DOS

DOS, short for "Disk Operating System",[1] is an acronym for several closely related operating systems that dominated the IBM PC compatible market between 1981 and 1995, or until about 2000 if one includes the partially DOS-based Microsoft Windows versions 95, 98, and Millennium Edition.
Related systems include MS-DOS, PC-DOS, DR-DOS, FreeDOS, GLaDOS, PTS-DOS, ROM-DOS, JM-OS, and several others.
In spite of the common usage, none of these systems were simply named "DOS" (a name given only to an unrelated IBM mainframe operating system in the 1960s). A number of unrelated, non-x86 microcomputer disk operating systems had "DOS" in their name, and are often referred to simply as "DOS" when discussing machines that use them (e.g. AmigaDOS, AMSDOS, ANDOS, Apple DOS, Atari DOS, Commodore DOS, CSI-DOS, ProDOS, and TRS-DOS). While providing many of the same operating system functions for their respective computer systems, programs running under any one of these operating systems would not run under others.

Design
All MS-DOS-type operating systems run on machines with the Intel x86 or compatible CPUs, mainly the IBM PC and compatibles. Machine-dependent versions of MS-DOS were produced for many non-IBM-compatible x86-based machines, with variations from relabelling of the Microsoft distribution under the manufacturer's name, to versions specifically designed to work with non-IBM-PC-compatible hardware. DOS-C's predecessor DOS/NT ran on Motorola 68000 CPU's.
DOS is a single-user, single-task operating system with basic kernel functions that are non-reentrant: only one program at a time can use them. There is an exception with Terminate and Stay Resident (TSR) programs, and some TSRs can allow multitasking. However, there is still a problem with the non-reentrant kernel: once a process calls a service inside of operating system kernel (system call), it must not be interrupted with another process calling system call, until the first call is finished.
The DOS kernel provides various functions for programs (an application program interface), like displaying characters on-screen, reading a character from the keyboard, accessing disk files and more.
DOS by default provides a primitive ability for shell scripting, via batch files (with the filename extension .BAT). These are text files that can be created in any DOS text editor, such as the MS-DOS Editor. They are executed in the same fashion as compiled programs, and run each line of the batch file as a command. Batch files can also make use of several internal commands, such as goto and conditional statements. gosub and simple arithmetic is supported in some third-party shells but can also be faked via strange workarounds; however, no real form of programming is usually enabled.
The operating system offers a hardware abstraction layer that allows development of character-based applications, but not for accessing most of the hardware, such as graphics cards, printers, or mice. This required programmers to access the hardware directly, usually resulting in each application having its own set of device drivers for each hardware peripheral. Hardware manufacturers would release specifications to ensure device drivers for popular applications were available.

Drive naming scheme
In DOS, drives are referred to by identifying letters. Standard practice is to reserve "A" and "B" for floppy drives. On systems with only one floppy drive DOS assigns both letters to the drive, prompting the user to swap disks as programs alternate access between them. This facilitates copying from floppy to floppy or having a program run from one floppy while accessing its data on another. Hard drives were originally assigned the letters "C" and "D". DOS could only support one active partition per drive. As support for more hard drives became available, this developed into first assigning a drive letter to each drive's active primary partition, then making a second pass over the drives to allocate letters to logical drives in the extended partition, then a third pass to give any other non-active primary partitions their names (where such additional partitions existed and contained a DOS-supported file system.) Lastly, DOS allocates letters for optical disc drives, RAM disks, and other hardware. Letter assignments usually occur in the order the drivers are loaded, but the drivers can instruct DOS to assign a different letter; drivers for network drives, for example, typically assign letters nearer the end of the alphabet.
Because DOS applications use these drive letters directly (unlike the /dev directory in Unix-like systems), they can be disrupted by adding new hardware that needs a drive letter. An example is the addition of a new hard drive having a primary partition where a pre-existing hard drive contains logical drives in extended partitions; the new drive will be assigned a letter that was previously assigned to one of the extended partition logical drives. Moreover, even adding a new hard drive having only logical drives in an extended partition would still disrupt the letters of RAM disks and optical drives. This problem persisted through the 9x versions of Windows until NT, which preserves the letters of existing drives until the user changes them.

Boot sequence
The boot sector on PC-compatible computers (MBR) is located at track zero. The boot sector on all disc devices are then in turn loaded into memory segment 0000:7C00, and if the sector contains the values "0x55 0xAA" at position 0x1FE, it's considered to be valid and is executed. On harddiscs each of the four partitions are searched for an active partition (bit-7=1 at pos 0x1BE+0x10*n).
The boot sector code loads the DOS-BIOS into segment 0000:0600; which is located in the file IO.SYS on MS-DOS systems. In some cases the boot sector instead relocates itself into 0000:0600 and loads the partition boot code into 0000:7C00 and executes it.
The DOS-BIOS will then load the DOS kernel, located in MSDOS.SYS on MS-DOS systems. In the DOS-kernel Windows 9x, the DOS-BIOS and kernel are combined in IO.SYS, and MSDOS.SYS is used as a text configuration file.
The kernel then loads the \CONFIG.SYS file to parse configuration parameters. The SHELL variable specifies the location of the shell which defaults to \COMMAND.COM.
The shell is loaded and executed.
The startup batch file AUTOEXEC.BAT is then run by the shell. DR-DOS allows specification of the startup batch file through a parameter in the SHELL statement.:392
The BIOS and kernel files loaded by the boot sector must be contiguous and be the first two directory entries. As such, removing and adding this file is likely to render the media unbootable. It is, however, possible to replace the shell at will, a method that can be used to start the execution of dedicated applications faster.
Variations from MS DOS re-name the BIOS and kernel files, for example, in DR-DOS and PC-DOS IBMBIO.COM is used in place of IO.SYS and IBMDOS.COM in place of MSDOS.SYS. On systems designed for PC-DOS v1.10 the signature 0x55 0xAA at position 0x1FE is not checked.

Other Animation Techniques

Drawn on film animation: a technique where footage is produced by creating the images directly on film stock, for example by Norman McLaren, Len Lye and Stan Brakhage.

Paint-on-glass animation: a technique for making animated films by manipulating slow drying oil paints on sheets of glass, for example by Aleksandr Petrov.

Erasure animation: a technique using tradition 2D medium, photographed over time as the artist manipulates the image. For example, William Kentridge is famous for his charcoal erasure films.

Pinscreen animation: makes use of a screen filled with movable pins, which can be moved in or out by pressing an object onto the screen. The screen is lit from the side so that the pins cast shadows. The technique has been used to create animated films with a range of textural effects difficult to achieve with traditional cel animation.

Sand animation: sand is moved around on a back- or front-lighted piece of glass to create each frame for an animated film. This creates an interesting effect when animated because of the light contrast.

Flip book: A flip book (sometimes, especially in British English, called a flick book) is a book with a series of pictures that vary gradually from one page to the next, so that when the pages are turned rapidly, the pictures appear to animate by simulating motion or some other change. Flip books are often illustrated books for children, but may also be geared towards adults and employ a series of photographs rather than drawings. Flip books are not always separate books, but may appear as an added feature in ordinary books or magazines, often in the page corners. Software packages and websites are also available that convert digital video files into custom-made flip books.

Other techniques and approaches :
Character animation
Chuckimation
Multi-sketching
Special effects animation
Animatronics
Stop motion

Stop motion

Stop-motion animation is used to describe animation created by physically manipulating real-world objects and photographing them one frame of film at a time to create the illusion of movement. There are many different types of stop-motion animation, usually named after the type of media used to create the animation. Computer software is widely available to create this type of animation.

Puppet animation typically involves stop-motion puppet figures interacting with each other in a constructed environment, in contrast to the real-world interaction in model animation. The puppets generally have an armature inside of them to keep them still and steady as well as constraining them to move at particular joints. Examples include The Tale of the Fox (France, 1937), Nightmare Before Christmas (US, 1993), Corpse Bride (US, 2005), Coraline (US, 2009), the films of Jiří Trnka and the TV series Robot Chicken (US, 2005–present).
Puppetoon, created using techniques developed by George Pal, are puppet-animated films which typically use a different version of a puppet for different frames, rather than simply manipulating one existing puppet.

Clay animation, or Plasticine animation often abbreviated as claymation, uses figures made of clay or a similar malleable material to create stop-motion animation. The figures may have an armature or wire frame inside of them, similar to the related puppet animation (below), that can be manipulated in order to pose the figures. Alternatively, the figures may be made entirely of clay, such as in the films of Bruce Bickford, where clay creatures morph into a variety of different shapes. Examples of clay-animated works include The Gumby Show (US, 1957–1967) Morph shorts (UK, 1977–2000), Wallace and Gromit shorts (UK, as of 1989), Jan Švankmajer's Dimensions of Dialogue (Czechoslovakia, 1982), The Trap Door (UK, 1984). Films include Wallace and Gromit: Curse of the Were-Rabbit, Chicken Run and The Adventures of Mark Twain

Cutout animation is a type of stop-motion animation produced by moving 2-dimensional pieces of material such as paper or cloth. Examples include Terry Gilliam's animated sequences from Monty Python's Flying Circus (UK, 1969–1974); Fantastic Planet (France/Czechoslovakia, 1973) ; Tale of Tales (Russia, 1979), The pilot episode of the TV series (and sometimes in episodes) of South Park (US, 1997).

Silhouette animation is a variant of cutout animation in which the characters are backlit and only visible as silhouettes. Examples include The Adventures of Prince Achmed (Weimar Republic, 1926) and Princes et princesses (France, 2000).

Model animation refers to stop-motion animation created to interact with and exist as a part of a live-action world. Intercutting, matte effects, and split screens are often employed to blend stop-motion characters or objects with live actors and settings. Examples include the work of Ray Harryhausen, as seen in films such Jason and the Argonauts (1961), and the work of Willis O'Brien on films such as King Kong (1933 film).

Go motion is a variant of model animation which uses various techniques to create motion blur between frames of film, which is not present in traditional stop-motion. The technique was invented by Industrial Light & Magic and Phil Tippett to create special effects scenes for the film The Empire Strikes Back (1980). Another example is Vermithrax from Dragonslayer (1981 film).

Object animation refers to the use of regular inanimate objects in stop-motion animation, as opposed to specially created items.
Graphic animation uses non-drawn flat visual graphic material (photographs, newspaper clippings, magazines, etc.) which are sometimes manipulated frame-by-frame to create movement. At other times, the graphics remain stationary, while the stop-motion camera is moved to create on-screen action.

Pixilation involves the use of live humans as stop motion characters. This allows for a number of surreal effects, including disappearances and reappearances, allowing people to appear to slide across the ground, and other such effects. Examples of pixilation include The Secret Adventures of Tom Thumb and Angry Kid shorts.

Computer Animation

Computer animation encompasses a variety of techniques, the unifying factor being that the animation is created digitally on a computer.

2D animation
2D animation figures are created and/or edited on the computer using 2D bitmap graphics or created and edited using 2D vector graphics. This includes automated computerized versions of traditional animation techniques such as of tweening, morphing, onion skinning and interpolated rotoscoping.
Examples: Foster's Home for Imaginary Friends, Danny Phantom, Waltz with Bashir
Analog computer animation
Flash animation
PowerPoint animation

3D animation
3D animation are digitally modeled and manipulated by an animator. In order to manipulate a mesh, it is given a digital skeletal structure that can be used to control the mesh. This process is called rigging. Various other techniques can be applied, such as mathematical functions (ex. gravity, particle simulations), simulated fur or hair, effects such as fire and water and the use of Motion capture to name but a few, these techniques fall under the category of 3d dynamics. Many 3D animations are very believable and are commonly used as Visual effects for recent movies.

Terms
Photo Realistic Animation, is used primarily for animation that attempts to resemble real life, Using advanced rendering that makes detailed skin, plants, water, fire, clouds, etc. to mimic real life. Examples include Up (2009, USA), Kung-Fu Panda, Ice Age (2002, USA).
Cel-shaded animation, is used to mimic traditional animation using CG software. Shading looked stark and less blending colors. Examples include, Skyland (2007, France), Appleseed (2007, Japan), The Legend of Zelda: Wind Waker (2002, Japan)
Motion capture, is used when live action actors wear special suits that allow computers to copy their movements into CG characters. Examples include Polar Express (2004, USA), Beowulf (2007), Disney's A Christmas Carol (2009 USA), Avatar (2009, USA).
2D animation techniques tend to focus on image manipulation while 3D techniques usually build virtual worlds in which characters and objects move and interact. 3D animation can create images that seem real to the viewer.