APIIT CE0073-5: Computer Systems Low Level Techniques Project

This project presents a comprehensive exploration of assembly language, focusing on its practical application through the design of a calculator. The assignment begins with an abstract and introduction to assembly language, emphasizing its role in communicating with computers at a low level and its benefits in terms of performance and security. The project delves into recent processor architectures, comparing and contrasting CISC and RISC designs, highlighting their similarities and differences. The core of the project involves the system design of a calculator in assembly language, outlining requirements, objects, and limitations. The project also discusses potential future enhancements and concludes with a summary of the benefits of understanding assembly language for computer systems. Appendices provide example assembly code for various shapes and operations.

Name
Intake code.
Subject.
Project Title.
Date Assigned:
Date Completed :
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Table of contents for every detailed section.
Abstract …………………………………………………………………………… 3
Introduction ………………………………………………………………………...4
Recent Processors architecture ……………………………………………………...5
System Design …………………………………………………………………….. 7
Limitation………………………………………………………………………….. 8
Future Enhancement …………………………………………………………………9
Conclusion ………………………………………………………………………….. 10
Reference ……………………………………………………………………………11
Appendix …………………………………………………………………………….. 12
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Abstract
Assembly language abbreviated as asm makes it possible for humans to communicate with
computers. It is a low level programming language. It is the closest method of communication
humans can engage in with a computer. It makes it possible for programmers to observe the
flow of data and execution in a program. It is dependent on machine code instructions
Assembly has a lot of benefits such that it is difficult , close to impossible, to decompile the
code once the program has been compiled which implies one can observe a program already
compiled to see the assembly language. Another advantage is that it is useful for low level
operations that are hardware-specific like kernel components and bootloaders. Assembly
language has less overhead on its code as compared to high level languages thus making its code
run faster and uses less memory. It is the best for writing interrupt service routines and other
memory resident programs.
Forensic uses Assembly to find out what a process has been done during the incident. This is
achieved by recovering the trail of function calls it has made when executing that can be
retrieved from the process assembly code and stack from the memory. Assembly makes it
possible for the programmer to track the flow of data and execution in a program.
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Introduction on Assembly Language with research and analysis for the given case study
Assembly language uses an assembler is a program that takes in the basic computer instructions
and converts them into a pattern of bits which the computer's processor can use to undertake its
basic operations.
Assembly is the most powerful computer programming language available. Programmers get
insight to write effective code in high-level languages when they understand assembly language.
The instructions written in assembly language are changed to machine code of 0s and 1s by use
of a translator. The translator translates one by one to execute machine instructions. The machine
only executes what you want it to do and the necessary activities to perform the task thus makes
program execution fast as possible.
It gives access to I/O and themachine-dependent registers as well as the control of the exact
code behavior in critical sections . Assembly language makes a programmer have an
understanding of instruction set architecture. A microprocessor executes a program written in
assembly language.
The various programs that compile low level programming languages include TASM, TLINK
and GUI Turbo Assembler.
Assembly language
Computer assembly language is a single executable machine language instruction It is a
combination of letters which suggests the operation of an instruction
LD stands for LoaD . LDA stands for LoaD Accumulator. LOAD and STORE commands are
used to allocate to and deallocate from a register. The MOV instruction moves data around (See
Appendix 1)
Interrupts are used to call a subroutine of the system to be executed. There are two types of
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interrupts that include a read character from standard input,the result is stored in AL. The write
character to standard output, DL = character to write. (See Appendix 2 and Appendix 3)
The main directives of assembly language are starting addresses for programs, then starting the
values for memory locations and specify the end of program text. Assembly language takes loop
instructions that provide an easy method to repeat a certain block of statements severally.
Nested loops was implemented to generate the right pyramid (see picture 2)
Advantages of Assembly Language
It helpd the prgrammer know how to interface with the BIOS, the Operating system and the
processor. One knows data representation in the memory as well us other external devices like
the USB , micro card and the hard disks. A programmer gets an understanding of how the
processor executes as well as access the instructions via ther internal harddisk and the external
devices and processs the data.
Assembly needs less memory thus less time to execute a program, It makes the execution of
complex jobs that are hardware specific be easy. It is best for writing memory residing programs
as well as interrupt servce routines. It is the best to hand the jobs that are time critical.
Use of Assembly in forensic
Since assembly is more secure and it directly manages PC hardware it is best for use in
forensic.Since they are used to separate the ASCII and UNICODE characters from binary
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records from that could fast-track a method toward finding shrouded information.
Assembly is used with the signature file to scan a thin client gadget to find harmful injected
scripts.
Assembly language gives huge information which can be acquired by correlating this
information through analyzing the thread stacks in forensic analysis Assemblies have a lot of
metadata that include version number, localization details, and other product details. This is
important in forensic.
Recent processors architecture and describe the similarities and differences
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CISC which is the complex instruction Set Computer abbreviated and the Reduced Instruction
Set computer abbreviated as RISC are the main architectures used in designing and
manufacturing microprocessors of the current CPUs.
The similarity between CISC and RISC is that both of them have a similar layout of the silicon
thus their basic design is the same. They both have multiple processing cores. The L1 and L2
cache are dedicated to each other. They have L3 cache that is shared.
They have the cryptographic, miscellaneous I/O controllers, input and output interfaces, PCIe
controllers.
Both of them get instructions from memory by fetching the instructions. They process these
instructions to manipulate data within the computer. They can be used with compatible low level
software to execute the same programs.
They are dependent on electrical power to operate and dissipate heat. They can be implemented
with memory caches and pipelines to improve the processing speed.
The difference between the two is below:
CISC
It is an instruction set that was designed mainly to use a small number of machine language
instructions to perform the required computing job at a high speed.
It is used by x86 architectures
It uses a highly optimized set of instructions which are small.
It is Programmer Oriented
It is complex since it requires several clock cycles to execute instructions.
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Fewer registers thus requires less RAM.
Complex instructions thus shor program lengths
Instructions use variable formats containing several addressing modes.
Used in desktops, laptops applications as it uses a microprogrammed control unit.
Has varying formats from 16-64 bits for each instruction.
Flexible to accommodate code expansion
RISC
It is intended to give the necessary capability in an efficient manner . It entails a full set of
computer instructions. RISC,
Uses a large , complex and set of instructions.
It is machine Oriented.
Needs one clock cycle to execute instructions thus simple.
More registers thus requires more RAM.
Fixed format 32-bit
Its instructions have few fixed formats with little address modes.
Has simple instructions thus long program length
Used in applications of mobile phones and tablets the hardwired units
It is used in ARM
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Code expansion create problems
System Design
I will be building a calculator in assembly language.
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Requirements
The Calculator will have the following mathematics operations ( + )addition, (-) subtraction, (x)
multiplication, (/)division .
It should calculate any integers passed to it.
The system should have a menu that will guide the user operations
The system should allow input from the user.
The system should output the input the user has entered.
The system should send a message to the user to continue or exit the program
The objects that we will have include
A Key that will store the keys the user has entered
An Expression which will store given Expression string that will be processed
Display that will sprint out and display the entered keys as well as the calculation result
Result object that will store the results of the calculations.
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Limitation
The programme does not distinguish if the user entered a letter or number. It converts the letter
in the the equivalent ASII digit and proceeds to do the given calculation
The system does not provide the correct result when a user inputs decimal digits.
The programme does not proceed after the user does a single computation. If the user presses a
key to continue it terminates.
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Future Enhancement
The calculator should be able to perform other mathematical operations such as finding the
remainder, percentages, square root as well as square.
The program will be able to let the user proceed with another operation after one operation has
ended.
The program will be able to detect if a user inputs a letter in the place of a number.
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Conclusion
A good understanding of the mechanism and the functionality of assembly language helps us to
understand the computer systems better. This is because it operates at the most complicated
stage which is the lowest level in the computer systems. It provides the necessary knowledge on
the operating of the memory and also the computer frameworks. The knowledge of assembly
language makes one understand the computer memory and also the file. Assembly language is
very helpful for understanding the computer architecture and programs system. It gives a deep
understanding of how the system works like the processorI t helps one to understand the
algorithm of the program to the processor working and registering the registers of the computer.
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References
1. Jeff Prosise, “RISC vs. CISC: The Real Story -- What makes the PowerPC a RISC processor
and the Pentium a CISC? http://www.zdnet.com/pcmag/pctech/content/14/18/tu1418.001.html
2. Eilam, E., 2011. Reversing: Secrets of Reverse Engineering. s.l.:John Wiley & Sons.
3. Alazab, M. and Watters, P. (2015). Digital forensic techniques for static analysis of NTFS
images. [online] ResearchGate. Available at:
https://www.researchgate.net/publication/265155000_Digital_forensic_techniques_for_static_an
alysis_ of_NTFS_images
4. David, J. (2015). Difference between RISC and CISC architecture. [online] FIRMWARE
DEVELOPER. Available at: http://www.firmcodes.com/difference-risc-sics-architecture/
5. Burdach, M. (2005). Digital forensics of the physical memory. Warsaw University.
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Appendix 1
Assembly code for an Upward pyramid
org 100h
.model small
.data
space dw 11
star dw 1
.code
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main proc
mov cx, 7
outer:
mov bx,cx ; stores
mov cx,space
k:
mov dl,32
mov ah,02
int 21h
loop k
dec space
mov cx, star
l:
mov dl, '*' ; top pyramid
mov ah, 02
int 21h
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loop l
inc star
inc star
mov dl, 0Ah
mov ah, 02
int 21h
mov dl, 0Dh
mov ah, 02
int 21h
mov cx, bx
loop outer
Appendix 2 : Reverse cube shape
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; You may customize this and other start-up templates;
; The location of this template is c:\emu8086\inc\0_com_template.txt
org 100h
.model small
.data
space dw 11
star dw 1
spac1 dw 1
star1 dw 13
.code
main proc
mov cx, 7
outer:
mov bx,cx ; stores here
mov cx,space
k:
mov dl,32
mov ah,02
int 21h
loop k
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dec space
mov cx, star
l:
mov dl, '*' ; top pyramid
mov ah, 02
int 21h
loop l
inc star
inc star
mov dl, 0Ah
mov ah, 02
int 21h
mov dl, 0Dh
mov ah, 02
int 21h
mov cx, bx
loop outer
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mov cx, 7
outer1:
mov bx,cx ; stores here
mov cx,space1
k1:
mov dl,32
mov ah,02
int 21h
loop k1
inc space
mov cx, star
l1:
mov dl, '*' ; top pyramid
mov ah, 02
int 21h
loop l
dec star
dec star
mov dl, 0Ah
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mov ah, 02
int 21h
mov dl, 0Dh
mov ah, 02
int 21h
mov cx, bx
loop outer1
ret
end main
endp
Appendix 2: Right Pyramid
;RIGHT PYRAMID
.MODEL SMALL
.STACK 100H
.CODE
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MAIN PROC
MOV BX,1
MOV CX,5
L1:
PUSH CX
MOV AH,2
MOV DL,32
L2:
INT 21H
LOOP L2
MOV CX,BX
MOV DL,'*'
L3:
INT 21H
LOOP L3
MOV AH,2
MOV DL,10
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INT 21H
MOV DL,13
INT 21H
INC BX ;THIS IS FOR REVERSE PYRAMID
;INC BX
;INC BX
POP CX
LOOP L1
EXIT:
MOV AH,4CH
INT 21H
MAIN ENDP
END MAIN
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System Screenshots
Nested Loops
Picture 1: Running assembly code
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Picture 2: Right pyramid
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