System Programming

Page 1 of 31 MAHARASHTRA STATE BOARD OF TECHNICAL EDUCATION (Autonomous)

(ISO/IEC - 27001 - 2005 Certified)

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SUMMER – 12 EXAMINATIONS Model Answer

Q.1. a) Attempt any THREE of the following: i) List various applications of system software (1 mark for each point, any four points) 1) It increases the productivity of computer which depends upon the effectiveness, efficiency and sophistication of the systems programs. 2) Compilers are system programs that accept people like languages and translate them into machine language. 3) Loaders are system programs that prepare machine language program for execution. 4) Macro processors allow programmers to use abbreviation. 5) Provides efficient management of various resources. 6) It manages multiprocessing, paging, segmentation, resource allocation. 7) Operating system and file systems allow flexible storing and retrieval of information. ii) Distinguish between multiprogramming and multiprocessing (1 mark for each difference)

1)

2)

3)

4)

Multiprogramming It is the interlarded execution of two of more processed by a processor without waiting for external event. Multiprogramming loads more than one program in to the memory, so that processor can switch between any of the loaded program. These systems are designed to maximize CPU usage. i.e. Number of processes run on a single processor In these several programmes are running at a time, like windows with many programmes open.

Multiprocessing 1) It is the simultaneous execution of two or more processes by a multiprocessor within a single computer system. 2) Multiprocessing involves the execution of multiple concurrent processes in a system instead of processing a single process at any one instant. 3) It means a process is run on multiple processors. So execution speed up is achieved 4) It means that computer can process more than one thing at a time.



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iii) Explain the working of Bucket Sort. (2 marks for explanation, 2 marks for example) The sort involves examine the least significant digit of the keyword first, and the item is then assigned to a bucket uniquely depend on the value of the digit. After all items have been distributed the buckets items are merged in order and then the process is repeated until no more digits are left. A number system of base P requires P buckets. There are serious disadvantages to using it internally on a digital compiler 1) It takes two separate processes, a separation and a merge 2) It requires a lot of extra Storage for the buckets. The average time required for the sort is ( N log P(K) ) where N is the table size, K is the maximum key size & P is the radix of the radix sort. The extra storage required is N P.



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iv) Explain hash and random entry search (1 mark for hash, 3 marks for random entry) Ans. In hash and random entry search the random entry number K generated from the key by methods similar to their used in address calculation. If the K th position s avoid, then the new element is put there; is not then some other call must be found for the insertion. The first problem is the generation of a random number from the key. The four character EBCDIC keywords divide the keywords by the table length N and use the remainder. This scheme works well as long as N and the key size have no common factors. For a given group of in keywords the remainder should be fairly evenly distributed over O---(N-1). Another method is to treat the keyword as a binary fraction and multiply it by another binary fraction. The second problem is the procedure to be followed when the first trial entry result in a filled position. There are a member of methods of resolving this problem. 1) Random entry with replacement: A sequence of random numbers is generated from the keyword from each of these a number between 1 and N is formed and the table is protect at the position. Probing are terminated when a void space is found. Notice that the random numbers generated are independence and it is perfectly possible to probe the same position twice. 2) Random entry without replacement: This is the same as above except that any attempt to prove the same position twice is bypassed. This method holds advantage over the only when proves are expensive e.g. for files on tape or drum. 3) Open addressing: If the first probe gives a position K and that position is filled, then the next location K+1 is probed and so on until a free position is found. If the search runs off the bottom of the table, then it is renewed at the top.



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Q.1. b) Attempt any ONE of the following: i) Describe database required by each pass of loader. (3 marks for pass1 database, 3 marks for pass2 database) Ans. Pass 1 data bases 1) Input object decks 2) Initial program load Address (IPLA) supplied by the programmer on the operating system that specifies the address to load the first segment. 3) A program load address (PLA) counter, used to rap truck of each segments assigned location. 4) A tab, global External symbol table (GEST) that is used to store each external symbol and its corresponding assigned core address. 5) A copy of the input to be used by pass2. This may be stored on an auxiliary storage device, such as magnetic tape, disk on drum, on the original object deck may be reread by loader a second time for pass 2.

1) 2) 3) 4) 5)

Pass 2 data bases Copy of object programs inputted to pass 1 Initial Program Load address parameter (IPLA) The Program load address counter (PLA) The Global External symbol table (GEST) prepared by pass 1, containing each symbol and its corresponding absolute address value. An array, the Local External Symbol Array (LESA), which is used to establish a correspondence between the ESD ID numbers, used an ESO and RLD cards and the corresponding External Symbols absolute address value.

ii) With neat diagram explain intermediate phase of compiler. (3 marks for diagram, 3 marks for explanation) Ans. The compiler creates an intermediate form of source program. It affords 2 advantages 1) It facilitates optimization of object code. 2) It allows a logical separation between machine independent and machine dependent. One intermediate form is a parse tree. For E.G



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Q.2) Attempt any TWO of the following: a) (2 marks for each technique) The possible algorithm for four optimization techniques are as follows:1) Elimination of common sub expression 2) Compile time compute. 3) Boolean expression optimization. 4) Move invariant computations outside of loops. 1) Elimination of common sub expression: -The elimination of duplicate matrix entries can result in a more can use and efficient object program. The common subexpression must be identical and must be in the same statement. The elimination algorithm is as follows:i) Place the matrix in a form so that common subexpression can be recognized. ii) Recognize two subexpressins as being equivalent. iii) Eliminate one of them. iv) After the rest of the matrix to reflect the elimination of this entry.



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For example:-

2) Compile time compute:- Doing computation involving constants at compile time save both space and execution time for the object program. The algorithm for this optimization is as follows:i) Scan the matrix. ii) Look for operators, both of whose operands were literals. iii) When it found such an operation it would evaluate it, create new literal, delete old line iv) Replace all references to it with the uniform symbol for the new literal. v) Continue scanning the matrix for more possible computation. For e.g.A = 2 276 / 92 B The compile time computation would be




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Matrix Before optimization M1 M2 M3 M4

*

2

276

/

M1

92

M2

B

=

A

M3

Matrix After optimization M1 M2 *

6

B

=

A

M3

M3 M4

3)Boolean expression optimization:- We may use the properties of boolean expression to shorten their computation. e.g. In a statement If a OR b Or c, Then …… when a, b & c are expression rather than generate code that will always test each expression a, b, c. We generate code so that if a computed as true, then b OR c is not computed, and similarly for b. 4) Move invariant computation outside of loops:- If computation within a loop depends on a variable that does not change within that loop, then computation may be moved outside the loop. This requires a reordering of a part of the matrix. There are 3 general problems that need to be solved in an algorithm. i) Recognition of invariant computation. ii) Discovering where to move the invariant computation. ii) Moving the invariant computation. b) State and explain four basic task of Macroprocessor? (2 marks for each task) Ans: The 4 basic task of Macroprocessor is as follows:1) Recognize the macro definitions. 2) Save the Macro definition. 3) Recognize the Macro calls. 4) Perform Macro Expansion. 1) Recognize the Macro definitions:- A macroprocessor must recognize macro definitions identified by the MACRO and MEND pseudo-ops. When MACROS



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and MENDS are nested, the macroprocessor must recognize the nesting and correctly match the last or outer MEND with the first MACRO. 2) Save the Macro definition:- The processor must store the macro instruction definitions which it will need for expanding macro calls. 3) Recognize the Macro calls:- The processor must recognize macro call that appear as operation mnemonics. This suggest that macro names be handled as a type of opcode. 4) Perform Macro Expansion:- The processor must substitute for macro definition arguments the corresponding arguments from a macro call, the resulting symbolic text is then substituted for the macro call. c) Explain the purpose of various phases of a compiler. Clearly mention the required input and output generated by each of these phases. (For correct listing of phases 1 mark, 1 mark for each phase) Ans: The different phases of compiler is as follows:1) Lexical Phase:i) Its main task is to read the source program and if the elements of the program are correct it generates as output a sequence of tokens that the parser uses for syntax analysis. ii) The reading or parsing of source program is called as scanning of the source program. iii) It recognizes keywords, operators and identifiers, integers, floating point numbers, character strings and other similar items that form the source program. iv) The lexical analyzer collects information about tokens in to their associated attributes. 2) Syntax Phase:1st i) In this phase the compiler must recognize the phases (syntatic construction); each phrase is a semantic entry and is a string of tokens that has meaning, and 2nd Interpret the meaning of the constructions. ii) Syntactic analysis also notes syntax errors and assure some sort of recovery. Once the syntax of statement is correct, the second step is to interpret the meaning (semantic). There are many ways of recognizing the basic constructs and interpreting the meaning.



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iii) Syntax analysis uses rules (reductions) which specifies the syntax form of source language. iv) These reduction defines the basic syntax construction and appropriate compiler routine (action routine) to be executed when a construction is recognized. v) The action routine interpret the meaning and generate either code or intermediate form of construction. 3) Interpretation Phase:- This phase is typically a routine that are called when a construct is recognized. The purpose of these routines is to on intermediate form of source program and add information to identifier table. 4) Code optimization Phase:- Two types of optimization is performed by compiler, machine dependent and machine independent. Machine dependent optimization is so intimately related to instruction that the generated. It was incorporated into the code generation phase. Where are Machine independent optimization was done in a separate optimization phase. 5) Storage Assignment:- The purpose of this phase is as follows:i) Assign storage to all variables referenced in source program. ii) Assign storage to all temporary locations that are necessary for intermediate results. iii) Assign storage to literals. iv) Ensure that storage is allocated and appropriate locations are intralized. 6) Code generation:i) This phase produce a program which can be in Assembly or machine language. ii)This phase has matrix as input. iii) It uses the code production in the matrix to produce code. iv)It also reference the identifier table in order to generate address & code conversion.



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7) Assembly phase:-The compiler has to generate the machine language code for computer to understand. The task to be done is as follows:i) Generating code ii) Resolving all references. iii) Defining all labels. iv) Resolving literals and symbolic table. OR Q.2)c) (1mark for each phase) Ans. 1) Lexical Analysis:- This phase takes as input the original program and if the elements of the program are correct it generates some meaningful units called “tokens” 2) Syntax Analysis:- This phase takes as input the tokens generated by lexical phase and if the syntax of the statement is correct it generates a parse tree representation. 3) Sementic Analysis:- This phase performs the check on the meaning of the st statement and performs the necessary modifications in the parse tree representation. (If the structure of compiler does not include sementic analysis then in such a case sementic analysis is assumed to take place within the syntax an analysis phase) 4) Intermediate code generation:- This phase takes as input the pass tree Representation and generates an intermediate representation to break the complexity of the statement and hence helps in faster translation. 5) Code optimization:- This phase is responsible for generating an optimized Intermediate representation so that the resulting code would get executed Faster. 6) Code Generation:- This phase is responsible for generating the target program which can be assembly language program or machine language Program. 7) Symbol table:- It is used for keeping a track on the symbols encountered in the program. 8) Error handler:- It is responsible for the detection reporting and the handling of the errors which can occur in any of the compilation phase.



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Q.3) Attempt any FOUR of the following: a) What is loader? How it works? Explain with diagramatically? (2 marks for diagram, 2 marks for explanation) Ans: The loader is a program which accepts the object program decks prepares these programs for execution by the computer and initiates the execution. The loader must perform four functions. 1) Allocate space in memory for the program (allocation) 2) Resolve symbolic references between object decks (linking) 3) Adjust all address dependent locations, such as address constants, to corresponds to the allocated space (relocation) 4) Physically place the machine instruction and data into memory (loading).

Fig General loading scheme In simple loading scheme, the assembler o/p the machine language translation of a program on a secondary storage device and a loader is placed in core. The loader places into memory the machine language version of the users program and transfers control to it. Since the loader program is much smaller than the assembler, this makes more core available to the users program



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There are different types of loader scheme. 1) 2) 3) 4)

Compile and Go loader Absolute loaders Binary symbolic subroutine (BSS) loaders Direct linking loader.

b) State functions of relocating loader (4 marks for explanation) Ans. Relocating loader avoids possible reassembling of all subroutines when a single subroutine is changed and perform the tasks of allocation and linking for the programmer. The BSS loader allows many procedure segments yet only one data segment. The assembler assembles each procedure segment independently and passes on to the loader the text and information as to relocation and intersegment references. The o/p of a relocating assembler using a BSS scheme is the object program and information about all other program it references. For each source program the assembler o/p a text prefixed by a transfer vector that consist of addresses containing names of the subroutines referenced by the source program. The assembler would also provide the loader with additional information such as the length of the entire program and the length of the transfer vector position. After loading the text and the transfer vector into core, the loader would load each subroutine identified in the transfer vector. It would the place a transfer instruction to the corresponding subroutine in each entry in the transfer vector. The BSS loader scheme is other used on compiler with a fixed length direct address instruction format. The relocation bit solves the problem of relocation, the transfer vector is used to solve the problem of linking and the program length information solves the problem of allocation.



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c) State the use of macro with suitable example (2 marks for explanation, 2 marks for example) Ans. Macros are single line abbreviation for groups of instructions. For every occurrence of this one. Line macro instruction, the macro processing assemble will substitute the entire block. By defining the appropriate macro instruction can assembly language programmer can tailor his own higher level facility in a convenient manner, at no cost in control over the structured of his program. He can achieve the conciseness and ease in coding of high level language without losing the basic advantage of assembly language programming. Integral macro operation simplifies debugging and program modification and they facilitate standardization. Many computer manufactures use macro instructions to automate the writing of “tailors” operating systems in a process called system generation. Macro instructions are usually considered an extension of the basic assembler language and macro processor is viewed as an extension of the basic assembler algorithm. Macro INCR A 1, Data A 2, Data A 3, Data MENO . . INCR . . A 2, Data INCR . . DATA OC F’ S’ A 2, Data A 3, Data

expanded sources

A 1, Data A 3, Data . . A 1, Data

. . Data DC F’ S’



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d) Draw the flowchart of Pass-I of assembler. (4 marks for correct flow chart)



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e) Explain the foundation of system programming (2 marks for diagram, 2 marks for explanation) Ans.

People Application Programming Compilers

Loaders I/O program

Assemblers

Macro processors

Text editor File system

Schedule

be baggily aids Libraries

searching and sorting

Memory management

device management

System programs leg compiler, loaders, macro processor, operating systems were developed to make computer better adapted to the needs of their users. Compiler is system program that accept people life languages and translate them into machine language. Loaders are system programs that prepare machine language programs for execution. Macro processors allow programmers to use abbreviations. Operating system and file system allows flexible storing and retrieval of information. The productivity of each computer is heavily dependent upon the effectiveness, efficiency and sophistication of the system programs.

Q.4) a) Attempt any THREE of the following: i) What is macro? Explain macroprocessor and macro definition. (2 mark for macro, 1 marks for macroprocessor, 1 mark for macro definition) Ans. The assembly language programmer often finds that certain set of instructions get repeated often in the code. Instead of repeating the set of instructions the programmer can take advantage of macro facility where macro is defined as “Single line abbreviation for group of instructions”



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For e.g.:The requirement of programmer is as follows:. . . A 1, Data A 2, Data A 3, Data . . . A 1, Data A 2, Data A 3, Data . . .

The above requirement can be achieved by using macro facility as follows:MACRO INCR A 1, Data Macro definition

A 2, Data A 3, Data MEND . . . INCR . . INCR . END



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The meaning of INCR is not known to the assembler because it is programmer defined and hence we need a Macroprocessor that would take if and process it. Macroprocessor is responsible for processing a Macro. There are 4 functions (task) of Macroprocessor, i) Recognize macro definition. ii) Save the Macro definition. iii) Recognize the Macro calls iv) Perform macro expansion. Macro definition:- As seen in previous example i.e. MACRO INCR A 1, Data A 2, Data A 3, Data MEND Macro definition is nothing but a code or a program that would be enclosed within an MACRO and MEND pseudo opcode. It is requires by Macroprocessor for recognizing and saving it for Macro expansion.

ii) Explain different data structures used by Phase-II assembler. (4 marks for explanation) Ans. The various data structure used is as follows:i) Copy file:- It is prepared by pass 1 to be used by pass 2. ii) Location counter:- It is used to assign address to instruction and addressed to symbol defined in the program.




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iii) Machine operation Table (MOT) or Mnemonic Opcode Table (MOT):- It is used to indicate for each instruction. a) Symbolic mnemonic b) Instruction length c) Binary machine opcode. d) Format. iv) Pseudo-operation Table (POT):- It indicate for each pseudo-op the symbolic mnemonic and action to be taken in pass 2 Or It is consulted to process pseudo like DS, DC, Drop & using. v) Symbol Table (ST):- It is used to generate the address of the symbol address in the program. vi) Base table (BT):- It indicate which registers are currently specified as base register by USING Pseudo-ops. vii) INST workspace:- It is used for holding each instruction and its various parts are being getting assembled. viii) PUNCH CARD workspace:- It is used for punching (outputting) the assembled instruction on to cards. ix) PRINT LINE workspace:- It is used for generating a printed assembly listing for programmers reference. x) Object card:- This card contain the object program in a format required by the loader. iii) Explain how to reduce different process in compiler. (1 mark for each process) Ans. There are 4 different ways to reduce process in compiler. They are as follows:1) 2) 3) 4)

Elimination of common subexpression Compile time compute. Boolean expression optimization Move invariant computation outside of loop.



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1) Elimination of common subexpression:- The elimination of duplicate matrix enteries can result in more concise and efficient object program. The common subexpression must be identical and must be in same statement. 2) Compile time compute:- Doing computation involving constants at compile time save both space and execution time for the object program. 3) Boolean expression optimization:- We may use the properties of Boolean expression to shorten their computation. 4) Move invariant computation outside of the loops :-If computation within a loop depends on a variable that does not change within that loop, then computation may be moved outside the loop. a) Recognition of invariant computation b) Discovering where to move the invariant computation. c) Moving the invariant computation. iv) Compare linker and loader Ans. (1 mark for each difference) Linker

Loader

1) Linker is s system program which 1) Loader is a system program that link different object module to places the object program in memory and prepare it for form a program. execution and start the execution. 2) Many object module are combined and given to loader

2) Loader accept the combined version of object module.

3) Linker accepts the input (.obj file) from compiler or assembler.

3) Loader accepts the input from linker.

4) Source code is given to complier which generates object code, which is given to linker, which forms machine code and is given to loader

4) Source code is given to complier which generates object code, which is given to linker, which forms machine code and is given to loader which then makes it executable in processor memory and is executed.



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Q.4) b) Attempt any ONE of the following: i) Describe the function of interpretation phase of compiler. (6 marks for explanation) Ans. The interpretation phase is typically a collection of routines that are called when a construct is recognized in the syntactic phase. The purpose of these routine is to create an intermediate form of the source program and add information to the identifier table. The separation of the syntactic phase from the interpretation phase is a logical division. The former phase recognizes syntactic constructs while the latter interpret the precise meaning in to the matrix or identifier table. The database used by interpretation phase is as follows:1) 2) 3) 4)

Uniform symbol table. Stack Identifier table. Matrix

1) Uniform Symbol table:- It contains source program in uniform table. 2) Stack:- It contains the tokens currently being parsed by the syntax and interpretation phase. 3) Identifier table:- It describes the identifiers used in the source program. 4) Matrix:- It is the primary intermediate form of the program. ii) Describe the main function of lexical phase of compiler. Ans. (6 marks for explanation) i) It is the only phase which is allowed to communicate with the original source program. ii) This phase take as input the original source program and generate some meaningful units called “tokens”. iii) The other functions performed by lexical phase are as follows:-



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a) It is responsible for removing the comments and white space from the program. b) It is also responsible for generating the copy of a program with errors marked in it. c) The program that perform lexical analysis is called as lexical analyzer or scanner. The three tasks of lexical analysis phase are:1) To parse the source program in to basic elements or tokens of the language. 2) To build a literal table and an identifier table. 3) To build a uniform symbol table. The database used are:1) Source program:- Original form of program appear to the compiler as string of character. 2) Terminal table:- A permanent database that has an entry for each terminal symbol. 3) Literal table:- It describe literals used in the source program. 4) Identifier table:- Describe identifiers used in the source program. 5) Uniform symbol table. Q.5) Attempt any TWO of the following: a) Explain overlay structure in detail. (2 mark for diagram, 6 marks for explanation) Ans. The subroutines of a program are needed at different times. For e.g. Pass 1 and pass 2 of an assembler are call other subroutine it is possible to produce an overlay structure that identifiers mutually exclusive subroutines. In order for the overlay structure to work it is necessary for the module loader to the various procedures as they are needed. The portion of the loader that actually intercepts the “calls” and loads the necessary procedure is collect the overlay supervision or simply the upper.




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A (20 K)

B (20 K)

D (10 K)

70 K e (30 K)

E (20 K)

Overlay structure Above program consisting of five subprogram (A, B, C, D & E) that require look bytes of core. The arrow indicate that subprogram A only calls B, D and E; subprogram B only calls C and E; subprogram D only calls E; and subprogram C and E do not call any other routine procedures B and D are never in use at the same time; neither are C and E. If are load only those procedures that are actually to be used at any particular time, the amount of core needed is equal to the longest path of the overlay structure. This happens to be 70k. Overlay reduces the memory requirement of a program. It also makes it possible to execute program where size exceeds the amount of memory which cane ne allocated to them. For the execution of overlay structured program, the root is loaded in memory and given control for the execution. Other overlays are loaded as and when headed. Loading of an overlay overwrite a previously loaded overlay with the same load origin.



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b) Draw the block diagram of the phases of compiler. (8 marks for correct complete diagram) Ans.

OR (There are two diagrams for this question. so any one diagram can be considered)



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c) Explain Binary search and Linear search. (4 marks for each search)

Ans. Binary search:- A more systematic copy of searching an ordered table is: start at the middle of the table and compare the keyword with the middle entry. The keyword may be equal to greater than or smaller than the item checked. The next action taken for each of these outcomes is as follows: 1) If equal , the symbol is found 2) If greater, use the top half of the given table as a new table to search




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3) If smaller, use the bottom half of the table. This method effectively divides the table in half an every probe, systematically bracketing the item searched for. The search is terminate with a ‘not found’ condition when the length of the last suitable searched is down to 1 and the item has not been found. Symbol 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15

AL EX FN FU IF IW LE LO NC OP OR RO RN JE T1

probe1

probe2

probe3

probe4

IFFU

IF