I. Concept Questions

1. Name the five key concepts about an operating system that you thinks a user needs to know and understand. 

ans..
Users would be greatly benefitted by an understanding of these main properties of operating systems:

1. User Command Interface
This is the interface from which the user issues commands to the operating system. Also called the “shell” (container inside which the entire user interface is presented), this is the visible interface with which users interact. For most users, the User Interface is the operating system.

2. Device Manager
This component monitors all devices, channels, and control units. The Device Manager must select the most efficient method for allocation of a system’s devices, printers, terminals, disk drives, and other hardware. This is based on a pre-determined scheduling policy, and the Device Manager makes allocations, starts operations, and ultimately deallocates devices.

3. Processor Manager
This component is responsible for allocating the central processing unit (CPU). The status of each process must be tracked, and the Processor Manager handles matters such as process prioritization and multithreading. The tasks of the Processor Manager can be divided into two main categories: accepting or rejecting incoming jobs (handled by the Job Scheduler) and determining which process is given access to the CPU and for how long (handled by the Process Scheduler).

4. Memory Manager
This component controls main memory. It evaluates the validity of each memory request, and allocates memory space (as needed and available). For multi-user systems, the Memory Manager maintains a log of what memory resources are in use by which users. When items stored in main memory are no longer needed, the Memory Manager handles memory deallocation.

5. File Manager
This component tracks every file in the system. These files include data files, assemblers, compilers, and applications. The File Manager can use predetermined access policies to enforce restrictions on file access. It also handles all other file permissions. The File Manager allocates file resources by opening a particular file and deallocates resources by closing the file.

Yes!!! we need to know this things if you study the Operating System because. this five concept is very important on how the system work and also how to work and understand the useer needs.

2. list three tangible (physical) resources of a computer system and explain how it works.

ans...

1. Computer memory

=refers to devices that are used to store data or programs (sequences of instructions) on a temporary or permanent basis for use in an electronic digital computer. Computers represent information in binary code, written as sequences of 0s and 1s. Each binary digit (or "bit") may be stored by any physical system that can be in either of two stable states, to represent 0 and 1. Such a system is called bistable. This could be an on-off switch, an electrical capacitor that can store or lose a charge, a magnet with its polarity up or down, or a surface that can have a pit or not. Today, capacitors and transistors, functioning as tiny electrical switches, are used for temporary storage, and either disks or tape with a magnetic coating, or plastic discs with patterns of pits are used for long-term storage.

Computer memory is usually meant to refer to the semiconductor technology that is used to store information in electronic devices. Current primary computer memory makes use of integrated circuits consisting of silicon-based transistors. There are two main types of memory: volatile and non-volatile

2. The Central Processing Unit (CPU)

=The processor is the portion of a computer system that carries out the instructions of a computer program, and is the primary element carrying out the computer's functions. This term has been in use in the computer industry at least since the early 1960s [1]. The form, design and implementation of CPUs have changed dramatically since the earliest examples, but their fundamental operation remains much the same.

3. Hard disk drive

=HDDs record data by magnetizing ferromagnetic material directionally, to represent either a 0 or a 1 binary digit. They read the data back by detecting the magnetization of the material. A typical HDD design consists of a spindle that holds one or more flat circular disks called platters, onto which the data is recorded. The platters are made from a non-magnetic material, usually aluminum alloy or glass, and are coated with a thin layer of magnetic material, typically 10–20 nm in thickness — for reference, standard copy paper may be between 0.07 millimetres (70,000 nm) and 0.18 millimetres (180,000 nm) thick.[8] — with an outer layer of carbon for protection. Older disks used iron(III) oxide as the magnetic material, but current disks use a cobalt-based alloy.[citation nee

This tree tangible (physical) resources is a hardware that very useful in a computer system because if one this hardware not function the hall computer system also is unable to function...

3. Explain the Following 

A. Internal Fragmentation. How does it occur?

ans...

=Internal Fragmentation: Internal fragmentation is the space wasted inside of allocated memory blocks because of restriction on the allowed sizes of allocated blocks. Allocated memory may be slightly larger than requested memory; this size difference is memory internal to a partition, but not being used.

=Internal Fragmentation is a Fixed Partitions suffer from inefficient memory use - any process, no matter how small, occupies an entire partition. This waste is called Internal Fragmentation.

B. External Fragmentation. How does it occurs?

External Fragmentation: External Fragmentation happens when a dynamic memory allocation algorithm allocates some memory and a small piece is left over that cannot be effectively used. If too much external fragmentation occurs, the amount of usable memory is drastically reduced. Total memory space exists to satisfy a request, but it is not contiguous.

C. Compaction.

= Compaction is the External Fragmentation by shuffling memory contents to place all free memory together in one large block

4. Cache Memory how it works?

Caching is a technology based on the memory subsystem of your computer, having as main role the increase of computing power while maintaining 
computer price at a low level. Let's take for example a Random Access Memory. RAM's are basically used to temporarily store data retrieved from the hard disk - or any other sources - so that the processor has faster access to the information required (RAMs are much faster than hard drives, floppy drives or CD-ROM drives).

Let's take for example an action when the processor requests an information stored on the hard drive. Fetching information from the hard drive takes time, because hard drives are very sluggish in relation to the processor clock. Thus, every time information is retrieved, processing time is lost, although the requested information may be the same, over and over again.

The cache memory has the role of backing up the RAM. This means that before retrieving the information from the hard drive, the computer first looks for it in the cache memory. If it is present in the cache, then it is instantly relayed to the processor. This could quickly turn into a disadvantage if the requested information cannot be found in the cache, because processing time is first being lost by checking the cache, then actually retrieving the information from the hard drive.

The two processes are called 'cache hit' and 'cache miss', in case the requested information cannot be found in the cache memory. Usually, the cache maximum size is extremely small in relation to the large storage devices. However, with the help of multiple cache layers processing speed can be further improved.

5. Which is the Fastest cache's L1, L2,L3,? Why?

ans.. L1

To make all the cache memories run at the same speed as the L1 cache - 10 nanoseconds - would be extremely expensive and in fact the computer doesn't need large amounts of cache memory due to locality of reference. Locality of reference means that no matter how large or small in size a running application is, only a small part of the respective program is being stored into the cache at one given time.

This is because the vast majority of programs mostly contain fairly large amounts of code lines which are executed only once. The other lines are represented by program loops which are executed over and over again. Less than 10 percent of processor time is spent by the programs running at one time.

= Because L2 cache, on the other hand, is represented by small memory banks posted on the motherboard, while processors with two cache layers - the memory banks on the motherboard exist between the processor and the main system memory - represent a level 3 cache.