Computer Architecture –
An Introduction
CS2052 Computer Architecture
Computer Science & Engineering
University of Moratuwa
Dilum Bandara
Dilum.Bandara@uom.lk

From Outside
2
Input
Output
Processor
Memory
Hard disk
DVD ROM
Graphics
card
Ethernet
Source: techwench.com

From Outside (Cont.)
Source: Daniel Zanetti, wikimedia.org
3
Source: Amazon.com
Touch pad
Touch screen
Wireless
Screen size
Weight
Battery capacity
SD Card slot
Sensors

From Inside
Source: http://rays-place.net
4
Source: http://news.techgenie.com

From Inside (Cont.)
5
Source: www.laptopaid.com
Source: http://techgoesboom.com

From Inside (Cont.)
6
iPhone 6

What We Are Going To Study?
 How these internal components look like?
 Top-down approach with schematics
 How do they fit together?
 How to program them?
 How to improve their performance?
7

Very High-Level View of a Computer
 CPU – execute instructions
 Memory – store program & data
System Bus
 IO devices – receive inputs & produce outputs
 Bus – interconnects everything by transferring data
8
Central
Processing
Unit (CPU)
Main
Memory
Input/output
(IO) Devices

Blocks of a Microprocessor
9
Program
Memory
Instruction
Register
STACK Program Counter
Instruction
Decoder
Timing, Control, & Register selection
Accumulator
RAM &
Data
Registers
ALU
IO
IO
FLAG &
Special
Purpose
Registers
Source: Makis Malliris & Sabir Ghauri, UWE

Blocks of a Microprocessor (Cont.)
10
Literal
Address
Operation
Program
Memory
Instruction
Register
Address
STACK Program Counter
Instruction
Decoder
Timing, Control and Register selection
Accumulator
RAM &
Data
Registers
ALU
IO
IO
FLAG &
Special
Function
Registers
Clock
Reset
Interrupts
Program Execution Section Register Processing Section
Set up
Set up
Modify
Internal data bus
Source: Makis Malliris & Sabir Ghauri, UWE

Arithmetic & Logic Unit (ALU)
 Data processing
unit
 Arithmetic unit
 Performs
arithmetic
operations
 Logic unit
 Performs logical
operations
11
Accumulator
Source: Introduction to PIC Microcontroller – Part 1 by Khan Wahid

Registers
 Type of memory located inside CPU
 Can hold a single piece of data
 This data is useful in both data processing & control
functionalities
 Several types of CPU registers
 Program Counter (PC)
 Instruction Register (IR)
 Accumulator or working register
 Special purpose registers
 Flag register
 General purpose registers
12

Program Counter (PC)
 Used to keep track of memory address of next
instruction to be executed
 When instructions are fetched, always
instruction pointed by PC is fetched into CPU
 Once the instruction is fetched, PC is updated to
point to next instruction
 PC = PC + d
13

Instruction Register (IR)
 Once fetched, instructions are stored in IR for
execution
 Located closely to control unit which decodes
the instruction
14

Accumulator (A) / Working Register (W)
 Results of arithmetic & logical operations always
go to accumulator
 Connected directly to output of ALU
15
Source: Introduction to PIC Microcontroller – Part 1 by Khan Wahid

FLAG/STATUS Register
 Individual bits Indicate status of ALU operations
Source: www.plantation-productions.com/Webster/www.artofasm.com/Linux/HTML/RealArithmetic.html
16

17
Internal Structure
B
C
D
E
ALU
A
Address Bus
PC
IR
ALU
Control Unit
FLAG
+1
CTRL Bus Data Bus
Source : Dr. Chathura de Silva, CSE, UoM

18
Sample Program
100: Load A,10
101: Load B,15
102: Add A,B
103: STORE A,[20]
Load A,10
Load B,15
ADD A,B
STORE A,[20]
100
101
102
103
104
105
Program memory
18
19
20
21
00
00
00
00
Data memory

19
Instruction Execution Sequence
1. Fetch next instruction from memory to IR
2. Change PC to point to next instruction
3. Determine type of instruction just fetched
4. If instruction needs data from memory,
determine where it is
5. Fetch data if needed into register
6. Execute instruction
7. Go to step 1 & continue with next instruction

20
Before execution of 1st fetch cycle
B
C
D
E
ALU
A
Address Bus
100
IR
ALU
Control Unit
FLAG
+1
CTRL Bus Data Bus
Source: Dr. Chathura de Silva, CSE, UoM

21
After 1st fetch cycle …
B
C
D
E
ALU
A
Address Bus
101
ALU
Load A,10
Control Unit
FLAG
+1
CTRL Bus Data Bus

22
After 1st instruction cycle …
B
C
D
E
ALU
10
Address Bus
101
ALU
Load A,10
Control Unit
FLAG
+1
CTRL Bus Data Bus

23
Sample Program (Cont.)
100: Load A,10
101: Load B,15
102: Add A,B

24
After 2nd fetch cycle …
B
C
D
E
ALU
A
Address Bus
102
ALU
Load B,15
Control Unit
FLAG
+1
CTRL Bus Data Bus

25
After 2nd instruction cycle …
15
C
D
E
ALU
10
Address Bus
102
ALU
Load B,15
Control Unit
FLAG
+1
CTRL Bus Data Bus

26
Sample Program (Cont.)
100: Load A,10
101: Load B,15
102: Add A,B

27
After 3rd fetch cycle …
15
C
D
E
ALU
10
Address Bus
103
ALU
ADD A,B
Control Unit
FLAG
+1
CTRL Bus Data Bus

28
After 3rd instruction cycle …
15
C
D
E
ALU
25
Address Bus
103
ALU
ADD A,B
Control Unit
FLAG
+1
CTRL Bus Data Bus

Architectural Differences
 Length of microprocessors’ data word
 4, 8, 16, 32, 64, & 128 bit
 Speed of instruction execution
 Clock rate & processor speed
 Size of direct addressable memory
 CPU architecture
 Instruction set
 Number & types of registers
 Support circuits
 Compatibility with existing software & hardware
development systems 29

Microprocessor vs. Microcontroller
 Microprocessor – CPU & various IO functions are packed
as separate ICs
 Microcontroller – Most IO functions are integrated into
same package with CPU
30
Program
Memory
Microprocessor
Clock
Data
Storage
I/O
I/O
I/O
Program
Memory
Microprocessor
Core
Real-time
Clock
I/O
I/O
I/O
Data
Storage

Programming Hierarchies
31
Source: Introduction to PIC Microcontroller – Part 1 by Khan Wahid

Programming Language Levels
 Machine code (40s-50s)
 0001000000111000 0001001000110100
 0101110000000000
 0001110000000000 0001001000110101
 Hex notation (50s-60s)
 1038 1234
 5C00
 1E00 1235
Source: http://mentalfloss.com/article/53160/meet- 32
refrigerator-ladies-who-programmed-eniac

Programming Language Levels (Cont.)
 Assembler
 Machine code (60s-70s)
.define const = 6
num1: .byte [1]
num2: .byte [2]
move.b num1,d0
addq.b #const,d0
move.b d0,num2
 High-level languages
 C code fragment (70s-80s)
#define const 6
int num1, num2;
num2 = num1 + const; 33

When is Assembler Appropriate?
 Parts of a program where absolute speed is
critical
 More effective use of CPU registers & instruction set
 Can produce code that runs faster than that produced
by a compiler
 There may be no other way to access a particular
feature of hardware
 Compiler might not provide library functions to access
IO ports or to disable/enable interrupts
 Compiler might not take advantage of CPU special
instructions
 BCD arithmetic, binary-ASCII conversion, table lookups, high
speed copying of entire blocks of data 34

Building Digital Solutions to
Computational Problems
35
 Labs & design project
 Product specs
 Algorithms, RTL, etc.
 Flowcharts
 State transition diagrams
 Logic equations
 Circuit schematics
 Verilog or VHDL code
 Assembler
 C, C++
 TTL Gates (AND, OR, XOR ... )
 Programmable Logic
 Custom ASICs
 FPGAs
 MCs, DSPs

Real-World Performance Metrics
 Commercial digital designs seek the most
appropriate trade-offs for the target application
 Time-to-market is also very important
36
Cost
Commodity Products
Speed
Scientific Computing,
Simulation
Energy
Portable Devices
Capacity
Multimedia,
Scientific Computing,
Simulation