Table 1. Software Hierarchy Levels.
Level
Description
Application Program
Software designed for a particular class of
applications.
High-Level Language (HLL)
Programs are compiled into either assembly language
or machine language. Each statement usually
translates into multiple machine language instructions.
Examples are C++, Pascal, Java, and Visual Basic.
Operating System
Contains procedures that can be called from programs
written in either high-level language or assembly
language. This system may also contain an application
programming interface (API).
Assembly Language (ASM)
Uses instruction mnemonics that have a one-to-one
correspondence with machine language.
Machine Language (ML)
Numeric instructions and operands that can be stored
in memory and directly executed by the computer
processor.
Essential Tools
• An assembler is a program that converts source-code
programs into a machine language (object file).
• A linker joins together two or more object files and
produces a single executable file.
• A debugger loads an executable program, displays
the source code, and lets the programmer step
through the program one instruction at a time, and
display and modify memory.
Figure 1. Machine Language Generation by ASM and
HLL programs.
ASM
ML
ML
HLL
ML
ML
ML
Table 2. Comparison of Assembly Language to HLLs.
Type of Application
High-Level Language
Assembly Language
Business application
software, written for
single platform, medium
to large size.
Formal structures make it
easy to organize and
maintain large sections of
code.
No formal structure.
Programmer must impose an
artificial structure.
Hardware device driver.
Language may not provide
for direct hardware access.
Awkward coding techniques
must be used, resulting in
possible maintenance
problems.
Hardware access is
straightforward and simple.
Easy to maintain when the
programs are short and well
documented.
Business application
written for multiple
platforms (different
operating systems).
Usually very portable. The
source code can be
recompiled on each target
operating system with
minimal changes.
Must be recoded separately
for each platform, often
using an assembler with a
different syntax. Difficult to
maintain.
Embedded systems and
computer games
requiring direct
hardware access.
Produces too much
executable code, and may
not run efficiently.
Ideal, because the
executable code is small
and runs quickly.
Figure 2. Assembly Language Subroutines Used as
Hardware Interfaces.
Application
Program
Interface
Subroutine
Hardware
Operating
System
Device Driver
Subroutine
Machine Language
• Consists of binary numbers
• The "native" language of the computer
• Each ML instruction contains an op code (operation
code) and zero or more operands.
• Examples:
Opcode Operand
Meaning
------------------------------------------------40
increment the AX register
05
0005
add 0005 to AX
Page 7: Bits, Bytes, and Doublewords:
byte
byte
0 0 1 0 0 1 1 0 0 1 1 0 1 01 0
word
Each 1 or 0 is called a bit.
bit
Table 3. Storage Sizes and Ranges of Unsigned Integers.
Storage Type
Bits
Range (low - high)
Unsigned byte
8
0 to 255
Unsigned word
16
0 to 65,535
Unsigned doubleword
32
0 to 4,294,967,295
Unsigned quadword
64
0 to 18,446,744,073,709,551,615
Table 4. Digits in Various Number Systems.
System
Base
Possible Digits
Binary
2
01
Octal
8
01234567
Decimal
10
0123456789
Hexadecimal
16
0123456789ABCDEF
Page 9. ASCII Digit String.
Format
ASCII binary
Value
"01000001"
ASCII decimal
"65"
ASCII hexadecimal
"41"
ASCII octal
"101"
Table 5. Binary Bit Position Values.
2n
Decimal Value
2n
Decimal Value
20
1
28
256
21
2
29
512
22
4
210
1024
23
8
211
2048
24
16
212
4096
25
32
213
8192
26
64
214
16384
27
128
215
32768
Figure 3. Converting Binary to Decimal.
8
+1
9