1. CS/COE0447 Computer Organization & Assembly Language
Pre-Chapter 2

2. Example: Chapter 1 example
Question 1.48: If a computer issues 30 network requests per second and each request is on average 64 KB, will a 100 Mbit Ethernet link be sufficient? (printer, accessing files, …)
KB = 10^3 bytes
Byte = 8 bits
Mbit = 10^6
A 100 Mbit Ethernet: 10^8 bit/s “bitrate”
Answer: on board

3. “C Program” Down to “Numbers”
void swap(int v[], int k) {
int temp;
temp = v[k];
v[k] = v[k+1];
v[k+1] = temp; }
swap:
muli $2, $5, 4
add $2, $4, $2
lw $15, 0($2)
lw $16, 4($2)
sw $16, 0($2)
sw $15, 4($2)
jr $31
compiler … … … … … … …
assembler

4. “Numbers” in Memory … … … … … … …

5. Stored Program Concept
program fetch
data load/store
program A
program A
disk I/O
program
counter
data A
program C
program B
program B
data B
processor
hard disk
main memory

6. Stored Program Concept, Cont’d
Programs (instructions) are stored in memory as a stream of bits (numbers)
Indistinguishable from data
More than one programs can reside in memory at the same time
Programs can be modified by the processor or I/O just as data can be modified
Instructions
Language of the machine
Describes primitive actions, supported directly by the machine
Instructions are fetched by the processor, are decoded and they determine processor actions

7. Number Representation
What is the natural “base” for numbers?
2? 10? 16? 27?
Unary is inefficient in space
All other bases are a compact way of re-presenting numbers…
X X X
X X
(U N A R Y) = =
X X X X X

8. Example: Base 10 (Decimal)
Digits: 0, 1, 2, 3, 4, 5, 6, 7, 8, 9 (10 of them)
Example:
3217 = (3103) + (2102) + (1101) + (7100)

9. Numbers and Bases in General
Number Base B  B unique values per digit
Base 10: {0, 1, 2, 3, 4, 5, 6, 7, 8, 9}
Base 2: {0, 1}
Base 16: {0, 1, 2, 3, 4, 5, 6, 7, 8, 9, A, B, C, D, E, F}
(Unsigned) number representation
d31d30…d1d0 is a 32-digit non-negative number
Value = d31B31 + d30B30 + … + d1B1 + d0B0
N-digit base B  BN unique values

10. Example: Base 2 (Binary)
Digits: 0, 1 (2 of them)
“Binary digit” = “Bit”
Example:
11010two = (124) + (123) + (022) + (121) + (020) = = 26ten
Choice for machine implementation!
1 = on, 0 = off

11. Base Conversion Let’s do decimal-to-binary conversion
Aten = dn-1dn-2…d1d0two
Given a base-10 number A, come up with n-digit binary number that has the same value!
X = the number
Let N be the largest power of 2 that fits into X
Put a 1 in that position
X = X – 2^N
Repeat until you are done!

12. Base Conversion, cont’d
From binary to decimal
From decimal to binary
From binary to hexadecimal
From hexadecimal to binary
From decimal to hexadecimal? (more complicated; later)

13. Base Conversion, cont’d
0000
0001 1
0010 2
0011 3
0100 4
0101 5
0110 6
0111 7
1000 8
1001 9
1010 A 10
1011 B 11
1100 C 12
1101 D 13
1110 E 14
1111 F 15

14. Base Conversion, cont’d
Binary to hex (base 16), or hex to binary base conversion is rather straightforward
Take 4 bits in binary and convert them into one hex digit and vice versa
Since binary notation tends to be long, hex notation is frequently used in assembly language (and in C programs).
More on binary number representation will be discussed when we study arithmetic

15. Program Performance Program performance is measured in terms of time!
Program execution time has to do with
Number of instructions executed to complete a job
How many clock cycles are needed to execute a single instruction
The length of the clock cycle (clock cycle time)

16. Clock, Clock Cycle Time Circuits in computers are “clocked”
At each clock rising (or falling) edge, some specified actions are done, usually within the next rising (or falling) edge
Function block
(made of circuits)
clock cycle time
clock

17. Program Performance Time = (# of clock cycles)  (clock cycle time)
# of clock cycles = (# of instructions executed)  (average cycles per instruction)
Time = (# of instructions executed)  (average clock cycles per instruction)  (clock cycle time)
More of “program performance” issues will be discussed in Chapter 4.

18. Example
You have a machine with a CPU running at 1GHz. The same company releases its 2GHz CPU with 100% compatibility with the existing 1GHz CPU, and you are considering upgrading. What is the expected performance improvement from doing so? Assume that programs have 40% memory-access instructions, and each memory access takes 10ns on average. All other instructions take exactly one cycle for execution.