1. CSE115: Introduction to Computer Science I
Dr. Carl Alphonce
219 Bell Hall

2. Announcements
Cell phones off
Name signs out

3. Today’s lessons Instructions are encoded as bit strings
Machine languages
Fetch-Decode-Execute cycle
Assembly languages
High-level languages
Requirements for a programming language

4. Computer Organization
Central Processing Unit (CPU)
Registers
General purpose (e.g. R1 – R16)
Special purpose (e.g. Program Counter and Instruction Register)
Arithmetic Logic Unit (ALU)
Memory

5. Computer Organization
Memory (RAM)
Processor (CPU) R1 R2
. . .
R16 PC IR
ALU

6. Encoding instructions
Example
INSTR ARG1 ARG2
ADD Reg1 Reg2

7. Instruction decoding
“ADD”
OP CODE R1 R2
Circuitry to decode rest of instruction and carry it out (“execute” the instruction)
This wire will carry a 1 only if the op code of the instruction is 1101.

8. Fetch-Decode-Execute cycle
Fetch an instruction (& update PC)
Decode instruction
Execute instruction
(load instruction into IR from location in PC)
Fetch
Update PC
Decode
Execute

9. Low-level languages Machine language Assembly language
Assembly language
ADD R1 R2

10. High level languages Java
We can write “x + y” instead of “ADD R1 R2” (in addition to with several MOV instructions)
Others: C#, Erlang, Python, ML, Prolog, Lisp, etc.