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of memory, such as the monochrome display area on colour machines. Then, DOS' many subcomponents had to be loaded into these UMBs in the correct sequence to use the blocks of memory as efficiently as possible. Some TSR programs required additional memory while loading, which was freed up again once loading was complete. Fortunately, there were few dependencies amongst these modules, so it was possible to load them in almost any sequence. Exceptions were that to successfully cache CD-ROMs, most disk caches had to be loaded after any CD-ROM drivers, and that the modules of most network stacks had to be loaded in a certain sequence, essentially working progressively up through the layers of the
225:, it became less relevant still, as this version of Windows provides much of the functionality of the DOS device drivers to DOS applications running under Windows, such as CD, network and sound support; the memory map of Windows 95 DOS boxes was automatically optimised. However, not all DOS programs could execute in this environment. Specifically, programs that tried to directly switch from real mode to protected mode would not work as this was not allowed in the
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For a period in the early 1990s, manual optimization of the DOS memory map became a highly prized skill, allowing for the largest applications to run on even the most complex PC configurations. The technique was to first create as many UMBs as possible, including remapping allocated but unused blocks
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A basic yet effective method used to optimize conventional memory was to load HIMEM.SYS as a device, thereafter loading EMM386.EXE as a device with the "RAM AUTO" option which allows access into the UMA by loading device drivers as devicehigh. This method effectively loads the fundamental memory
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made the necessity of the upper memory area less relevant, as
Windows applications were not directly affected by DOS' base memory limits, but DOS programs running under Windows (with Windows itself acting as a multitasking manager) were still thus constrained. With the release of
172:. This configuration was not a trivial process. As it was largely automated by the installation program of QEMM, this program survived on the market; indeed, it worked well with DR DOS' own HMA and UMB support and went on to be one of the best-selling utilities for the PC.
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support, task swapping, and
Undelete. Considerable amounts of the team's management attention was diverted to new features such as file transfer software, undelete and network installation Eventually this situation reached a crisis point at the end of July 1990, and, led by
121:, and I/O ports for peripherals, much of this 384 KB of address space was unused. As the 640 KB memory restriction became ever more of an obstacle, techniques were found to fill the empty areas with RAM. These areas were referred to as
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On many systems including modern ones it is possible to use memory reserved for shadowing expansion card ROM as upper memory. Many chipsets reserve up to 384 KB RAM for this purpose and since this RAM is generally unused it may be used as
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in June 1991. Eventually, even more DOS data structures were moved out of conventional memory, allowing up to 631 KB out of 640 KB to be left free. Starting from version 6.0 of MS-DOS, Microsoft even included a program called
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The advantage of DR DOS 5.0 over the combination of an older DOS plus QEMM was that the DR DOS kernel itself and almost all of its data structures could be loaded into high memory. This left virtually
233:(VCPI) API (which was introduced to allow DOS programs that needed protected mode to enter it from the virtual 8086 mode set up by a memory manager, as described above) didn't work in Windows 95. Only the
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for XT-class computers, allowed normal memory to be mapped into the 0xA0000-EFFFF address range, giving up to 952 KB for DOS programs. Programs such as
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was removed at the cost of software compatibility. This usage of the upper memory area is different from using upper memory blocks, which was used to free
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to make it appear in the upper memory area. As with the 386-based upper memory described above, the extra RAM could be used to load TSR files, or as a
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Configuration was not automatic - free UMBs had to be identified by hand, manually included in the line that loaded EMM386 from
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managers into conventional memory, and thereafter everything else into the UMA. Conventional memory glutton programs such as
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so this method of providing upper memory blocks is usually provided by the expanded memory manager (for example
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could also be loaded into the UMA in a similar fashion, hence freeing up a large amount of conventional memory.
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The next stage in the evolution of DOS was for the operating system to use upper memory blocks (UMBs) and the
453:. p. 10. MS-PCA1179169 (MS-PCA1179159-MS-PCA1179191). MS7020988 (MS7020978-MS7021010). Depo. Ex. 1109.
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the base memory free, allowing configurations with up to 620 KB out of 640 KB free.
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One of the most important stimulanta for adding features was competitive pressure from
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computers, it was possible to add more memory to the motherboard and use a custom
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address space, but left the amount of addressable memory (640 KB) intact.
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by moving device drivers and TSRs into the upper 384 KB of the 1
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it was running in. Also, programs that tried making the switch using the
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500:"UMBPCI V3.89 - c't magazine's hardware-UMB-driver for DOS and Win95/98"
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which was used to automatically optimize conventional memory by moving
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The upper memory area is located between 640 KB and 1024 KB.
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Plaintiff's
Exhibit 3473. CA.No.2:96CV645B Plaintiff's Exhibit 477.
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or compatible. IBM reserved the uppermost 384 KB of the
526:"What is high memory, why do I care, and how can I use it?"
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upper memory with a custom device driver, such as UMBPCI.
237:(DPMI) API for switching to protected mode was supported.
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for managing the upper memory blocks is specified in the
331:, which accessed video memory directly, needed to be
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149:, could perform most of the basic functionality of
145:in 1990. DR DOS' built-in memory manager,
250:Upper memory blocks can be created by mapping
335:to handle this memory layout. Therefore, the
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27:Physical memory region on IBM PC compatibles
444:"MS-DOS 5.0 Development Post-Mortem Report"
254:into the upper memory area when running in
141:(HMA). This occurred with the release of
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109:However, even with video RAM, the ROM
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192:(TSR) programs to the upper memory.
442:Dryfoos, Mike, ed. (1991-09-18) .
79:'s 1024 KB address space for
25:
272:application programming interface
231:Virtual Control Program Interface
175:This functionality was copied by
532:from the original on 2018-10-05
506:from the original on 2019-12-30
464:from the original on 2019-04-02
416:"Memory Map (x86) - OSDev Wiki"
385:Global EMM Import Specification
1:
277:eXtended Memory Specification
216:The increasing popularity of
235:DOS Protected Mode Interface
190:terminate-and-stay-resident
578:
449:(mail as court document).
258:. This is similar to how
153:and comparable programs.
325:memory management unit
262:can be emulated using
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557:DOS memory management
528:. San Jose, CA, USA.
524:Atkinson, Cy (2001).
357:DOS memory management
68:A0000–0xFFFFF) in an
42:DOS memory management
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179:with the release of
362:Conventional memory
341:conventional memory
337:640 KB barrier
123:upper memory blocks
64:and 1024 KB (
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455:Comes v Microsoft
256:virtual 8086 mode
246:Virtual 8086 Mode
227:virtual 8086 mode
100:memory-mapped I/O
46:upper memory area
16:(Redirected from
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307:address decoder
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264:extended memory
260:expanded memory
252:extended memory
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534:. Retrieved
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170:AUTOEXEC.BAT
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60:of 640
56:between the
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18:Upper memory
329:Lotus 1-2-3
218:Windows 3.0
119:Option ROMs
92:Option ROMs
551:Categories
536:2020-02-07
510:2020-02-07
468:2019-07-22
425:2020-12-20
402:References
284:Shadow RAM
181:MS-DOS 5.0
166:CONFIG.SYS
147:EMM386.EXE
115:Video BIOS
88:Video BIOS
475:DRDOS 5.0
451:Microsoft
291:real mode
198:OSI model
177:Microsoft
104:ROM BASIC
58:addresses
52:) is the
530:Archived
504:Archived
459:Archived
396:A20 line
391:LOADHIGH
387:(GEMMIS)
351:See also
314:RAM disk
186:MEMMAKER
333:patched
321:AllCard
270:). The
212:Windows
303:IBM XT
297:IBM XT
268:EMM386
206:MSCDEX
117:, the
113:, the
70:IBM PC
54:memory
44:, the
484:BradS
462:(PDF)
447:(PDF)
381:(HMA)
375:(EMS)
369:(XMS)
133:Usage
562:BIOS
319:The
310:PROM
151:QEMM
127:UMBs
111:BIOS
81:BIOS
74:8088
479:UMB
301:On
159:all
129:).
96:RAM
84:ROM
77:CPU
50:UMA
40:In
553::
502:.
471:.
434:^
418:.
345:MB
316:.
280:.
200:.
106:.
90:,
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66:0x
62:KB
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125:(
48:(
20:)
Text is available under the Creative Commons Attribution-ShareAlike License. Additional terms may apply.
