Apple Event November 10, 2020. Introducing the new MacBook Air, 13‑inch MacBook Pro, and Mac mini, all with the Apple M1 chip. A modern version of OS X: openconnect is should work on most recent OS X versions. It has been tested and seems to function correctly as far back as 10.9. Mac OS X TUN/TAP driver, which allows for creation of the virtual network interface. The built openconnect package is available using macports.

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A computer is an electronic device that people used to accept information. Information is in the digitalized data form. Computer gives sequence of instructions on the data and how the data is to be processed. Computer will based on the program and manipulates it for some result. Nowadays, every family also will have a least 1 computer. Computer is very important in this world for everyone. However, desktop and laptop computers that most people use that can often used to refer to the computer.

1.2 Operating System

Computer is an electronic device that consists of hardware and software. Hardware is the physical medium of a computer while software is a series of instructions in non-physical form. Hardware and software must be work together in a computer. To make a basic computer work, a system program called Operating System is required. Operating system is the chief of software which maintains all the activities hardware and software, and make sure they are work properly. Operating system provides one or more interface for user to control the computer. There are three user interface included command-line interface, menu-driven interface and graphical user interface.

Virtual Memory

Managing main memory, especially if it needs to be shared among multiple concurrent tasks or different users, is a challenging problem. While the size of memory has been increasing steadily and modern CPUs now use long address fields capable of generating very large address spaces, the amount of memory available and actually installed in most computers remains a limiting factor. This situation is not likely to change anytime soon as new applications, especially those using sound, graphics, and video, are capable of utilizing all the memory available. Virtual memory addresses the problems of sharing limited memory through architectural and OS software mechanisms that hide the presence of physical memory and present instead an abstract view of main memory to all applications. In this chapter, we describe the concept of virtual memory and the main implementation schemes.

2.0 Operating System

An operating system is the essential software of every computer. Types of existing operation system for computers or Smartphone are included UNIX, Microsoft Windows, Linux, Mac OS, IOS, Android and etc. Among them, Microsoft Windows is the most popular OS that widely used for the all types of personal computer. Every operating system may have their special characteristics, features, and control interface. Therefore, they will have their own advantages as well as disadvantages of usage.

2.1 Microsoft Windows

Windows is the most common operating system that designed for every type of computer. Windows was introduced by Microsoft Corporation in 1985. Initially, Windows was not an operating system but an application program that run on its commend-line operating system, MS-DOS. Until the year 1995, a 'real' operating system was designed by Microsoft Corporation, called Windows 95. Windows 95 was the first operating system using graphical user interface (GUI) as its primary method of communication with user. Because of many bugs occurred in Windows 95, a new Windows was released to replace it called Windows 98. Windows 98 are sooner replaced by Windows XP which is a powerful operating system that still widely used in today computer. Windows XP is known as the best and the fastest performance operating system ever of Microsoft. The evolution of Windows continues until now, among them, Windows 7 which introduced in 2009 is the most stable and security strongly improved operating system. Beside the GUI, most of the Windows are also integrated a commend-line windows-to-system administrator for advance management.

Windows consist of two main components, the kernel mode and user mode. In kernel mode, all machine instructions are allowed and system memory is accessible. For user mode, certain instructions are not allowed and system memory is not accessible. Operating system will be executed in kernel mode only while application programs are only executed in user mode. The data stored in Windows are organized in FAT or NTFS. Compare with FAT, NTFS is better to use because data can be recovered for all types of errors including those that occur in critical disk sectors.

Among the operating systems, Windows is much easier to use with its friendly user interface. Because there are a lot of Windows users, many software are special designed for Windows, therefore more selections of software can be chosen and used. However, one of the disadvantages for Windows is the security issues. Windows always be the target of viruses and other malware. Other than that, the response of Windows will be slowed down as applications were installed or the computer was used over time. Even these applications were uninstalled, performance will still remained slow and will not return back to the performance like new installed OS.

2.2 MAC OS

Mac OS was developed by Apple Inc. in the early of 1980s. Mac OS was a totally graphical user interface-based (GUI) operating system without any command line program. This GUI-based of operating system bought much more convenient to the user on that time to use a computer. After the CEO of Apple Inc. - Steve Jobs had acquired the NeTX Computer; a UNIX-based operating system was developed and called Mac OS X. Mac OS X is combined with the NeXT Computer’s NeXTSTEP operating system and the Mach kernel. Mac OS X is a powerful multitasking operating system that only special designed for Apple computer.

Not like Windows or Linux, Mac OS is using HFS (hierarchical file system) as default file system. Mach kernel in the Mac OS X was originally conceived as an extensible, simple, communications microkernel. Mach kernel provides a small set of abstractions that have been designed to be both powerful and simple. The main kernel abstractions are including:

Tasks. The units of resource ownership; each task contains port right namespace, a virtual address space, and one or more threads.

Threads. The units of processor execution within a task.

Address space. In conjunction with memory managers, Mach kernel implements the notion of a sparse virtual address space and shared memory.

Memory objects. The internal units of memory management. Memory objects include regions and named entries; they are representations of potentially persistent data that may be mapped into address spaces.

Ports. Secure, simplex communication channels, can be accessed only via receive and send capabilities.

IPC. Notifications, Message queues, semaphores remote, procedure calls, and lock sets.

Time. Waiting, timers, and Clocks.

Mac OS is a typical GUI-based operating system; the ease of use interface save user’s a lot of time and energy to maintain. Applications on Mac OS are also rarely crashed. Malware like worms, Trojans, viruses are hardly seen to infect the system as well. But compare with Windows, Mac OS is difficult to theme and customize. Applications like games are less support with Mac OS.

2.3 Windows vs. Mac OS

Between these two computer operating system, windows is more suitable for the home user. Because user is much easier to use with window’s friendly user interface. Because there are a lot of Windows users, many software are special designed for Windows. For the graphical design or some fields, Mac OS is a best choice. Because users easier to create and draw something using the Mac OS. But Mac OS interface are not friendly like windows. User may take some times to adapt it.

2.4 Apple IOS

IOS is an operating system for the apple handheld devices which is iPhone, iPad, iPod and so on. This operating system is based on the Macintosh OS X. This operating system is designed for the multi touch screen devices. This operating system support and respond to the various user gestures which is swipe, pinch and tap. User also can create a custom gestures. IOS also provides some features for the users that make users easier to use.

Other features like:

Spotlight Search

Siri

AppStore and iTunes

Gesture Recognition

iCloud and so on

Now, Apple released IOS 6 and above. IOS 6 giving more features to make things you does everyday even better. It’s free and easy to upgrade wirelessly on your iPhone, iPad, or iPod touch. Some apple users will jailbreak his iDevice. After jailbreaking, apple user can download some tweaks to make his iDevice more vivid and there are a lot of changes.

2.5 Android

Android are installed in many Smartphone. Android is based on the Linux. It is also designed for the touch screen phone and tablet computer. It is backed by Google and the other members of the Open Handset Alliance. Because of Android's open source nature, so that the devices which are installing the android operating system should be cheaper to produce. The T-Mobile G1, announced on September 23, 2008, was the first Android OS Smartphone to be officially introduced to the market.

In the Market, many brands are selling the android Smartphone. So, there have many competitors in the market. So, they will keep release difference level of Smartphone to meet the consumer needed. Because, not every consumer can afford spend about Rm 1000 to Rm 2000 to buy a Smartphone.

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2.6 IOS vs. Android

Between these two Smartphone’s operating system, IOS is a closed system and android is an open system. IOS is better than android when they are managing their memory. Android allow the user to use the memory until the system is hang. IOS will auto terminate the previous apps and free up the space. So, system will so smoothly and performs better. But IOS device is very expansive, not every customer can afford. Android is difference, because customer only uses rm400 and above can buy a android Smartphone. For sure, user will face the hang and lag problems.

2.7 Conclusion

Operating system is the essential software for any computer. The most popular OS are Windows, Mac OS and Linux. Although Linux and Mac OS are powerful and competitive, Windows are still trusted by many users to continue using it and no easy to be replaced.

3.0 Virtual Memory

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Virtual memory is a feature of an operating system that enables a process to use a memory (RAM) address space that is independent of other processes running in the same system, and use a space that is larger than the actual amount of RAM present, temporarily relegating some contents from RAM to a disk, with little or no overhead.

Structure of virtual memory:

Paging: Divide the address space into fixed size pages

Segmentation: Divide the address space into variable size segments

3.1 Virtual Memory with Paging

In a paging implementation, the virtual address space is divided into a sequence of equal-sized contiguous blocks called pages. Paging is a technique that used by virtual memory. That can ensure we can get the data we need as fast as possible. From the storage device to main memory, the operating system will copy a few pages. When a program request some pages that are not in main memory, system will copy the two pages which in the memory and another pages will back to the disk. If the page is not in the memory that operating system request, that page fault occurs. When the address of the page being requested is invalid, the invalid page is fault occurs. Normally, the program will be not responding or aborted.

The most common page size is between 1K to 16K bytes. Similarly, the available physical memory is divided into a number of equal-sized contiguous blocks called page frames. The page size is identical to the page frame size. At runtime, any page can reside in any frame of the physical memory.

3.1.1 Demand Paging

Paging greatly simplifies the problem of placement, since any page can be loaded into any free page frame. But paging can also be used to solve the problem of limited memory size so that programs larger than the available main memory could be executed without requiring the programmer to specify an overlay structure. This is accomplished by implementing dynamic memory allocation mechanisms, where pages are loaded at the time they are actually needed rather than statically before program execution. This approach is called demand paging.

It requires a mechanism that signals a 'missing page' when reference is made to a page currently not resident in main memory. Such a missing page event is called a page fault. It invokes the operating system; in a lengthy procedure, the OS find the desired page, loads it into a selected frame, and restarts the process that caused the page fault.

3.2 Virtual Memory with Segmentation

There are many instances where a process consists of more than the three basic segments: code, data and stack. For example, a process with multiple threads needs a separate stack for each thread, where each stack grows and shrinks independently. Similarly, files may be mapped temporarily into the address space of a process to simplify accessing their contents. Such files may also grow and shrink as the process executes. Placing multiple dynamically changing entities into a single address space is a difficult problem.

Segmentation solves the problem in an elegant way. It implements virtual memory as a collection of address spaces, each of which is termed a segment and may be a different size. This organization permits the system to mirror the organization of a given application by using a separate segment for each logical component, such as a function, a module comprising multiple functions, an array, a table, or a stack. Each such component has a name by which it is identified by the programmer.

There are two different schemes for building a segmented virtual memory. One treats the segment as the basic unit for memory allocation and assumes that memory can be dynamically allocated and relocated in variable size blocks. The second employs paging as a means of allocating space for a segment. That is, each segment is itself subdivided into fixed-size pages to facilitate allocation.

3.3 Paging with Segmentation

To provide a multi-segment address space for each process and, at the same time, permit a simple placement algorithm, the principles of paging and segmentation have been combined into one memory management scheme. Under this scheme, memory is organized in variable-size segments, and, from the user’s perspective, there is not much difference between pure segmentation and segmentation with paging. From the point of view of the operating system, however, segments are not contiguous portions of memory. Rather, each segment is subdivided into pages of fixed-size.

3.4 Interrupt Process

An interrupt is an event that alters the sequence in which the processor executes instructions. Interrupt divided into 2 major types which are Planned and Unplanned. Planned interrupt is specifically requested by the currently running program. Unplanned interrupt is caused by an event that might or might not be related to the currently running program.

There are few types of interrupts:

Supervisor calls or SVC interrupts

I/O interrupts

External interrupts

Restart interrupts

Program interrupts

Machine Check interrupts

All these interrupts are caused by machine malfunctions. When an interrupt occurs, the hardware saves pertinent information about the program that was interrupted and, if possible, disables the processor for further interrupts of the same type. The hardware then routes control to the appropriate interrupt handler routine. The program status word or PSW is a key resource in this process.

3.5 Conclusion

Virtual memory combines your computer’s RAM with temporary space on your hard disk. When RAM runs low, virtual memory moves data from RAM to a space called a paging file. Moving data to and from the paging file frees up RAM to complete its work.

4.0 Conclusion and Recommendation

Operating system is the chief of software which maintains all the activities hardware and software, and make sure they are work properly. Operating system provides one or more interface for user to control the computer. There are three user interface included command-line interface, menu-driven interface and graphical user interface.

If your computer lacks the random access memory (RAM) needed to run a program or operation, Windows uses virtual memory to compensate. The more RAM your computer has, the faster your programs will generally run. If a lack of RAM is slowing your computer, you might be tempted to increase virtual memory to compensate.

In my opinion, when users choosing the OS, users should choose the OS which suitable for them. Not depend on the brand. Therefore, main memory is very important. It can make the computer performs more better.

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