1.Bootstrap Program
In computing, booting is a bootstrapping process that starts operating systems when the user turns on a computer system. Most computer systems can only execute code found in the memory (ROM or RAM); modern operating systems are mostly stored on hard disk drives, LiveCDs and USB flash drive. Just after a computer has been turned on, it doesn't have an operating system in memory. The computer's hardware alone cannot perform complicated actions of the operating system, such as loading a program from disk on its own; so a seemingly irresolvable paradox is created: to load the operating system into memory, one appears to need to have an operating system already installed.

2.Difference of interrupt and trap and thier use.
Trap is actually a software generated interrupt caused either by an error (for example division by zero, invalid memory access etc.), or by an specific request by an operating system service generated by a user program. Trap is sometimes called Exception. The hardware or software can generate these interrupts. When the interrupt or trap occurs, the hardware therefore, transfer control to the operating system which first preserves the current state of the system by saving the current CPU registers contents and program counter's value. after this, the focus shifts to the determination of which type of interrupt has occured. For each type of interrupt, separate segmants of code in the operating system determine what action should be taken and thus the system keeps on functioning by executing coputational instruction, I/O instruction, torage instruction etc.

3. Monitor mode,
or RFMON (Radio Frequency Monitor)mode,allows a computer with a wireless network interface card (NIC) to monitor all traffic received from the wireless network. Unlike promiscuous mode, which is also used for packet sniffing, monitor mode allows packets to be captured without having to associate with an access point or ad-hoc network first. Monitor mode only applies to wireless networks, while promiscuous mode can be used on both wired and wireless networks. Monitor mode is one of the six modes that 802.11 wireless cards can operate in: Master (acting as an access point), Managed (client, also known as station), Ad-hoc, Mesh, Repeater, and Monitor mode.

4.User mode
In User mode, the executing code has no ability to directly access hardware or reference memory. Code running in user mode must delegate to system APIs to access hardware or memory. Due to the protection afforded by this sort of isolation, crashes in user mode are always recoverable. Most of the code running on your computer will execute in user mode.

5.Device Status Table

Device-status table contains entry for each I/O deviceindicating its type, address, and state.

6.Direct memory access
Direct memory access (DMA) is a feature of modern computers and microprocessors that allows certain hardware subsystems within the computer to access system memory for reading and/or writing independently of the central processing unit. Many hardware systems use DMA including disk drive controllers, graphics cards, network cards and sound cards. DMA is also used for intra-chip data transfer in multi-core processors, especially in multiprocessor system-on-chips, where its processing element is equipped with a local memory (often called scratchpad memory) and DMA is used for transferring data between the local memory and the main memory. Computers that have DMA channels can transfer data to and from devices with much less CPU overhead than computers without a DMA channel. Similarly a processing element inside a multi-core processor can transfer data to and from its local memory without occupying its processor time and allowing computation and data transfer concurrency.

7.Difference of RAM and DRAM
Random-access memory (usually known by its acronym, RAM) is a form of computer data storage. Today, it takes the form of integrated circuits that allow stored data to be accessed in any order (i.e., at random). The word random thus refers to the fact that any piece of data can be returned in a constant time, regardless of its physical location and whether or not it is related to the previous piece of data.[1] By contrast, storage devices such as tapes, magnetic discs and optical discs rely on the physical movement of the recording medium or a reading head. In these devices, the movement takes longer than data transfer, and the retrieval time varies based on the physical location of the next item. The word RAM is often associated with volatile types of memory (such as DRAM memory modules), where the information is lost after the power is switched off. Many other types of memory are RAM, too, including most types of ROM and flash memory called NOR-Flash.

Dynamic random access memory (DRAM) is a type of random access memory that stores each bit of data in a separate capacitor within an integrated circuit. Since real capacitors leak charge, the information eventually fades unless the capacitor charge is refreshed periodically. Because of this refresh requirement, it is a dynamic memory as opposed to SRAM and other static memory.

8.Main memory
Refers to physical memory that is internal to the computer. The word main is used to distinguish it from external mass storage devices such as disk drives. Another term for main memory is RAM.

9.Magnetic Disk
Magnetic storage and magnetic recording are terms from engineering referring to the storage of data on a magnetized medium. Magnetic storage uses different patterns of magnetization in a magnetizable material to store data and is a form of non-volatile memory. The information is accessed using one or more read/write heads. As of 2009, magnetic storage media, primarily hard disks, are widely used to store computer data as well as audio and video signals. In the field of computing, the term magnetic storage is preferred and in the field of audio and video production, the term magnetic recording is more commonly used. The distinction is less technical and more a matter of preference.

10.Storage Hierarchy
The hierarchical arrangement of storage in current computer architectures is called the memory hierarchy. It is designed to take advantage of memory locality in computer programs. Each level of the hierarchy has the properties of higher bandwidth, smaller size, and lower latency than lower levels.Most modern CPUs are so fast that for most program workloads, the locality of reference of memory accesses and the efficiency of the caching and memory transfer between different levels of the hierarchy are the practical limitation on processing speed. As a result, the CPU spends much of its time idling, waiting for memory I/O to complete. This is sometimes called the space cost, as a larger memory object is more likely to overflow a small/fast level and require use of a larger/slower level.