By definition, device nodes correspond to resources that an operating-system kernel has already allocated. Unix identified those resources by a ”major number” and a ”minor number”, both stored as part of the structure of a node. The assignment of these numbers occurs uniquely in different operating systems and on different computer platforms. Generally, the major number identifies the device driver and the minor number identifies a particular device (possibly out of many) that the driver controls: in this case the system may pass the minor number to a driver as an argument. In presence of dynamic number allocation however, this may not be the case (e.g. on FreeBSD 5 and up).

As with other special file types, the computer system accesses device nodes using standard system calls and treats them like regular computer files. Two standard types of device files exist, differentiated by the type of hardware with which they interface and the way the operating system processes input and output operations: character devices and block devices.

Character devices

”Character special files” or ”character devices” relate to devices through which the system transmits data one character at a time. These device nodes often serve for stream communication with devices such as mice, keyboards, virtual terminals, and serial modems, and usually do not support random access to data.

In most implementations, character devices use unbuffered input and output routines. The system reads each character from the device immediately or writes each character to the device immediately.

Block devices

”Block special files” or ”block devices” correspond to devices through which the system moves data in the form of blocks. These device nodes often represent addressable devices such as hard disks, CD-ROM drives, or memory-regions.

Block devices often support random access and seeking, and generally use buffered input and output routines. The operating system allocates a data buffer to hold a single block each for input and output. When a program sends a request to read data from or to write data to the device, the system stores each character of that data in the appropriate buffer. When the buffer fills up, the appropriate operation takes place (data transfer) and the system clears the buffer.

Adapted from the Wikipedia article Device file, under the G. N. U. Free Documentation License. Please also see http://en.wikipedia.org/wiki

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File Allocation Table (FAT) is a computer file system architecture now widely used on many computer systems and most memory cards, such as those used with digital cameras. FAT file systems are commonly found on floppy disks, flash memory cards, digital cameras, and many other portable devices because of their relative simplicity. Performance of FAT compares poorly to most other file systems as it uses overly simplistic data structures, making file operations time-consuming, and makes poor use of disk space in situations where many small files are present.

For floppy disks, the FAT has been standardized as ECMA-107 and ISO/IEC 9293. Those standards include only FAT12 and FAT16 without long filename support; long filenames with FAT is partially patented.

The FAT file system is relatively straightforward technically and is supported by virtually all existing operating systems for personal computers. This makes it a useful format for solid-state memory cards and a convenient way to share data between operating systems.

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Adapted from the Wikipedia article File Allocation Table, under the G. N. U. Free Documentation License. Please also see http://en.wikipedia.org/wiki

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Control-C is a common computer command. It is generated by pressing the key while holding down the key on a computer keyboard. The equivalent key combinations on Mac OS computers is Command-C.

In graphical user interface environments that use the control key to control the active program, control-C is often used to copy highlighted text to the clipboard. In many command-line interface environments, control-C is used to abort the current task and regain user control. It is a special sequence which causes the operating system to send a signal to the active program. Usually the signal causes it to end, but the program may “catch” it and do something else, typically returning control to the user.

Adapted from the Wikipedia article Control-C, under the G. N. U. Free Documentation License. Please also see http://en.wikipedia.org/wiki

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Jupiter Cantab was formed by Richard Altwasser and Steven Vickers.

Both had been on the design team for the Sinclair ZX Spectrum. Altwasser did some work on the development of the ZX-81 and in the design of the hardware of the Spectrum. Vickers adapted and expanded the 4K ZX-80 ROM to the 8K ZX-81 ROM and wrote most of the ROM for the Spectrum. The Jupiter Ace was named after the early British computer, the ACE. The name was chosen to emphasize the “firsts” of using the FORTH language as more efficient for personal computers.

FORTH is a threaded code programming language that also acted as operating system. The system was adapted to the disk-less tape-using home computer hardware.

On average, and for similar programs, ACE’s FORTH was 5 times faster and needing half the RAM (RAM was an expensive luxury at the time) of an equivalent program written in interpreted BASIC. Forth programs usage tends to be more RAM efficient as the bigger programs are, the more they reuse previously-defined code .

For such reasons FORTH was chosen to deliver better performance and [structured programming] flexibility.

Adapted from the Wikipedia article Jupiter Ace, under the G. N. U. Free Documentation License. Please also see http://en.wikipedia.org/wiki

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SMP has many uses in science, industry, and business which often use custom-programmed software for multithreaded (multitasked) processing. However, most consumer products such as word processors and computer games are written in such a manner that they cannot gain large benefits from concurrent systems. For games this is usually because writing a program to increase performance on SMP systems can produce a performance loss on uniprocessor systems. , however, multi-core chips are becoming more common in new computers, and the balance between installed uni- and multi-core computers may change in the coming years.

Uniprocessor and SMP systems require different programming methods to achieve maximum performance. Therefore two separate versions of the same program may have to be maintained, one for each. Programs running on SMP systems may experience a performance increase even when they have been written for uniprocessor systems. This is because hardware interrupts that usually suspend program execution while the kernel handles them can execute on an idle processor instead. The effect in most applications (e.g. games) is not so much a performance increase as the appearance that the program is running much more smoothly. In some applications, particularly compilers and some distributed computing projects, one will see an improvement by a factor of (nearly) the number of additional processors.

In situations where more than one program executes at the same time, an SMP system will have considerably better performance than a uni-processor because different programs can run on different CPUs simultaneously.

Systems programmers must build support for SMP into the operating system: otherwise, the additional processors remain idle and the system functions as a uniprocessor system.

In cases where an SMP environment processes many jobs, administrators often experience a loss of hardware efficiency. Software programs have been developed to schedule jobs so that the processor utilization reaches its maximum potential. Good software packages can achieve this maximum potential by scheduling each CPU separately, as well as being able to integrate multiple SMP machines and clusters.

Access to RAM is serialized; this and cache coherency issues causes performance to lag slightly behind the number of additional processors in the system (aga).

Adapted from the Wikipedia article Symmetric Multi-Processing, under the G. N. U. Free Documentation License. Please also see http://en.wikipedia.org/wiki

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Computer criminals placed Download.ject on financial and corporate websites running IIS 5.0 on Windows 2000, breaking in using a known vulnerability. (A patch existed for the vulnerability, but many administrators had not applied it.) The attack was first noticed June 23, although some researchers think it may have been in place as early as June 20.

Download.ject appended a fragment of JavaScript to all web pages from the compromised servers. When any page on such a server was viewed with Internet Explorer (IE) for Windows, the JavaScript would run, retrieve a copy of one of various backdoor and key logging programs from a server located in Russia and install it on the user’s machine, using two holes in IE — one with a patch available, but the other without. These vulnerabilities were present in all versions of IE for Windows except the version included in Windows XP Service Pack 2 , which was only in beta testing at the time.

Both the server and browser flaws had been exploited before this. This attack was notable, however, for combining the two, for having been placed upon popular mainstream websites (although a list of affected sites was not released) and for the network of compromised sites used in the attack reportedly numbering in the thousands, far more than any previous such compromised network.

Microsoft advised users on how to remove an infection and to browse with security settings at maximum. Security experts also advised switching off JavaScript, using a web browser other than Internet Explorer, using an operating system other than Windows, or staying off the Internet altogether.

This particular attack was neutralised on June 25 when the server from which Download.ject installed a backdoor was shut down. Microsoft issued a patch for Windows 2000, 2003 and XP on July 2.

Although not a sizable attack compared to email worms of the time, the fact that almost all existing installations of IE — 95% of web browsers in use at the time — were vulnerable, and that this was the latest in a series of IE holes leaving the underlying operating system vulnerable, caused a notable wave of concern in the press. Even some business press started advising users to switch to other browsers, despite that the then-prerelease Windows XP SP2 being invulnerable to the attack.

Adapted from the Wikipedia article Download.ject, under the G. N. U. Free Documentation License. Please also see http://en.wikipedia.org/wiki

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Apple Computer has begun incorporating a Trusted Platform Module into their Apple Macintosh line of computers, and making use of it in such applications as Rosetta. Parts of the operating system not fully x86-native run through the Rosetta PowerPC binary translator, which in turn requires the Trusted Platform Module for proper operation. (This description applies to the developer preview version, but the mechanism differs in the release version.) Recently, the OSx86 project has been releasing patches to circumvent this mechanism. There are also industrial solutions available like Matrix Software License Protection System.

Microsoft reduced common Windows based software cracking with the release of the Next-Generation Secure Computing Base initiative in future versions of their operating system.

Adapted from the Wikipedia article Software cracking, under the G. N. U. Free Documentation License. Please also see http://en.wikipedia.org/wiki

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Commodore 1541 disk drive, with open disk slot. This version uses a Newtronics drive mechanism, and the rotating lever is used to hold the disk in place.:$endImage–> The Commodore 1541 (aka CBM 1541, and originally called VIC-1541), made by Commodore International, was the best-known floppy disk drive for the Commodore 64 home computer. The 1541 was a single-sided 170 kilobyte drive for 5¼” disks. The 1541 followed the previous Commodore 1540 (meant for the VIC-20).

The disk drive used Group Code Recording (GCR) and contained a MOS 6502 microprocessor, doubling as a disk controller and on-board disk operating system processor. The number of sectors per track varied from 17 to 21 (an early implementation of Zone Bit Recording). The drive’s built-in disk operating system was CBM DOS 2.6.

Adapted from the Wikipedia article Commodore 1541, under the G. N. U. Free Documentation License. Please also see http://en.wikipedia.org/wiki

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process is an instance of a computer program that is being executed. It contains the program code and its current activity. Depending on the operating system (OS), a process may be made up of multiple threads of execution that execute instructions concurrently.

A computer program is a passive collection of instructions, a process is the actual execution of those instructions. Several processes may be associated with the same program; for example, opening up several instances of the same program often means more than one process is being executed.

Multitasking is a method to allow multiple processes to share processors (CPUs) and other system resources. Each CPU executes a single task at a time. However, multitasking allows each processor to switch between tasks that are being executed without having to wait for each task to finish. Depending on the operating system implementation, switches could be performed when tasks perform input/output operations, when a task indicates that it can be switched, or on hardware interrupts.

A common form of multitasking is time-sharing. Time-sharing is a method to allow fast response for interactive user applications. In time-sharing systems, context switches are performed rapidly. This makes it seem like multiple processes are being executed simultaneously on the same processor. The execution of multiple processes seemingly simultaneously is called concurrency.

For security and reliability reasons most modern operating systems prevent direct communication between independent processes, providing strictly mediated and controlled inter-process communication functionality.

Adapted from the Wikipedia article Process (computing), under the G. N. U. Free Documentation License. Please also see http://en.wikipedia.org/wiki

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run time, run-time, runtime, or execution time refers most literally to the time during which a program is running (executing). It contrasts to other phases of program development and use, such as compile time, link time, load time, etc. Closely linked to this most basic sense is the state of the entire system on which the program is running, which affects the program’s execution and which varies between instances. Therefore “runtime” also refers to the broader idea of a single installation of a given software or computer program on a single computer, and how that particular instance behaves while running.

A “run-time error” is detected after or during the installation or copying of the program, whereas a “compile-time error” is detected by the compiler before the program is so installed and started. Type checking, storage allocation, and even code generation and code optimization may be done at compile-time or upon a run-time, depending on the language and compiler.

The term runtime as a noun can also refer to a program’s installation on a computer and the resulting run-time environment, the collection of software service available after its installation. These services may be provided by the operating system, or by a run-time system, such as a virtual machine or a collection of program libraries.

Adapted from the Wikipedia article Run time (computing), under the G. N. U. Free Documentation License. Please also see http://en.wikipedia.org/wiki

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