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OSdata.com: memory maps 

OSdata.com

Memory maps

    Summary: Memory maps (not to be confused with memory mapped I/O) are diagrams or charts that show how an operating system divides up main memory.

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PC-DOS and MS-DOS memory map

high memory
segmentoffsetsizecontents
0000h0000h1024interrupt vector table
 0400h172BIOS communication area
 04ACh68reserved by IBM
 04F0h16user communication area
 0500h256DOS communication area
 0600hvariesoperating system:
IBMBIO.COM (DOS interface to the BIOS)
IBMDOS.COM (DOS interrupt handlers and interrupt 21h service routines
DOS buffers, control areas, and device drivers
COMMAND.COM (resident portion), interrupt 22h, 23h, and 24h handlers, routine to reload transient portion of COMMAND.COM
memory-resident utilities
transient applications
transient portion of COMMAND.COM
9000hFFFFh highest address of user memory
A000h0000h128Kreserved area of ROM
A000h0000h beginning of area used by EGA and PS/2 video systems
B000h0000h4000monochrome video memory
 0800h16Kcolor graphics adaptor (CGA) video memory
C000h0000h192KROM expansion and control area
 8000h ROM for hard disk
D000h  ROM expansion and control area
E000h  ROM expansion and control area
F000h0000h16Kreserved ROM
 4000h40Kbase system ROM, ROM BASIC
 E000h8KROM BIOS
low memory

    If a TSR is created in assembly langauge, the programmer has exact control over the use of memory and can omit the heap area and place the initialization code at the end of the segment (where it can be released after initialization).

    If a TSR is created in C, the small-memory model must be used. Because of the severe memory limitations, the programmer should not use C allocation functions (such as malloc and calloc), as these add to the heap. A small heap must be assigned because some C library routines (such as fprintf) allocate memory from the heap.

    Variables required by MS-DOS interrupt handlers must be placed at the beginning of the code segment.


Mac Plus memory map

high memory
addresscontents
$EFFFFFend of VIA space
$E80000beginning of VIA space
$DFFFFFend of IWM space
$D00000beginning of IWM space
$BFFFFFend of SCC write
$B00000beginning of SCC write
$9FFFFFend of SCC read
$900000beginning of SCC read
$5FFFFFend of SCSI
$580000beginning of SCSI
$41FFFFend of ROM
$400000beginning of ROM
$3FFFFFend of RAM for 4MB Mac Plus
$27FFFFend of RAM for 2.5MB Mac Plus
$1FFFFFend of RAM for 2MB Mac Plus
$0FFFFFend of RAM for 1MB Mac Plus
variessound buffer
variesSystem Error Handler area
variesmain screen (ScrnBase)
variesMacsBugs (optional)
variesRAM cache (optional)
variesJump Table (A5 relative)
variesapplication and QuickDraw globals (A5 relative)
variesstack (A7)
variesApplication Heap (ApplZone)
$001600beginning of System Heap (SysZone)
$000E00beginning of Toolbox A-trap table
$000800additional low-memory global area
$000400beginning of OS A-trap table
$000100beginning of low-memory global area
$000000beginning of RAM
Motorola 680x0 vectors
low memory

Mac Plus video memory locations

systemmain screenalternate screen
Macintosh 128K$1A700$12700
Macintosh 512K$7A700$72700
Macintosh Plus, 1 Mb$FA700$F2700
Macintosh Plus, 2Mb$1FA700$1F2700
Macintosh Plus, 2.5Mb$27A700$272700
Macintosh Plus, 4 Mb$3FA700$3F2700

Mac Plus sound memory locations

systemmain sound bufferalternate sound buffer
Macintosh 128K$1FD00$1A100
Macintosh 512K$7FD00$7A100
Macintosh Plus, 1Mb$FFD00$FA100
Macintosh Plus, 2Mb$1FFD00$1FA100
Macintosh Plus, 2.5Mb$27FD00$27A100
Macintosh Plus, 4 Mb$3FFD00$3FA100

further reading: books:

If you want your book reviewed, please send a copy to: Milo, POB 1361, Tustin, CA 92781, USA.

Price listings are for courtesy purposes only and may be changed by the referenced businesses at any time without notice.

further reading: books: general

    Structured Computer Organization, 4th edition; by Andrew S. Tanenbaum; Prentice Hall; October 1998; ISBN 0130959901; Paperback; 669 pages; $95.00; used by CS 308-273A (Principles of Assembly Languages) at McGill University School of Computer Science


    Computers: An Introduction to Hardware and Software Design; by Larry L. Wear, James R. Pinkert (Contributor), William G. Lane (Contributor); McGraw-Hill Higher Education; February 1991; ISBN 0070686742; Hardcover; 544 pages; $98.60; used by CS 308-273A (Principles of Assembly Languages) at McGill University School of Computer Science

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If you want your book reviewed, please send a copy to: Milo, POB 1361, Tustin, CA 92781, USA.


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    Copyright © 2001 Milo

    Last Updated: March 28, 2001

    Created: March 28, 2001

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