ASSEMBLING AND DISASSEMBLING

OF COMPUTER

SYSTEM

WARNING!~Unplug the system unit from the main power source.~Do not tamper with the power box.~Remove accessories that are metallic or can get caught in the system unit.

DISASSEMBLING OF COMPUTER SYSTEM

Steps:1. Remove screws and cover.2. Unplug power cords.3. Unplug IDE and FDD ribbons from HDD, FDD and

motherboard.4. Unlock and remove the cooling fan.5. Remove the RAM from the motherboard.6. Remove the hard disk drive carefully.7. Remove the floppy disk drive carefully.8. Remove the CD-Rom drive carefully.9. Unscrew and remove the PCI cover.10.Unscrew expansion cards(video card) and remove

from the motherboard.11.Unscrew the motherboard diagonally from the last

screw removed.

RECAP!1.Remove system unit casing.2.Unplug all the power cords.3.Unplug IDE and FDD ribbons.4.Unlock and remove the cooling fan.5.Remove the RAM from the

motherboard.6.Remove the various drives (HDD, FDD,

CD Drive) carefully.7.Unscrew and remove the PCI cover.8.Unscrew and remove various expansion

cards (video card, graphics card, NIC) from the motherboard.

9.Unscrew the motherboard diagonally from the last screw removed.

**Putting it back together**

~LAST OUT, FIRST IN~

INTERPRETERS AND

COMPILERS

INTERPRETERSTranslates and

executes program statements one by

one.

COMPILERSIs a translator whose

source language is a high-level language and whose object language is close to a machine language of an actual computer – either in

assembly language or some variety of machine

language.

THE COMPILATION PROCESSLEXICAL ANALYSIS

SYNTAX ANALYSIS

SEMANTIC ANALYSIS

INTERMEDIATE CODE GENERATION

CODE OPTIMIZATION

CODE GENERATION

SYMBOL TABLE

MANAGEMENT

ERROR HANDLIN

G

LEXICAL ANALYSIS-Is also referred to as scanning.- In this phase, the stream of characters making up the source program is read from left to right and are grouped into tokens.

TOKEN - is a sequence of characters having a collective meaning.LEXEME - the character sequence forming a token.

:= called assignment operator

Example: identifier A := operand1 + operand2 * 701. The identifier identifierA;2. The assignment symbol :=3. The identifier operand1;4. The operator +;5. The identifier operand2;6. The operator * and;7. The number 70.

SYNTAX ANALYSIS

-is also referred to as parsing.-In this phase, the tokens are grouped into grammatical phrases that are used by the compiler to generate output.

Assignment statement

identifier

identifierA

:=expression

expression

identifier

operand1

+ expressionexpression

identifier

operand2

* expression

number

70

SEMANTIC ANALYSIS

- The process of type checking is an important task performed during this phase. :=

id1 +

id2 *

id3 int-to-real

70

INTERMEDIATE CODE GENERATION

-During this phase, the compiler generated an intermediate representation of the source program.

temp1 := int-to-real (70)temp2 := id3 * temp1temp3 := id2 + temp2id1 := temp3

CODE OPTIMIZATION-In this phase, some compilers attempts to improve the intermediate code generated by the previous phase(intermediate code generation).

temp1 := id3 * 70.0id1 := id2 + temp1

CODE GENERATION-The last phase of the compilation process.-It is in this phase wherein the source program’s target code is generated.

F- signifies the fact that we are dealing with floating-point numbers

#-symbol that indicates a constant value1. MOVF id3, R22. MULF #70.0, R23. MOVF id2, R14. ADDF R2, R15. MOVF R1, id1

SYMBOL-TABLE MANAGEMENT

-The compiler performs an important function of recording the identifiers used in the source program and collect various attributes of each identifier.

SYMBOL TABLE REPRESENTATION

NAME OF IDENTIFIER TYPE LENGTH INITIAL VALUE

IdentifierA real 8 0Operand1 real 3 5Operand2 real 3 7

ERROR DETECTION AND REPORTING

OS SCHEDULINGTypes of Schedulers include:

1. First-Come, First-Served  (FCFS)

2. Shortest-Job-First  (SJF)3. Priority Scheduling  (PS) 4. Round-Robin   (RR)

Performance metrics include: CPU Utilization   - Percentage of time that the

CPU is doing useful work (i.e.

not idling). 100% is perfect.Wait time             - Average time a process spends

in the run queue.Throughput        - Number of processes

completed / time unit.Response Time    - Average time elapsed from

when process is submitted until

useful output is obtained.Turnaround Time - Average time elapsed from

when process is submitted to when it has completed.

FCFS- simply executes processes to completion in the order they are submitted.EXAMPLE:

PROCESS CPU REQUIREMENT TOA WAITING TIMEP1 24 0 P1 = 0-0 = 0P2 9 0 P2 = 24-0 = 24P3 3 0 P3 = 33-0 = 33

36/36=1X100% 57/3-#of process = 100%-CPU utilization =19A.W.T.

P1 P2 P3

0 24 33 36

Total turnaround time

Shortest-Job-First (SJF) 

-is exactly like FCFS except that instead of choosing the job at the front of the

queue, it will always choose the shortest job (i.e. the job that takes the least

time) available. We will use a sorted list to order the processes from longest to shortest.

When adding a new process/task, we need to figure out the where in the list

to insert it.

NON-PREEMPTIVE SCHEDULING - Is a strategy that even if a higher

priority process is ready, the running process is allowed to continue until

either it is locked or has completed its execution.

PREEMPTIVE SCHEDULING- Is a strategy where the CPU is

suspended when a higher priority process is in the ready queue.

Priority (PRI) 

-is associated with each process. We can think of

the SJF algorithm as a special case of PRI.

Processes with equal priorities may be scheduled in accordance with FCFS.

ROUND ROBIN (RR) -is a preemptive scheduler, which is designed especially for time-sharing systems. In other words, it does not

wait for a process to finish or give up control.

- In RR, each process is given a time slot to run. If the process does not finish, it will “get back in line” and

receive another time slot until it has completed. We will implement RR

using a FIFO queue where new jobs are inserted at the tail end.