1843:
380:
1851:
766:
4158:
4148:
4138:
4128:
4118:
807:. The next bit (bit 2) specifies whether the operation is used with the GDT or the LDT. The lowest two bits (bit 1 and bit 0) of the selector are combined to define the privilege of the request, where the values of 0 and 3 represent the highest and the lowest privilege, respectively. This means that the byte offset of descriptors in the descriptor table is the same as the 16-bit selector, provided the lower three bits are zeroed.
351:, equivalent to 256 KB, could be accessed at a time. Because changing a segment register in protected mode caused a 6-byte segment descriptor to be loaded into the CPU from memory, the segment register load instruction took many tens of processor cycles, making it much slower than on the 8086; therefore, the strategy of computing segment addresses on-the-fly in order to access data structures larger than 128
611:
398:. The segment sizes were also increased to 32 bits, meaning that the full address space of 4 gigabytes could be accessed without the need to switch between multiple segments. In addition to the increased size of the address bus and segment registers, many other new features were added with the intention of increasing operational security and stability. Protected mode is now used in virtually all modern
259:(386) in 1985. Due to the enhancements added by protected mode, it has become widely adopted and has become the foundation for all subsequent enhancements to the x86 (IA-32) architecture, although many of those enhancements, such as added instructions and new registers, also brought benefits to the real mode.
1963:
series. If a
Windows 1.x or 2.x program is written properly and avoids segment arithmetic, it will run the same way in both real and protected modes. Windows programs generally avoid segment arithmetic because Windows implements a software virtual memory scheme, moving program code and data in memory
3124:
The reason why software task switching is so popular is that it can be faster than hardware task switching. Intel never actually developed the hardware task switching, they implemented it, saw that it worked, and just left it there. Advances in multitasking using software have made this form of task
366:
to run unmodified on the newer 286. Real mode also served as a more basic mode in which protected mode could be set up, solving a sort of chicken-and-egg problem. To access the extended functionality of the 286, the operating system would set up some tables in memory that controlled memory access in
1968:
to memory blocks when not running. Starting an old program while
Windows 3.0 is running in protected mode triggers a warning dialog, suggesting to either run Windows in real mode or to obtain an updated version of the application. Updating well-behaved programs using the MARK utility with the
778:
In real mode each logical address points directly into a physical memory location, every logical address consists of two 16-bit parts: The segment part of the logical address contains the base address of a segment with a granularity of 16 bytes, i.e. a segment may start at physical address 0, 16,
1958:
was able to run real mode programs in 16-bit protected mode; when switching to protected mode, it decided to preserve the single privilege level model that was used in real mode, which is why
Windows applications and DLLs can hook interrupts and do direct hardware access. That lasted through the
1858:
In addition to adding virtual 8086 mode, the 386 also added paging to protected mode. Through paging, system software can restrict and control a task's access to pages, which are sections of memory. In many operating systems, paging is used to create an independent virtual address space for each
1886:
to a page table. A page table was also originally four kilobytes in size and contained 1,024 page table entries (PTE). Each PTE contained a pointer to the actual page's physical address and are only used when the four-kilobyte pages are used. At any given time, only one page directory may be in
822:
The segment address inside the descriptor table entry has a length of 24 bits so every byte of the physical memory can be defined as bound of the segment. The limit value inside the descriptor table entry has a length of 16 bits so segment length can be between 1 byte and 2 byte. The calculated
595:
Protected mode has a number of features designed to enhance an operating system's control over application software, in order to increase security and system stability. These additions allow the operating system to function in a way that would be significantly more difficult or even impossible
847:
For maintaining compatibility with 286 protected mode a new default flag (D-bit, for short) was added. If the D-bit of a code segment is off (0) all commands inside this segment will be interpreted as 16-bit commands by default; if it is on (1), they will be interpreted as 32-bit commands.
1913:
was made possible on the x86 architecture. The TSS allows general-purpose registers, segment selector fields, and stacks to all be modified without affecting those of another task. The TSS also allows a task's privilege level, and I/O port permissions to be independent of another task's.
1917:
In many operating systems, the full features of the TSS are not used. This is commonly due to portability concerns or due to the performance issues created with hardware task switches. As a result, many operating systems use both hardware and software to create a multitasking system.
831:
The segment address inside the descriptor table entry is expanded to 32 bits so every byte of the physical memory can be defined as bound of the segment. The limit value inside the descriptor table entry is expanded to 20 bits and completed with a granularity flag (G-bit, for short):
343:. Several shortcomings such as the inability to make BIOS and DOS calls due to inability to switch back to real mode without resetting the processor prevented widespread usage. Acceptance was additionally hampered by the fact that the 286 only allowed memory access in 64
504:(21st address line) also must be enabled to allow the use of all the address lines so that the CPU can access beyond 1 megabyte of memory (Only the first 20 are allowed to be used after power-up, to guarantee compatibility with older software written for the Intel 8088-based
839:
If G-bit is one limit has a granularity of 2 bytes, i.e. segment size may be 1 × 2, 2 × 2, ..., 2 × 2 bytes. If paging is off, the calculated linear address equals the physical memory address. If paging is on, the calculated linear address is used as input of
367:
protected mode, set the addresses of those tables into some special registers of the processor, and then set the processor into protected mode. This enabled 24-bit addressing, which allowed the processor to access 2 bytes of memory, equivalent to 16
586:
With the release of the 386, protected mode could be exited by loading the segment registers with real mode values, disabling the A20 line and clearing the PE bit in the CR0 register, without the need to perform the initial setup steps required with the 286.
393:
With the release of the 386 in 1985, many of the issues preventing widespread adoption of the previous protected mode were addressed. The 386 was released with an address bus size of 32 bits, which allows for 2 bytes of memory accessing, equivalent to 4
1882:. Originally, a page directory was the size of one page, four kilobytes, and contained 1,024 page directory entries (PDE), although subsequent enhancements to the x86 architecture have added the ability to use larger page sizes. Each PDE contained a
742:
Due to these limitations, some programs originally designed to run on the 8086 cannot be run in virtual 8086 mode. As a result, system software is forced to either compromise system security or backward compatibility when dealing with
779:
32, ..., 2 − 16. The offset part of the logical address contains an offset inside the segment, i.e. the physical address can be calculated as physical_address = segment_part × 16 + offset, if the address
3052:
The paging process allows the operating system to overcome the real physical memory limits. However, it also has a direct impact on performance because of the time necessary to write or retrieve data from
493:
was used to reset the 286 CPU, which was a lot faster and cleaner than the keyboard controller method (and does not depend on IBM AT-compatible hardware, but will work on any 80286 CPU in any system).
646:
the 80286 remains upwardly compatible with most 8086 and 80186 application programs. Most 8086 application programs can be re-compiled or re-assembled and executed on the 80286 in
Protected Mode.
3033:
654:, were the most apparent changes to application programmers. This was not without its limitations. If an application utilized or relied on any of the techniques below, it would not run:
723:
Virtual 8086 mode, however, is not completely backward compatible with all programs. Programs that require segment manipulation, privileged instructions, direct hardware access, or use
720:. Virtual 8086 mode is designed to allow code previously written for the 8086 to run unmodified and concurrently with other tasks, without compromising security or system stability.
489:
and often the interrupt mask in the real-time clock chip's RAM. This allowed the BIOS to restore the CPU to a similar state and begin executing code before the reset. Later, a
2083:
The memory access control system according to claim 4, wherein said first address mode is a real address mode, and said second address mode is a protected virtual address mode.
2911:
2891:
2682:
2664:
2646:
2628:
500:(GDT) must first be created with a minimum of three entries: a null descriptor, a code segment descriptor and data segment descriptor. In an IBM-compatible machine, the
2951:
A downside to using V86 mode is speed: every IOPL-sensitive instruction will cause the CPU to trap to kernel mode, as will I/O to ports which are masked out in the TSS.
622:, numbered from 0 to 3, with ring 0 being the most privileged and 3 being the least. The use of rings allows for system software to restrict tasks from accessing data,
2722:
2508:
2261:
2207:
2155:
2098:
1969:
MEMORY parameter avoids this dialog. It is not possible to have some GUI programs running in 16-bit protected mode and other GUI programs running in real mode. In
232:
with earlier x86 processors. Protected mode may only be entered after the system software sets up one descriptor table and enables the
Protection Enable (PE)
2176:
2140:
The purpose of protected mode is not to protect your program. The purpose is to protect everyone else (including the operating system) from your program.
3125:
switching faster (some say up to 3 times faster) than the hardware method. Another reason is that the Intel way of switching tasks isn't portable at all
2818:
This has been impossible to-date and has forced BIOS development teams to add support into the BIOS for 32 bit function calls from 32 bit applications.
2398:
3285:
2230:
3037:
2780:
2761:
2742:
168:
4182:
4098:
477:
Until the release of the 386, protected mode did not offer a direct method to switch back into real mode once protected mode was entered.
3759:
3232:
3180:
2356:
2576:
1930:
1.x try to switch the processor between protected and real modes. This is both slow and unsafe, because a real mode program can easily
355:(the combined size of the two data segments) became impractical, even for those few programmers who had mastered it on the 8086/8088.
2700:
2489:
2060:
650:
For the most part, the binary compatibility with real-mode code, the ability to access up to 16 MB of physical memory, and 1 GB of
3807:
2183:
512:
models). After performing those two steps, the PE bit must be set in the CR0 register and a far jump must be made to clear the
3138:
3101:
2286:
4151:
3955:
3779:
3561:
3532:
2683:"Intel 64 and IA-32 Architectures Software Developer's Manual Combined Volumes 3A, 3B, 3C, and 3D: System Programming Guide"
2665:"Intel 64 and IA-32 Architectures Software Developer's Manual Combined Volumes 3A, 3B, 3C, and 3D: System Programming Guide"
2647:"Intel 64 and IA-32 Architectures Software Developer's Manual Combined Volumes 3A, 3B, 3C, and 3D: System Programming Guide"
2629:"Intel 64 and IA-32 Architectures Software Developer's Manual Combined Volumes 3A, 3B, 3C, and 3D: System Programming Guide"
4141:
2913:
Intel 64 and IA-32 Architectures
Software Developer's Manual Combined Volumes 3A, 3B, 3C, and 3D: System Programming Guide
2893:
Intel 64 and IA-32 Architectures
Software Developer's Manual Combined Volumes 3A, 3B, 3C, and 3D: System Programming Guide
2616:
80386SX — low cost version of the 80386. This processor had 16 bit external data bus and 24-bit external address bus.
4161:
2315:
2972:
2541:
2464:
161:
3066:
3336:
3280:
2334:
What is interesting is that the designers of the time never suspected anyone would ever need more than 1 MB of RAM.
1859:
task, preventing one task from manipulating the memory of another. Paging also allows for pages to be moved out of
2850:... secondly, protected mode was also incompatible with the vast amount of real-mode code around at the time.
3978:
3752:
3255:
3225:
362:
on power up. Real mode functioned virtually identically to the 8086, allowing the vast majority of existing 8086
1842:
4103:
3448:
3346:
2429:
1883:
731:
that must be served by the operating system. In addition, applications running in virtual 8086 mode generate a
2932:
2863:
2831:
3726:
3275:
3260:
1682:
bit, and determines which privilege levels can far-jump to this segment (without changing privilege level):
783:
is enabled, or (segment_part × 16 + offset) mod 2, if A20 is off. Every segment has a size of 2 bytes.
313:
As the cost of memory decreased and memory use increased, the 1 MB limitation became a significant problem.
4187:
3963:
3801:
3321:
3306:
3265:
2405:
1981:
154:
3190:
1964:
when programs are not running, so manipulating absolute addresses is dangerous; programs should only keep
694:
and its successors can take advantage of the binary compatibility with real mode to run many
Windows 2.x (
3940:
3487:
3434:
332:
20:
4121:
4008:
3998:
3988:
3841:
3745:
3502:
3341:
3218:
2448:
3161:... both rely on the Intel processors ability to switch tasks, they rely on it in different ways.
2234:
290:. At the time, 1 megabyte was considered a relatively large amount of memory, so the designers of the
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3537:
3356:
3316:
3311:
3270:
224:
When a processor that supports x86 protected mode is powered on, it begins executing instructions in
132:
331:
The initial protected mode, released with the 286, was not widely used; for example, it was used by
3927:
3580:
3467:
3331:
2529:
2453:
2036:
619:
605:
509:
482:
4131:
3993:
3968:
3874:
3326:
1910:
760:
497:
194:
836:
If G-bit is zero limit has a granularity of 1 byte, i.e. segment size may be 1, 2, ..., 2 bytes.
485:) which involved resetting the CPU via the keyboard controller and saving the system registers,
425:
required for virtualizing the protected mode itself, however, had to wait for another 20 years.
3945:
3897:
3795:
3714:
3653:
3542:
3522:
3471:
3429:
229:
98:
3175:
2360:
358:
The 286 maintained backward compatibility with its precursor (the 8086) by initially entering
3973:
3497:
3463:
3365:
3301:
2041:
1896:
814:
address of the segment, a limit value for the segment size, and some attribute bits (flags).
505:
433:
With the release of the 386, the following additional features were added to protected mode:
291:
214:
2122:
3694:
3668:
2993:
1875:
513:
413:
Furthermore, learning from the failures of the 286 protected mode to satisfy the needs for
218:
2788:. Santa Clara, California: Intel. 1987. Appendix C 8086/8088 Compatibility Considerations.
626:
or executing privileged instructions. In most environments, the operating system and some
8:
3851:
3663:
3615:
3492:
2724:
Intel 64 and IA-32 Architectures
Software Developer's Manual Volume 1: Basic Architecture
2510:
Intel 64 and IA-32 Architectures
Software Developer's Manual Volume 1: Basic Architecture
2263:
Intel 64 and IA-32 Architectures Software Developer's Manual Volume 1: Basic Architecture
2209:
Intel 64 and IA-32 Architectures Software Developer's Manual Volume 1: Basic Architecture
2157:
Intel 64 and IA-32 Architectures Software Developer's Manual Volume 1: Basic Architecture
2100:
Intel 64 and IA-32 Architectures Software Developer's Manual Volume 1: Basic Architecture
1989:
724:
667:
202:
3185:
2068:
2008:, all under control of a 32-bit kernel. However, 64-bit operating systems (which run in
379:
19:
This article is about the x86 processor mode. For Internet Explorer Protected Mode, see
4093:
4077:
4003:
3600:
3507:
3195:
1993:
1906:
1871:. This allows for more memory to be used than physically available in primary storage.
728:
422:
118:
3869:
3768:
3709:
3658:
3590:
3547:
3388:
2968:
2537:
2460:
2026:
1977:
1931:
1864:
711:
687:
466:
418:
403:
299:
88:
4046:
4041:
3884:
3689:
3241:
3146:
3109:
2129:
732:
399:
237:
4036:
3935:
3633:
3595:
3566:
2602:
2556:
2497:. Santa Clara, CA: Intel. 1986. Section 2.1 Memory Organization and Segmentation.
2384:
1868:
1860:
317:
intended to solve this limitation along with others with the release of the 286.
279:
198:
122:
102:
3200:
2799:
765:
421:, which allowed multiple virtualized 8086 processors to be emulated on the 386.
4051:
4018:
4013:
3818:
3719:
3643:
3605:
3477:
3085:
Only one page directory may be active at a time, indicated by the CR3 register.
2012:) no longer use this, since virtual 8086 mode has been removed from long mode.
716:
With the release of the 386, protected mode offers what the Intel manuals call
651:
457:
206:
34:
1850:
4176:
4028:
3831:
3826:
3628:
3585:
3424:
3378:
2053:
1997:
1965:
744:
627:
446:
414:
126:
112:
3007:
2319:
3512:
3205:
1985:
751:, which dropped backward compatibility for "ill-behaved" DOS applications.
736:
699:
490:
3070:
4072:
3638:
3620:
3403:
3393:
3383:
2561:
2270:. May 2019. Section 2.1 Brief History of Intel 64 and IA-32 Architecture.
1970:
1955:
702:) applications in protected mode, which ran in real mode in Windows 2.x.
695:
691:
678:
Use of BIOS functions, due to the BIOS interrupts being reserved by Intel
388:
326:
275:
92:
82:
78:
72:
2769:. Santa Clara, California: Intel. 1987. Section 1.3.1 Memory Management.
3836:
2792:
2005:
1960:
1936:
1879:
799:, in which the 13 upper bits (bit 3 to bit 15) contain the index of an
748:
486:
307:
268:
58:
52:
2000:(e.g. for changing the screen-resolution using BIOS functionality) in
1934:
a computer. OS/2 1.x defines restrictive programming rules allowing a
614:
Example of privilege ring usage in an operating system using all rings
3983:
3864:
3575:
3482:
3408:
3373:
2021:
2009:
1902:
686:
application programs violated these rules. Due to these limitations,
623:
395:
359:
225:
108:
48:
3737:
3210:
2433:
347:
segments, addresed by its four segment registers, meaning that only
3917:
3912:
3902:
3892:
3704:
3186:
Overview of the Protected Mode Operations of the Intel Architecture
2936:
2867:
2835:
1700:= 1 then code with the same or a lower privilege level relative to
780:
501:
368:
363:
352:
344:
295:
287:
844:
The 386 processor also uses 32 bit values for the address offset.
747:. An example of such a compromise can be seen with the release of
3907:
3699:
3398:
450:
62:
2800:"Memory access control method and system for realizing the same"
2061:"Memory access control method and system for realizing the same"
453:, and other 386 processor variants which use the older 286 bus.)
2750:. Santa Clara, CA: Intel. 1987. Section 1.2 Modes of Operation.
2689:. Section 9.9.2 Switching Back to Real-Address Mode, page 9-14.
1973:, real mode was no longer supported and could not be accessed.
1846:
Common method of using paging to create a virtual address space
1837:
442:
437:
210:
136:
690:
was introduced with the 386. Despite such potential setbacks,
271:, a predecessor to the 286, was originally designed with a 20-
3648:
2917:
2897:
2728:
2686:
2668:
2650:
2632:
2514:
2267:
2213:
2161:
2104:
2031:
610:
407:
340:
336:
314:
256:
252:
248:
2855:
1944:
program to run in either real or protected mode. Some early
255:(286) processor, and later extended with the release of the
2385:"General Information FAQ for the Coherent Operating System"
2116:
2114:
2001:
1949:
1945:
1927:
1826:
Bit 52 of the 80386 descriptor is not used by the hardware.
1783:
bit, which should generally be cleared for system segments;
303:
283:
2731:. May 2019. Section 6.3.5 Calls to Other Privilege Levels.
3684:
2773:
2216:. May 2019. Section 2.1.2 The Intel 286 Processor (1982).
2150:
2148:
2107:. May 2019. Section 2.1.3 The Intel 386 Processor (1985).
1874:
The x86 architecture allows control of pages through two
683:
478:
449:(The 32-bit physical address space is not present on the
272:
244:
233:
190:
38:
3206:
Akernelloader switching from real mode to protected mode
2708:. Santa Clara, CA: Intel. 1986. Chapter 7, Multitasking.
2111:
851:
572:; clear prefetch queue; (using far jump instruction jmp)
217:
designed to increase an operating system's control over
3058:
3780:
Memory management as a function of an operating system
3191:
TurboIRC.COM tutorial to enter protected mode from DOS
2168:
2145:
633:
618:
In protected mode, there are four privilege levels or
472:
2294:
PC Microprocessor Developments and Features Tutorials
463:
Ability to switch back to real mode without resetting
298:
for use by applications and the operating system and
2530:"12.10. Protected Mode Operation and Device Drivers"
1689:= 0 then only code with the same privilege level as
2962:
2594:
2559:, Intel's 32-bit Wonder: The 80386 Microprocessor,
2484:
2482:
2225:
2223:
823:linear address equals the physical memory address.
2920:. May 2019. Section 20.2.7 Sensitive Instructions.
2754:
2521:
2452:
428:
3036:. Microsoft TechNet. May 28, 2003. Archived from
3008:"ProtectedMode overview [deinmeister.de]"
3000:
2904:
2823:
2735:
2635:. Section 21.33.1 Segment Wraparound, page 21-34.
4174:
2671:. Section 9.10.2 STARTUP.ASM Listing, page 9-19.
2479:
2220:
2200:
2093:
2091:
1992:) or Windows 3.x applications (through the
739:(I/O), which can negatively impact performance.
3028:
3026:
2924:
2653:. 9.9.1 Switching to Protected Mode, page 9-13.
2350:
2348:
2346:
2344:
2342:
2963:Dabak, Prasad; Millind Borate (October 1999).
2702:Intel 80386 Programmer's Reference Manual 1986
630:run in ring 0 and applications run in ring 3.
3753:
3226:
2782:80286 and 80287 Programmer's Reference Manual
2763:80286 and 80287 Programmer's Reference Manual
2744:80286 and 80287 Programmer's Reference Manual
2281:
2279:
2277:
2088:
1980:is still used for running applications, e.g.
162:
146:First supported platform shown in parentheses
4099:International Symposium on Memory Management
3095:
3093:
3023:
2988:
2986:
2984:
2693:
2501:
2440:
2339:
1854:Paging (on Intel 80386) with page size of 4K
810:The descriptor table entry defines the real
3067:"Advanced Embedded x86 Programming: Paging"
2900:. May 2019. Section 20.2 Virtual 8086 Mode.
2517:. May 2019. Section 3.1 Modes of Operation.
2164:. May 2019. Section 3.1 Modes of Operation.
402:which run on the x86 architecture, such as
306:(Basic Input/Output System) and memory for
3760:
3746:
3233:
3219:
2956:
2884:
2404:(Press release). Microsoft. Archived from
2307:
2274:
735:with the use of instructions that involve
247:architecture in 1982, with the release of
169:
155:
3139:"news: Multitasking for x86 explained #1"
3136:
3130:
3102:"news: Multitasking for x86 explained #1"
3099:
3090:
2981:
2574:
2455:Upgrading and Repairing PCs, 17th Edition
2254:
1901:Through the use of the rings, privileged
640:Intel 80286 Programmer's Reference Manual
481:devised a workaround (implemented in the
282:. This allowed the processor to access 2
2930:
2861:
2829:
2717:
2715:
1849:
1841:
764:
609:
378:
2577:"Sending software to do hardware's job"
2449:"P2 (286) Second-Generation Processors"
2446:
2174:
2123:"Guide: What does protected mode mean?"
1952: 1.x, and Windows used this mode.
1771:= 0 then the segment is a data segment.
1764:= 1 then the segment is a code segment;
16:Operational mode of x86-compatible CPUs
4175:
2994:"Global Descriptor table - OSDev Wiki"
2600:
2354:
2313:
2249:1985 Intel launches Intel386 processor
2231:"Intel Global Citizenship Report 2003"
539:; save control register 0 (CR0) to EBX
243:Protected mode was first added to the
3767:
3741:
3240:
3214:
2712:
852:Structure of segment descriptor entry
754:
3201:Code Project Protected Mode Tutorial
3196:Protected Mode Overview and Tutorial
2527:
2120:
1976:In modern 32-bit operating systems,
1921:
705:
4183:Programming language implementation
3808:Input–output memory management unit
2491:80386 Programmer's Reference Manual
2399:"Microsoft XENIX 286 Press Release"
634:Real mode application compatibility
599:
524:; enter protected mode (set PE bit)
473:Entering and exiting protected mode
13:
3064:
1996:subsystem) and certain classes of
554:; set PE bit by ORing, save to EBX
14:
4199:
3169:
2931:Robinson, Tim (August 26, 2002).
2862:Robinson, Tim (August 26, 2002).
2830:Robinson, Tim (August 26, 2002).
2601:Shvets, Gennadiy (June 3, 2007).
2447:Mueller, Scott (March 24, 2006).
786:
596:without proper hardware support.
4157:
4156:
4147:
4146:
4137:
4136:
4127:
4126:
4117:
4116:
3337:Object-oriented operating system
2565:, November 25, 1986, pp. 150-152
2357:"Introduction to Protected-Mode"
2314:Risley, David (March 23, 2001).
2004:2.0 (and later OS/2) and 32-bit
1909:(TSS), introduced with the 286,
3979:Concurrent mark sweep collector
2675:
2657:
2639:
2621:
2568:
2550:
2528:Hyde, Randall (November 2004).
2422:
2391:
2377:
2359:. Internals.com. Archived from
2182:. ftp.utcluj.ro. Archived from
1890:
429:386 additions to protected mode
4104:Region-based memory management
3347:Supercomputer operating system
3181:Introduction to Protected-Mode
3069:. Embedded.com. Archived from
2603:"Intel 80386 processor family"
2067:. May 23, 1995. Archived from
187:protected virtual address mode
1:
2575:Tom Yager (6 November 2004).
2047:
1863:and onto a slower and larger
496:To enter protected mode, the
383:An Intel 80386 microprocessor
4152:Memory management algorithms
3964:Automatic Reference Counting
3802:Translation lookaside buffer
3322:Just enough operating system
3307:Distributed operating system
2318:. PCMechanic. Archived from
773:
189:, is an operational mode of
7:
4142:Automatic memory management
3941:C dynamic memory allocation
3435:User space and kernel space
2459:(Book) (17 ed.). Que.
2015:
1739:= 1 then the segment grows
1728:= 0 then the segment grows
590:
423:Hardware x86 virtualization
300:the remaining 384 kilobytes
286:of memory, equivalent to 1
21:Mandatory Integrity Control
10:
4204:
4162:Memory management software
4009:Tracing garbage collection
3842:Virtual memory compression
3342:Real-time operating system
3145:. NewOrder. Archived from
3108:. NewOrder. Archived from
1894:
1835:
1791:Descriptor Privilege Level
1417:
1414:
1202:
1035:
1032:
758:
709:
603:
386:
374:
324:
320:
262:
18:
4112:
4086:
4060:
4027:
3954:
3926:
3883:
3850:
3817:
3788:
3775:
3677:
3614:
3560:
3538:Multilevel feedback queue
3533:Fixed-priority preemptive
3521:
3456:
3447:
3417:
3364:
3355:
3317:Hobbyist operating system
3312:Embedded operating system
3294:
3248:
3137:zwanderer (May 2, 2004).
3100:zwanderer (May 2, 2004).
2935:. berliOS. Archived from
2866:. berliOS. Archived from
2834:. berliOS. Archived from
2430:"MINIX Information Sheet"
1831:
1625:
1622:
1619:
1616:
1613:
1610:
1607:
1604:
1601:
1596:
1593:
1590:
1587:
1584:
1228:
1225:
1222:
1219:
1216:
1213:
1210:
1207:
769:Virtual segments of 80286
668:Writing to a code segment
417:, Intel added a separate
3936:Static memory allocation
3928:Manual memory management
3581:General protection fault
3332:Network operating system
3286:User features comparison
2175:Collins, Robert (2007).
2037:Ring (computer security)
1243:80386 Segment descriptor
861:80286 Segment descriptor
795:is replaced by a 16-bit
606:Ring (computer security)
518:
201:to use features such as
195:central processing units
3994:Garbage-first collector
3969:Boehm garbage collector
3875:x86 memory segmentation
3327:Mobile operating system
2965:Undocumented Windows NT
2177:"Protected Mode Basics"
1926:Operating systems like
1911:preemptive multitasking
1878:: page directories and
791:In protected mode, the
761:X86 memory segmentation
682:In reality, almost all
661:Privileged instructions
498:Global Descriptor Table
335:(from 1982), Microsoft
294:reserved the first 640
228:, in order to maintain
3999:Mark–compact algorithm
3796:Memory management unit
3430:Loadable kernel module
2967:(Book). Hungry Minds.
2355:Kaplan, Yariv (1997).
2121:root (July 14, 2007).
1855:
1847:
826:
817:
770:
664:Direct hardware access
648:
615:
569:; save EBX back to CR0
384:
230:backward compatibility
99:System Management Mode
3498:Process control block
3464:Computer multitasking
3302:Disk operating system
3176:Protected Mode Basics
2074:on September 26, 2007
2042:x86 assembly language
1897:Computer multitasking
1895:Further information:
1853:
1845:
1836:Further information:
768:
759:Further information:
644:
613:
604:Further information:
445:physical and virtual
387:Further information:
382:
325:Further information:
292:IBM Personal Computer
3946:new and delete (C++)
3669:Virtual tape library
3261:Forensic engineering
1990:virtual DOS machines
1811:Default operand size
1663:(Bit 42) depends on
675:Overlapping segments
514:prefetch input queue
219:application software
4188:X86 operating modes
3852:Memory segmentation
3678:Supporting concepts
3664:Virtual file system
2933:"Virtual 8086 Mode"
2864:"Virtual 8086 Mode"
2832:"Virtual 8086 Mode"
2436:on January 7, 2014.
2387:. January 23, 1993.
1948:operating systems,
725:self-modifying code
410:, and many others.
29:Part of a series on
4094:Automatic variable
4078:Unreachable memory
4004:Reference counting
3974:Cheney's algorithm
3956:Garbage collection
3601:Segmentation fault
3449:Process management
3034:"What Is PAE X86?"
2942:on October 3, 2002
2873:on October 3, 2002
2841:on October 3, 2002
2325:on August 29, 2008
1994:Windows on Windows
1988:programs (through
1907:Task State Segment
1856:
1848:
771:
755:Segment addressing
658:Segment arithmetic
616:
385:
339:(around 1984) and
197:(CPUs). It allows
119:x86 virtualization
4170:
4169:
4122:Memory management
3870:Virtual 8086 mode
3769:Memory management
3735:
3734:
3591:Memory protection
3562:Memory management
3556:
3555:
3548:Shortest job next
3443:
3442:
3242:Operating systems
2807:US Patent 5483646
2065:US Patent 5483646
2027:Assembly language
1978:virtual 8086 mode
1922:Operating systems
1865:secondary storage
1634:
1633:
1630:
1629:
1237:
1236:
1233:
1232:
727:will generate an
718:virtual 8086 mode
712:Virtual 8086 mode
706:Virtual 8086 mode
688:virtual 8086 mode
638:According to the
467:Virtual 8086 mode
419:virtual 8086 mode
404:Microsoft Windows
400:operating systems
179:
178:
89:Virtual 8086 mode
4195:
4160:
4159:
4150:
4149:
4140:
4139:
4130:
4129:
4120:
4119:
4047:Dangling pointer
4042:Buffer over-read
4014:Strong reference
3885:Memory allocator
3762:
3755:
3748:
3739:
3738:
3690:Computer network
3454:
3453:
3362:
3361:
3235:
3228:
3221:
3212:
3211:
3164:
3163:
3158:
3157:
3151:
3134:
3128:
3127:
3121:
3120:
3114:
3097:
3088:
3087:
3082:
3081:
3075:
3062:
3056:
3055:
3049:
3048:
3042:
3030:
3021:
3020:
3018:
3017:
3012:
3004:
2998:
2997:
2990:
2979:
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2960:
2954:
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2908:
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2888:
2882:
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2827:
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2815:
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2804:
2796:
2790:
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2771:
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2768:
2758:
2752:
2751:
2749:
2739:
2733:
2732:
2719:
2710:
2709:
2707:
2697:
2691:
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2673:
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2661:
2655:
2654:
2643:
2637:
2636:
2625:
2619:
2618:
2613:
2612:
2607:
2598:
2592:
2591:
2589:
2587:
2572:
2566:
2554:
2548:
2547:
2534:Write Great Code
2525:
2519:
2518:
2505:
2499:
2498:
2496:
2486:
2477:
2476:
2474:
2473:
2458:
2444:
2438:
2437:
2432:. Archived from
2426:
2420:
2419:
2417:
2416:
2410:
2403:
2395:
2389:
2388:
2381:
2375:
2374:
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2352:
2337:
2336:
2331:
2330:
2324:
2311:
2305:
2304:
2302:
2301:
2291:
2290:(Tutorial/Guide)
2283:
2272:
2271:
2258:
2252:
2251:
2246:
2245:
2239:
2233:. Archived from
2227:
2218:
2217:
2204:
2198:
2197:
2195:
2194:
2188:
2181:
2172:
2166:
2165:
2152:
2143:
2142:
2137:
2136:
2130:Delorie Software
2127:
2118:
2109:
2108:
2095:
2086:
2085:
2080:
2079:
2073:
2057:
1971:Windows 3.1
1956:Windows 3.0
1250:
1249:
1239:
1238:
868:
867:
857:
856:
805:descriptor table
794:
600:Privilege levels
582:
579:
576:
573:
570:
567:
564:
561:
558:
555:
552:
549:
546:
543:
540:
537:
534:
531:
528:
525:
522:
350:
238:control register
171:
164:
157:
61:emulation mode (
26:
25:
4203:
4202:
4198:
4197:
4196:
4194:
4193:
4192:
4173:
4172:
4171:
4166:
4108:
4082:
4056:
4037:Buffer overflow
4023:
3950:
3922:
3879:
3846:
3813:
3784:
3771:
3766:
3736:
3731:
3673:
3634:Defragmentation
3619:
3610:
3596:Protection ring
3565:
3552:
3524:
3517:
3439:
3413:
3351:
3290:
3244:
3239:
3172:
3167:
3155:
3153:
3149:
3135:
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3118:
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3112:
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3091:
3079:
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3046:
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3024:
3015:
3013:
3010:
3006:
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2992:
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2982:
2975:
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2676:
2663:
2662:
2658:
2645:
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2640:
2627:
2626:
2622:
2610:
2608:
2605:
2599:
2595:
2585:
2583:
2573:
2569:
2557:Charles Petzold
2555:
2551:
2544:
2526:
2522:
2507:
2506:
2502:
2494:
2488:
2487:
2480:
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2445:
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2428:
2427:
2423:
2414:
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2408:
2401:
2397:
2396:
2392:
2383:
2382:
2378:
2369:
2367:
2363:
2353:
2340:
2328:
2326:
2322:
2316:"A CPU History"
2312:
2308:
2299:
2297:
2296:. BrainBell.com
2289:
2287:"A+ - Hardware"
2285:
2284:
2275:
2260:
2259:
2255:
2243:
2241:
2237:
2229:
2228:
2221:
2206:
2205:
2201:
2192:
2190:
2186:
2179:
2173:
2169:
2154:
2153:
2146:
2134:
2132:
2125:
2119:
2112:
2097:
2096:
2089:
2077:
2075:
2071:
2059:
2058:
2054:
2050:
2018:
1924:
1899:
1893:
1869:hard disk drive
1861:primary storage
1840:
1834:
1829:
1580:
1575:
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1565:
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1128:
1123:
1118:
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1103:
1098:
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1028:
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1008:
1003:
998:
993:
988:
983:
978:
973:
968:
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958:
953:
948:
943:
938:
933:
928:
923:
918:
913:
908:
903:
898:
893:
888:
883:
878:
873:
854:
829:
820:
792:
789:
776:
763:
757:
745:legacy software
714:
708:
636:
608:
602:
593:
584:
583:
580:
577:
574:
571:
568:
565:
562:
559:
556:
553:
550:
547:
544:
541:
538:
535:
532:
529:
526:
523:
520:
475:
431:
391:
377:
348:
329:
323:
265:
199:system software
175:
123:Intel Pentium 4
24:
17:
12:
11:
5:
4201:
4191:
4190:
4185:
4168:
4167:
4165:
4164:
4154:
4144:
4134:
4132:Virtual memory
4124:
4113:
4110:
4109:
4107:
4106:
4101:
4096:
4090:
4088:
4084:
4083:
4081:
4080:
4075:
4070:
4064:
4062:
4058:
4057:
4055:
4054:
4052:Stack overflow
4049:
4044:
4039:
4033:
4031:
4025:
4024:
4022:
4021:
4019:Weak reference
4016:
4011:
4006:
4001:
3996:
3991:
3986:
3981:
3976:
3971:
3966:
3960:
3958:
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3905:
3900:
3895:
3889:
3887:
3881:
3880:
3878:
3877:
3872:
3867:
3862:
3860:Protected mode
3856:
3854:
3848:
3847:
3845:
3844:
3839:
3834:
3829:
3823:
3821:
3819:Virtual memory
3815:
3814:
3812:
3811:
3805:
3799:
3792:
3790:
3786:
3785:
3783:
3782:
3776:
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3772:
3765:
3764:
3757:
3750:
3742:
3733:
3732:
3730:
3729:
3724:
3723:
3722:
3720:User interface
3717:
3707:
3702:
3697:
3692:
3687:
3681:
3679:
3675:
3674:
3672:
3671:
3666:
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3656:
3651:
3646:
3644:File attribute
3641:
3636:
3631:
3625:
3623:
3612:
3611:
3609:
3608:
3606:Virtual memory
3603:
3598:
3593:
3588:
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3578:
3572:
3570:
3558:
3557:
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3519:
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3505:
3500:
3495:
3490:
3485:
3480:
3478:Context switch
3475:
3460:
3458:
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3444:
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3427:
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3215:
3209:
3208:
3203:
3198:
3193:
3188:
3183:
3178:
3171:
3170:External links
3168:
3166:
3165:
3129:
3089:
3065:Gareau, Jean.
3057:
3022:
2999:
2980:
2973:
2955:
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2791:
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2087:
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2034:
2029:
2024:
2017:
2014:
1998:device drivers
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1920:
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1744:
1733:
1707:
1706:
1705:
1704:may jump here.
1694:
1693:may jump here;
1658:
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864:
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841:
837:
828:
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819:
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788:
787:Protected mode
785:
775:
772:
756:
753:
710:Main article:
707:
704:
680:
679:
676:
673:
672:Executing data
670:
665:
662:
659:
652:virtual memory
635:
632:
628:device drivers
601:
598:
592:
589:
521:; MASM program
519:
474:
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454:
440:
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376:
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322:
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308:add-on devices
264:
261:
207:virtual memory
185:, also called
183:protected mode
181:In computing,
177:
176:
174:
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159:
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148:
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143:
142:
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69:Protected mode
66:
56:
43:
42:
37:modes for the
35:Microprocessor
31:
30:
15:
9:
6:
4:
3:
2:
4200:
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4068:Fragmentation
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4048:
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4029:Memory safety
4026:
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4017:
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4000:
3997:
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3832:Memory paging
3830:
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3827:Demand paging
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3586:Memory paging
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3425:Device driver
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3366:Architectures
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3162:
3152:on 2007-02-12
3148:
3144:
3140:
3133:
3126:
3115:on 2007-02-12
3111:
3107:
3103:
3096:
3094:
3086:
3076:on 2008-05-16
3072:
3068:
3061:
3054:
3043:on 2008-04-22
3039:
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3009:
3003:
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2974:0-7645-4569-8
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2809:. May 6, 1998
2808:
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2543:1-59327-003-8
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2466:0-7897-3404-4
2462:
2457:
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2450:
2443:
2435:
2431:
2425:
2411:on 2014-10-21
2407:
2400:
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2380:
2366:on 2007-06-22
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2250:
2240:on 2008-03-22
2236:
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2211:
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2189:on 2011-07-07
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499:
494:
492:
488:
487:stack pointer
484:
480:
468:
465:
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459:
455:
452:
448:
447:address space
444:
441:
439:
436:
435:
434:
426:
424:
420:
416:
415:multiuser DOS
411:
409:
405:
401:
397:
390:
381:
372:
370:
365:
361:
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346:
342:
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216:
215:multi-tasking
212:
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200:
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192:
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184:
172:
167:
165:
160:
158:
153:
152:
150:
149:
145:
144:
138:
134:
131:
128:
127:AMD Athlon 64
124:
120:
117:
114:
113:AMD Athlon 64
110:
107:
104:
100:
97:
94:
90:
87:
84:
80:
77:
74:
70:
67:
64:
60:
57:
54:
50:
47:
46:
45:
44:
40:
36:
33:
32:
28:
27:
22:
3859:
3621:file systems
3513:Time-sharing
3160:
3154:. Retrieved
3147:the original
3142:
3132:
3123:
3117:. Retrieved
3110:the original
3105:
3084:
3078:. Retrieved
3071:the original
3060:
3051:
3045:. Retrieved
3038:the original
3014:. Retrieved
3002:
2964:
2958:
2950:
2944:. Retrieved
2937:the original
2926:
2912:
2906:
2892:
2886:
2875:. Retrieved
2868:the original
2857:
2849:
2843:. Retrieved
2836:the original
2825:
2817:
2811:. Retrieved
2806:
2794:
2781:
2775:
2762:
2756:
2743:
2737:
2723:
2701:
2695:
2677:
2659:
2641:
2623:
2615:
2609:. Retrieved
2596:
2584:. Retrieved
2580:
2570:
2560:
2552:
2536:. O'Reilly.
2533:
2523:
2509:
2503:
2490:
2470:. Retrieved
2454:
2442:
2434:the original
2424:
2413:. Retrieved
2406:the original
2393:
2379:
2368:. Retrieved
2361:the original
2333:
2327:. Retrieved
2320:the original
2309:
2298:. Retrieved
2293:
2262:
2256:
2248:
2242:. Retrieved
2235:the original
2208:
2202:
2191:. Retrieved
2184:the original
2170:
2156:
2139:
2133:. Retrieved
2099:
2082:
2076:. Retrieved
2069:the original
2064:
2055:
1986:DOS extender
1975:
1954:
1941:
1935:
1925:
1916:
1900:
1891:Multitasking
1887:active use.
1873:
1867:, such as a
1857:
1820:
1816:
1810:
1806:
1800:
1796:
1790:
1786:
1781:Segment type
1780:
1776:
1768:
1761:
1754:
1750:
1740:
1736:
1729:
1725:
1718:
1714:
1710:
1701:
1697:
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1675:
1671:
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1660:
1654:
1650:
1644:
1640:
1635:
1597:
1242:
1203:
860:
846:
843:
830:
821:
811:
809:
804:
800:
796:
793:segment_part
790:
777:
741:
737:input/output
722:
717:
715:
700:Windows 2.1x
681:
649:
645:
639:
637:
617:
594:
585:
581:CLEAR_LABEL:
495:
491:triple fault
476:
432:
412:
392:
357:
330:
312:
266:
242:
223:
203:segmentation
193:-compatible
186:
182:
180:
68:
41:architecture
4073:Memory leak
3639:Device file
3629:Boot loader
3543:Round-robin
3468:Cooperative
3404:Rump kernel
3394:Multikernel
3384:Microkernel
3281:Usage share
2586:24 November
2562:PC Magazine
1984:compatible
1880:page tables
1821:Granularity
696:Windows 2.0
692:Windows 3.0
578:CLEAR_LABEL
389:Intel 80386
327:Intel 80286
276:address bus
103:Intel 386SL
93:Intel 80386
83:Intel 80286
79:Unreal mode
73:Intel 80286
63:NEC V20/V30
4177:Categories
3837:Page table
3569:protection
3525:algorithms
3523:Scheduling
3472:Preemptive
3418:Components
3389:Monolithic
3256:Comparison
3156:2007-07-29
3119:2007-07-29
3080:2007-07-29
3047:2007-07-29
3016:2007-07-29
2946:2007-07-25
2877:2007-07-25
2845:2007-07-25
2813:2007-07-25
2611:2007-07-24
2472:2017-07-11
2415:2015-08-17
2370:2007-07-24
2329:2007-07-24
2300:2007-07-24
2244:2007-07-14
2238:(Timeline)
2193:2009-07-31
2135:2007-07-14
2078:2007-07-14
2048:References
2006:Windows NT
1961:Windows 9x
1937:Family API
1905:, and the
1903:call gates
1755:Executable
1680:Conforming
749:Windows NT
624:call gates
269:Intel 8086
53:Intel 8086
3984:Finalizer
3865:Real mode
3659:Partition
3576:Bus error
3503:Real-time
3483:Interrupt
3409:Unikernel
3374:Exokernel
3150:(Article)
3113:(Article)
3041:(Article)
3011:(Website)
2606:(Article)
2581:InfoWorld
2364:(Article)
2323:(Article)
2022:Long mode
2010:long mode
1719:direction
1713:= 0 then
1674:= 1 then
803:inside a
774:Real mode
729:exception
396:gigabytes
369:megabytes
360:real mode
353:kilobytes
349:4 × 64 KB
296:kilobytes
240:0 (CR0).
226:real mode
213:and safe
109:Long mode
49:Real mode
3918:ptmalloc
3913:mimalloc
3903:jemalloc
3893:dlmalloc
3789:Hardware
3705:Live USB
3567:resource
3457:Concepts
3295:Variants
3276:Timeline
2803:(Patent)
2072:(Patent)
2016:See also
1655:Readable
1645:Accessed
797:selector
781:line A20
591:Features
502:A20 line
364:software
345:kilobyte
333:Coherent
302:for the
288:megabyte
278:for its
3989:Garbage
3908:libumem
3810:(IOMMU)
3700:Live CD
3654:Journal
3618:access,
3616:Storage
3493:Process
3399:vkernel
3266:History
3249:General
3143:NewOrer
3106:NewOrer
3074:(Guide)
2940:(Guide)
2871:(Guide)
2839:(Guide)
2126:(Guide)
1966:handles
1884:pointer
1819:is the
1809:is the
1801:Present
1799:is the
1789:is the
1779:is the
1753:is the
1717:is the
1678:is the
1653:is the
1643:is the
1636:Where:
840:paging.
460:offsets
458:segment
456:32-bit
451:80386SX
375:The 386
321:The 286
263:History
236:in the
4061:Issues
3508:Thread
3379:Hybrid
3357:Kernel
2971:
2540:
2463:
1876:arrays
1838:Paging
1832:Paging
1602:Limit
1418:Limit
1204:Unused
1036:Limit
812:linear
551:PE_BIT
506:IBM PC
483:IBM AT
443:32-bit
438:Paging
280:memory
211:paging
137:VIA C3
135:mode (
4087:Other
3898:Hoard
3804:(TLB)
3798:(MMU)
3710:Shell
3649:Inode
3053:disk.
2918:Intel
2898:Intel
2786:(PDF)
2767:(PDF)
2748:(PDF)
2729:Intel
2706:(PDF)
2687:Intel
2669:Intel
2651:Intel
2633:Intel
2515:Intel
2495:(PDF)
2409:(PDF)
2402:(PDF)
2268:Intel
2214:Intel
2187:(PDF)
2180:(PDF)
2162:Intel
2105:Intel
2032:Intel
1942:bound
1932:crash
1757:bit:
1721:bit:
1626:Base
1585:Base
1415:Base
1229:Base
1033:Base
801:entry
620:rings
510:PC/XT
408:Linux
341:Minix
337:Xenix
315:Intel
284:bytes
257:80386
253:80286
249:Intel
139:only)
65:only)
3271:List
2969:ISBN
2588:2014
2538:ISBN
2461:ISBN
2002:OS/2
1982:DPMI
1950:OS/2
1946:Unix
1928:OS/2
1823:bit;
1803:bit;
1741:down
1657:bit;
1647:bit;
1608:DPL
1211:DPL
733:trap
698:and
508:and
304:BIOS
267:The
59:8080
3727:PXE
3715:CLI
3695:HAL
3685:API
3488:IPC
1940:or
1787:DPL
1767:if
1760:if
1735:if
1724:if
1709:if
1702:DPL
1696:if
1691:DPL
1685:if
1670:if
827:386
818:286
684:DOS
575:jmp
566:EBX
560:CR0
557:mov
545:EBX
536:CR0
530:EBX
527:mov
479:IBM
273:bit
251:'s
245:x86
234:bit
191:x86
133:AIS
39:x86
4179::
3470:,
3159:.
3141:.
3122:.
3104:.
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2292:.
2276:^
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2247:.
2222:^
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2113:^
2103:.
2090:^
2081:.
2063:.
1730:up
1667::
1623:A
1620:R
1617:C
1614:X
1611:S
1605:P
1594:0
1591:D
1588:G
1226:A
1223:R
1220:C
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1214:S
1208:P
642:,
542:or
516:.
406:,
371:.
310:.
221:.
209:,
205:,
125:,
3761:e
3754:t
3747:v
3564:,
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1813:;
1807:D
1797:P
1793:;
1777:S
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1726:C
1715:C
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1698:C
1687:C
1676:C
1672:X
1665:X
1661:C
1651:R
1641:A
1598:U
1579:2
1574:3
1569:4
1564:5
1559:6
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1374:7
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1364:9
1359:0
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1344:3
1339:4
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1324:7
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1127:6
1122:7
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1112:9
1107:0
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1097:2
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1002:5
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982:9
977:0
972:1
967:2
962:3
957:4
952:5
947:6
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937:8
932:9
927:0
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897:6
892:7
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877:0
872:1
563:,
548:,
533:,
170:e
163:t
156:v
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