Derecho Fundamental al Debido Proceso

UNIX and Windows65 _{make use of hierarchical file systems as mechanisms to manage files}

efficiently.

Directories and files

A file system has a hierarchical structure consisting of files and directories (directories are file registers). At the top of the hierarchical structure is the root directory, and directories under it are called subdirectories.66

File manipulations

When searching for a file, we designate the path showing in which directory the file is located. There are two methods for doing this. For instance, if the hierarchical structure is as shown in the figure above, we can designate the path in the following ways:67

• Absolute path

Designating a path from the root directory68 <Example> Here is a way to designate “file1.”

\DIR3\file1 (The leading symbol “\” indicates the root directory.) • Relative path

Designating a path from the current directory69

<Example 1> Here is the designation of file2 when the current directory is “DIR2.” DIR4\file2

<Example 2> Here is the designation of file2 when the current directory is “DIR4.” file2

65 _{(Hints & Tips) What UNIX and MS-DOS call “directory” is called “folder” in Windows and MacOS.}

66 _{(Hints & Tips) Whereas directories and files can be made under a directory, files and directories cannot be made under a} file.

67 _{(FAQ) Concerning hierarchical file systems, there are exam questions like “Choose an appropriate designation as an} absolute path or as a relative path.” In those questions, the symbol for separating directories and files, as well as its use, will be explained in the question text.

68 _{(Hints & Tips) Here we are using the symbol “\” to separate directories and files, but some operating systems use the} symbol “/” instead.

69 _{Current directory: It is a directory in which the user is working at the moment.}

DIR 1 File 0 File 1 File 2 DIR 2 DIR 3 DIR 4 DIR 5 Root directory Root Subdirectory : Directory : File

2.2.5 Memory Management

Points

¾ Memory management uses two types of memory: real memory and virtual memory.

¾ The basic format of the virtual memory system is the paging method.

Another role of the control program, which is the “OS” in a narrow sense, is “memory management.” Memory management makes the most effective use of the memory as well as compensating for any lack of the main memory capacity. To this end, it effectively uses auxiliary storage as part of the memory.70

‹

Real Memory System

This is the system that manages the physical space of the main memory. Real memory can be controlled in various ways: partition, swapping, relocation, and overlay methods.

Partitioned method

When a program is placed in the main memory, the main memory is partitioned into several partitions, into which the program is loaded.72 _{Without memory management, fragmentation}

occurs, causing a situation which prevents programs from being stored even though empty space exists. Hence, to combine all empty areas together, compaction73 _{is necessary.}

Swapping (roll-in / roll-out)

Swapping refers to execution as the program keeps switching back and forth between the main

memory and auxiliary storage. If a program is entered with higher priority than the priority level of the currently executed program, the new program is immediately loaded into the main memory and is executed. However, if there is no space in the main memory, any program in the main memory can be moved to the auxiliary storage. Hence, this system compensates for a lack of main memory capacity by utilizing auxiliary storage. However, if swapping occurs frequently, it means that programs are switched back and forth many times, thus reducing the processing efficiency of the computer system.

Program X Program X

Program B

Program A Program A

70 _{Memory leak: Sometimes, for some reason, memory in the main memory, secured dynamically by an application, may} not get released but remains in the main memory. This is called memory leak. To eliminate memory leak, compaction must be performed.

71 _{Real memory system or “Real Storage (RS)”: This refers to the actually existing memory; it is the main memory.} 72 _{(Note) In partitioned method, multiple programs can be stored simultaneously, so multitasking is possible.}

73 _{Compaction: It means collecting empty memory areas to form a continuous area; also known as garbage collection.} Main memory

Swap out (roll out)

Swap in (roll in)

Relocation (Relocatable)

Relocation refers to the function wherein a program already assigned to a certain area is re-stored in another location. A program whose structure allows it to be relocated is called a relocatable program.74

Overlay method

The physical limitations of the main memory can be eliminated; that is, programs are divided into segment units, and only the necessary segments75 _{are loaded into the main memory to be executed.}

The entire program is stored in auxiliary storage, and the main memory contains only frequently used segments. Exclusive segments, which are never used simultaneously, are loaded from auxiliary storage to the main memory on an as-required basis.

For example, suppose that Segment A is a main routine used with high frequency while Segments B and C are subroutines called exclusively by Segment A. While Segment B is being executed, Segment C is in auxiliary storage. When Segment C is called, it is loaded in the area of Segment B. Consequently, the entire memory capacity of the program is “A + B + C,” but the capacity of the main memory is sufficient if it is at least the greater of “A + B” or “A + C.”

Segment A

Segment B Segment C