The Difference between Kernel Mode and User Mode - Assignment Example

Name: Course: Tutor: Date: Operating systems General 1. The difference between kernel mode and user mode? Why the difference important to an operating system? In Kernel mode, the running program code has maximum and free access to the underlying hardware. It can run any central processing unit instruction and make reference to any address in memory. Kernel mode is mostly dedicated to low-level, trustworthy operating system functions. In case of any crash in kernel mode it is usually vital since they halt the entire computer. User-mode, on the other hand running codes is unable of directly accessing hardware or making addresses to memory. User mode executing codes must reserve to system APIs to gain access to hardware or storage. Crashes in this mode are always recoverable since there is protection afforded by this type of isolation. The reason for this distinction is such that the kernel can track system critical resources and safeguard each user from other users. 2. Multiprogramming Multiprogramming is a type of consequent processing whereby many programs are run concurrently on a single processor. Since there is a single processor, unique programs cannot be executed. However, part of a program is executed by the operating system, then part of another henceforth. It is also the giving of computer resources to many concurrent application, task or user. 3. Why the process table is needed in a timesharing system? And if the process table also needed in personal computer systems in which only one process exists, that process taking over the entire machine until it is finished? The process table is actually essential to monitor the programs that the computer is executing. It is also needed to keep the status of a process that currently is under suspension, blocked or ready. Though many present computers execute multiple programs concurrently and processes do not take over the whole machine until they are completed. It is not essential in personal computer systems in which single processes exist since the single process has ultimate power over the system and hence no need for tracking. Processes 4. The three main states that a process can be in? And the meaning of each one briefly. The major three states a process can be are first running state which is when a process has the central processing unit and executes personal instructions of a program. Second is a blocked state which occurs when a process is blocked or prevented waiting for a certain resource, information or certain happening. Third is a ready state which occurs when a program is set to execute on the central processing unit. 5. The fundamental difference between a process and a thread Processes contain their own address spaces, must use IPC to exchange data with child processes, have personal replica of the parent process data segment, and need replication of the parent processes. While threads on the other hand share spaces of addresses with its parent process, have direct access to its processes data segments, exchange data directly with its processes other threads and almost have no overhead. 6. Round-robin schedulers normally maintain a list of all run able processes, with each process occurring exactly once in the list. What would happen if a process occurred twice in the list? Can you think of any reason for allowing this? If at any point a process appears than once in the list created by round-robin, then it receives two separate turns for each list pass. The main reason of permitting this is to implement a priority primitive system because the more it appears on the list the greater the time percentage the central processing unit will take on that process. Memory management 7. The difference between a physical address and a virtual address Physical address is the addresses destined to a physical memory point in the primary storage while a virtual address is the address of anything that resides in virtual memory. Data kept at a virtual address may reside in the primary or secondary storage. Alternatively, real storage makes use of physical addresses which are the elements that memory chips react to on the bus. While virtual addresses are logical addresses that reference to an address space of a process. 8. Consider a swapping system in which memory consists of the following hole sizes in memory order: 10 KB, 4 KB, 20 KB, 18 KB, 7 KB, 9 KB, 12 KB, and 15 KB. Which hole is taken for successive segment requests of a. 12 KB b. 10 KB c. 9 KB for first fit? Now repeat the question for best fit, worse fit, and next fit. For first fit: for the sequence of request 12KB, 2KB and 13KB, the policy will choose: 20KB hole for 10KB request we would have after this allocation holes (10,4,2,18,7,9,12,15). 10KB hole for 9KB request we would then have holes (8, 4, 2, 18, 7, 9, 12, 15). And 12KB hole for 10KB request we would then have the holes (8, 4, 2, 5, 7, 9, 12, 15). Best fit: 12KB hole (10, 4, 20, 0, 7, 9, 12, and 15). 4KB hole (10, 2, 20, 7, 9, 12, and 15). 15KB hole (10, 2, 20, 7, 9, 12, and 2). Worst fit: 20KB (10, 4, 2, 18, 7, 9, 12, 15). 12KB (10, 4, 2, 16, 7, 9, 12, 15.) 16KB (10, 4, 2, 3, 7, 9, 12, 15.) 9. A computer with a 32-bit address uses a two-level page table. Virtual addresses are split into a 9-bit top-level field, an 11-bit second-level page table field, and an offset. How large are the pages and how many are there in the address space? Offset = 32 – 9 – 11 = 12 bits Page size = 2^12 B = 4 KB Total number of pages possible = 2^9 * 2^11 = 2^20 I/O 10. What DMA is and why it is used. It is a component of present computers and microprocessors that permit some hardware subsystems bound within the computer to gain system memory access for writing and reading separately from the CPU. It is majorly applied in intra-cheap data exchange. Print spooling make able to a user to continue working while the printer does its job. If an application provides data directly to a printer, the computer must wait until that job is completed before it can enable the user to move on. If the text is large or graphic is complicated, the user may be forced to wait for a long time. 11. Why output files for the printer are normally spooled on disk before being printed The main purpose of spooling output files for the printer before being printed is to be able to allow the user to continue working on the machine while the printer performs its tasks. If it were that applications give data directly to the printer, the user will be delayed from using the computer since the computer must be patient for the tasks to be completed hence compelling users to wait for longer periods. 12. An alternative to interrupts is polling. Are there any circumstances you can think have in which polling is a better choice? Polling can be a better choice in tiny dedicated systems that are not executing multiple processes. Polling is of great importance where the expectation is that only little patience is expected. This can occur in device drivers, some low rated software’s where synchronization is imminent and short time intervals. File systems 13. Some operating systems provide a system call rename to give a file a new name. Is there any difference at all between using this call to rename a file, and just copying the file to a new file with the new name, followed by deleting the old one? Of course there is a difference, the rename call does not alter the creation identity, or the latest modification time, creating a new file may result it to obtain the current time as that of modification and creation. The copy will also not be a success if the disk is full or write protected. 14. NTFS uses Unicode for naming files. Unicode supports 16-bit characters. Give an advantage of Unicode file naming over ASCII file naming. Unicode defines lots of characters and maps each of them a distinct number, the Unicode code, from which it can be easily referenced. The details of how these codes are kept on disk or in computer storage is an issue of encoding. The main advantage of Unicode for file naming is that it permits easier communication and great interoperability than ASCII and any other character set. 15. Systems that support sequential files always have an operation to rewind files. Do systems that support random access files need an operation to rewind files? There is no need for an operation to rewind files. Random access of files does not require rewind operation from the fact that if you want to read the file again you can do so by just accessing byte 0. Works Cited Andrew, Tanenbaum and WoodHull S Albert. Operating systems: Design and implementation. Upple Saddle River: Prentice Hall, cop, 2009. Read More