sharing system resources requires operating system to ensure that an incorrect program cannot cause other programs to execute incorrectly.
provide hardware support to differetiate between at least two modes of operations
User mode- execution done on behalf od a user.
Monitor Mode - (also supervisor mode or system mode) -execution done on behalf of operating system.
I/O Protection
All I/O isntructions are privileged instructions.
Must ensure that a user program could never gain control of the computer in monitor mode (i.e., a user program that, as part od its execution, stores a new address in the interrupt vector).
Memory Protection
Must provide memory protection at least for the interrupt vector and the interrupt service routines
In order to have memory protection, add two registers that determine the range of legal addresses a program may access:
- base register - holds the smallest legal physical memory address.
- limit register - contains the size of the range.
Memory outside the defined range is protected.
CPU Protection
The VRM design approachremoves cable inductance fromthe distribution and reducesboard inductance. A load-changetransient occurs when coming outof or entering a low power mode.For some CPUs this load-changetransient can be on the order of13A. These are not only quickchanges in current demand, butalso long-lasting average currentrequirements. Even during nor-mal operation the currentdemand can still change by asmuch as 7A as activity levelschange within the processorcomponent. Maintaining voltagetolerance during these changesin current requires high-densitybulk capacitors with low EffectiveSeries Resistance (ESR). Thesehigh-current immediate demandson the circuits can cause compo-nents to fail. Circuit protectionprevents the VRM from damag-ing the CPU in the event of aVRM fault. If the VRM fails, theprocessor tries to pull too muchpower. A PolySwitch device canbe placed on the input pins to theVRMs that supply power to theprocessors, therefore protectingthe processors. If there is a fail-ure, only the VRM needs to bereplaced, rather than the moreexpensive CPU.
Main memory -Refers to physicalmemory that is internal to the computer. The word main is used to distinguish it from external mass storagedevices such as disk drives. Another term for main memory is RAM. The computer can manipulate only data that is in main memory. Therefore, every program you execute and every file you access must be copied from a storage device into main memory. The amount of main memory on a computer is crucial because it determines how many programs can be executed at one time and how much data can be readily available to a program. Because computers often have too little main memory to hold all the data they need, computer engineers invented a technique called swapping, in which portions of data are copied into main memory as they are needed. Swapping occurs when there is no room in memory for needed data. When one portion of data is copied into memory, an equal-sized portion is copied (swapped) out to make room. Now, most PCs come with a minimum of 32 megabytes of main memory. You can usually increase the amount of memory by inserting extra memory in the form of chips
Magnetic disk -A memory device, such as a floppy disk, a hard disk, or a removable cartridge, that is covered with a magnetic coating on which digital information is stored in the form of microscopically small, magnetized needles.
moving head disk mechanism
Magnetic tape -is a medium for magnetic recording generally consisting of a thin magnetizable coating on a long and narrow strip of plastic. Nearly all recording tape is of this type, whether used for recording audio or video or for computer data storage. It was originally developed in Germany, based on the concept of magnetic wire recording. Devices that record and playback audio and video using magnetic tape are generally called tape recorders and video tape recorders respectively. A device that stores computer data on magnetic tape can be called a tape drive, a tape unit, or a streamer. Magnetic tape revolutionized the broadcast and recording industries. In an age when all radio (and later television) was live, it allowed programming to be prerecorded. In a time when gramophone records were recorded in one take, it allowed recordings to be created in multiple stages and easily mixed and edited with a minimal loss in quality between generations. It is also one of the key enabling technologies in the development of modern computers. Magnetic tape allowed massive amounts of data to be stored in computers for long periods of time and rapidly accessed when needed. Today, many other technologies exist that can perform the functions of magnetic tape. In many cases these technologies are replacing tape. Despite this, innovation in the technology continues and tape is still widely used
The range of memory and storage devices within the computer system. The following list starts with the slowest devices and ends with the fastest. See storage and memory.
VERY SLOW
Punch cards (obsolete)
Punched paper tape (obsolete)
FASTER
Bubble memory
Floppy disks
MUCH FASTER
Magnetic tape
Optical discs (CD-ROM, DVD-ROM, MO, etc.)
Magnetic disks with movable heads
Magnetic disks with fixed heads (obsolete)
Low-speed bulk memory
FASTEST
Flash memory
Main memory
Cache memory
Microcode
Registers
Coherency – In computing, cache coherence (also cache coherency) refers to the integrity of data stored in local caches of a shared resource. Cache coherence is a special case of memory coherence. When clients in a system maintain caches of a common memory resource, problems may arise with inconsistent data. This is particularly true of CPUs in a multiprocessing system. Referring to the "Multiple Caches of Shared Resource" figure, if the top client has a copy of a memory block from a previous read and the bottom client changes that memory block, the top client could be left with an invalid cache of memory without any notification of the change. Cache coherence is intended to manage such conflicts and maintain consistency between cache and memory.
Consistency - In computer science, in a distributed system such as a distributed shared memory system or a distributed data store such as a database, filesystem, web caching or optimistic replication systems, there are a number of possible data consistency models. The system supports a given model if operations on memory follow specific rules. The data consistency model specifies a contract between programmer and system, wherein the system guarantees that if the programmer follows the rules, memory will be consistent and the results of memory operations will be predictable.
A memory device, such as a floppy disk, a hard disk, or a removable cartridge, that is covered with a magnetic coating on which digital information is stored in the form of microscopically small, magnetized needles.
The computer can manipulate only data that is in main memory. Therefore, every program you execute and every file you access must be copied from a storage device into main memory. The amount of main memory on a computer is crucial because it determines how many programs can be executed at one time and how much data can be readily available to a program.
Because computers often have too little main memory to hold all the data they need, computer engineers invented a technique called swapping, in which portions of data are copied into main memory as they are needed. Swapping occurs when there is no room in memory for needed data. When one portion of data is copied into memory, an equal-sized portion is copied (swapped) out to make room.
Now, most PCs come with a minimum of 32 megabytes of main memory. You can usually increase the amount of memory by inserting extra memory in the form of chips.
RAM is the acronym for Random Access Memory, the cheapest way to make your computer a more effective system. Adding RAM to your computer enables it operate more programs at once, speed up program launches, and avoid system crashes. When you start a program, it is loaded from the hard drive of the computer into RAM.Running a program in RAM allows it to run thousands times faster than if it were running directly from the hard drive; however, it is possible to load so many programs that the RAM or memory can no longer hold all of them. You then have to either close some of the programs or add more RAM to your computer.Upgrading your computer's memory chips is the best solution for improving your system. Upgrades, involving adding more RAM, are very convenient. Current memory prices are low enough that every computer owner should be able to do it. Installation requires little technical expertise, making the process quick and simple. Our goal at Computer Memory Chips Upgrade is to educate you on the basic facts of upgrading your computer's memory. We firmly believe an educated consumer equals a better buying experience for everyone involved. By possessing the necessary knowledge of computer memory chips, you will be able to get great computer performance at an optimal price. Dynamic random access memory (DRAM) is the most common kind of random access memory (RAM) for personal computers and workstations. The network of electrically-charged points in which a computer stores quickly accessible data in the form of 0s and 1s is called memory. Random access means that the PC processor can access any part of the memory directly rather than having to proceed sequentially from some starting place. DRAM is dynamic in that, unlike static RAM (SRAM), it needs to have its storage cells refreshed or given a new electronic charge every few milliseconds. Static RAM does not need refreshing because it operates on the principle of moving current that is switched in one of two directions rather than a storage cell that holds a charge in place. Static RAM is generally used for cache memory, which can be accessed more quickly than DRAM. DRAM stores each bit in a storage cell consisting of a capacitor and a transistor. Capacitors tend to lose their charge rather quickly; thus, the need for recharging. A variety of other RAM interfaces to the computer exist. These include: EDO RAM and SDRAM.
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. Without DMA, using programmed input/output (PIO) mode for communication with peripheral devices, or load/store instructions in the case of multicore chips, the CPU is typically fully occupied for the entire duration of the read or write operation, and is thus unavailable to perform other work. With DMA, the CPU would initiate the transfer, do other operations while the transfer is in progress, and receive an interrupt from the DMA controller once the operation has been done. This is especially useful in real-time computing applications where not stalling behind concurrent operations is critical. Another and related application area is various forms of stream processing where it is essential to have data processing and transfer in parallel, in order to achieve sufficient throughput.
Is there a way to get any third-party devices that are regularly sending SNMP traps to CIM7 to show up in the Device Status field relating to the trap severity? I am getting plenty of major error messages from one of my switches, but the device is still showing as normal.
User-mode Linux (UML) enables multiple virtual Linux systems (known as guests) to run as an application within a normal Linux system (known as the host). As each guest is just a normal application running as a process in user space, this approach provides the user with a way of running multiple virtual Linux machines on a single piece of hardware, offering excellent security and safety without affecting the host environment's configuration or stability.
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. Monitor mode may be used for malicious purposes, such as collecting traffic for WEP cracking. It may also be used for legitimate purposes such as monitoring one's own network to ensure its terms of use are being followed. This mode also somewhat useful during design phase of wi-fi network construction to discover how many wi-fi devices already using spectrum at given area and which channels are busiest and which are unused yet in local area. This helps to plan wi-fi network better and reduce interference with other wi-fi devices by choosing least used channels for new wi-fi network. Software such as KisMAC or Kismet in combination with protocol analyzers such as Wireshark or tcpdump provide a user interface for passive wireless network monitoring.
Bootstrapping (from an old expression "to pull oneself up by one's bootstraps") is a technique by which a simple computer program activates a more complicated system of programs. In the start up process of a computer system, a small program such as BIOS, initializes and tests that hardware, peripherals and external memory devices are connected, then loads a program from one of them and passes control to it, thus allowing loading of larger programs, such as an operating system.
A different use of the term bootstrapping is to use a compiler to compile itself, by first writing a small part of a compiler of a new programming language in an existing language to compile more programs of the new compiler written in the new language. This solves the "chicken and egg" causality dilemma.
Bootstrapping was shortened to booting, or the process of starting up any computer, which is the most common meaning for non-technical computer users. The verb "boot" is similarly derived.
A "bootstrap" most commonly refers to the simple program itself that actually begins the initialization of the computer's operating system, like GRUB, LILO or NTLDR. Modern personal computers have the ability of using their network interface card (NIC) for bootstrapping; on IA-32 (x86) and IA-64 (Itanium) this method is implemented by PXE and Etherboot.
The computer is regarded as starting in a "blank slate" condition - either its main memory is blank, or else its content is suspect due to a prior crash. Although magnetic core memory retains its state with the power off, there would still exist the problem of loading in to it the very first program. A special start program could be very large, and given the modern affordability of read-only memory chips, could constitute the entire program to be run (as in embedded systems) but such an arrangement is inflexible. The bootstrap part would be a short simple piece of code that loads the main code.
An interrupt is generally initiated by an I/O device, and causes the CPU to stop what its doing, save its context, jump to the appropriate interrupt service routine, complete it, restore the context, and continue execution. For example, a serial device may assert the interrupt line and then place an interrupt vector number on the data bus. The CPU uses this to get the serial device interrupt service routine, which it then executes as above.
A trap is usually initiated by the CPU hardware. When ever the trap condition occurs (on arithmetic overflow, for example), the CPU stops what it's doing, saves the context, jumps to the appropriate trap routine, completes it, restores the context, and continues execution. For example, if overflow traps are enabled, adding two very large integers would cause the overflow bit to be set AND the overflow trap service routine to be initiated.
