# Ch.1

```Computer Architectures
Jung H Kim
Dept of Systems Engineering
Chapter1.
Computing and Computers
Elements of Computers
Brain
Control
Execute
Instruction
Data
(100-3)*2(100-5)/3
Data
Processor
Control
Instruction
Execute
Data
Data
Paper
Memory
Input/
Output
Devices
Every Computer Must Have the Following Components
1. A processor capable of control and execute programs.
2. A memory for saving programs and data.
3. A means of transferring information between the memory and a processor and
between the computer and outside world.
Computation
Z = f(x)
Derived output
Given input
in order to evaluate f(x), express x as a sequence of function(or instruction set)
f1, f2, … , fn
Y1 = f1(x)
Y2 = f2 (Y1)
:
:
Y n-1 = f n-1(Y n-2)
Z = f n(Y n-1)
Limitation of Computers
Touring Machine ( reasonable computing machine)
:A function f is computable if f(x) can be executed by any specified x in a finite
number of steps.
P
X
… …
Memory
1. The machine should not store the answers to all possible problems.
2. The machine should only be required to solve problems to which a solution
procedure or a program can be given
3. It should process information at a finite time.
Limitation of Computers
Unsolvable Problem
Goldbach’s conjecture
: Every even integer greater than 2 is the sum of exactly two prime number
such as 8=3+5 and 12=5+7.
It is not known if the conjecture is true for every even integer, nor is any
reasonable procedure known to determine whether the conjecture is true.
Limitation of Computers
Intractable Problem
Factors : the nature of the given problem and computer power )
Example. Traveling sales problem
The brute-force approach : n!
The best algorithm : exp(n)
Two questions in the difficulty of the algorithm
1.Space complexity : How much memory space is needed to
execute it?
2.Time complexity : How much time is needed to execute it?
The VLSI Era
VLSI(Very Large Scale Integration)
LSI(Large Scale Integration)
MSI(Medium Scale Integration)
SSI(Small Scale Integration)
: profound impact on computer design and application
Current VLSI : photolithography technique
Ex)
CPU on a VLSI chip
Playstation 2 on a VLSI chip
Wafer scale integration( WSI )
The VLSI Era
CISC( Complex Instruction Set Computers )
Intel 80x86, Motorola 680x0
: Execution of even a small percentage of complex instructions can
reduce overall performance
RISC( Reduced Instruction Set Computers)
IBM 6600/ SUN SPARC
Von Neumann bottle neck
: CPU-memory speed disparity
It takes CPU about 5 times longer to obtain a word from memory
than from one of internal registers
-- how to reduce the bottle neck:
cache memory, interleaved
```