Transcript preChapter2WithColors

CS/COE0447
Computer Organization &
Assembly Language
Pre-Chapter 2
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“C Program” Down to “Numbers”
swap:
muli
add
lw
lw
sw
sw
jr
$2, $5, 4
$2, $4, $2
$15, 0($2)
$16, 4($2)
$16, 0($2)
$15, 4($2)
$31
void swap(int v[], int k)
{
int temp;
temp = v[k];
v[k] = v[k+1];
v[k+1] = temp;
}
00000000101000010…
00000000000110000…
10001100011000100…
10001100111100100…
10101100111100100…
10101100011000100…
00000011111000000…
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“Numbers” in Memory
00000000101000010…
00000000000110000…
10001100011000100…
10001100111100100…
10101100111100100…
10101100011000100…
00000011111000000…
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Stored Program Concept
program fetch
data load/store
program
counter
program A
data A
program B
data B
disk I/O
program A
program C
program B
processor
main memory
hard disk
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Stored Program Concept
• 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 are fetched by the processor, are decoded
and they determine processor actions
• Program Counter determines which instruction is fetched
next
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Stored Program Concept
• In fact, one of the great ideas in computer science is the
idea that programs could be stored just as data was
stored.
• Before that, people envisioned the hardware running a
fixed program, and data being stored in memory.
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…
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10
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Addresses and Contents shown in
Hex
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Number Systems
• Actual machine code is in binary
– O, 1 are high and low signals to hardware
• Hex (base 16) is often used by humans (code, simulator,
manuals, …) because
– 16 is a power of 2 (while 10 is not); mapping between
hex and binary is easy
– It’s more compact than binary
– We can write, e.g., 0x90000008 in programs rather
than 10010000000000000000000000001000
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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)
– A shorthand form we’ll also use:
103 102 101 100
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2
1
7
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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
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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) =
16 + 8 + 0 + 2 + 0 = 26ten
• Choice for machine implementation!
– 1 = on, 0 = off
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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!
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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)
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Base Conversion, cont’d
• Binary to hex (base 16), or hex to binary base conversion:
– 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
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Before moving on to chapter 2….
• We’ll mention some concepts in program performance,
so you have ideas in mind
• The text covers this in the Chapter 1 questions and in
Chapter 4. We’ll wait until Chapter 4 to cover this more
fully.
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Program Performance
• Program performance is measured in terms of time!
• Program execution time has to deals 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)
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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
• Instructions typically require more than one cycle to execute
Function block
(made of circuits)
clock cycle time
clock
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Program Performance
• time = (# of clock cycles)  (clock cycle time)
• # of clock cycles =
(# of instructions executed) 
(average cycles per instruction)
• We’ll do specific calculations when we get to Chapter 4.
• But now, let’s move on to Chapter 2
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