1 - How Assembly Language Works

Question 1

What are assemblers?

Answer 1

An assembler is a utility program that converts source code programs from assembly language into machine language.

Question 2

What are linkers?

Answer 2

A linker is a utility program that combines individual files created by an assembler into a single executable program.

Question 3

What is a debugger?

Answer 3

It lets you step through a program while it’s running and examine registers and memory.

Question 4

What is a “one-to-many relationship”?

Answer 4

In a one-to-many relationship, a single statement expands into multiple assembly language or machine instructions.

Question 5

Give an example of an embedded systems application.

Answer 5

Automobile fuel and ignition systems, AC control, security, flight control, printers, etc.

Question 6

What is a device driver?

Answer 6

Device drivers are programs that translate general operating system commands into specific references to hardware details that only the manufacturer knows.

Question 7

Is there type checking on pointer variables in assembly language?

Answer 7

No, there is no type checking!

Question 8

Translate the following to assembly language: X = (Y*4)+3

Answer 8

mov  eax, Y
mov  ebx, 4
imul  ebx
add  eax, 3
mov X, eax

Question 9

How is a computer made up of “virtual machines”?

Answer 9

Each layer represents a translation layer from a higher-level instruction set to a lower-level instruction set.

Question 10

Why is a translated program often faster than an interpreted one?

Answer 10

Translated programs are coded in a language that can be directly executed, but interpreted programs must be translated while they are running.

Question 11

Name the four virtual machine levels, from lowest to highest.

Answer 11

1. Digital logic
2. Instruction set architecture (ISA), or machine language
3. Assembly language
4. High-level language

Question 12

Why don’t programmers write applications in machine language?

Answer 12

Machine language provides no visual clues relating to the instruction syntax, so it is difficult to understand.

Question 13

How do you translate unsigned binary integers into decimal?

Answer 13

You just add up all the powers of 2 to the position values (right most 0, increasing to the left). For example, 00001001 is (2^3 + 2^0 ) = 9.

Question 14

How do you translate unsigned decimal integers to binary?

Answer 14

Repeatedly divide the integer by 2, saving each remainder as a binary digit in reverse order.

For example, 9/2 is 4 with a remainder of 1, so put 1 at the right. Then 4/2 is 0, 2/2 is 0, and finally 1/2 is 0 with a remainder of 1, so put that on left. 9 becomes 1001.

Question 15

How do you add binary digits?

Answer 15

You just add them like whole numbers, carrying the 1 (from 1+1 = 10) to the top of the next left column..

For example,
100
+ 1 1 1
= 1011.

Question 16

What are the integer storage sizes for an x86 computers?

Answer 16

1. byte (8 bits)
2. word (16 bits)
3. doubleword (32 bits)
4. quadword (64 bits)
5. doublequadword (128 bits)

Question 17

What are the large measurements of memory and disk space?

Answer 17

1. kilobyte (2^10)
2. megabyte (2^20)
3. gigabyte (2^30)
4. terabyte (2^40)
5. petabyte (2^50)
6. exabyte (2^60)
7. zettabyte (2^70)
8. yottabyte (2^80)

Question 18

How do you convert unsigned decimal to hexadecimal?

Answer 18

Repeatedly divide the decimal value by 16 an retain each remainder.

For example, 422/16 is 26 with R6, so put 6 on the right. 26/16 is 1 with RA, so put A on the right. 1/16 is 0 with R1, so put 1 on the left. This makes 1A6.

Question 19

How do you do hexadecimal addition?

Answer 19

The same as decimal addition, but you carry over 1 and subtract 16 from the current sum.

For example, 
  1
  6A2
\+49A
======
  B3C

Question 20

What are the signed binary integers?

Answer 20

For x86 processors, the MSB (most significant digit) is 0 when positive and 1 when negative.

e.g. 111101110 is negative and 00001010 is positive.

Question 21

What is two’s complement representation?

Answer 21

You can calculate how a negative number is represented by reversing all the bits and adding 1.

For example, if you start with 00000001, the reverse is 11111110, and if you add 1, you’d get 11111111, which represents -1 in decimal.

Question 22

How do you create the two’s complement of a hexadecimal integer?

Answer 22

You subtract each digit from 15 (F), then add 1. For example, 6A3D becomes 95C2, and adding one makes this 95C3.

Question 23

How do you convert a signed binary integer into decimal?

Answer 23

First, if it’s negative, use its two’s complement to find its positive equivalent. Then, just convert it normally.

For example, if you start with 11110000, you can reverse the bits to 00001111 and add 1 to get 00010000, which is 16. Therefore, the original was -16.

Question 24

How do you do binary subtraction?

Answer 24

Just like normal subtraction, with borrowing from the top digit to the left whenever it’s 0-1.

01101
-00111
————
00110

Alternatively, you could add the top with the two’s complement of the bottom, and then just ignore the leftmost carry.

Question 25

What is ASCII?

Answer 25

When characters used only 8 bits (e.g. MS DOS), a unit 7-bit integer is assigned to each character. The last digit can be used to make various characters (e.g. Greek characters).

Question 26

What is ANSI?

Answer 26

The American National Standards Institute that defines an 8-bit character set with up to 256 characters, 128 of which are standard on a U.S. keyboard (others are international).

Question 27

What is the Unicode standard?

Answer 27

A universal way of defining characters and symbols (internationally accepted “code points”).

UTF-8 is used in html, with the same byte values as ASCII.

UTF-16 is used in recent versions of Microsoft windows.

UTF-32 is when space is no concern, but for fixed-width characters.

Question 28

What are ASCII strings?

Answer 28

A succession of bytes containing ASCII codes.

Question 29

What are the ASCSII control characters?

Answer 29

Character codes 0-31 carry out predefined actions. For example, code 8 is backspace, 9 is tab, 10 is line feed, etc.

Question 30

What is operator precedence?

Answer 30

The NOT operator has the highest precedence, followed by AND and OR. However, you can use parenthesis to force precedence.