[Information processing article writing] Utilization of programming language

• a
• a
• As a result, both are true, so they have the value of 1.

#include 
#include 
int main(void) {
char str[50]="nation";
char *p2="alter";
strcat(str, p2);
printf("%s", str);
return 0;
}
// nationalter

• strcat(str, p2); Outputs the two as a combined string.

Python

• A scripting language published by Guido van Rossum that is interpreter-based, object-oriented, easy to learn, and highly portable.

data type

Data types, strings and lists, tuples, dictionaries, and sets

• 튜플 corresponds to the Sequence data type and can store various data types in a given order, but the stored contents cannot be changed.
• If you want to change the content, you cannot change the content of that part like a list, so you have to change and save it separately.

operation problem

• if, elif, else

a＝["대", "한", "민 ", "국"]
for i in a：
print(i)

• ? In Python, print() outputs results with a line break at the end.

def cs(n);
s＝0
for num in range(n＋1);
s＋＝num
return s
print(cs(11)) // 66

• Note that it is up to 12, not 11.
• Sum from 0 to 12

JAVA

Exception

• Errors that occur during run time that may result in malfunctions or adverse effects on results.
• Error that occurs when the array index exceeds its range
• Error that occurs when trying to read a file that does not exist
• ? Grammatical errors in programming languages ​​correspond to ‘errors’.

operator

• ? The operator with the lowest priority is the assignment operator (=).

operation problem

modularization

• Software modules can be expressed as subroutines, functions, etc. in programming languages.
• As the number of modules increases, the size of each module relatively decreases, and interaction between modules increases, causing an overload phenomenon.
• ? Modularization allows systems to be managed intelligently and helps solve complexity problems.
• Modularity facilitates maintenance and modification of the system.

build tool

• Ant, Maven, Gradle
• ? Kerberos: A computer network authentication encryption protocol that operates based on “tickets.”

OSI Layer 7

Application > Representation > Session > Transport > Network > Data Link > Physical

data link layer

• Protocol: ? HDLC, PPP, LLC

application layer

• Protocol: HTTP

network layer protocol

IP protocol

• ? Header Length indicates the header length of the IP protocol in 32-bit word units.
• ? Packet Length indicates the length of the entire packet including the IP header, and the maximum size is 232-1 bit.
• Time To Live specifies the time a sending host can survive on the network before transmitting a packet.
• Version Number indicates the version number of the IP protocol.
• ? It mainly functions to specify addresses and set routes.
• ? Checksum function is provided and calculated with the checksum field set to '0'.
• If you look at the header formats of IP, UDP, and TCP, there is space for checksum.
• This part is used to check if data is altered or broken while the packet header is being transmitted.
• Checksum: A method of protecting the integrity of transmitted data in the form of redundancy checking.

IP 주소체계

• IPv4 display method: 4-part decimal number of 8 bits each
• IPv4 automatically sets the host address and supports unicast.
• IPv4 has different network and host address lengths for each class.

ICMP(Internet Control Message Protocol)

• A protocol used to transmit error information in case a transmission error occurs during the IP operation process in the TCP/IP layer structure.

TCP protocol

TCP header

• Sequence Number: A number is assigned to each byte being transmitted.
• Acknowledgment Number: Defines the number of bytes to be received from the other host.
• Checksum: Checks for errors in segments containing data.
• ? The window size is the buffer size on the transmitting and receiving side, and the maximum size is 65,535 bytes.

transport layer protocol

TCP protocol, connection-oriented

• Flow Control, Error Control, Congestion Control
• Provides two-way connection service
• Provides a service in the form of a virtual circuit connection

UDP protocol, connectionless oriented

• Simple header structure reduces overhead. Transmission speed is fast.
• ? Sequential transmission of data is not guaranteed.
• Unlike reliable TCP, it does not perform flow control, error control, or congestion control.
• It is often used in services that are completed with a single packet transmission and reception.

routing protocol

RIP routing protocol

• To manage routing information, a distance vector algorithm is used to dynamically determine the shortest path depending on the number of passing routers (Hop Count).
• ? The path selection metric is Hop Count.
• When routing protocols are classified into IGP and EGP, it corresponds to EGP. Protocol for establishing IGP internal routes
• EGP Protocol for establishing a route that can be accessed from the outside to the inside

Hop Count

• The part of the route located between the origin and destination
• The hop itself can be thought of as a router.

process

• Classification of programs, processors, and processes
• Dispatch: This refers to the process changing from the ready state to the running state when a processor is assigned.
• Process Control Block (PCB): Consists of information such as process identifier and process status.
• ? Context Switching: The process of storing the contents of the status register of a previous process and loading the register of another process.
• ? A thread exists within a process.

process scheduling

preemptive scheduling

Shortest Remaining Time (SRT), round-robin scheduling, multi-level queue, multi-level feedback queue scheduling

non-preemptive scheduling

First come first service (FCFS), Shortest job first (SJF), Priority, Highest response next (HRN)

• A scheduling technique that prevents another process from forcibly taking over an already allocated CPU.
• HRN Scheduling? A non-preemptive scheduling technique that complements the weaknesses of the least-job-first (SJF) technique.
• Priority = (waiting time + service time) / service time

disk scheduling

FCFS scheduling, SSTF scheduling, SCAN and LOCK scheduling, C-SCAN scheduling

SSTF Scheduling

• A technique that serves the request closest to the current head first

File Descriptor

• It is an abstract representation used in Unix OS to access files or other input/output resources, such as network sockets.
• It contains the information the system needs for file management.
• It is stored in auxiliary memory, and when the file is opened, it is moved to main memory.
• ? It is an integer representing a file or socket allocated from the system.
• Also called File Control Block.

operating system

UNIX

• One or more tasks can be performed in the background.
• ? Supports multiple users and multiple tasks.
• ? It has a tree-structured file system.
• It is highly portable and has high compatibility between devices.
• Most of them are written in C language and are highly portable.

configuration

• Hardware > Kernel > Shell > Utilities > User
• The main function of the shell is to interpret user commands and transmit them to the kernel.
• Provides programming functions to create repetitive command programs.
• Provides the ability to set the user environment using an initialization file.

cohesion and binding

? Design with high cohesion and low coupling.

Cohesion

Functional > Sequential > Communication > Procedural > Temporal (temporal) > Logical > Accidental

• Cohesion is a concept that represents the independence of a module and the degree of connection between components within the module.

Temporal cohesion

• When components within a module execute different functions together at the same time

Coupling

Content > Common > External > Control > Stamp > Data (data)

• Cohesion refers to the degree of connection with external modules rather than within the module or the degree of interdependence between modules.
• Allowing modules to share variables or exchange control information increases the degree of coupling.

Content Cohesion

• When one module references the internal functions and materials of another module

Automatic Repeat Request (ARQ)

? error control

• Stop-and-wait ARQ: Wait until ACK is received one by one before transmitting
• Go-back-N ARO: Send multiple items at once, receive one positive acknowledgment (ACK), and transmit subsequent data
• Selective-Repeat ARQ: Retransmit only the error part
• Adaptive ARQ: A method of increasing transmission efficiency by adaptively reducing the number of ARQs

Mutual Exclusion Technique

• A technique that allows only one process to use a shared resource at any time and prevents other processes from accessing the shared resource.
• When multiple processes use a shared resource simultaneously, each process takes turns using the shared resource. How to maintain critical areas
• Dekker algorithm ensures that there is no deadlock, guarantees mutual exclusion, and is resolved by software without separate commands.

synchronization technique

Semaphore

• Prevents multiple processes or threads from accessing shared resource data or critical sections (i.e., there is more than one synchronization target)

// ? 임계 구역의 접근을 제어하는 상호배제 기법
P(S) : while S＜=0 do skip；
S :＝S－1；
V(S) : S :＝S＋1；

Mutex

• Prevents one process or thread from accessing shared resource data or critical sections (i.e., there is only one synchronization target)

memory placement strategy

first-fit first-fit

• Technique for finding and allocating the first available space in main memory ### best-fit
• Use the smallest possible space

worst fit worst-fit

• How to use the largest

Terms related to

• Internal fragmentation: Size of space remaining after division
• External fragmentation: Space created by a size smaller than the program.

빈 기억공간의 크기가 20KB, 16KB, 8KB, 40KB일 때 기억장치 배치 전략으로 “Best Fit"을 사용하여 17KB의 프로그램을 적재할 경우 내부단편화의 크기는 얼마인가?
>> 17KB 프로그램이므로 가능한 공간 중 가장 작은 공간인 20KB를 선택하게 되고, 내부 단편화의 크기는 남는 공간이므로 3KB가 된다.

page replacement algorithm

FIFO page replacement algorithm

Optional page replacement algorithm

LRU page replacement algorithm

• Techniques for replacing pages that have been least recently used
• ? https://m.blog.naver.com/PostView.naver?isHttpsRedirect=true&blogId=botemi11&logNo=220062848209