1. Computer Architecture
Part II-A: CPU Organization

2. The Central Processing Unit
The operating hub and heart of every computer system
Composed of
Control Unit
Datapath
Each component inside the CPU has a specific role in executing a command
Communicates with other components of the system

3. Control Unit (CU) Regulates all activities inside the machine
Serves as “nerve center” that sends control signals to other units and senses their status
Connected to all components in the CPU as well as main memory

4. How The CU Is Connected
Registers
ALU
Control
Unit
Main Memory
CPU

5. Inside the CPU: The Datapath
Registers
ALU

6. Registers
Components used for data storage (can be read from or written to)
High speed memory locations used to store important information during CPU operations
Two types
Special
General-purpose

7. Special Registers Registers used for specific purposes
Used heavily during execution of CPU instructions

8. General Purpose Registers
CPU registers used as “scratch pad” during execution of machine-level instructions
Number varies between processors

9. Arithmetic Logic Unit (ALU)
Performs all mathematical and logical operations within the CPU
Operands not in the CPU would have to be retrieved from main memory

10. CPU-Memory Coordination
Bus - a group of wires that connect separate components
Types of bus:
Control bus (control signals)
Address bus (address information)
Data bus (instruction/data)

11. CPU-Memory Coordination
The different busses facilitate communication between the CPU and main memory
Actions of the two components are highly-synchronized to ensure efficient and timely execution of instructions

12. CPU Operations
Instructions do not reside in the CPU, they have to be fetched from memory
Each machine level instruction is broken down into a logical sequence of smaller steps

13. CPU Operations
Instructions are carried out by performing one or more of the following functions in some pre-specified sequence
Retrieving data from main memory
Putting data to main memory
Register data transfer
ALU operation

14. How An Instruction is Processed
Instruction is retrieved from memory
Analyze what the instruction is and how to execute it
Operands/parameters (if any) are fetched from main memory
Instruction is executed
Results are stored (CPU or MM)
Prepare for next instruction

15. Instruction Processing Example
Fetch instruction from memory
Decode it (turns out to be an ADD)
Get the two numbers to add from MM
Perform the addition
Where will it be stored?
Prepare for next instruction

16. Processing Data in Clusters
Information is organized into groups of fixed-size data that can be stored and retrieved in a single, basic operation
Each group of n bits is referred to as a word of information
Access to each word requires a distinct name (location/address)
Can also refer to a characteristic of other components (i.e. size of bus)

17. Word Length Size of a word specified in bits known as word length
Possible benefits of a large word length:
Faster processing (more data and/or instructions can be fetched at a time)
Greater numeric precision
More powerful instructions (e.g. instructions can have more operands)

18. Machine Language Composed of
Instruction
Data (instruction parameters)
Instructions and data are represented by a stream of 1s and 0s
Cumbersome to deal with when preparing programs; programmers use hexadecimal numbers
In some computers, both instruction and data are stored in a single memory location

19. Assembly: An Improvement on Machine Language
Symbols, called mnemonics, are used to represent instructions
Sample instruction
Advantage:
Easier recall of instructions
Disadvantage:
Need to convert mnemonics and hexadecimal numbers back to binary
Instruction parameters
add
(105),(8)
instruction
There is a strong possibility that hexadecimal numbers in relation to binary numbers may have to be reviewed here.

20. How Programs Are Loaded Into Main Memory
Programs are loaded as binary numbers
Assumptions:
An instruction is represented by a 2-digit hexadecimal number (e.g. add by 1A, mov by A0)
World length of instruction parameters: 3 hex digits (12 bits)
Instruction Instruction parameters
100
101
102
103
104
105
A01040F2
1A105008
A00F2200 …
100

21. Executing Multiple Programs
Programs share processor time
Time slicing
Supported by modern CPUs