Machine Language and Assembly Language

IBM 709 (1959)
Altair 8800 (1975)	IMSAI 8080 (1975)

Early computers were difficult to program and use
Input devices were switches, output devices were blinking lights
All communication with the computer was in binary machine language (1's and 0's)

Programming in machine language was very tedious and error-prone

00000100 10000010
00000001 10000001
00000101 10000100
00001011 10000100
00001101 00010000
00010100 00000010
00000101 10000011
00001111 00000000
00010100 00000011
00000101 10000011
00001111 00000000

Assembly language was invented as a shorthand for 1's and 0's

00000100 --> LOD (load)
00000001 --> SUB (subtract)
00000101 --> STO (store)
00000010 --> MUL (multiply)
10000001 --> X    (memory location 129)
10000010 --> Y    (memory location 130)
10000011 --> Z    (memory location 131)

Assembly language was easier to write, debug, and understand

Machine Code Assembly Code

00000100 10000010
00000001 10000001
00000101 10000100
00001011 10000100
00001101 00010000
00010100 00000010
00000101 10000011
00001111 00000000
00010100 00000011
00000101 10000011
00001111 00000000 LOD Y
SUB X
STO T1
CPL T1
JMZ 16
LOD #2
STO Z
HLT
LOD #3
STO Z
HLT

Programs called assemblers were written to do the translation from assembly to machine language automatically
Programming in assembly language was still tedious (but better than machine language)
High-level programming languages were invented to make assembly language programming easier

Assembly Code High-Level Language

LOD Y
SUB X
STO T1
CPL T1
JMZ 16
LOD #2
STO Z
HLT
LOD #3
STO Z
HLT if (x > y) {
z = 2;
} else {
z = 3;
}
Programs called compilers were written to do the translation from high-level languages to machine language automatically
First compiler written in 1952 by Grace Hopper

Grace Murray Hopper (1906-1992)
Much computer science research since then has focused on the development of ever more powerful and flexible computer languages

Machine Code		Assembly Code
`00000100 10000010` `00000001 10000001` `00000101 10000100` `00001011 10000100` `00001101 00010000` `00010100 00000010` `00000101 10000011` `00001111 00000000` `00010100 00000011` `00000101 10000011` `00001111 00000000`		`LOD Y` `SUB X` `STO T1` `CPL T1` `JMZ 16` `LOD #2` `STO Z` `HLT` `LOD #3` `STO Z` `HLT`

Assembly Code		High-Level Language
`LOD Y` `SUB X` `STO T1` `CPL T1` `JMZ 16` `LOD #2` `STO Z` `HLT` `LOD #3` `STO Z` `HLT`		`if (x > y) {` `z = 2;` `} else {` `z = 3;` `}`

Assembly Language Programming

We will experiment with assembly language programming on a simulated computer called PIPPIN
To understand assembly language we need to understand how a computer is organized at the hardware level
All computers are built out of the same fundamental pieces:
- Central processing unit (CPU)
- Memory (RAM)
- Input/output devices (keyboard, monitor, mouse, etc.)
- Secondary storage devices (disk drives, tape drives, CD-ROM drives, etc.)
The memory contains a large number of locations or cells, each one with its own address and contents
Memory cells contain binary data
Memory addresses are binary numbers
CPU contains a number of registers, each of which holds a single piece of binary data
A register is like a variable in a pseudocode algorithm
Most CPUs have at least the following registers:
- Program Counter (PC)
- Accumulator (ACC)
- Instruction Register (IR)
All CPUs have an Arithmetic-Logic Unit (ALU) that performs arithmetic and logical operations (addition, multiplication, logical AND, etc.)
Registers are connected by data paths to the memory and to each other
Example:

LOD #15  (load 15 into Accumulator)
STO X    (store Accumulator in memory location 129)
HLT      (halt)
List of all PIPPIN instruction codes
Examples of PIPPIN assembly language programs

Machine Language and Assembly Language

Grace Murray Hopper (1906-1992)

Assembly Language Programming