System Software - Unit 1

1. Define system software. 

It consists of variety of programs that supports the operation of the computer. This software makes it possible for the user to focus on the other problems to be solved without needing to know how the machine works internally. Eg: operating system, assembler, loader. 

2. Give some applications of operating system.

 to make the computer easier to use

 to manage the resources in computer

 process management

 data and memory management

 to provide security to the user.

 Operating system acts as an interface between the user and the system

Eg: windows, linux, unix, dos

3. Define compiler and interpreter. 

Compiler is a set of program which converts the whole high level language program to machine language program. Interpreter is a set of programs which converts high level language program to machine language program line by line

4. Define loader. 

Loader is a set of program that loads the machine language translated by the translator into the main memory and makes it ready for execution. 

5. What is the need of MAR register?

 MAR (memory address register) is used to store the address of the memory from which the data is to be read or to which the data is to be written.

6. Define indirect addressing

In the case of immediate addressing the operand field gives the memory location. The word from the given address is fetched and it gives the address of the operand. Eg:ADD R5, [600] Here the second operand is given in indirect addressing mode. First the word in memory location 600 is fetched and which will give the address of the operand.

 7. Define immediate addressing. 

In this addressing mode the operand value is given directly. There is no need to refer memory. The immediate addressing is indicated by the prefix „#‟. Eg: ADD #5 In this instruction one operand is in accumulator and the second operand is an immediate value the value 5 is directly added with the accumulator content and the result is stored in accumulator.

8. List out any two CISC and RISC machine. 

CISC –Power PC, Cray T3E RISC – VAX, Pentium Pro architecture

 9. What is the name of A and L register in SIC machine and also specify its use. 

A-accumulator Used for arithmetic operation. i.e., in the case of arithmetic operations one operand is in the accumulator, and other operand may be an immediate value, register operand or memory content. The operation given in the instruction is performed and the result is stored in the accumulator register. L-linkage register It is used to store the return address in the case of jump to subroutine (JSUB) instructions.

 10. What are the instruction formats used in SIC/XE architecture? Give any one format.

Format 1 (1 byte), Format 2 (2 bytes), Format 3 (3 bytes) & Format 4(4 bytes) Format 2:

8                 4      4

OPCODE   R1     R2

11. What is the difference between the instructions LDA # 3 and LDA THREE? 
In the first instruction immediate addressing is used. Here the value 3 is directly loaded into the accumulator register. In the second instruction the memory reference is used. Here the address (address assigned for the symbol THREE) is loaded into the accumulator register.