System Software

The System Software nothing but computer software it is designed to operate computer hardware and also provides maintenance of platform for running application software.

Types of Software

System software                                                                         2. Application software

Compiler                                                                                                   high level languages

Interpreter                                                                                                c, c++, JAVA etc.



Compiler: it translates high level language instructions into machine level language at a time.

Interpreter: line by line execution of a program called as an interpreter.

Assembler: it translates mnemonic codes into machine language.

Background of System Software

The System Software contains variety of programs that supports the operation of a computer. Enable the user to focus on the application to be solved without needing to know the details how the machine works internally. At first, the user is using many various types of system softwares. Then traditionally the user writing the programs by using one of the high level language like C, C++, JAVA, PASCAL etc. By using a text editor to create and modify the program.

Then we translate these programs into machine language by using the compiler. Similarly we can write the programs in assembly language using MACRO instructions, in this programs we can read and write the data to perform high level function.

System software and machine architecture

The main characteristic of System Software is differing from application software. That is machine dependency. Because System Software is depends on the machine. But application software is primarily concern with the solution of the problem, as using the computer tool. Due to this reason they are totally related to the architecture of the machine in which they have to run.

It is distinguished between the features of software that are truly fundamental and that are depends solely on the idiosyncies   of a particular machine. In order to avoid this problem we present the fundamental function of each pieces of software through the discussion of following:

SIC (Simplified Instructionset Computers)
CSIC (Complex Instructionset Computers)
RISC (Reduced Instructionset Computers)

SIC (Simplified Instruction Set Computers)

SIC is a hypothetical computer which is carefully design to include the hardware features. Most of all found in real machines while avoiding and usual and irrelevant complexities.

The following are the characteristics include in the SIC are machine architecture.


Memory consists of 8 bit/byte
Any 3 consecutive bytes from a word.
All addresses on SIC are byte addresses.
There are totally 215 bytes in the computer memory.


There are 5 (A, X, L, PC, Sw) registers all of which have special uses.
Each register is 24 bit- length.

Data formats:

Data formats categorized into two ways.

Integer: this are stored as 24 bit binary numbers and if negative values 2’s complement is added.

ASCII Characters: These characters stored by using 8 bit ASCII codes.

Instruction formats:

All machine instructions are of standard version of SIC and having 24- bit format.

Addressing Modes:

There are two Addressing Modes are available.

Direct Addressing Mode
Indexed Addressing Mode

Instruction formats:

Basic set of instructions provided by SIC are sufficient for many of them to perform a particular task. Those set of instructions include the load and storage registers.

LDA- Load Accumulator

STA- Store in Alpha (Store Accumulator)

LDX- Load Index Register

STX- Store Index Register

CSIC (Complex Instructionset Computers)

The full form of CSIC is Complex Instructionset Computers. These are relatively large and instruction sets are complicated.

VAX Architecture

It is family of a computer and was introduced by DEC (Digital Equipment Corporation). It is design for compatibility with earlier machine.


It consists of 8 bit or byte
All addresses used of byte addresses.
Two consecutive bytes form a word.
Four bytes form a long word
Eight bytes form a quad word
Sixteen bytes form a octa word


There are 16 general purpose registers denoted by R0 through R
All general purpose registers are 32 bit in length.

Data formats:

Integers stored as binary numbers in a byte word, long word, quad word and octa word.
Characters stored using 8 bit ASCII codes.
There are 4 useful floating point data formats.
For negative values 2’s complement is added.

Addressing modes:

It provides large number of Addressing modes.

Register mode
Register differ mode
Auto increment and decrement mode

Instruction formats:

Each instruction consists of operation code.
These followed by 6 operands specified depend on type of instruction.


RISC (Reduced Instruction Set Computers)

The full form of RISC is Reduced Instructionset Computers. This architecture mainly involves reducing execution time by simplifying Instructionset of computers.

Ultra space Architecture

This developed by Sun Micro Systems. it is one of the latest member in sparc family.


It consists of 8 bit or byte.
All addresses are bytes addresses.
2 consecutive bytes form a half word.
4 consecutive bytes form a word.
8 consecutive bytes form a double word.


It include large register file, it contains 100 general purpose registers.
But we can access only 32 registers.
This designed from R0 to R31.
R0 always contains value zero (0).
The other 24 registers available to a procedure can be visualized as window.

Data formats:

It provides the storage of integer, floating point values and characters.
Integers stored as 8-16-32 and 64 bit binary numbers.
Both signed and unsigned operations are in signed.
Is negative values 2’s complement is added.

Addressing modes:

An operand value may be specified as a part of instruction itself.

Instruction formats:

This is 3 basic instruction formats.
All this are 32 bit length.
If the Format 1 used for call instruction.
Format 2 used for branch instructions.
If the Format 3 used for register to load and store.

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