System Software Question Bank - Unit I & II

Define system software?

It consists of a variety of programs that support the operation of computer. This software makes it possible for the user to focus on an application or other problem to be solved, without needing to know the details of how the machine works internally.

2. What are the components of system software?

1. Text editor – To write programs in a high-level language.

2. Compiler – To translate high level language programs into machine language.

3. Loader or linker – To load the machine language program into memory.

4. Debugger – To help detect errors in the program.

5. Assembler -To translate assembly language program into machine language.

6. Macro processor – it is a part of assembler for translation.

3. What are the functions of assemblers?

To translate assembly language program into machine language and assigning machine addresses to symbolic labels used by the programmer.

4.   What are the functions of loaders? 

To load the machine language program into memory

5. What are the functions of linkers?

Linkers are used to perform the linking operation. Linking is to combines two or more separate object programs and supplies the information needed to allow references between them.

6. What are the functions of compilers?

The function of compiler is to translate high level language programs into machine language. In order to convert into machine language the source program is split into tokens by lexical analysis. The statement is recognized by syntax analysis or parsing. The last step is the generation of object code.

7. What are the functions of text editors?

An interactive text editor is a program that allows a user to create and revise a target document. The term document includes objects such as computer programs, text, equations, tables diagrams line art etc.

8.   What are the functions of debuggers? To help detect errors in the program.

9. Name the registers available in SIC/XE machine?

Table below indicates the additional register details

Mnemonic Number Special use

B   3 Base register; used for addressing.

S    4 General working register – no special use.

T    5 General working register – no special use.

F     6 Floating-point accumulator (48 bits)

10. Write the addressing mode of SIC/XE machine? Two new relative addressing modes with format 3

Base relative b=1, p=0 TA (target address) = (B) + disp (0 ��������������� Program_counter relative b = 0, p = 1 TA = (PC) + disp (-2048 ������������� For base relative addressing the disp field is interpreted as 12 bit unsigned integer.

For program_counter relative addressing the disp field is interpreted as 12 bit signed integer with negative values are in 2’s complement form. For direct addressing b and p are set to 0. the disp field indicates the target address. Indexed addressing if x is set to 1. For immediate addressing i = 1 and n = 0. For indirect addressing i = 0 and n = 1 the value contained in this word is taken as the address of the operand value.

For simple addressing i and n are both 0. the address is taken as the location of the operand.

11. Write a data movement instruction for SIC machine?

LDA FIVE
STA ALPHA
LDCH CHARZ

12. Write a data movement instruction for SIC/XE machine?

STCH C1
-
-
-
ALPHA	RESW	1
FIVE	WORD	5
CHARZ	BYTE	C ‘Z’
C1	RESB	1

LDA #5

STA ALPHA

LDA #90

STCH C1

-

-

-
ALPHA RESW 1
C1 RESB 1

13. Write notes on CISC machines?

Complex instruction set computers (CISC) has a relatively large and complicated instruction set, several different instruction formats and lengths, and many addressing modes.

14. Write the data formats of VAX architecture?

Integers are stored as binary numbers in byte, word, longword, quadword, or octaword ; 2’s complement representation is used for negative values. Character are stored using 8-bit ASCII codes. Four different floating point data formats on the VAX ranging from 4 to 16 bytes.

VAX provides a packed decimal data format. Each byte represents two decimal digits, with each digit encoded using 4 bits of the byte. The sign is encoded in the last 4 bits of the byte.

Numeric format is used to represent numeric values with one digit per byte. The sign may appear either in the last byte or as a separate byte preceding the first digit. These variations are called trailing numeric and leading separate numeric.

VAX supports queues and variable-length bit strings.

15. How the instruction sets are formed in VAX architecture?

Variable length instruction formats. Each instruction consist of an operation code (1 or 2 bytes) followed by upto 6 operand specifiers depending on the type of instruction.

16. List the registers available in Pentium Pro microprocessor?

There are eight general-purpose registers, which are named as EAX, EBX, ECX, EDX, ESI, EBP and ESP.Each general purpose registers is 32 bits long. Registers EAX, EBX, ECX and EDX are generally used for data manipulation. EIP is a 32 bit register that contains a pointer to the next instruction to be executed.

Floating point computations are performed using a floating point unit (FPU) . this unit contain eight 80 bit data registers.

17. Write notes on RISC machines?

Reduced instruction set computers. This design can result in faster and less expensive process development, greater reliability, and faster instruction execution time.

A RISC system is characterized by a standard, fixed instruction length, and single-cycle execution of most instructions. Memory access is usually done by load and store instructions only. All instructions except for load and store are register-to register operations. There are typically large numbers of general purpose registers.

18. Name the various registers available in UltraSPARC architecture?

SPARC architecture includes a large register file that usually contains more than 100 general-purpose registers. Any procedure can access only 32 registers. The first eight of these registers can be accessed by all procedures on the system. The other 24 registers are visualized as a window thorough which part of the register file can be seen. In original SPARC architecture, the general purpose registers were 32 bits long. Later it was expanded to 64 bits.

19. Write the addressing mode of UltraSPARC machines?

1. Immediate mode – operand value specified as part of the instruction.

2. Register direct mode – in register

3. PC relative

4. Register indirect with displacement

5. Register indirect indexed.

20. Write notes on delayed branches?

Instruction execution is pipelined – while one instruction is being executed, the next one is being fetched from memory and decoded. SPARC branch instructions are delayed branches – the instruction immediately following the branch instruction is executed before the branch is taken.

21. Write the memory organization of Power PC architecture?

Memory consists of 8-bit bytes; all addresses used are byte addresses. Two consecutive bytes form a halfword; four bytes form a word; eight bytes form a doubleword; sisteen bytes form a quadword.

Power PC program can be written using a virtual address space of 2⁶⁴ bytes. This address space is divided into fixed-length segments, which are 256 megabytes long. Each segment is divided into pages, which are 4096 bytes long. The virtual address specified by instructions is automatically translated into a physical address.

22. Write the addressing mode of Power PC architecture?

Immediate, register direct. Instruction that address memory are load and store, and branch instruction. Load and store uses the following addressing modes

Mode Target address calculation

Register direct TA = (register)

Register indirect with index TA = (register –1) + (register –2) Register indirect with immediate index TA = (register) + displacement

23. What are methods for performing I/O operations in Power PC Architecture?

Two different methods for performing I/O operations. In one approach, the segments in the virtual address space are mapped onto an external address space. Segments that are mapped in this way are called direct-store segments.

I/O is performed using the regular virtual memory management hardware and software.

24. Write the register details of Cray T3E architecture?

32 general purpose registers. 64 bits long. Used to store and manipulate integer data and address.

32 floating-point registers. 64 bits long. 64 bit PC and several other status and control registers.

25. Write the addressing modes of Cray T3E architecture?

The operand value may be specified as part of the instruction itself or it may be in a register

Operands in memory are addressed using one of the following two modes

PC-relative TA = (PC) + displacement

Register indirect with displacement TA = (register) + displacement

Unit II

What are the functions of assembler?

The assembler perform functions such as translating mnemonic operation codes to their machine language equivalents and assigning machine addresses to symbolic labels used by the programmer.

2. Name the various assembler directives?

START Speficy the name and starting address for the program END Indicate the end of the source program and specify eth first

executable instruction in the program BYTE Generate character or hexadecimal constant. WORD Reserve the indicated number of bytes for a data area. RESW Reserve the indicated number of words for a data area.

Write the function of a simple SIC assembler?

Convert the mnemonic operation codes to their machine language equivalents.
b) Convert symbolic operands to their equivalent machine address.
c) Build the machine instructions in the proper format.
d) Convert the data constants specified in the source program into their internal
representation.
e) Write the object program and the assembly listing.

What is meant by forward reference?

A reference to a label that is defined later in the program is called forward reference.

FIRST STL RETADR

RETADR RESW 1

Here REGADR label is an example of forward reference because; the label is used before it is declared.

5. Write notes on the Header record in the object program?

The Header record contains the program name, starting address, and length. The format is

Col.1 H
Col. 2-7 Program name
Col 8-13 Starting address of object program
Col 14-19 Length of object program in bytes

6. Write notes on the Text record in the object program?

Text record contains the translated instructions and data of the program, together with an indication of the address where they are to be loaded. The format is

Col.1 T Col. 2-7 Starting address for object code in this record Col 8-9 Length of object code in this record in bytes Col 10-69 Object code, represented in hexadecimal

7. Write notes on the End record in the object program?

The End record marked the end of the object program and specifies the address in the program where execution is to begin. The format is

Col 1 E Col. 2-7 Address of first executable instruction in object program

8. What are the functions of Pass 1 of an assembler?

Assign address to all statements in the program. b) Save the values assigned to all labels for use in Pass2. c) Perform some processing of assembler directives.

9. What are the functions of Pass 2 of an assembler?

Assemble instruction.
b) Generate data value define by BYTE, WORD, etc.
c) Perform processing of assembler directives not done during Pass 1.
d) Write the object program and the assembly listing.

10. Write the data structure for symbol table in assembler?

The symbol table includes the name and value for each label in the source program, together with flags to indicate error conditions. This table may also contain other information about the data area or instruction labeled-for example its type and length.

11. List the details available in the intermediate file generated by Pass1?

The intermediate file contains each source statement together with its assigned address, error indicators, etc. This file is used as the input to Pass 2. This working copy of the source program can also be used to retain the results of certain operations that may be performed during Pass 1, so that these need not be performed during Pass 2. Similarly pointer into OPTAB and SYMTAB may also be retained for each operation code and symbol table used.

12. What is meant by program relocation?

When more than one program at a time, sharing the memory and other resources of the machine. The address for loading is not known in advance.

Since the assembler does not know the actual location where the program will be loaded, it cannot make the necessary changes in the address used in the program. The assembler can identify those part of the object program that need modification. An object program that contains the information necessary to perform his kind of modification is called relocatable program.

13. Write notes on the Modification record in the object program?

14. Define literals in assembly language?

The command for the loader must also be a part of the object program. We can accomplish it with a modification record. The format is

col 1	M
col 2 -7	Starting address of the address field to be modified, relative to the
	beginning of the program.
col 8 – 9	Length of the address field to be modified in half-bytes.

The programmer can be able to write the value of a constant operand as a part of the instruction that uses it. Such type of operand is called a literal. In some assembler languages the literal is identified with the prefix = which is followed by a specification of the literal value.

Ex:-

215 1062 WLOOP TD =X’ 05’ E32011

All of the literal operands used in a program are gathered together into ore or more literal pools.

The basic data structure needed to store literals is literal table LITTAB.

15. What is the structure of a literal table?

The basic data structure needed to store literals is literal table LITTAB. For each literals used this table contains the literal name, the operand value and length, and the address assigned to the operand when it is placed in a literal pool. LITTAB is often organized as a hash table, using the literal name or value as the key.

16. What are the various symbol defining statements?

Most assembler provides an assembler directive that allows the programmer to define symbols and specify their values. The assembler directive generally used is EQU. The general form is

symbol EQU value

This statement defines the given symbol in the SYMTAB and assigns to it the value specified.

Another common use of EQU is in defining mnemonic names for registers.

A EQU 0
X EQU 1
L EQU 2

There is another common assembler directive that can be used to indirectly assign values to symbols is ORG.

ORG value

17. What are program blocks?

Program blocks refer to segment of code that are rearranged within a single object program unit, and control sections to refer to segments that are translated into independent object program unit.

The assembler directive USE indicates which portions of the source program belong to the various blocks.

18. What is a control section in assembly language statement?

A control section is a part of the program that maintains its identity after assembly; each such control section can be loaded and relocated independently of

each other’ s.

When control sections form logically related parts of a program, it is necessary to provide some means for linking them together.

19. What are external references?

Control sections are independently loaded and located, the assembler is unable to process these references in the usual way. The assembler has no idea where any other control section will be located at execution time. Such references between control sections are called external references.

20. What are external symbols?

They are symbols that are defined in a control section, and may be used by other sections.

21. Write notes on Define record?

A Define record gives information about external symbols that are defined in this control section. The format is

col 1 D
col 2-7 Name of external symbol defined in this control section.

col 8 – 13 Relative address of symbol within this control section.
col 14 – 73 Repeat information in col 2-13.

22. Write notes on Refer record?

A Refer record lists symbols that are used external references by the control section. The format is

col 1 R
col 2 – 7 Name of external symbol referred to in this control section.
col 8 – 73 names of other external reference symbols.

23. Define load-and-go assembler?

There are two main types of one-pass assembler.

One type produces object code directly in memory for immediate execution. This type generate object program in memory for immediate execution. No object program is written out, and no loader is needed. This kind of load-and-go assembler is useful in a system that is oriented toward program development and testing. 

24. What is the function of multi-pass assembler?

Restrictions such as prohibiting forward reference in symbol definition are not normally a serious inconvenience for the programmer. The general solution is the multi-pass assembler that can make as any passes as are needed to process the definitions of symbols. The portions of the program that involve forward references in symbol definitions are saved during pass1.

25. Name the various sections in SPARC assembler?

SPARC assembler language program is divided into units called sections. The assembler provides a set of predefined section names. They are

.TEXT Executable instructions
.DATA Initialized read/write data
.RODATA Read only data
.BSS Unintialized data areas