📄 hod.html
字号:
<td>IP</td>
<td>Points to the currently executing code.</td>
</tr>
<tr>
<td>SS</td>
<td align="center">:</td>
<td>SP</td>
<td>Points to the current stack position.</td>
</tr>
</table>
<p>If you'll notice, the value in the segment register is multiplied by 16 (or
shifted left 4 bits) and then added to the offest register. Together they create
a 20 bit address. Thus, there are many combinations of the segment and offset
registers that will produce the same address. The standard notation for a SEGment/OFFset
pair is:</p>
<table width="98%" border="0" cellspacing="2" cellpadding="2">
<tr align="center">
<td>SEGMENT</td>
<td>:</td>
<td>OFFSET or A000</td>
<td>:</td>
<td>0000 (in hexadecimal)</td>
</tr>
</table>
<p>Where SEGMENT = 0A000h and OFFSET = 00000h.<br>
(This happens to be the address of the upper left pixel on a 320x200x256 screen.)<br>
You may be wondering what would happen if you were to have a segment value of
0FFFFh and an offset value of 0FFFFh.</p>
<p>Notice how <0FFFFh * 16 (or 0FFFF0h ) + 0FFFFh = 1,114,095> is larger
than 1,048,576 (or 1 MEG).</p>
<p>This means that more than 1 MB of memory is actually accessible! Well, to actually
use that extra bit of memory, you would have to enable something called the
A20 line, which just enables the 21st bit for addressing. This little extra
bit of memory is usually called "HIGH MEMORY" and is used when you
load something into high memory or say DOS = HIGH in your AUTOEXEC.BAT file
or DEVICEHIGH=MOUSE.SYS in your CONFIG.SYS file (HIMEM.SYS and EMS386.EXE actually
manage that).</p>
<p>Here is an illustration of a typical memory map:</p>
<p>The IBM PC handles its address space in 64k segments, divided into <br>
16k fractions and then further as necessary:</p>
<p><pre>
*********************************************************************
*start *start*end * *
*addr. *addr.*addr.* usage *
*(dec) * (hex) * *
*********************************************************************
* *640k RAM Area* *
*********************************************************************
* 0k * * start of RAM, first K is interrupt vector table *
* 16k *0000-03FF* PC-0 system board RAM ends *
* 32k *0400-07FF* *
* 48k *0800-0BFF* *
*********************************************************************
* 64k *1000-13FF* PC-1 system board RAM ends *
* 80k *1400-17FF* *
* 96k *1800-1BFF* *
* 112k *1C00-1FFF* *
*********************************************************************
* 128k *2000-23FF* *
* 144k *2400-27FF* *
* 160k *2800-2BFF* *
* 176k *2C00-2FFF* *
*********************************************************************
* 192k *3000-33FF* *
* 208k *3400-37FF* *
* 224k *3800-3BFF* *
* 240k *3C00-3FFF* *
*********************************************************************
* 256k *4000-43FF* PC-2 system board RAM ends *
* 272k *4400-47FF* *
* 288k *4800-4BFF* *
* 304k *4C00-4FFF* *
*********************************************************************
* 320k *5000-53FF* *
* 336k *5400-57FF* *
* 352k *5800-5BFF* *
* 368k *5C00-5FFF* *
*********************************************************************
* 384k *6000-63FF* *
* 400k *6400-67FF* *
* 416k *6800-6BFF* *
* 432k *6C00-6FFF* *
*********************************************************************
* 448k *7000-73FF* *
* 464k *7400-77FF* *
* 480k *7800-7BFF* *
* 496k *7C00-7FFF* *
*********************************************************************
* 512k *8000-83FF* *
* 528k *8400-87FF* *
* 544k *8800-8BFF* the original IBM PC-1 BIOS limited memory to *
* 560k *8C00-8FFF* 544k *
*********************************************************************
* 576k *9000-93FF* *
* 592k *9400-97FF* *
* 609k *9800-9BFF* *
* 624k *9C00-9FFF* to 640k (top of RAM address space) *
* 639k * * some RLL and SCSI hard disk adapters, some four *
* * * floppy controller cards, some AMI and PS/2 BIOS, *
* * * and assorted other cards sometimes try to use the*
* * * last K for storing temporary data. This can *
* * * cause trouble with programs which assume they *
* * * have a full 640k, and will prevent backfilling *
* * * memory with some memory managers. Beware! *
*********************************************************************
*A0000 ***** 64k ***** EGA/VGA starting address *
*A0000 ***** 64k ***** Toshiba 1000 DOS ROM (MS-DOS 2.11V) *
*********************************************************************
* 640k *A0000-A95B0* MCGA 320x200 256 color video buffer *
* * -AF8C0* MCGA 640x480 2 color video buffer *
* * -A3FFF* *
* 656k *A4000-A7FFF* *
* 672k *A8000-ABFFF*this 64k segment may be used for contiguous DOS *
* 688k *AC000-AFFFF*RAM with appropriate hardware and software *
*********************************************************************
*B0000 ***** 64k ***** mono and CGA address *
*********************************************************************
* 704k *B0000-B3FFF*4k mono display | The PCjr and early Tandy 1000*
* 720k *B4000-B7FFF* | BIOS revector direct write to*
* 736k *B8000-BBFFF*16k CGA | the B8 area to the Video Gate*
* 756k *BC000-BFFFF* | Array and reserved system RAM*
*********************************************************************
*C0000 ***** 64k *************** expansion ROM *
*********************************************************************
* 768k *C0000-C3FFF*16k EGA BIOS C000:001E EGA BIOS signature *
* * * (the letters 'IBM') *
* *C0000-C7FFF*32k VGA BIOS extension (typical) *
* 784k *C4000-C5FFF* *
* *C6000-C63FF*256 bytes IBM PGC video communications area *
* *C6400-C7FFF* *
* 800k *C8000-CBFFF*16k hard disk controller BIOS, drive 0 default *
* *CA000 * some 2nd floppy (HD) controller BIOSes *
* 816k *CC000-CDFFF* 8k IBM PC Network NETBIOS *
* *CE000-CFFFF* *
*********************************************************************
*D0000 ***** 64k ***** expansion ROM *
*********************************************************************
* 832k *D0000-D7FFF*32k IBM Cluster Adapter | PCjr first ROM cart. *
* * DA000*voice communications | address area. *
* 848k *D4000-D7FFF* | Common EMS board *
* 864k *D8000-DBFFF* | paging area. *
* *D8000-DBFFF* IBM Token Ring default Share RAM address *
* *DC000 * IBM Token Ring default BIOS/MMIO address *
* 880k *DC000-DFFFF* | *
* *DE000 *4k TI Pro default video buffer *
*********************************************************************
*E0000 ***** 64k ***** expansion ROM *
* wired to ROM sockets in the original IBM AT *
* used by ABIOS extensions on some PS/2 models *
*********************************************************************
* 896k *E0000-E3FFF* | PCjr second ROM cart.*
* 912k *E4000-E7FFF* | address area *
* 928k *E8000-EBFFF* | *
* 944k *EC000-EFFFF* | spare ROM sockets on *
* * * | IBM AT (reserved in *
* * * | hardware) *
*********************************************************************
*F0000 ***** 64k ***** system *
*********************************************************************
* 960k *F0000-F3FFF*reserved by IBM | cartridge address *
* 976k *F4000- * | area (PCjr cartridge *
* *F6000 *ROM BASIC Begins | BASIC) *
* 992k *F8000-FB000* | *
* 1008k*FC000-FFFFF*ROM BASIC and original | *
* * *BIOS (Compatibility BIOS | *
* * *in PS/2) | *
* 1024k* FFFFF*end of memory (1024k) for 8088 machines *
*********************************************************************
* 384k *100000-15FFFF* 80286/AT extended memory area, 1Mb mbd. *
* 15Mb *100000-FFFFFF* 80286/AT extended memory address space *
* 15Mb *160000-FDFFFF* Micro Channel RAM expansion (15Mb ext. mem) *
* 128k *FE0000-FFFFFF* system board ROM (PS/2 Advanced BIOS) *
*********************************************************************
* 64k *C0000000-C000FFFF* Weitek "Abacus" math coprocessor *
* * * memory-mapped I/O *
+*******************************************************************+</pre>
<p><b><font size="4"><a name="4"></a>Timeline:</font></b></p>
<p>In May 1982, Microsoft released MS-DOS v1.1 to IBM, for the IBM PC. It supported
320KB double-sided floppy disk drives. Microsoft also released MS-DOS v1.25,
similar to v1.1 but for IBM-compatible computers.</p>
<p>In March 1983, MS-DOS v2.0 for PCs is announced. It was written from scratch,
supporting 10 MB hard drives, a tree-structured file system, and 360 KB floppy
disks. October saw IBM introducing PC-DOS v2.1 with the IBM PCjr.</p>
<p>In March 1984, Microsoft released MS-DOS v2.1 for the IBM PCjr. Microsoft released
MS-DOS v2.11 a short time later. It included enhancements to better allow conversion
into different languages and date formats. In August, Microsoft released MS-DOS
v3.0 for PCs. It added support for 1.2MB floppy disks, and bigger (than 10 MB)
hard disks. In November, Microsoft released MS-DOS v3.1, adding support for
Microsoft networks.</p>
<p>In January 1986, Microsoft released MS-DOS v3.2. It added support for 3.5-inch
720 KB floppy disk drives. Microsoft released MS-DOS v3.25 as well.</p>
<p>In April 1987, IBM announced DOS v3.3 for PCs, for $120. In August Microsoft
shipped MS-DOS v3.3. In November Compaq shipped MS-DOS v3.31 with support for
over 32MB drives.</p>
<p>In 1988 Digital Research transformed CP/M into DR DOS. In June Microsoft released
MS-DOS v4.0, including a graphical/mouse interface. In July IBM shipped DOS
v4.0, which included a shell menu interface and support for hard disk partitions
over 32 MB. In November Microsoft released MS-DOS v4.01.</p>
<p>In April 1990, Microsoft introduced Russian MS-DOS v4.01 for the Soviet market.<br>
May saw Digital Research releasing DR DOS v5.0.</p>
<p>In June 1991, Microsoft released MS-DOS v5.0. It added a full-screen editor,
undelete and unformat utilities and task swapping. GW-BASIC is replaced with
Qbasic, based on Microsoft's QuickBASIC. In September Digital Research Inc.
releases DR DOS v6.0, for $100.</p>
<p>In March 1993, Microsoft introduced the MS-DOS v6.0 upgrade, including DoubleSpace
disk compression. 1 million copies of the new and upgraded versions were sold
through retail channels within the first 40 days. In November, Microsoft released
MS-DOS v6.2.</p>
<p>In February 1994, Microsoft released MS-DOS v6.21, removing DoubleSpace disk
compression. April IBM releases PC-DOS v6.3. In June Microsoft releases MS-DOS
v6.22, bringing back disk compression under the name DriveSpace.</p>
<p>In February 1995, IBM announced PC DOS v7, with integrated data compression
from Stac Electronics (Stacker). In April, IBM released PC DOS v7. In August
of 1995 Microsoft introduced Windows 95, it included MS DOS v7.0 but it's clear
that DOS is going to remain a constant for several years to come.</p>
<p><b>DOS HISTORY CHART: (system file sizes in bytes)</b></p>
<table width="99%" border="1" cellspacing="2" cellpadding="2" align="center">
<tr>
<td>DOS TYPE AND VERSION</td>
<td>DATE</td>
<td>COMMAND.COM</td>
<td>IO.SYS or IBMBIO.COM</td>
<td>MSDOS.SYS or IBMDOS.COM</td>
</tr>
<tr>
<td>PC 1.0</td>
<td>8-4-81</td>
<td>3,231</td>
<td>1,920 </td>
<td> 6,400</td>
</tr>
<tr>
<td>MS 1.0</td>
<td>8-4-81</td>
<td>3,231 </td>
<td>1,920</td>
<td> 6,400</td>
</tr>
<tr>
<td>PC 1.1</td>
<td>5-7-82</td>
<td>4,959 </td>
<td>1,920</td>
<td> 6,400</td>
</tr>
<tr>
<td>PC 2.0</td>
<td>3-8-83</td>
<td>17,792</td>
<td>4,608 </td>
<td>17,152</td>
</tr>
<tr>
<td>MS 2.0</td>
<td>3-8-83</td>
<td>17,792</td>
<td>4,608 </td>
<td>17,152</td>
</tr>
<tr>
<td>PC 2.1</td>
<td>10-20-83</td>
<td>17,792</td>
<td>4,736</td>
<td>17,024</td>
</tr>
<tr>
<td>MS 2.11</td>
<td>11-17-83</td>
<td>15,957</td>
<td>6,836</td>
<td>17,176</td>
</tr>
<tr>
<td>PC 2.11</td>
<td>5-30-84</td>
<td>18,272</td>
<td>5,120 </td>
<td> 17,408</td>
</tr>
<tr>
<td>PC 3.0</td>
<td>8-14-84</td>
<td>22,042 </td>
<td>8,964</td>
<td>27,920</td>
</tr>
<tr>
<td>MS 3.0</td>
<td>8-14-84</td>
<td>22,042 </td>
<td>8,964</td>
<td>27,920</td>
⌨️ 快捷键说明
复制代码
Ctrl + C
搜索代码
Ctrl + F
全屏模式
F11
切换主题
Ctrl + Shift + D
显示快捷键
?
增大字号
Ctrl + =
减小字号
Ctrl + -