IBM Basic Assembly Language - General Characteristics

General Characteristics

The architecture of IBM mainframes has undergone several extensions over the years, including System/360, System/370 XA, ESA/390, and z/Architecture. Each of these architectures has retained compatibility with most of the features of its predecessor. BAL uses the native instruction set of these machines. It is thus closer to the hardware than third-generation languages such as COBOL.

The instruction set consists of the low-level operations supported by the hardware, such as:

Instruction Mnemonic Description
LOAD L copy a value from memory to a register
STORE ST copy a value from a register to memory
COMPARE C compare a register value with a value in memory
Shift SLL, SRL move the bits of a register left or right
START SUBCHANNEL SSCH start a sub-channel I/O operation using a string of Channel Command Words

The extreme simplicity of these operations means that a program written in assembler will usually be much longer than an equivalent program in, say, COBOL or Fortran. In the past, the speed of hand-coded assembler programs was often felt to make up for this drawback, but with the advent of optimizing compilers, C for the mainframe, and other advances, assembler has lost much of its appeal. IBM continues to upgrade the assembler, however, and it is still used when the need for speed or very fine control is paramount.

Another reason to use assembler is that not all operating system functions can be accessed in high level languages. The application program interface of mainframe operating systems is defined as a set of assembly language "macro" instructions, that typically invoke Supervisor Call (SVC) or Diagnose (DIAG) hardware instructions to invoke operating system routines. It is possible to use operating system services from programs written in high-level languages by use of assembler subroutines.

Read more about this topic:  IBM Basic Assembly Language

Other articles related to "general characteristics":

Critique Of Pure Reason - Terms and Phrases - Intuition and Concept
... Mediate representations represent things by representing general characteristics of things ... can represent the chair by representing general characteristics of the chair being brown, being wooden, being a chair, and so forth ... The perception represents the chair directly, and not by means of any general characteristics ...

Famous quotes containing the word general:

    As a general rule, do not kick the shins of the opposite gentleman under the table, if personally unaquainted with him; your pleasantry is liable to be misunderstood—a circumstance at all times unpleasant.
    Lewis Carroll [Charles Lutwidge Dodgson] (1832–1898)