Examples of Disk Operating Systems that were the OS itself

•  The DOS/360initial/simple operating system for the IBM System/360family of mainframe
computers (it later became DOS/VSE, and was eventually just called VSE).

•  The  DOS operating system for DEC PDP-11 minicomputers (this OS and the computers it
ran on were nearly obsolete by the time PCs became common, with various descendants and other
replacements).

•  DOSfor the IBM PC compatible platform
The best known family of operating systems named "DOS" is  that running on IBM PCs type
hardware using the Intel CPUs or their compatible cousins from  other makers. Any DOS in this
family is usually just referred to as  DOS. The original was licensed to IBM by Microsoft, and
marketed by them as  "PC-DOS". When Microsoft licenced it to other hardware manufacturers, it
was called  MS-DOS. Digital Research produced a compatible variant known as  "DR-DOS", which
was eventually taken over (after a buyout of Digital Research) by Novell. This became "Open DOS"
for a while after the relevant division of Novell was sold to Caldera International, now called SCO.
There is also a free version named "Free DOS".
DOS consists of an input/output system, a command processor and several utilities. The
utilities are individual program files found on your DOS disk. While part ofDOS, these files are not
needed often enough to make it necessary or practical to keep them in the computer's RAM all the
time. FORMAT.COM, the program that formats blank disks, is an  example of a DOS utility.
Sometimes these utilities are called external commands (as  opposed to internal commands which are included as part of the file COMMAND.COM and remain resident in memory at all times; e.g.,
DIR and COPY).
The command processor is also a file you see on the disk, but once read into the computer's
memory, it usually resides there. Some programs provide their own command processor, and there
are times when the command processor will be overwritten in memory by a program and have to be
reloaded when the program stops executing.
The input/output system consists of two files and a ROM (Read Only Memory) chip. While the two
files are on your disks and are loaded into memory when the computer starts, they are normally
hidden from your view and not available to you for changing.

Examples of disk operating systems that were extensions to the OS

•  The  DOS operating system for the Apple Computer's Apple II family of computers. This
was the primary operating system for this family from 1979 with the introduction of the floppy disk
drive until 1983 with the introduction of  Pro DOS; many people continued using it long after that
date. Usually it was called Apple DOS to distinguish it from MS-DOS.
•  Commodore DOS, which was used by 8-bit Commodore computers. Unlike most other
DOS systems, it was integrated into the disk drives, not loaded into the computer's own memory.
•  Atari DOS, which was used by the Atari 8-bit family of computers. The Atari OS only
offered low-level disk-access, so an extra layer called DOS was booted off of a floppy that offered
higher level functions such as filesystems.
•  MSX-DOS, for the MSX computer standard. Initial version, released in 1984, was  nothing
but MS-DOS 1.0 ported to Z80; but in 1988 it evolved to version 2, offering facilities such as
sub directories, memory management and environment strings. The MSX -DOS kernel resided in
ROM (built-in on the disk controller) so basic file access capacity was available even without the
command interpreter, by using BASIC extended commands.
•  Disc Filing System(DFS) This was an optional component for the BBC Micro, offered as a
kit with a disk controller chip, a ROM chip, and a handful of logic  chips, to be installed inside the
computer. See also Advanced Disc Filing System.
•  AMSDOS, for the Amstrad CPC computers.
•  GDOS and G+DOS, for the +D and DISCiPLE disk interfaces for the ZX Spectrum.

History of DOS

In the early days of computers, there were no disk drives; delay lines, punched cards, paper
tape, magnetic tape, magnetic drums, were used instead. And in  the early days of microcomputers,
paper tape or audio cassette tape (see Kansas City standard) or nothing were used instead. In the
latter case, program and data entry was done at front panel  switches directly into memory or
through a computer terminal / keyboard, sometimes controlled by a ROM BASIC interpreter; when
power was turned off after running the program, the information so entered vanished.
Both hard disks and floppy disk drives require software to manage rapid access to block storage of
sequential and other data. When microcomputers rarely had expensive disk drives of any kind, the
necessity to have software to manage such devices (ie, the 'disk's) carried much status. To have one
or the other was a mark of distinction and prestige, and so was having the Disk sort of an Operating
System. As prices for both disk hardware and operating system software decreased, there were
many such microcomputer systems.
Mature versions of the Commodore, SWTPC, Atari and Apple home computer systems all
featured a disk operating system (actually called 'DOS' in  the case of the Commodore 64 (CBM
DOS), Atari 800 (Atari DOS), and Apple II machines (Apple DOS)), as did (at the other end of the
hardware spectrum, and much earlier) IBM's System/360, 370 and (later) 390 series of mainframes
(e.g., DOS/360:  Disk  Operating  System / 360and DOS/VSE:  Disk  Operating  System /  Virtual
Storage Extended). Most home computer DOS'es were stored on a floppy disk always to be booted
at start-up, with the notable exception of Commodore, whose DOS resided on ROM chips in the
disk drives themselves, available at power-on.
In large machines there were other disk operating systems, such as IBM's VM, DEC's RSTS
/ RT-11 / VMS / TOPS-10 / TWENEX, MIT's ITS / CTSS, Control  Data's assorted NOS variants, Harris's Vulcan, Bell Labs' Unix, and so on. In microcomputers, SWTPC's 6800 and 6809 machines
used TSC's FLEX disk operating system, Radio Shack's TRS-80machines used TRS-DOS, their
Color Computer used OS-9, and most of the Intel 8080 based machines from  IMSAI, MITS
(makers of the legendary Altair 8800), Cromemco, North Star, etc used the CP/M-80 disk operating
system. See list of operating systems.
Usually, a disk operating system was loaded from a disk. Only a very few comparable
DOSes were stored elsewhere than floppy disks; among these exceptions were the British BBC
Micro's optional Disc Filing System, DFS, offered as a kit with a disk controller chip, a ROM chip,
and a handful of logic chips, to be installed inside the computer; and Commodore's CBM DOS,
located in a ROM chip in each disk drive.

Disk operating system

Disk Operating System(specifically) and  disk operating system(generically), most often
abbreviated as DOS(not to be confused with the DOS family of disk operating systems for the IBM
PC compatible platform), refer to operating system software used in most computers that provides
the abstraction and management of secondary storage devices and the information on them (e.g.,
file systems for organizing files of all sorts). Such software is referred to as a disk operating system
when the storage devices it manages are made of rotating platters (such as hard disks or floppy
disks).
In the early days of micro computing, memory space was often limited, so the disk operating
system was an extension of the operating system. This component was only loaded if it was needed.
Otherwise, disk-access would be limited to low-level operations such as reading and writing disks
at the sector-level.
In some cases, the  disk operating system component (or even the operating system) was
known as DOS.
Sometimes, a disk operating system can refer to the entire operating system if it is loaded off
a disk and supports the abstraction and management of disk devices. An  example is DOS/360. On
the PC compatible platform, an entire family of operating systems was called DOS.

Laptop computers

A laptop computer or simply laptop (also notebook computer or notebook) is a small
personal computer designed for mobility. Usually all of the peripherals needed to operate the laptop
are built in to a single unit. Most laptops contain batteries to facilitate operation without a readily
available electrical outlet. 

Non IBM-compatible personal computers

Though many personal computers are IBM PC compatible using either Microsoft Windows
or closed and open-source Unix-likes such as Linux, a number of other personal computer types are
also popular.
A leading alternative to the IBM PC is the Apple Macintosh, a  combination of proprietary
hardware and operating system. The Macintosh orignally used the Motorola 68000 series, then
shifted to the IBM and Motorola Power PC processors.
In January 2006, Apple shifted its architecture to the same Intel chip found in IBM
compatibles, allowing their computers to run Apple's own Mac OS X as well as other IBM PC
Compatible Operating Systems.
Further PC and PW (Personal Workstation) types through time:
•  Amiga (previously produced by Commodore, now under license from Amiga Inc.) 
•  Acorn Archimedes & Risc PC
•  Atari ST
•  Be OS Be Box
•  Pegasos
•  NEC PC-9800 (At one time, in Japan)
•  NeXT workstations
•  Sun SPARC station
•  SGI workstations like the SGI Indigo and SGI Onyx
The term "personal computer" is often avoided by advocates of the  above computer systems,
ostensibly because of the association it has to the "PC" in "IBM PC".

Main memory

A PC's main memory place (or primary storage) is fast storage space that is directly
accessible by the CPU. It is generally used for storing relatively short-term data needed for software
execution. Main memory is usually much faster than mass storage devices like hard disks or optical
discs, but usually cannot retain data for more than a few fractions of a second without power and is
more expensive. Therefore, it is not generally suitable for long-term or archival data storage. As
with the CPU, most PCs use some form of semiconductor random access memory such as DRAM
or SRAM as their primary storage.


Hard disk drive

The disk drives use a sealed head/disk assembly (HDA) which was  first introduced by
IBM's "Winchester" disk system. The use of a sealed assembly allowed the use of positive air
pressure to drive out particles from the surface of the disk, which improves reliability.
If the mass storage controller provides for expandability, a PC may also be upgraded by the addition
of extra hard disk or optical drives. For example, DVD-ROMs, CD-ROMs, and various optical disc
recorders may all be added by the user to certain PCs. Standard internal storage device interfaces
are ATA, Serial ATA, SCSI, and CF+ Type II in 2005. 

Graphics - Video card 

The graphics card - otherwise called a graphics adapter, video adapter, or video card - processes and
renders the graphics output from the computer to the VDU or computer monitor and is an essential
part of the modern computer. On older and budget models graphics cards tended to be integrated
with the motherboard but, more commonly, they are supplied in PCI, AGP, or PCI Express format.
Graphic cards are also the most glamorized computer component as it is the component which
creates all the visual effects on the computer which is essential for playing games.

Mouse Computing

Operating a mechanical mouse (Fig. 2).
1: Moving the mouse turns the ball.
2: X and Y rollers grip the ball and transfer movement.
3: Optical encoding disks include light holes.
4: Infrared LEDs shine through the disks.
5: Sensors gather light pulses to convert to X and Y velocities.

A  mouse is a handheld pointing device for computers, being a small object fitted with one
or more buttons and shaped to sit naturally under the hand. The underside of the mouse houses a
device that detects the mouse's motion relative to the flat surface on which it moves. The mouse's
2D motion is typically translated into the motion of a pointer on the display.
It is called a mouse primarily because the cord on early models resembled the rodent's tail,
and also because the motion of the pointer on the screen can be mouse-like (Fig. 2).