Basic Computer Organization
Background for CS260
Basic Components
•
•
•
•
•
CPU
Main Memory
External Memory
I/O devices
Bus
Main Bus
CPU
Main
Memory
Disk
Drive
Video
All devices communicate through the bus with each other and
with the CPU. CPU access of the bus takes precedence.
CPU – a very simple one!
Accumulator
Instruction Reg
ALU
Stack Pointer
Flags
internal
bus
external
bus
MEMORY
addresses
100
17
101
106
a
b
102
103
104
105
values
EXAMPLE OPERATION
Changing the value of a memory location
(decrement by 2)
100
101
102
103
104
105
17
104
106
a
b
106
accumulator
1.
LOAD value from
memory into the CPU’s
accumlator
100
17
101
106
a
b
102
103
104
105
104 106
accumulator
106
2
104
2.
SUBTRACT 2 from
accumulator. Goes through
the ALU
100
17
101
106
a
b
102
103
104
105
2
104
Accumulator (AC)
3.
STORE the result in the AC
into the proper location in
main memory
100
17
101
104 106
a
b
102
103
104
105
2
What’s the connection?
• The operation in c would look like
– I = I – 2;
• The operation in assembly language is
– LOAD 101
– SUB 105
– STORE 101
• More details involved
• More hardware knowledge required
• Not as clear to read/write/understand
We want to see the connection!
C++
compiler
assembly
Why?
In order to better understand what we
are actually instructing the computer to
do when we write in the higher level language.