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A bootloader is software that is responsible for
booting In computing Computing is any goal-oriented activity requiring, benefiting from, or creating computing machinery. It includes the study and experimentation of algorithm of an algorithm (Euclid's algorithm) for calculating the greatest ...
a computer. When a computer is turned off, its softwareincluding operating systems, application code, and dataremains stored on
non-volatile memory Non-volatile memory (NVM) or non-volatile storage is a type of computer memory that can retain stored information even after power is removed. In contrast, volatile memory needs constant power in order to retain data. Examples of non-volatile ...
. When the computer is powered on, it typically does not have an operating system or its loader in
random-access memory Random-access memory (RAM; ) is a form of computer memory In computing Computing is any goal-oriented activity requiring, benefiting from, or creating computing machinery. It includes the study and experimentation of algorithmic proces ...
(RAM). The computer first executes a relatively small program stored in
read-only memory Read-only memory (ROM) is a type of non-volatile memory used in computers and other electronic devices. Data stored in ROM cannot be electronically modified after the manufacture of the memory device. Read-only memory is useful for storing sof ...
(ROM) along with a small amount of needed data, to access the nonvolatile device or devices from which the operating system programs and data can be loaded into RAM. The small program that starts this sequence is known as a bootstrap loader, bootstrap or boot loader. This small program's only job is to load other data and programs which are then executed from RAM. Often, multiple-stage boot loaders are used, during which several programs of increasing complexity load one after the other in a process of
chain loading Chain loading is a method used by computer program A computer program is a collection of instructions that can be executed by a computer to perform a specific task. A computer program is usually written by a computer programmer in a programm ...
. Some computer systems, upon receiving a boot signal from a human operator or a peripheral device, may load a very small number of fixed instructions into memory at a specific location, initialize at least one CPU, and then point the CPU to the instructions and start their execution. These instructions typically start an input operation from some peripheral device (which may be switch-selectable by the operator). Other systems may send hardware commands directly to peripheral devices or I/O controllers that cause an extremely simple input operation (such as "read sector zero of the system device into memory starting at location 1000") to be carried out, effectively loading a small number of boot loader instructions into memory; a completion signal from the I/O device may then be used to start execution of the instructions by the CPU. Smaller computers often use less flexible but more automatic boot loader mechanisms to ensure that the computer starts quickly and with a predetermined software configuration. In many desktop computers, for example, the bootstrapping process begins with the CPU executing software contained in ROM (for example, the
BIOS In computing, BIOS (, ); an acronym for Basic Input/Output System and also known as the System BIOS, ROM BIOS or PC BIOS) is firmware used to perform Computer hardware, hardware initialization during the booting process (power-on startup), and t ...

BIOS
of an
IBM PC The IBM Personal Computer (model 5150, commonly known as the IBM PC) is the first computer released in the IBM PC model line and the basis for the IBM PC compatible IBM PC compatible computers are similar to the original IBM PC The IBM ...

IBM PC
or an
IBM PC compatible IBM PC compatible computers are similar to the original IBM PC The IBM Personal Computer (model 5150, commonly known as the IBM PC) is the first computer released in the IBM PC model line and the basis for the IBM PC compatible IBM PC c ...
) at a predefined address (some CPUs, including the Intel x86 series are designed to execute this software after reset without outside help). This software contains rudimentary functionality to search for devices eligible to participate in booting, and load a small program from a special section (most commonly the
boot sector A boot sector is the disk sector, sector of a persistent data storage device (e.g., hard disk, floppy disk, optical disc, etc.) which contains machine code to be loaded into random-access memory (RAM) and then executed by a computer system's bu ...
) of the most promising device, typically starting at a fixed
entry point In computer programming Computer programming is the process of designing and building an executable In computing, executable code, an executable file, or an executable program, sometimes simply referred to as an executable or binary, cau ...

entry point
such as the start of the sector.


First-stage boot loader

Boot loaders may face peculiar constraints, especially in size; for instance, on the IBM PC and compatibles, a boot sector should typically work in only 32 KB (later relaxed to 64 KB) of system memory and only use instructions supported by the original
8088 The Intel 8088 ("''eighty-eighty-eight''", also called iAPX 88) microprocessor A microprocessor is a computer processor where the data processing logic and control is included on a single integrated circuit An integrated circuit or ...
/
8086 The 8086 (also called iAPX 86) is a 16-bit 16-bit microcomputers are computers in which 16-bit microprocessors were the norm. A 16-bit register can store 216 different values. The range (computer programming), range of integer values that can b ...
processors. The first stage of PC boot loaders (FSBL, first-stage boot loader) located on
fixed disk A hard disk drive (HDD), hard disk, hard drive, or fixed disk is an electro-mechanical data storage device File:Reel-to-reel recorder tc-630.jpg, On a reel-to-reel tape recorder (Sony TC-630), the recorder is data storage equipment an ...
s and
removable drive A disk enclosure is a specialized casing designed to hold and power disk drives while providing a mechanism to allow them to communicate to one or more separate computers. Drive enclosures provide power to the drives therein and convert the data ...
s must fit into the first 446
bytes The byte is a unit of digital information that most commonly consists of eight bit The bit is a basic unit of information in computing Computing is any goal-oriented activity requiring, benefiting from, or creating computing machinery. It ...
of the
Master Boot Record A master boot record (MBR) is a special type of boot sector A boot sector is the disk sector, sector of a persistent data storage device (e.g., hard disk, floppy disk, optical disc, etc.) which contains machine code to be loaded into random-a ...
in order to leave room for the default 64-byte
partition table 272x272px, GParted is a popular utility used for disk partitioning Disk partitioning or disk slicing is the creation of one or more regions on secondary storage A spindle of DVD-RW's. Computer data storage is a technology consisting of c ...
with four partition entries and the two-byte boot signature, which the BIOS requires for a proper boot loader — or even less, when additional features like more than four partition entries (up to 16 with 16 bytes each), a disk signature (6 bytes), a disk timestamp (6 bytes), an
Advanced Active Partition A master boot record (MBR) is a special type of boot sector A boot sector is the sector of a persistent data storage device File:Reel-to-reel recorder tc-630.jpg, On a reel-to-reel tape recorder (Sony TC-630), the recorder is data storage ...
(18 bytes) or special
multi-boot 300px, GRUB, with entries for Ubuntu and Windows Vista, an example of ''dual booting'' Multi-booting is the act of installing multiple operating system An operating system (OS) is system software that manages computer hardware, computer soft ...
loaders have to be supported as well in some environments. In
floppy A floppy disk or floppy diskette (sometimes casually referred to as a floppy or diskette) is a type of disk storage Disk storage (also sometimes called drive storage) is a general category of storage mechanisms where data is recorded by vario ...

floppy
and
superfloppy The floppy disk is a data storage and transfer medium that was ubiquitous from the mid-1970s well into the 2000s. Besides the 3Β½-inch and 5ΒΌ-inch formats used in IBM PC compatible systems, or the 8-inch format that preceded them, many propri ...
Volume Boot Record A volume boot record (VBR) (also known as a volume boot sector, a partition boot record or a partition boot sector) is a type of boot sector A boot sector is the disk sector, sector of a persistent data storage device (e.g., hard disk, flopp ...
s, up to 59 bytes are occupied for the
Extended BIOS Parameter Block In computing Computing is any goal-oriented activity requiring, benefiting from, or creating computing machinery. It includes the study and experimentation of algorithmic processes and development of both computer hardware , hardware and softwar ...
on
FAT12 File Allocation Table (FAT) is a file system In computing Computing is any goal-oriented activity requiring, benefiting from, or creating computing machinery. It includes the study and experimentation of algorithmic processes and developm ...
and
FAT16 File Allocation Table (FAT) is a file system In computing Computing is any goal-oriented activity requiring, benefiting from, or creating computing machinery. It includes the study and experimentation of algorithmic processes and develo ...
volumes since DOS 4.0, whereas the
FAT32 File Allocation Table (FAT) is a file system In computing Computing is any goal-oriented activity requiring, benefiting from, or creating computing machinery. It includes the study and experimentation of algorithmic processes and developm ...
EBPB introduced with DOS 7.1 requires even 87 bytes, leaving only 423 bytes for the boot loader when assuming a sector size of 512 bytes. Microsoft boot sectors therefore traditionally imposed certain restrictions on the boot process, for example, the boot file had to be located at a fixed position in the root directory of the file system and stored as consecutive sectors, conditions taken care of by the SYS command and slightly relaxed in later versions of DOS. The boot loader was then able to load the first three sectors of the file into memory, which happened to contain another embedded boot loader able to load the remainder of the file into memory. When Microsoft added LBA and FAT32 support, they even switched to a boot loader reaching over ''two'' physical sectors and using 386 instructions for size reasons. At the same time other vendors managed to squeeze much more functionality into a single boot sector without relaxing the original constraints on only minimal available memory (32 KB) and processor support (8088/8086). For example, DR-DOS boot sectors are able to locate the boot file in the FAT12, FAT16 and FAT32 file system, and load it into memory as a whole via CHS or LBA, even if the file is not stored in a fixed location and in consecutive sectors.
BIOS In computing, BIOS (, ); an acronym for Basic Input/Output System and also known as the System BIOS, ROM BIOS or PC BIOS) is firmware used to perform Computer hardware, hardware initialization during the booting process (power-on startup), and t ...

BIOS
(in x86 system) and
UEFI The Unified Extensible Firmware Interface (UEFI) is a publicly available specification A specification often refers to a set of documented requirements to be satisfied by a material, design, product, or service. A specification is often a type ...
is not only load the
operating system An operating system (OS) is system software System software is software designed to provide a platform for other software. Examples of system software include operating systems (OS) like macOS, Linux, Android (operating system), Android and Mi ...

operating system
from a non-volatile device, it also initializes system hardware for operating system. Examples of first-stage bootloaders include
BIOS In computing, BIOS (, ); an acronym for Basic Input/Output System and also known as the System BIOS, ROM BIOS or PC BIOS) is firmware used to perform Computer hardware, hardware initialization during the booting process (power-on startup), and t ...

BIOS
,
coreboot The software project coreboot, formerly known as LinuxBIOS, is aimed at replacing proprietary ( or ) found in most computers with a lightweight firmware designed to perform only the minimum number of tasks necessary to load and run a modern or ...
, Libreboot and
Das U-Boot Das U-Boot (subtitled "the Universal Boot Loader" and often shortened to U-Boot; see ''History History (from Greek , ''historia'', meaning "inquiry; knowledge acquired by investigation") is the study of the past. Events occurring before the i ...
.


Second-stage boot loader

Second-stage boot loaders, such as
GNU GRUB GNU GRUB (short for GNU GRand Unified Bootloader, commonly referred to as GRUB) is a boot loader A bootloader is software that is responsible for booting In computing, booting is the process of starting a computer. It can be initiated ...
,
rEFInd rEFInd is a boot manager for UEFI The Unified Extensible Firmware Interface (UEFI) is a specification that defines a software interface between an operating system An operating system (OS) is system software that manages computer hardwa ...
,
BOOTMGR The booting, startup process of Windows NT 6 (Windows Vista and later) differ from the startup process part of Windows NT startup process, previous versions of Windows. In this article, unless otherwise specified, what is said about Windows Vist ...
,
Syslinux The Syslinux Project is a suite of five different boot loader A bootloader is software that is responsible for booting a computer. When a computer is turned off, its softwareincluding operating systems, application code, and dataremains stored o ...
,
NTLDR NTLDR (abbreviation An abbreviation (from Latin Latin (, or , ) is a classical language belonging to the Italic branch of the Indo-European languages. Latin was originally spoken in the area around Rome, known as Latium. Through the p ...
or BootX, are not themselves operating systems, but are able to load an operating system properly and transfer execution to it; the operating system subsequently initializes itself and may load extra
device driver In computing Computing is any goal-oriented activity requiring, benefiting from, or creating computing machinery. It includes the study and experimentation of algorithmic processes and development of both computer hardware , hardware and soft ...
s. The second-stage boot loader does not need drivers for its own operation, but may instead use generic storage access methods provided by system firmware such as the BIOS or
Open Firmware Open Firmware is a standard defining the interfaces of a computer firmware In computing Computing is any goal-oriented activity requiring, benefiting from, or creating computing machinery. It includes the study and experimentation of algorith ...
, though typically with restricted hardware functionality and lower performance. Many boot loaders (like GNU GRUB, rEFInd, Windows's BOOTMGR, Syslinux, and Windows NT/2000/XP's NTLDR) can be configured to give the user multiple booting choices. These choices can include different operating systems (for dual or multi-booting from different partitions or drives), different versions of the same operating system (in case a new version has unexpected problems), different operating system loading options (e.g., booting into a rescue or safe mode), and some standalone programs that can function without an operating system, such as memory testers (e.g.,
memtest86+ MemTest86 and Memtest86+ are memory test software programs designed to test and stress testStress test may refer to: *Cardiac stress test, testing of the heart (a.k.a. "treadmill test") *Stress testing of software, hardware, or nuclear plants ...
), a basic shell (as in GNU GRUB), or even games (see
List of PC Booter games Many IBM PC compatible games released between 1981 and about 1990 were self-booting and did not use an existing operating system such as MS-DOS or IBM PC DOS. The phrase "IBM PC compatible self-booting disk" is often shortened to "PC booter". Self- ...
). Some boot loaders can also load other boot loaders; for example, GRUB loads BOOTMGR instead of loading Windows directly. Usually, a default choice is preselected with a time delay during which a user can press a key to change the choice; after this delay, the default choice is automatically run so normal booting can occur without interaction. The boot process can be considered complete when the computer is ready to interact with the user, or the operating system is capable of running system programs or application programs. Many
embedded system An embedded system is a computer system A computer is a machine that can be programmed to carry out Sequence, sequences of arithmetic or logical operations automatically. Modern computers can perform generic sets of operations known as Co ...
s must boot immediately. For example, waiting a minute for a
digital television Digital television (DTV) is the transmission of television audiovisual Audiovisual (AV) is electronic media 200px, Graphical representations of electrical audio data. Electronic media uses either analog (red) or digital (blue) signal pr ...
or a
GPS navigation device A satellite navigation device, colloquially called a GPS receiver, or simply a GPS, is a device that is capable of receiving information from GNSS satellites and then calculate the device's geographical position. Using suitable software, the d ...
to start is generally unacceptable. Therefore, such devices have software systems in ROM or
flash memory Flash memory is an electronic Electronic may refer to: *Electronics Electronics comprises the physics, engineering, technology and applications that deal with the emission, flow and control of electrons in vacuum and matter. It uses act ...
so the device can begin functioning immediately; little or no loading is necessary, because the loading can be precomputed and stored on the ROM when the device is made. Large and complex systems may have boot procedures that proceed in multiple phases until finally the operating system and other programs are loaded and ready to execute. Because operating systems are designed as if they never start or stop, a boot loader might load the operating system, configure itself as a mere process within that system, and then irrevocably transfer control to the operating system. The boot loader then terminates normally as any other process would.


Network booting

Most computers are also capable of booting over a
computer network A computer network is a set of computer A computer is a machine that can be programmed to Execution (computing), carry out sequences of arithmetic or logical operations automatically. Modern computers can perform generic sets of operati ...
. In this scenario, the operating system is stored on the disk of a
server Server may refer to: Computing *Server (computing) In computing Computing is any goal-oriented activity requiring, benefiting from, or creating computing machinery. It includes the study and experimentation of algorithmic processes and dev ...
, and certain parts of it are transferred to the client using a simple protocol such as the
Trivial File Transfer Protocol Trivial File Transfer Protocol (TFTP) is a simple lockstep In the United States, lockstep marching or simply lockstep is marching in a very close single file (formation), file in such a way that the leg of each person in the file moves in the same ...
(TFTP). After these parts have been transferred, the operating system takes over the control of the booting process. As with the second-stage boot loader, network booting begins by using generic network access methods provided by the network interface's boot ROM, which typically contains a
Preboot Execution Environment In computing, the Preboot eXecution Environment, PXE (most often pronounced as ''pixie'', often called PXE Boot/''pixie boot''.) specification describes a standardized client–server model, client–server environment that booting, boots a sof ...
(PXE) image. No drivers are required, but the system functionality is limited until the operating system kernel and drivers are transferred and started. As a result, once the ROM-based booting has completed it is entirely possible to network boot into an operating system that itself does not have the ability to use the network interface.


See also

*
Comparison of boot loaders The following tables compare general and technical information for a number of available boot loaders. General information Technical information Note: The column MBR (Master Boot Record) refers to whether or not the boot loader can be stored ...


Notes


References

{{reflist, refs= {{Cite book , title=The MS-DOS Encyclopedia: versions 1.0 through 3.2 , author-first1=Ray , author-last1=Duncan , author-first2=Steve , author-last2=Bostwick , author-first3=Keith , author-last3=Burgoyne , author-first4=Robert A. , author-last4=Byers , author-first5=Thom , author-last5=Hogan , author-first6=Jim , author-last6=Kyle , author-first7=Gordon , author-last7=Letwin , author-link7=Gordon Letwin , author-first8=Charles , author-last8=Petzold , author-link8=Charles Petzold , author-first9=Chip , author-last9=Rabinowitz , author-first10=Jim , author-last10=Tomlin , author-first11=Richard , author-last11=Wilton , author-first12=Van , author-last12=Wolverton , author-first13=William , author-last13=Wong , author-first14=JoAnne , author-last14=Woodcock , contribution=Technical advisors , contributor-first1=Mark , contributor-last1=Zbikowski , contributor-link1=Mark Zbikowski , contributor-first2=Paul , contributor-last2=Allen , contributor-link2=Paul Allen , contributor-first3=Steve , contributor-last3=Ballmer , contributor-link3=Steve Ballmer , contributor-first4=Reuben , contributor-last4=Borman , contributor-first5=Rob , contributor-last5=Borman , contributor-first6=John , contributor-last6=Butler , contributor-first7=Chuck , contributor-last7=Carroll , contributor-first8=Mark , contributor-last8=Chamberlain , contributor-first9=David , contributor-last9=Chell , contributor-first10=Mike , contributor-last10=Colee , contributor-first11=Mike , contributor-last11=Courtney , contributor-first12=Mike , contributor-last12=Dryfoos , contributor-first13=Rachel , contributor-last13=Duncan , contributor-first14=Kurt , contributor-last14=Eckhardt , contributor-first15=Eric , contributor-last15=Evans , contributor-first16=Rick , contributor-last16=Farmer , contributor-first17=Bill , contributor-last17=Gates , contributor-link17=Bill Gates , contributor-first18=Michael , contributor-last18=Geary , contributor-first19=Bob , contributor-last19=Griffin , contributor-first20=Doug , contributor-last20=Hogarth , contributor-first21=James W. , contributor-last21=Johnson , contributor-first22=Kaamel , contributor-last22=Kermaani , contributor-first23=Adrian , contributor-last23=King , contributor-first24=Reed , contributor-last24=Koch , contributor-first25=James , contributor-last25=Landowski , contributor-first26=Chris , contributor-last26=Larson , contributor-first27=Thomas , contributor-last27=Lennon , contributor-first28=Dan , contributor-last28=Lipkie , contributor-first29=Marc , contributor-last29=McDonald , contributor-link29=Marc McDonald , contributor-first30=Bruce , contributor-last30=McKinney , contributor-first31=Pascal , contributor-last31=Martin , contributor-first32=Estelle , contributor-last32=Mathers , contributor-first33=Bob , contributor-last33=Matthews , contributor-first34=David , contributor-last34=Melin , contributor-first35=Charles , contributor-last35=Mergentime , contributor-first36=Randy , contributor-last36=Nevin , contributor-first37=Dan , contributor-last37=Newell , contributor-first38=Tani , contributor-last38=Newell , contributor-first39=David , contributor-last39=Norris , contributor-first40=Mike , contributor-last40=O'Leary , contributor-first41=Bob , contributor-last41=O'Rear , contributor-link41=Bob O'Rear , contributor-first42=Mike , contributor-last42=Olsson , contributor-first43=Larry , contributor-last43=Osterman , contributor-first44=Ridge , contributor-last44=Ostling , contributor-first45=Sunil , contributor-last45=Pai , contributor-first46=Tim , contributor-last46=Paterson , contributor-link46=Tim Paterson , contributor-first47=Gary , contributor-last47=Perez , contributor-first48=Chris , contributor-last48=Peters , contributor-first49=Charles , contributor-last49=Petzold , contributor-link49=Charles Petzold , contributor-first50=John , contributor-last50=Pollock , contributor-first51=Aaron , contributor-last51=Reynolds , contributor-link51=Aaron R. Reynolds , contributor-first52=Darryl , contributor-last52=Rubin , contributor-first53=Ralph , contributor-last53=Ryan , contributor-first54=Karl , contributor-last54=Schulmeisters , contributor-first55=Rajen , contributor-last55=Shah , contributor-first56=Barry , contributor-last56=Shaw , contributor-first57=Anthony , contributor-last57=Short , contributor-first58=Ben , contributor-last58=Slivka , contributor-first59=Jon , contributor-last59=Smirl , contributor-first60=Betty , contributor-last60=Stillmaker , contributor-first61=John , contributor-last61=Stoddard , contributor-first62=Dennis , contributor-last62=Tillman , contributor-first63=Greg , contributor-last63=Whitten , contributor-first64=Natalie , contributor-last64=Yount , contributor-first65=Steve , contributor-last65=Zeck , date=1988 , edition=Completely reworked , publisher=
Microsoft Press Microsoft Press is the publishing arm of Microsoft, usually releasing books dealing with various current Microsoft technologies. Microsoft Press' first introduced books were ''The Apple Macintosh Book'' by Cary Lu and ''Exploring the IBM PCjr Home ...
, location=Redmond, Washington, USA , isbn=1-55615-049-0 , lccn=87-21452 , oclc=16581341 (xix+1570 pages; 26 cm) (NB. This edition was published in 1988 after extensive rework of the withdrawn 1986 first edition by a different team of authors

{{cite book , title=DOS Internals , author-first=Geoff , author-last=Chappell , chapter=Chapter 2: The System Footprint , editor-first1=Andrew , editor-last1=Schulman , editor-first2=Amorette , editor-last2=Pedersen , date=January 1994 , edition=1st printing, 1st , series=The Andrew Schulman Programming Series , publisher= Addison Wesley Publishing Company , isbn=978-0-201-60835-9 (xxvi+738+iv pages, 3.5"-flopp

https://web.archive.org/web/20200222111608/https://www.pcjs.org/pubs/pc/programming/DOS_Internals/]) Errata

https://web.archive.org/web/20200222111853/https://gopher.tildeverse.org/gopher.viste.fr/1/programming/PC/DOS/DOS%2520Internals/crtdrv

/ref> {{cite magazine , title=DR DOS 5.0 - The better operating system? , author-first=Winn L. , author-last=Rosch , magazine=
PC Magazine ''PC Magazine'' (shortened as ''PCMag'') is an American computer magazine Computer magazines are about computers and related subjects, such as computer network, networking and the Internet. Most computer magazines offer (or offered) advice, so ...
, date=1991-02-12 , volume=10 , number=3 , page=241-246, 257, 264, 266 , url=https://books.google.com/books?id=YxFTezF9-sMC&pg=PT250 , access-date=2019-07-26 , url-status=live , archive-url=https://archive.today/20190725223320/https://books.google.nl/books?id=YxFTezF9-sMC&pg=PT250&lpg=PT250&redir_esc=y%23v=onepage&q&f=false , archive-date=25 July 2019 , quote= €¦ SYS has been improved under DR DOS 5.0 so you don't have to worry about leaving the first cluster free on a disk that you want to make bootable. The DR DOS system files can be located anywhere on the disk, so any disk with enough free space can be set to boot your system. €¦ (NB. The source attributes this to the SYS utility while in fact this is a feature of the advanced bootstrap loader in the boot sector. SYS just plants this sector onto the disk.)
{{anchor, Paul_1997_ODA3{{cite web , author-first=Matthias R. , author-last=Paul , title=Caldera OpenDOS 7.01/7.02 Update Alpha 3 IBMBIO.COM - README.TXT and BOOT.TXT - A short description of how OpenDOS is booted , url=http://www.uni-bonn.de/~uzs180/download/ibmbioa3.zip , date=1997-10-02 , orig-year=1997-09-29 , access-date=2009-03-29 , url-status=dead , archive-url=https://web.archive.org/web/20031004074600/http://www-student.informatik.uni-bonn.de/~frinke/ibmbioa3.zip , archive-date=2003-10-04}
Op702src.zip is an unofficial renamed distribution of the ibmbioa3.zip file -->
/ref> {{cite web , title=FAT32 in DR-DOS , author-first=Matthias R. , author-last=Paul , date=2001-01-17 , work=opendos@delorie , url=http://www.delorie.com/opendos/archives/browse.cgi?p=opendos/2001/01/17/02:29:47 , access-date=2017-10-06 , url-status=live , archive-url=https://web.archive.org/web/20171006205537/http://www.delorie.com/opendos/archives/browse.cgi?p=opendos%2F2001%2F01%2F17%2F02%3A29%3A47 , archive-date=2017-10-06 , quote= €¦The
DR-DOS DR-DOS (written as DR DOS, without a hyphen, in versions up to and including 6.0) is an operating system of the DOS family, written for IBM PC-PC compatible, compatible personal computers. It was originally developed by Gary A. Kildall's ...
boot sector €¦searches for the
IBMBIO.COM IBMBIO.COM is a system file in many DOS operating systems. It contains the system initialization code and all built-in device drivers. It also loads the DOS kernel ( IBMDOS.COM) and optional pre-loadable system components (like for disk compre ...
( DRBIOS.SYS) file and then loads the *whole* file into memory before it passes control to it. €¦}
{{cite web , title=Can't copy , author-first=Matthias R. , author-last=Paul , date=2002-02-20 , work=opendos@delorie , url=http://www.delorie.com/opendos//archives/browse.cgi?p=opendos/2002/02/20/16:17:57 , access-date=2017-10-06 , url-status=live , archive-url=https://web.archive.org/web/20171006211007/http://www.delorie.com/opendos//archives/browse.cgi?p=opendos%2F2002%2F02%2F20%2F16%3A17%3A57 , archive-date=2017-10-06 , quote= €¦The
DR-DOS DR-DOS (written as DR DOS, without a hyphen, in versions up to and including 6.0) is an operating system of the DOS family, written for IBM PC-PC compatible, compatible personal computers. It was originally developed by Gary A. Kildall's ...
boot sector loads the whole
IBMBIO.COM IBMBIO.COM is a system file in many DOS operating systems. It contains the system initialization code and all built-in device drivers. It also loads the DOS kernel ( IBMDOS.COM) and optional pre-loadable system components (like for disk compre ...
file into memory before it executes it. It does not care at all about the IBMDOS.COM file, which is loaded by IBMBIO.COM. €¦The DR-DOS boot sector €¦will find the €¦kernel files as long as they are logically stored in the root directory. Their physical location on the disk, and if they are fragmented or not, is don't care for the DR-DOS boot sector. Hence, you can just copy the kernel files to the disk (even with a simply
COPY Copy may refer to: * Copying or the product of copying (including the plural "copies"); the duplication of information or an artifact ** Cut, copy and paste, a method of reproducing text or other data in computing ** File copying ** Photocopying, a ...
), and as soon as the boot sector is a DR-DOS sector, it will find and load them. Of course, it is difficult to put all this into just 512 bytes, the size of a single sector, but this is a major convenience improvement if you have to set up a DR-DOS system, and it is also the key for the DR-DOS multi-OS
LOADER Loader can refer to: * Loader (equipment) * Loader (computing) ** LOADER.EXE, an auto-start program loader optionally used in the startup process of Microsoft Windows ME * Loader (surname) * Fast loader * Speedloader * Boot loader ** LOADER.COM (ak ...
utility to work. The
MS-DOS MS-DOS ( ; acronym for Microsoft Disk Operating System, also known as Microsoft DOS) is an operating system An operating system (OS) is system software System software is software designed to provide a platform for other software. Example ...
kernel files must reside on specific locations, but the DR-DOS files can be anywhere, so you don't have to physically swap them around each time you boot the other OS. Also, it allows to upgrade a DR-DOS system simply by copying the kernel files over the old ones, no need for SYS, no difficult setup procedures as required for MS-DOS/ PC DOS. You can even have multiple DR-DOS kernel files under different file names stored on the same drive, and LOADER will switch between them according to the file names listed in the BOOT.LST file. €¦}
{{cite web , title=The continuing saga of Windows 3.1 in enhanced mode on OmniBook 300 , author-first=Matthias R. , author-last=Paul , orig-year=2017-08-07 , date=2017-08-14 , work=MoHPC - the Museum of HP Calculators , url=http://hpmuseum.org/forum/thread-8774-post-76925.html#pid76925 , access-date=2017-10-06 , url-status=live , archive-url=https://web.archive.org/web/20171006204718/http://hpmuseum.org/forum/thread-8774-post-76925.html , archive-date=2017-10-06 , quote= €¦the
DR-DOS DR-DOS (written as DR DOS, without a hyphen, in versions up to and including 6.0) is an operating system of the DOS family, written for IBM PC-PC compatible, compatible personal computers. It was originally developed by Gary A. Kildall's ...
FDISK #REDIRECT fdisk#REDIRECT fdisk In computing Computing is any goal-oriented activity requiring, benefiting from, or creating computing machinery. It includes the study and experimentation of algorithmic processes and development of both computer ...
does not only partition a disk, but can also format the freshly created volumes and initialize their boot sectors in one go, so there's no risk to accidentally mess up the wrong volume and no need for FORMAT /S or SYS. Afterwards, you could just copy over the remaining DR-DOS files, including the system files. It is important to know that, in contrast to
MS-DOS MS-DOS ( ; acronym for Microsoft Disk Operating System, also known as Microsoft DOS) is an operating system An operating system (OS) is system software System software is software designed to provide a platform for other software. Example ...
/ PC DOS, DR-DOS has "smart" boot sectors which will actually "mount" the file-system to search for and load the system files in the root directory instead of expecting them to be placed at a certain location. Physically, the system files can be located anywhere and also can be fragmented. €¦}


External links


Bootloader - OSDev Wiki
Boot loaders