Operating Systems Villanova Test 1
what is a bootstrap program, where is it stored
A bootstrap program is the initial program that the computer runs when it is powered up or rebooted. It initializes all aspects of the system, from CPU registers to device controllers to memory contents. Typically, it is stored in read-only memory (ROM) or electrically erasable programmable read-only memory (EEPROM), known by the general term firmware, within the computer hardware.
Why can an operating system be viewed as a resource allocator
A computer system has many resources that may be required to solve a problem: CPU time, memory space, file-storage space, I/O devices, and so on. The operating system acts as the manager of these resources. Facing numerous and possibly conflicting requests for resources, the operating system must decide how to allocate them to specific programs and users so that it can operate the computer system efficiently and fairly.
what are two faster alternatives to implementing the jvm in software on top of host operating system
A faster software technique is to use a just-in-time (JIT) compiler. The first time a Java method is invoked, the bytecodes for the method are turned into native machine language for the host system, and then cached for subsequent invocations. A potentially faster technique is to run the JVM in hardware on a special Java chip that executes the Java bytecode operations as native code.
what role do device controllers and device drivers play in a computer system
A general-purpose computer system consists of CPUs and multiple device controllers that are connected through a common bus. Each device controller is in charge of a specific type of device. The device controller is responsible for moving the data between the peripheral devices that it controls and its local buffer storage. Typically, operating systems have a device driver for each device controller. This device driver understands the device controller and presents a uniform interface for the device to the rest of the operating system.
describe why multi-core processing is more efficient than placing each processor on its own chip
A large reason why it is more efficient is that communication between processors on the same chip is faster than processors on separate chips.
what is a loopback and when its it used
A loopback is a special IP address: 127.0.0.1. When a computer refers to IP address 127.0.0.1, it is referring to itself. When using sockets for client/server communication, this mechanism allows a client and server on the same host to communicate using the TCP/IP protocol.
in what way does the jvm protect and manage memory
After a class is loaded, the verifier checks that the .class file is valid Java bytecode and does not overflow or underflow the stack. It also ensures that the bytecode does not perform pointer arithmetic, which could provide illegal memory access. The JVM also automatically manages memory by performing garbage collection — the practice of reclaiming memory from objects no longer in use and returning it to the system.
explain the term "at most once" and "exactly once" and indicate how they relate to remote procedure calls
Because a remote procedure call can fail in any number of ways, it is important to be able to handle such errors in the messaging system. 8 The term "at most once" refers to ensuring that the server processes a particular message sent by the client only once and not multiple times. This is implemented by merely checking the timestamp of the message. The term "exactly once" refers to making sure that the message is executed on the server once and only once so that there is a guarantee that the server received and processed the message.
Why are clustered systems considered to provide high-availability service?
Clustered systems are considered high-availability in that these types of systems have redundancies capable of taking over a specific process or task in the case of a failure. The redundancies are inherent due to the fact that clustered systems are composed of two or more individual systems coupled together.
name the three types of sockets used in java and the classes that implement them
Connection-oriented (TCP) sockets are implemented with the Socket class. Connectionless (UDP) sockets use the DatagramSocket class. Finally, the MulticastSocket class is a subclass of the DatagramSocket class. A multicast socket allows data to be sent to multiple recipients.
describe why direct memory access is considered efficient mechanism for preforming i/o
DMA is efficient for moving large amounts of data between I/O devices and main memory. It is considered efficient because it removes the CPU from being responsible for transferring data. DMA instructs the device controller to move data between the devices and main memory.
explain the purpose of external data representation
Data can be represented differently on different machine architectures (e.g., little-endian vs. big-endian). XDR represents data independently of machine architecture. XDR is used when transmitting data between different machines using an RPC.
explain the fundamental differences between the unix fork() and windows createprocess() functions
Each function is used to create a child process. However, fork() has no parameters; CreateProcess() has ten. Furthermore, whereas the child process created with fork() inherits a copy of the address space of its parent, the CreateProcess() function requires specifying the address space of the child process.
describe two approaches to provide direct sharing of resouces in virtual machine concept
First, it is possible to share a minidisk, and thus to share files. This scheme is modeled after a physical shared disk, but is implemented by software. Second, it is possible to define a network of virtual machines, each of which can send information over the virtual communications network. Again, the network is modeled after physical communication networks, but is implemented in software.
describe two approaches to the binding of client and server ports during RPC calls
First, the binding information may be predetermined, in the form of fixed port addresses. At compile time, an RPC call has a fixed port number associated with it. Second, binding can be done dynamically by a rendezvous mechanism. Typically, an operating system provides a rendezvous daemon on a fixed RPC port. A client then sends a message containing the name of the RPC to the rendezvous daemon requesting the port address of the RPC it needs to execute. The port number is returned, and the RPC calls can be sent to that port until the process terminates (or the server crashes).
why should a web server not run as a single threaded process
For a web server that runs as a single-threaded process, only one client can be serviced at a time. This could result in potentially enormous wait times for a busy server.
computer systemss can be divided into four components what are they
Hardware, operating system, application programs, and users.
explain cache coherency
In multiprocessor environments, two copies of the same data may reside in the local cache of each CPU. Whenever one CPU alters the data, the cache of the other CPU must receive an updated version of this data. Cache coherency involves ensuring that multiple caches store the most updated version of the stored data.
describe the operating systems two modes of operation
In order to ensure the proper execution of the operating system, most computer systems provide hardware support to distinguish between user mode and kernel mode. A mode bit is added to the hardware of the computer to indicate the current mode: kernel (0) or user (1). When the computer system is executing on behalf of a user application, the system is in user mode. However, when a user application requests a service from the operating system (via a system call), it must transition from user to kernel mode to fulfill the request
There are two different ways that commands can be processed by a command interpreter. One way is to allow the command interpreter to contain the code needed to execute the command. The other way is to implement the commands through system programs. Compare and contrast the two approaches.
In the first approach, upon the user issuing a command, the interpreter jumps to the appropriate section of code, executes the command, and returns control back to the user. In the second approach, the interpreter loads the appropriate program into memory along with the appropriate arguments. The advantage of the first method is speed and overall simplicity. The disadvantage to this technique is that new commands require rewriting the interpreter program which, after a number of modifications, may get complicated, messy, or too large. The advantage to the second method is that new commands can be added without altering the command interpreter. The disadvantage is reduced speed and the clumsiness of passing parameters from the interpreter to the system program.
why is main memory not suitable for permanent program storage or backup purposes? what is the main disadvantages to using magnetic disk drives as opposed to main memeory
Main memory is a volatile memory in that any power loss to the system will result in erasure of the data stored within that memory. While disk drives can store more information permanently than main memory, disk drives are significantly slower.
explain marshalling
Marshalling involves the packaging of parameters into a form that can be transmitted over the network. When the client invokes a remote procedure, the RPC system calls the appropriate stub, passing it the parameters provided to the remote procedure. This stub locates the port on the server and marshals the parameters. If necessary, return values are passed back to the client using the same technique.
distinguish between uniform memory access and non uniform memory access systems
On UMA systems, accessing RAM takes the same amount of time from any CPU. On NUMA systems, accessing some parts of memory may take longer than accessing other parts of memory, thus creating a performance penalty for certain memory accesses.
what are the advantages and disadvantages of using micro kernel approach
One benefit of the microkernel approach is ease of extending the operating system. All new services are added to user space and consequently do not require modification of the kernel. The microkernel also provides more security and reliability, since most services are running as user — rather than kernel — processes. Unfortunately, microkernels can suffer from performance decreases due to increased system function overhead.
difference between physical virtual and logical memory
Physical memory is the memory available for machines to execute operations (i.e., cache, random access memory, etc.). Virtual memory is a 2 method through which programs can be executed that requires space larger than that available in physical memory by using disk memory as a backing store for main memory. Logical memory is an abstraction of the computer's different types of memory that allows programmers and applications a simplified view of memory and frees them from concern over memory-storage limitations.
describe some requirements or goals when designing an operating system
Requirements can be divided into user and system goals. Users desire a system that is convenient to use, easy to learn, and to use, reliable, safe, and fast. System goals are defined by those people who must design, create, maintain, and operate the system: The system should be easy to design, implement, and maintain; it should be flexible, reliable, error-free, and efficient.
describe the solaris 10 containers
Solaris containers — or zones — provides a virtual layer between the operating system and its applications. Only one kernel is present and the hardware is not virtualized. However, the operating system and its devices are virtualized, providing processes within a container that they are the only running application on the system.
distinguish between system and application programs
System programs are not part of the kernel, but still are associated with the operating system. Application programs are not associated with the operating of the system.
list the four major categories of the benefits of multithreaded programming, explain each
The benefits of multithreaded programming fall into the categories: responsiveness, resource sharing, economy, and utilization of multiprocessor architectures. Responsiveness means that a multithreaded program can allow a program to run even if part of it is blocked. Resource sharing occurs when an application has several different threads of activity within the same address space. Threads share the resources of the process to which they belong. As a result, it is more economical to create new threads than new processes. Finally, a single-threaded process can only execute on one processor regardless of the number of processors actually present. Multiple threads can run on multiple processors, thereby increasing efficiency.
advantages of higher level language to implement an operating system
The code can be written faster, is more compact, and is easier to understand and debug. In addition, improvements in compiler technology will improve the generated code for the entire operating system by simple recompilation. Finally, an operating system is far easier to port — to move to some other hardware — if it is written in a higher-level language.
describe the compute-server and file-server types of server systems
The compute-server system provides an interface to which a client can send a request to perform an action (for example, read data from a database); in response, the server executes the action and sends back results to the client. The file-server system provides a file-system interface where clients can create, update, read, and delete files. An example of such a system is a Web server that delivers files to clients running Web browsers.
explain the difference between I/O bound process and a cpu bound process
The differences between the two types of processes stem from the number of I/O requests that the process generates. An I/O-bound process spends more of its time seeking I/O operations than doing computational work. The CPU-bound process infrequently requests I/O operations and spends more of its time performing computational work.
purpose of an interrupt vector
The interrupt vector is merely a table of pointers to specific interrupt-handling routines. Because there are a fixed number of interrupts, this table allows for more efficient handling of the interrupts than with a general-purpose, interrupt-processing routine.
explain why a modular kernel may be the best of the current operating system design techniques
The modular approach combines the benefits of both the layered and microkernel design techniques. In a modular design, the kernel needs only to have the capability to perform the required functions and know how to communicate between modules. However, if more functionality is required in the kernel, then the user can dynamically load modules into the kernel. The kernel can have sections with well-defined, protected interfaces, a desirable property found in layered systems. More flexibility can be achieved by allowing the modules to communicate with one another.
name and describe the different states that a process can exist in at any given time
The possible states of a process are: new, running, waiting, ready, and terminated. The process is created while in the new state. In the running or waiting state, the process is executing or waiting for an event to occur, respectively. The ready state occurs when the process is ready and waiting to be assigned to a processor and should not be confused with the waiting state mentioned earlier. After the process is finished executing its code, it enters the termination state.
explain the main difference between a short term and long term scheduler
The primary distinction between the two schedulers lies in the frequency of execution. The short-term scheduler is designed to frequently select a new process for the CPU, at least once every 100 milliseconds. Because of the short time between executions, the shortterm scheduler must be fast. The long-term scheduler executes much less frequently; minutes may separate the creation of one new process and the next. The long-term scheduler controls the degree of multiprogramming. Because of the longer interval between executions, the long-term scheduler can afford to take more time to decide which process should be selected for execution.
three general methods used to pass parameters to the operating system during system calls
The simplest approach is to pass the parameters in registers. In some cases, there may be more parameters than registers. In these cases, the parameters are generally stored in a block, or table, of memory, and the address of the block is passed as a parameter in a register. Parameters can also be placed, or pushed, onto the stack by the program and popped off the stack by the operating system.
relationship between an api and the system call interface and the operating system
The system-call interface of a programming language serves as a link to system calls made available by the operating system. This interface intercepts function calls in the API and invokes the necessary system call within the operating system. Thus, most of the details of the operating-system interface are hidden from the programmer by the API and are managed by the run-time support library.
distinguish between virtualization and simulation
Virtualization is the process whereby the system hardware is virtualized, thus providing the appearance to guest operating systems and applications that they are running on native hardware. In many virtualized environments, virtualization software runs at near native speeds. Simulation is the approach whereby the actual system is running on one set of hardware, but the guess system is compiled for a different set of hardware. Simulation software must simulate — or emulate — the hardware that the guest system is expecting. Because each instruction for 6 the guest system must be simulated in software rather than hardware, simulation is typically much slower than virtualization.
explain the concept of a contest switch
Whenever the CPU starts executing a new process, the old process's state must be preserved. The context of a process is represented by its process control block. Switching the CPU to another process requires performing a state save of the current process and a state restore of a different process. This task is known as a context switch. When a 7 context switch occurs, the kernel saves the context of the old process in its PCB and loads the saves context of the new process scheduled to run.
