems.
Input/Output Control System (IOCS) is any of several packages on early IBM entry-level and mainframe computers that provided low level access to records on peripheral equipment. IOCS provides functionality similar to 1960s packages from other vendors, e.g., File Control Processor (FCP) in RCA 3301 Realcom Operating System, GEFRC in GECOS, and to the later Record Management Services (RMS) in DEC VAX/VMS
The OS/360 Object File Format is the standard object module file format for the IBM DOS/360, OS/360 and VM/370, Univac VS/9, and Fujitsu BS2000 mainframe operating systems. In the 1990s, the format was given an extension with the XSD-type record for the MVS Operating System to support longer module names in the C Programming Language. This format is still in use by the z/VSE operating system. In contrast, it has been superseded by the GOFF file format on the MVS Operating System and on the z/VM Operating System. Since the MVS and z/VM loaders will still handle this older format, some compilers have chosen to continue to produce this format instead of the newer GOFF format.
TERSE is an IBM archive file format that supports lossless compression. A TERSE file may contain a sequential data set, a partitioned data set (PDS), partitioned data set extended (PDSE), or a large format dataset (DSNTYPE=LARGE). Any record format (RECFM) is allowed as long as the record length is less than 32 K. Records may contain printer control characters.
