-
Notifications
You must be signed in to change notification settings - Fork 0
/
Copy pathThe Kernel Boot Process - Gustavo Duarte.mhtml
11991 lines (9597 loc) · 620 KB
/
The Kernel Boot Process - Gustavo Duarte.mhtml
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
698
699
700
701
702
703
704
705
706
707
708
709
710
711
712
713
714
715
716
717
718
719
720
721
722
723
724
725
726
727
728
729
730
731
732
733
734
735
736
737
738
739
740
741
742
743
744
745
746
747
748
749
750
751
752
753
754
755
756
757
758
759
760
761
762
763
764
765
766
767
768
769
770
771
772
773
774
775
776
777
778
779
780
781
782
783
784
785
786
787
788
789
790
791
792
793
794
795
796
797
798
799
800
801
802
803
804
805
806
807
808
809
810
811
812
813
814
815
816
817
818
819
820
821
822
823
824
825
826
827
828
829
830
831
832
833
834
835
836
837
838
839
840
841
842
843
844
845
846
847
848
849
850
851
852
853
854
855
856
857
858
859
860
861
862
863
864
865
866
867
868
869
870
871
872
873
874
875
876
877
878
879
880
881
882
883
884
885
886
887
888
889
890
891
892
893
894
895
896
897
898
899
900
901
902
903
904
905
906
907
908
909
910
911
912
913
914
915
916
917
918
919
920
921
922
923
924
925
926
927
928
929
930
931
932
933
934
935
936
937
938
939
940
941
942
943
944
945
946
947
948
949
950
951
952
953
954
955
956
957
958
959
960
961
962
963
964
965
966
967
968
969
970
971
972
973
974
975
976
977
978
979
980
981
982
983
984
985
986
987
988
989
990
991
992
993
994
995
996
997
998
999
1000
From: <Saved by Blink>
Snapshot-Content-Location: https://web.archive.org/web/20151004202005/http://duartes.org/gustavo/blog/post/kernel-boot-process/
Subject: The Kernel Boot Process - Gustavo Duarte
Date: Sat, 5 Aug 2023 04:39:36 -0000
MIME-Version: 1.0
Content-Type: multipart/related;
type="text/html";
boundary="----MultipartBoundary--rQWPx81qSpC5b4sYqcvMxv0aEOS11OWu15QJu1guX1----"
------MultipartBoundary--rQWPx81qSpC5b4sYqcvMxv0aEOS11OWu15QJu1guX1----
Content-Type: text/html
Content-ID: <frame-43939F4476DB9DC79FEEB59C479568AB@mhtml.blink>
Content-Transfer-Encoding: quoted-printable
Content-Location: https://web.archive.org/web/20151004202005/http://duartes.org/gustavo/blog/post/kernel-boot-process/
<!DOCTYPE html><html lang=3D"en" ml-update=3D"aware" class=3D"no-touch"><he=
ad><meta http-equiv=3D"Content-Type" content=3D"text/html; charset=3DUTF-8"=
><link rel=3D"stylesheet" type=3D"text/css" href=3D"cid:css-c0598f97-da99-4=
e24-bcc7-934ee965729d@mhtml.blink" /><link rel=3D"stylesheet" type=3D"text/=
css" href=3D"cid:css-76e93cc8-48f5-4f2d-98f6-26b4da126ca7@mhtml.blink" /><l=
ink rel=3D"stylesheet" type=3D"text/css" href=3D"cid:css-066a39a3-2c57-45ca=
-9af3-0ba2dcfd1a29@mhtml.blink" /><link rel=3D"stylesheet" type=3D"text/css=
" href=3D"cid:css-21bedd40-226f-4d1f-9d0a-cf3d6dd76281@mhtml.blink" /><link=
rel=3D"stylesheet" type=3D"text/css" href=3D"cid:css-fbe936e2-4531-44c1-b9=
dd-c222f31af41e@mhtml.blink" /><link rel=3D"stylesheet" type=3D"text/css" h=
ref=3D"cid:css-f4ee67b6-3263-4857-be43-ec776807f9d8@mhtml.blink" /><link re=
l=3D"stylesheet" type=3D"text/css" href=3D"cid:css-5f2ee528-ab59-486f-bfd1-=
32a3bfc4a331@mhtml.blink" /><link rel=3D"stylesheet" type=3D"text/css" href=
=3D"cid:css-67773d63-09ac-4c43-9895-b65c95616557@mhtml.blink" /><link rel=
=3D"stylesheet" type=3D"text/css" href=3D"cid:css-ed9b75f9-25d8-4f77-8535-4=
3f67634aba0@mhtml.blink" /><link rel=3D"stylesheet" type=3D"text/css" href=
=3D"cid:css-4e006586-08ce-4f38-8cf6-1bfde8dda299@mhtml.blink" />
<link rel=3D"stylesheet" type=3D"text/css" href=3D"https://web.archive.org/=
_static/css/banner-styles.css?v=3DS1zqJCYt">
<link rel=3D"stylesheet" type=3D"text/css" href=3D"https://web.archive.org/=
_static/css/iconochive.css?v=3DqtvMKcIJ">
<!-- End Wayback Rewrite JS Include -->
=20
<meta http-equiv=3D"X-UA-Compatible" content=3D"IE=3Dedge">
<meta name=3D"viewport" content=3D"width=3Ddevice-width, initial-scale=
=3D1">
<title>The Kernel Boot Process - Gustavo Duarte</title>
<meta name=3D"author" content=3D"Gustavo Duarte">
=20
<meta name=3D"description" content=3D"The previous post explained how c=
omputers boot up right up to the point where the boot loader, after stuffin=
g the kernel image into memory, is about =E2=80=A6">
=20
=20
<link rel=3D"canonical" href=3D"https://web.archive.org/web/20151004202=
005/http://duartes.org/gustavo/blog/post/kernel-boot-process">
<link href=3D"https://web.archive.org/web/20151004202005im_/http://duar=
tes.org/gustavo/blog/favicon.ico" rel=3D"shortcut icon">
<link href=3D"https://web.archive.org/web/20151004202005/http://feeds.f=
eedburner.com/GustavoDuarte" rel=3D"alternate" title=3D"Gustavo Duarte" typ=
e=3D"application/atom+xml">
<link href=3D"https://web.archive.org/web/20151004202005cs_/http://font=
s.googleapis.com/css?family=3DOpen+Sans:400,400italic,700|PT+Serif:400,700"=
rel=3D"stylesheet" type=3D"text/css">
<link href=3D"https://web.archive.org/web/20151004202005cs_/http://maxc=
dn.bootstrapcdn.com/font-awesome/4.2.0/css/font-awesome.min.css" rel=3D"sty=
lesheet">
<link rel=3D"stylesheet" href=3D"https://web.archive.org/web/2015100420=
2005cs_/http://maxcdn.bootstrapcdn.com/bootstrap/3.3.1/css/bootstrap.min.cs=
s">
<link href=3D"https://web.archive.org/web/20151004202005cs_/http://duar=
tes.org/gustavo/blog/stylesheets/signal.css" rel=3D"stylesheet">
<!--<link href=3D"/gustavo/blog/stylesheets/screen.css" media=3D"screen=
, projection" rel=3D"stylesheet" type=3D"text/css">-->
=20
=20
</head>
<body style=3D""><!-- BEGIN WAYBACK TOOLBAR INSERT -->
<div id=3D"wm-ipp-base" lang=3D"en" style=3D"display: block; direction: ltr=
; height: 1px;">
<template shadowmode=3D"closed"><div id=3D"wm-ipp" style=3D"position:fixed;=
left:0;top:0;right:0;">
<div id=3D"donato" style=3D"position:relative;width:100%;">
<div id=3D"donato-base">
<iframe id=3D"donato-if" src=3D"cid:frame-EAD2F2EB8292235D155436E95CF02=
022@mhtml.blink" scrolling=3D"no" frameborder=3D"0" style=3D"width:100%; he=
ight:100%">
</iframe>
</div>
</div><div id=3D"wm-ipp-inside" style=3D"display: none;">
<div id=3D"wm-toolbar" style=3D"position:relative;display:flex;flex-flow:=
row nowrap;justify-content:space-between;">
<div id=3D"wm-logo" style=3D"/*width:110px;*/padding-top:12px;">
<a href=3D"https://web.archive.org/web/" title=3D"Wayback Machine hom=
e page"><img src=3D"https://web.archive.org/_static/images/toolbar/wayback-=
toolbar-logo-200.png" alt=3D"Wayback Machine" style=3D"width:100px" border=
=3D"0"></a>
</div>
<div class=3D"c" style=3D"display:flex;flex-flow:column nowrap;justify-=
content:space-between;flex:1;">
<form class=3D"u" style=3D"display:flex;flex-direction:row;flex-wrap:=
nowrap;" target=3D"_top" method=3D"get" action=3D"https://web.archive.org/w=
eb/submit" name=3D"wmtb" id=3D"wmtb"><input type=3D"text" name=3D"url" id=
=3D"wmtbURL" value=3D"http://duartes.org/gustavo/blog/post/kernel-boot-proc=
ess/" style=3D"flex:1;" autocomplete=3D"off"><input type=3D"submit" value=
=3D"Go">
</form>
<div style=3D"display:flex;flex-flow:row nowrap;align-items:flex-end;=
">
<div class=3D"s" id=3D"wm-nav-captures" style=3D"flex:1;"><=
a class=3D"t" href=3D"https://web.archive.org/web/*/http://duartes.org/gust=
avo/blog/post/kernel-boot-process/" title=3D"See a list of every capture fo=
r this URL">306 captures</a><div class=3D"r" title=3D"Timespan for captures=
of this URL">20 Aug 2008 - 6 Jun 2023</div></div>
<div class=3D"k">
<a href=3D"https://web.archive.org/web/20151004202005/http://duar=
tes.org/gustavo/blog/post/kernel-boot-process/" id=3D"wm-graph-anchor">
<div id=3D"wm-ipp-sparkline" title=3D"Explore captures for this=
URL" style=3D"position: relative">
<canvas id=3D"wm-sparkline-canvas" width=3D"700" height=3D"27=
" border=3D"0"></canvas>
<div class=3D"yt" style=3D"display: none; width: 25px; height: =
27px;"></div><div class=3D"mt" style=3D"display: none; width: 2px; height: =
27px;"></div></div>
</a>
</div>
</div>
</div>
<div class=3D"n">
<table>
<tbody>
<!-- NEXT/PREV MONTH NAV AND MONTH INDICATOR -->
<tr class=3D"m">
<td class=3D"b" nowrap=3D"nowrap"><a href=3D"https://web.archiv=
e.org/web/20150817152000/http://duartes.org/gustavo/blog/post/kernel-boot-p=
rocess/" title=3D"17 Aug 2015"><strong>Aug</strong></a></td>
<td class=3D"c" id=3D"displayMonthEl" title=3D"You are here: 20=
:20:05 Oct 04, 2015">OCT</td>
<td class=3D"f" nowrap=3D"nowrap"><a href=3D"https://web.archiv=
e.org/web/20151108021555/http://duartes.org:80/gustavo/blog/post/kernel-boo=
t-process" title=3D"08 Nov 2015"><strong>Nov</strong></a></td>
</tr>
<!-- NEXT/PREV CAPTURE NAV AND DAY OF MONTH INDICATOR -->
<tr class=3D"d">
<td class=3D"b" nowrap=3D"nowrap"><a href=3D"https://web.archiv=
e.org/web/20150906204828/http://duartes.org:80/gustavo/blog/post/kernel-boo=
t-process/" title=3D"20:48:28 Sep 06, 2015"><img src=3D"https://web.archive=
.org/_static/images/toolbar/wm_tb_prv_on.png" alt=3D"Previous capture" widt=
h=3D"14" height=3D"16" border=3D"0"></a></td>
<td class=3D"c" id=3D"displayDayEl" style=3D"width:34px;font-si=
ze:22px;white-space:nowrap;" title=3D"You are here: 20:20:05 Oct 04, 2015">=
04</td>
<td class=3D"f" nowrap=3D"nowrap"><a href=3D"https://web.archiv=
e.org/web/20151008063330/http://duartes.org:80/gustavo/blog/post/kernel-boo=
t-process" title=3D"06:33:30 Oct 08, 2015"><img src=3D"https://web.archive.=
org/_static/images/toolbar/wm_tb_nxt_on.png" alt=3D"Next capture" width=3D"=
14" height=3D"16" border=3D"0"></a></td>
</tr>
<!-- NEXT/PREV YEAR NAV AND YEAR INDICATOR -->
<tr class=3D"y">
<td class=3D"b" nowrap=3D"nowrap"><a href=3D"https://web.archiv=
e.org/web/20140906141656/http://duartes.org/gustavo/blog/post/kernel-boot-p=
rocess/" title=3D"06 Sep 2014"><strong>2014</strong></a></td>
<td class=3D"c" id=3D"displayYearEl" title=3D"You are here: 20:=
20:05 Oct 04, 2015">2015</td>
<td class=3D"f" nowrap=3D"nowrap"><a href=3D"https://web.archiv=
e.org/web/20161021052118/http://duartes.org:80/gustavo/blog/post/kernel-boo=
t-process" title=3D"21 Oct 2016"><strong>2016</strong></a></td>
</tr>
</tbody>
</table>
</div>
<div class=3D"r" style=3D"display:flex;flex-flow:column nowrap;align-it=
ems:flex-end;justify-content:space-between;">
<div id=3D"wm-btns" style=3D"text-align:right;height:23px;">
<span class=3D"xxs">
<div id=3D"wm-save-snapshot-success">success</div>
<div id=3D"wm-save-snapshot-fail">fail</div>
<a id=3D"wm-save-snapshot-open" href=3D"https://web.archive.org/w=
eb/20151004202005/http://duartes.org/gustavo/blog/post/kernel-boot-process/=
#" title=3D"Share via My Web Archive" style=3D"display: none;">
<span class=3D"iconochive-web"></span>
</a>
<a href=3D"https://archive.org/account/login.php" title=3D"Sign I=
n" id=3D"wm-sign-in" style=3D"display: inline-block;">
<span class=3D"iconochive-person"></span>
</a>
<span id=3D"wm-save-snapshot-in-progress" class=3D"iconochive-web=
" style=3D"display: none;"></span>
</span>
<a class=3D"xxs" href=3D"http://faq.web.archive.org/" title=
=3D"Get some help using the Wayback Machine" style=3D"top:-6px;"><span clas=
s=3D"iconochive-question" style=3D"color:rgb(87,186,244);font-size:160%;"><=
/span></a>
<a id=3D"wm-tb-close" href=3D"https://web.archive.org/web/201510042=
02005/http://duartes.org/gustavo/blog/post/kernel-boot-process/#close" styl=
e=3D"top:-2px;" title=3D"Close the toolbar"><span class=3D"iconochive-remov=
e-circle" style=3D"color:#888888;font-size:240%;"></span></a>
</div>
<div id=3D"wm-share" class=3D"xxs">
<a href=3D"https://web.archive.org/web/20151004202005/http://web.ar=
chive.org/screenshot/http://duartes.org/gustavo/blog/post/kernel-boot-proce=
ss/" id=3D"wm-screenshot" title=3D"screenshot" style=3D"visibility: hidden;=
">
<span class=3D"wm-icon-screen-shot"></span>
</a>
<a href=3D"https://web.archive.org/web/20151004202005/http://duarte=
s.org/gustavo/blog/post/kernel-boot-process/#" id=3D"wm-video" title=3D"vid=
eo">
<span class=3D"iconochive-movies"></span>
</a>
<a id=3D"wm-share-facebook" href=3D"https://web.archive.org/web/201=
51004202005/http://duartes.org/gustavo/blog/post/kernel-boot-process/#" dat=
a-url=3D"https://web.archive.org/web/20151004202005/http://duartes.org/gust=
avo/blog/post/kernel-boot-process/" title=3D"Share on Facebook" style=3D"ma=
rgin-right:5px;" target=3D"_blank"><span class=3D"iconochive-facebook" styl=
e=3D"color:#3b5998;font-size:160%;"></span></a>
<a id=3D"wm-share-twitter" href=3D"https://web.archive.org/web/2015=
1004202005/http://duartes.org/gustavo/blog/post/kernel-boot-process/#" data=
-url=3D"https://web.archive.org/web/20151004202005/http://duartes.org/gusta=
vo/blog/post/kernel-boot-process/" title=3D"Share on Twitter" style=3D"marg=
in-right:5px;" target=3D"_blank"><span class=3D"iconochive-twitter" style=
=3D"color:#1dcaff;font-size:160%;"></span></a>
</div>
<div style=3D"padding-right:2px;text-align:right;white-space:nowrap;"=
>
<a id=3D"wm-expand" class=3D"wm-btn wm-closed" href=3D"https://web.=
archive.org/web/20151004202005/http://duartes.org/gustavo/blog/post/kernel-=
boot-process/#expand"><span id=3D"wm-expand-icon" class=3D"iconochive-down-=
solid"></span> <span class=3D"xxs" style=3D"font-size:80%;">About this capt=
ure</span></a>
</div>
</div>
</div>
<div id=3D"wm-capinfo" style=3D"border-top:1px solid #777;display:none;=
overflow: hidden">
<div id=3D"wm-capinfo-notice" source=3D"api"></div>
<div id=3D"wm-capinfo-collected-by">
<div style=3D"background-color:#666;color:#fff;font-weight:bold;text-al=
ign:center">COLLECTED BY</div>
<div style=3D"padding:3px;position:relative" id=3D"wm-collected-by-cont=
ent">
<div style=3D"display:inline-block;vertical-align:top;width:50%=
;">
<span class=3D"c-logo" style=3D"background-image:url(https://archive.org=
/services/img/webwidecrawl);"></span>
Organization: <a style=3D"color:#33f;" href=3D"https://archive.org/detail=
s/webwidecrawl" target=3D"_new"><span class=3D"wm-title">Internet Archive</=
span></a>
<div style=3D"max-height:75px;overflow:hidden;position:relative;">
<div style=3D"position:absolute;top:0;left:0;width:100%;height:75px;back=
ground:linear-gradient(to bottom,rgba(255,255,255,0) 0%,rgba(255,255,255,0)=
90%,rgba(255,255,255,255) 100%);"></div>
The Internet Archive discovers and captures web pages through many diffe=
rent web crawls.
At any given time several distinct crawls are running, some for months, and=
some every day or longer.
View the web archive through the <a href=3D"http://archive.org/web/web.php"=
>Wayback Machine</a>.
</div>
</div>
<div style=3D"display:inline-block;vertical-align:top;width:49%;">
<span class=3D"c-logo" style=3D"background-image:url(https://archive.org=
/services/img/liveweb)"></span>
<div>Collection: <a style=3D"color:#33f;" href=3D"https://archive.org/det=
ails/liveweb" target=3D"_new"><span class=3D"wm-title">Live Web Proxy Crawl=
s</span></a></div>
<div style=3D"max-height:75px;overflow:hidden;position:relative;">
<div style=3D"position:absolute;top:0;left:0;width:100%;height:75px;back=
ground:linear-gradient(to bottom,rgba(255,255,255,0) 0%,rgba(255,255,255,0)=
90%,rgba(255,255,255,255) 100%);"></div>
Content crawled via the <a href=3D"http://archive.org/web/web.php">Wayba=
ck Machine</a> Live Proxy mostly by the Save Page Now feature on web.archiv=
e.org.
<br><br>
Liveweb proxy is a component of Internet Archive=E2=80=99s wayback machine =
project. The liveweb proxy captures the content of a web page in real time,=
archives it into a ARC or WARC file and returns the ARC/WARC record back t=
o the wayback machine to process. The recorded ARC/WARC file becomes part o=
f the wayback machine in due course of time.
<br>
</div>
</div>
</div>
</div>
<div id=3D"wm-capinfo-timestamps">
<div style=3D"background-color:#666;color:#fff;font-weight:bold;text-al=
ign:center" title=3D"Timestamps for the elements of this page">TIMESTAMPS</=
div>
<div>
<div id=3D"wm-capresources" style=3D"margin:0 5px 5px 5px;max-height:=
250px;overflow-y:scroll !important"></div>
<div id=3D"wm-capresources-loading" style=3D"text-align:left;margin:0=
20px 5px 5px;display:none"><img src=3D"https://web.archive.org/_static/ima=
ges/loading.gif" alt=3D"loading"></div>
</div>
</div>
</div></div></div><link rel=3D"stylesheet" type=3D"text/css" href=3D"http=
s://web.archive.org/_static/css/banner-styles.css?v=3DS1zqJCYt"><link rel=
=3D"stylesheet" type=3D"text/css" href=3D"https://web.archive.org/_static/c=
ss/iconochive.css?v=3DqtvMKcIJ"><div class=3D"wb-autocomplete-suggestions "=
></div></template></div><div id=3D"wm-ipp-print">The Wayback Machine - http=
s://web.archive.org/web/20151004202005/http://duartes.org/gustavo/blog/post=
/kernel-boot-process/</div>
<!-- END WAYBACK TOOLBAR INSERT -->
=20
<div class=3D"masthead">
<div role=3D"banner" class=3D"container masthead">
<h1><a href=3D"https://web.archive.org/web/20151004202005/http://duar=
tes.org/gustavo/blog/" _pageexpand_=3D"4">Gustavo Duarte</a></h1>
=20
<h2>brain food for hackers</h2>
=20
</div>
</div>
<nav class=3D"navbar navbar-default" role=3D"navigation">
<div class=3D"container" id=3D"blogNav">
<div class=3D"navbar-header">
<button type=3D"button" class=3D"navbar-toggle collapsed" data-=
toggle=3D"collapse" data-target=3D"#bs-example-navbar-collapse-1">
<span class=3D"sr-only">Toggle navigation</span>
<span class=3D"icon-bar"></span>
<span class=3D"icon-bar"></span>
<span class=3D"icon-bar"></span>
</button>
<a class=3D"navbar-brand" href=3D"https://web.archive.org/web/2=
0151004202005/http://duartes.org/gustavo/blog" _pageexpand_=3D"8">Blog</a>
</div>
<!-- Collect the nav links, forms, and other content for toggling -=
->
<div class=3D"collapse navbar-collapse" id=3D"bs-example-navbar-col=
lapse-1">
<ul class=3D"nav navbar-nav">
<li>
<a href=3D"https://web.archive.org/web/20151004202005/h=
ttp://duartes.org/gustavo/blog/archives/" _pageexpand_=3D"16">Archives</a>
</li>
<li><a href=3D"https://web.archive.org/web/20151004202005/h=
ttp://duartes.org/gustavo/blog/about/" _pageexpand_=3D"20">About</a></li>
<li>
<a href=3D"https://web.archive.org/web/20151004202005/h=
ttp://feeds.feedburner.com/GustavoDuarte" rel=3D"subscribe-rss" title=3D"su=
bscribe via RSS" _pageexpand_=3D"24">Subscribe
</a>
</li>
<li>
<a href=3D"https://web.archive.org/web/20151004202005/h=
ttp://twitter.com/food4hackers" title=3D"follow me" _pageexpand_=3D"28">
<i class=3D"fa fa-twitter"></i>
</a>
</li>
<li>
<a href=3D"https://web.archive.org/web/20151004202005/h=
ttp://feeds.feedburner.com/GustavoDuarte" rel=3D"subscribe-rss" title=3D"su=
bscribe via RSS" _pageexpand_=3D"32">
<i class=3D"fa fa-rss"></i>
</a>
</li>
</ul>
</div><!-- /.navbar-collapse -->
</div><!-- /.container -->
</nav>
<div id=3D"main" class=3D"container">
<div id=3D"content">
<div class=3D"row no-gutters">
<div class=3D"col-lg-10">
<article class=3D"hentry" role=3D"article">
=20
<header>
=20
<h1 class=3D"entry-title">The Kernel Boot Process</h1>
=20
=20
<p class=3D"meta">
=20
=20
<time datetime=3D"2008-06-23T02:20:17-06:00" pubdate=3D"" data-updated=3D"t=
rue">Jun 23<span>rd</span>, 2008</time>
=20
</p>
=20
</header>
<div class=3D"entry-content"><p> The previous post explained <a href=3D"htt=
ps://web.archive.org/web/20151004202005/http://duartes.org/gustavo/blog/pos=
t/how-computers-boot-up" _pageexpand_=3D"64">how computers boot up</a> righ=
t up to the point where the boot loader, after stuffing the kernel image in=
to memory, is about to jump into the kernel entry point. This last post ab=
out booting takes a look at the guts of the kernel to see how an operating =
system starts life. Since I have an <a href=3D"https://web.archive.org/web/=
20151004202005/http://duartes.org/gustavo/blog/post/reality-driven-developm=
ent" _pageexpand_=3D"68">empirical bent</a> I=E2=80=99ll link heavily to th=
e sources for Linux kernel 2.6.25.6 at the <a href=3D"https://web.archive.o=
rg/web/20151004202005/http://lxr.linux.no/" _pageexpand_=3D"72">Linux Cross=
Reference</a>. The sources are very readable if you are familiar with C-li=
ke syntax; even if you miss some details you can get the gist of what=E2=80=
=99s happening. The main obstacle is the lack of context around some of th=
e code, such as when or why it runs or the underlying features of the mach=
ine. I hope to provide a bit of that context. Due to brevity (hah!) a lot o=
f fun stuff - like interrupts and memory - gets only a nod for now. The po=
st ends with the highlights for the Windows boot. </p>
<p> </p><p> At this point in the Intel x86 boot story the processor is run=
ning in real-mode, is able to address 1 MB of memory, and RAM looks like th=
is for a modern Linux system: </p> <p align=3D"center"> <img alt=3D"RAM =
contents after boot loader runs" src=3D"https://web.archive.org/web/2015100=
4202005im_/http://static.duartes.org/img/blogPosts/memoryAfterBootloader.pn=
g" _pageexpand_=3D"76"> <font size=3D"-1"><br>RAM contents after boot loa=
der is done</font> </p> <p> The kernel image has been loaded to memory by =
the boot loader using the BIOS disk I/O services. This image is an exact co=
py of the file in your hard drive that contains the kernel, e.g. <b>/boot/v=
mlinuz-2.6.22-14-server</b>. The image is split into two pieces: a small pa=
rt containing the real-mode kernel code is loaded below the 640K barrier; t=
he bulk of the kernel, which runs in protected mode, is loaded after the fi=
rst megabyte of memory. </p> <p> The action starts in the real-mode kernel=
header pictured above. This region of memory is used to implement the <a h=
ref=3D"https://web.archive.org/web/20151004202005/http://lxr.linux.no/linux=
+v2.6.25.6/Documentation/i386/boot.txt" _pageexpand_=3D"80"> Linux boot p=
rotocol</a> between the boot loader and the kernel. Some of the values ther=
e are read by the boot loader while doing its work. These include amenities=
such as a human-readable string containing the kernel version, but also cr=
ucial information like the size of the real-mode kernel piece. The boot loa=
der also <i>writes</i> values to this region, such as the memory address fo=
r the command-line parameters given by the user in the boot menu. Once the =
boot loader is finished it has filled in all of the parameters required by =
the kernel header. It=E2=80=99s then time to jump into the kernel entry poi=
nt. The diagram below shows the code sequence for the kernel initialization=
, along with source directories, files, and line numbers: </p> <p align=3D=
"center"> <img alt=3D"Architecture-specific Linux Kernel Initialization" =
src=3D"https://web.archive.org/web/20151004202005im_/http://static.duartes.=
org/img/blogPosts/kernelInitPartOne.png" _pageexpand_=3D"84"> <font siz=
e=3D"-1"><br>Architecture-specific Linux Kernel Initialization</font> </p> =
<p> The early kernel start-up for the Intel architecture is in file <a hr=
ef=3D"https://web.archive.org/web/20151004202005/http://lxr.linux.no/linux+=
v2.6.25.6/arch/x86/boot/header.S" _pageexpand_=3D"88">arch/x86/boot/header.=
S</a>. It=E2=80=99s in assembly language, which is rare for the kernel at l=
arge but common for boot code. The start of this file actually contains boo=
t sector code, a left over from the days when Linux could work without a bo=
ot loader. Nowadays this boot sector, if executed, only prints a =E2=80=9Cb=
ugger_off_msg=E2=80=9D to the user and reboots. Modern boot loaders ignore =
this legacy code. After the boot sector code we have the first 15 bytes of =
the real-mode kernel header; these two pieces together add up to 512 bytes,=
the size of a typical disk sector on Intel hardware.</p> <p> After these =
512 bytes, at offset 0x200, we find the very first instruction that runs a=
s part of the Linux kernel: the real-mode entry point. It=E2=80=99s in <a =
href=3D"https://web.archive.org/web/20151004202005/http://lxr.linux.no/linu=
x+v2.6.25.6/arch/x86/boot/header.S#L110" _pageexpand_=3D"92">header.S:110</=
a> and it is a 2-byte jump written directly in machine code as 0x3aeb. You=
can verify this by running hexdump on your kernel image and seeing the byt=
es at that offset =E2=80=93 just a sanity check to make sure it=E2=80=99s n=
ot all a dream. The boot loader jumps into this location when it is finishe=
d, which in turn jumps to <a href=3D"https://web.archive.org/web/201510042=
02005/http://lxr.linux.no/linux+v2.6.25.6/arch/x86/boot/header.S#L229" _pag=
eexpand_=3D"96">header.S:229</a> where we have a regular assembly routine c=
alled start_of_setup. This short routine sets up a stack, zeroes the <a hre=
f=3D"https://web.archive.org/web/20151004202005/http://en.wikipedia.org/wik=
i/.bss" _pageexpand_=3D"100">bss</a> segment (the area that contains stati=
c variables, so they start with zero values) for the real-mode kernel and t=
hen jumps to good old C code at <a href=3D"https://web.archive.org/web/201=
51004202005/http://lxr.linux.no/linux+v2.6.25.6/arch/x86/boot/main.c#L122" =
_pageexpand_=3D"104">arch/x86/boot/main.c:122</a>. </p> <p> main() does so=
me house keeping like detecting memory layout, setting a video mode, etc. I=
t then calls <a href=3D"https://web.archive.org/web/20151004202005/http://=
lxr.linux.no/linux+v2.6.25.6/arch/x86/boot/pm.c#L153" _pageexpand_=3D"108">=
go_to_protected_mode()</a>. Before the CPU can be set to protected mode, ho=
wever, a few tasks must be done. There are two main issues: interrupts and =
memory. In real-mode the <a href=3D"https://web.archive.org/web/20151004202=
005/http://en.wikipedia.org/wiki/Interrupt_vector_table" _pageexpand_=3D"11=
2">interrupt vector table</a> for the processor is always at memory address=
0, whereas in protected mode the location of the interrupt vector table is=
stored in a CPU register called IDTR. Meanwhile, the translation of logic=
al memory addresses (the ones programs manipulate) to linear memory address=
es (a raw number from 0 to the top of the memory) is different between real=
-mode and protected mode. Protected mode requires a register called GDTR to=
be loaded with the address of a <a href=3D"https://web.archive.org/web/201=
51004202005/http://en.wikipedia.org/wiki/Global_descriptor_table" _pageexpa=
nd_=3D"116">Global Descriptor Table</a> for memory. So go_to_protected_mode=
() calls <a href=3D"https://web.archive.org/web/20151004202005/http://lxr.=
linux.no/linux+v2.6.25.6/arch/x86/boot/pm.c#L144" _pageexpand_=3D"120">setu=
p_idt()</a> and <a href=3D"https://web.archive.org/web/20151004202005/http=
://lxr.linux.no/linux+v2.6.25.6/arch/x86/boot/pm.c#L115" _pageexpand_=3D"12=
4">setup_gdt()</a> to install a temporary interrupt descriptor table and gl=
obal descriptor table.</p> <p> We=E2=80=99re now ready for the plunge into=
protected mode, which is done by <a href=3D"https://web.archive.org/web/20=
151004202005/http://lxr.linux.no/linux+v2.6.25.6/arch/x86/boot/pmjump.S#L31=
" _pageexpand_=3D"128">protected_mode_jump</a>, another assembly routine. =
This routine enables protected mode by setting the PE bit in the CR0 CPU r=
egister. At this point we=E2=80=99re running with <a href=3D"https://web.ar=
chive.org/web/20151004202005/http://en.wikipedia.org/wiki/Paging" _pageexpa=
nd_=3D"132">paging</a> <b>disabled</b>; paging is an optional feature of th=
e processor, even in protected mode, and there=E2=80=99s no need for it yet=
. What=E2=80=99s important is that we=E2=80=99re no longer confined to the =
640K barrier and can now address up to 4GB of RAM. The routine then calls t=
he 32-bit kernel entry point, which is <a href=3D"https://web.archive.org=
/web/20151004202005/http://lxr.linux.no/linux+v2.6.25.6/arch/x86/boot/compr=
essed/head_32.S#L35" _pageexpand_=3D"136">startup_32</a> for compressed ke=
rnels. This routine does some basic register initializations and calls <=
a href=3D"https://web.archive.org/web/20151004202005/http://lxr.linux.no/li=
nux+v2.6.25.6/arch/x86/boot/compressed/misc.c#L368" _pageexpand_=3D"140">de=
compress_kernel()</a>, a C function to do the actual decompression. </p><=
p>decompress_kernel() prints the familiar =E2=80=9CDecompressing Linux=E2=
=80=A6=E2=80=9D message. Decompression happens in-place and once it=E2=80=
=99s finished the uncompressed kernel image has overwritten the compressed=
one pictured in the first diagram. Hence the uncompressed contents also st=
art at 1MB. decompress_kernel() then prints =E2=80=9Cdone.=E2=80=9D and the=
comforting =E2=80=9CBooting the kernel.=E2=80=9D By =E2=80=9CBooting=E2=
=80=9D it means a jump to the final entry point in this whole story, given=
to Linus by God himself atop <a href=3D"https://web.archive.org/web/201510=
04202005/http://en.wikipedia.org/wiki/Halti" _pageexpand_=3D"144">Mountain =
Halti</a>, which is the protected-mode kernel entry point at the start of t=
he second megabyte of RAM (0x100000). That sacred location contains a rout=
ine called, uh, <a href=3D"https://web.archive.org/web/20151004202005/http:=
//lxr.linux.no/linux+v2.6.25.6/arch/x86/kernel/head_32.S#L86" _pageexpand_=
=3D"148">startup_32</a>. But <i>this</i> one is in a different directory, y=
ou see. </p> <p> The second incarnation of startup_32 is also an assembly=
routine, but it contains 32-bit mode initializations. It clears the bss se=
gment for the protected-mode kernel (which is the <i>true</i> kernel that w=
ill now run until the machine reboots or shuts down), sets up the final glo=
bal descriptor table for memory, builds page tables so that paging can be t=
urned on, enables paging, initializes a stack, creates the final interrupt=
descriptor table, and finally jumps to to the architecture-independent ke=
rnel start-up, <a href=3D"https://web.archive.org/web/20151004202005/http:=
//lxr.linux.no/linux+v2.6.25.6/init/main.c#L507" _pageexpand_=3D"152">start=
_kernel()</a>. The diagram below shows the code flow for the last leg of th=
e boot: </p> <p align=3D"center"> <img alt=3D"Architecture-independent=
Linux Kernel Initialization" src=3D"https://web.archive.org/web/2015100420=
2005im_/http://static.duartes.org/img/blogPosts/kernelInitPartTwo.png" _pag=
eexpand_=3D"156"> <font size=3D"-1"><br>Architecture-independent Linux Ker=
nel Initialization</font> </p> <p> start_kernel() looks more like typical =
kernel code, which is nearly all C and machine independent. The function is=
a long list of calls to initializations of the various kernel subsystems a=
nd data structures. These include the scheduler, memory zones, time keeping=
, and so on. start_kernel() then calls <a href=3D"https://web.archive.org/=
web/20151004202005/http://lxr.linux.no/linux+v2.6.25.6/init/main.c#L432" _p=
ageexpand_=3D"160">rest_init()</a>, at which point things are almost all wo=
rking. rest_init() creates a kernel thread passing another function, <a hre=
f=3D"https://web.archive.org/web/20151004202005/http://lxr.linux.no/linux+v=
2.6.25.6/init/main.c#L808" _pageexpand_=3D"164">kernel_init()</a>, as the e=
ntry point. rest_init() then calls <a href=3D"https://web.archive.org/web/2=
0151004202005/http://lxr.linux.no/linux+v2.6.25.6/kernel/sched.c#L3959" _pa=
geexpand_=3D"168">schedule()</a> to kickstart task scheduling and goes to =
sleep by calling <a href=3D"https://web.archive.org/web/20151004202005/htt=
p://lxr.linux.no/linux+v2.6.25.6/arch/x86/kernel/process_32.c#L180" _pageex=
pand_=3D"172">cpu_idle()</a>, which is the idle thread for the Linux kernel=
. cpu_idle() runs forever and so does process zero, which hosts it. Wheneve=
r there is work to do =E2=80=93 a runnable process =E2=80=93 process zero g=
ets booted out of the CPU, only to return when no runnable processes are av=
ailable. </p> <p> But here=E2=80=99s the kicker for us. This idle loop is =
the end of the long thread we followed since boot, it=E2=80=99s the final d=
escendent of the very first <i>jump</i> executed by the processor after pow=
er up. All of this mess, from reset vector to BIOS to MBR to boot loader to=
real-mode kernel to protected-mode kernel, all of it leads right here, ju=
mp by jump by jump it ends in the idle loop for the boot processor, cpu_idl=
e(). Which is really kind of cool. However, this can=E2=80=99t be the whol=
e story otherwise the computer would do no work. </p> <p> At this point, t=
he kernel thread started previously is ready to kick in, displacing process=
0 and its idle thread. And so it does, at which point kernel_init() start=
s running since it was given as the thread entry point. <a href=3D"https:/=
/web.archive.org/web/20151004202005/http://lxr.linux.no/linux+v2.6.25.6/ini=
t/main.c#L808" _pageexpand_=3D"176">kernel_init()</a> is responsible for in=
itializing the remaining CPUs in the system, which have been halted since b=
oot. All of the code we=E2=80=99ve seen so far has been executed in a singl=
e CPU, called the boot processor. As the other CPUs, called application pro=
cessors, are started they come up in real-mode and must run through several=
initializations as well. Many of the code paths are common, as you can see=
in the code for <a href=3D"https://web.archive.org/web/20151004202005/http=
://lxr.linux.no/linux+v2.6.25.6/arch/x86/kernel/head_32.S#L86" _pageexpand_=
=3D"180">startup_32</a>, but there are slight forks taken by the late-comin=
g application processors. Finally, kernel_init() calls <a href=3D"https:/=
/web.archive.org/web/20151004202005/http://lxr.linux.no/linux+v2.6.25.6/ini=
t/main.c#L769" _pageexpand_=3D"184">init_post()</a>, which tries to execut=
e a user-mode process in the following order: /sbin/init, /etc/init, /bin/i=
nit, and /bin/sh. If all fail, the kernel will panic. Luckily init is usual=
ly there, and starts running as PID 1. It checks its configuration file to=
figure out which processes to launch, which might include X11 Windows, pro=
grams for logging in on the console, network daemons, and so on. Thus ends =
the boot process as yet another Linux box starts running somewhere. May you=
r uptime be long and untroubled. </p> <p> The process for Windows is simil=
ar in many ways, given the common architecture. Many of the same problems =
are faced and similar initializations must be done. When it comes to boot o=
ne of the biggest differences is that Windows packs all of the real-mode ke=
rnel code, and some of the initial protected mode code, into the boot loade=
r itself (C:\NTLDR). So instead of having two regions in the same kernel im=
age, Windows uses different binary images. Plus Linux completely separates =
boot loader and kernel; in a way this automatically falls out of the open s=
ource process. The diagram below shows the main bits for the Windows kernel=
: </p><p> </p><p align=3D"center"> <img alt=3D"Windows Kernel Initiali=
zation" src=3D"https://web.archive.org/web/20151004202005im_/http://static.=
duartes.org/img/blogPosts/windowsKernelInit.png" _pageexpand_=3D"188"> =
<font size=3D"-1"><br>Windows Kernel Initialization</font> </p> <p> The Wi=
ndows user-mode start-up is naturally very different. There=E2=80=99s no /s=
bin/init, but rather Csrss.exe and Winlogon.exe. Winlogon spawns <b>Servic=
es.exe</b>, which starts all of the Windows Services, and Lsass.exe, the lo=
cal security authentication subsystem. The classic Windows login dialog run=
s in the context of Winlogon. </p> <p> This is the end of this boot series=
. Thanks everyone for reading and for feedback. I=E2=80=99m sorry some thin=
gs got superficial treatment; I=E2=80=99ve gotta start somewhere and only s=
o much fits into blog-sized bites. But nothing like a day after the next; m=
y plan is to do regular =E2=80=9CSoftware Illustrated=E2=80=9D posts like t=
his series along with other topics. Meanwhile, here are some resources: </p=
> <ul> <li>The best, most important resource, is source code for real ker=
nels, either Linux or one of the BSDs.</li> <li>Intel publishes excellent=
<a href=3D"https://web.archive.org/web/20151004202005/http://www.intel.c=
om/products/processor/manuals/index.htm" _pageexpand_=3D"224">Software Deve=
loper=E2=80=99s Manuals</a>, which you can download for free.</li> =
<li><a href=3D"https://web.archive.org/web/20151004202005/http://www.amazon=
.com/exec/obidos/ASIN/0596005652/gustduar-20" _pageexpand_=3D"228">Understa=
nding the Linux Kernel</a> is a good book and walks through a lot of the Li=
nux Kernel sources. It=E2=80=99s getting outdated and it=E2=80=99s dry, b=
ut I=E2=80=99d still recommend it to anyone who wants to grok the kernel. =
<a href=3D"https://web.archive.org/web/20151004202005/http://www.amazon.=
com/exec/obidos/ASIN/0596005903/gustduar-20" _pageexpand_=3D"232">Linux Dev=
ice Drivers</a> is more fun, teaches well, but is limited in scope. Finally=
, Patrick Moroney suggested <a href=3D"https://web.archive.org/web/20151004=
202005/http://www.amazon.com/exec/obidos/ASIN/0672327201/gustduar-20" _page=
expand_=3D"236">Linux Kernel Development</a> by Robert Love in the comments=
for this post. I=E2=80=99ve heard other positive reviews for that book, so=
it sounds worth checking out. </li> <li>For Windows, the best ref=
erence by far is <a href=3D"https://web.archive.org/web/20151004202005/ht=
tp://www.amazon.com/exec/obidos/ASIN/0735625301/gustduar-20" _pageexpand_=
=3D"240">Windows Internals</a> by David Solomon and <a href=3D"https://web=
.archive.org/web/20151004202005/http://blogs.technet.com/markrussinovich/" =
_pageexpand_=3D"244">Mark Russinovich</a>, the latter of Sysinternals fame.=
This is a great book, well-written and thorough. The main downside is=
the lack of source code. </li> </ul><p></p>
<p>[Update: In a <a href=3D"https://web.archive.org/web/20151004202005/http=
://duartes.org/gustavo/blog/post/kernel-boot-process/#comment-13790" _pagee=
xpand_=3D"192">comment below</a>, Nix covered a lot of ground on the initia=
l root file system that I glossed over. Thanks to <a href=3D"https://web.ar=
chive.org/web/20151004202005/http://www.sirartisan.net/" _pageexpand_=3D"19=
6">Marius Barbu</a> for catching a mistake where I wrote =E2=80=9CCR3=E2=80=
=9D instead of GDTR]</p>
<p><a href=3D"https://web.archive.org/web/20151004202005/http://duartes.org=
/gustavo/blog/comments/kernel-boot.html" _pageexpand_=3D"200">104 Comments<=
/a></p>
</div>
<footer>
<div class=3D"inner clearfix">
<div class=3D"socialNav">
<div class=3D"socialNav">
<ul class=3D"socialNav">
<li style=3D"float:left">
<a href=3D"https://web.archive.org/web/20151004202005/http://tw=
itter.com/food4hackers" title=3D"follow me" _pageexpand_=3D"272">
<img src=3D"https://web.archive.org/web/20151004202005im_/h=
ttp://duartes.org/gustavo/blog/images/twitter.png" _pageexpand_=3D"284">
</a>
</li>
<li style=3D"float:right">
<a href=3D"https://web.archive.org/web/20151004202005/mailto:fo=
od4hackers@duartes.org" title=3D"email me" _pageexpand_=3D"276">
<img src=3D"https://web.archive.org/web/20151004202005im_/h=
ttp://duartes.org/gustavo/blog/images/email.png" _pageexpand_=3D"288">
</a>
</li>
<li>
<a href=3D"https://web.archive.org/web/20151004202005/http://fe=
eds.feedburner.com/GustavoDuarte" rel=3D"subscribe-rss" title=3D"subscribe =
via RSS" _pageexpand_=3D"280">
<img src=3D"https://web.archive.org/web/20151004202005im_/h=
ttp://duartes.org/gustavo/blog/images/rss.png" _pageexpand_=3D"292">
</a>
</li>
</ul>
</div>
</div>
</div>
<p class=3D"meta-footer">
<i class=3D"fa fa-user"></i>
=20
=20
<span>Posted by <span>Gustavo Duarte</span></span>
<i class=3D"fa fa-calendar"></i>
=20
=20
=20
<time datetime=3D"2008-06-23T02:20:17-06:00" pubdate=3D"" dat=
a-updated=3D"true">Jun 23<span>rd</span>, 2008</time>
=20
<i class=3D"fa fa-tags"></i>
=20
<span class=3D"categories">
=20
<a class=3D"category" href=3D"https://web.archive.org/web/2015100420200=
5/http://duartes.org/gustavo/blog/category/internals/" _pageexpand_=3D"248"=
>Internals</a>, <a class=3D"category" href=3D"https://web.archive.org/web/2=
0151004202005/http://duartes.org/gustavo/blog/category/linux/" _pageexpand_=
=3D"252">Linux</a>, <a class=3D"category" href=3D"https://web.archive.org/w=
eb/20151004202005/http://duartes.org/gustavo/blog/category/software-illustr=
ated/" _pageexpand_=3D"256">Software Illustrated</a>
=20
</span>
</p>
=20
<div class=3D"sharing">
=20
=20
=20
</div>
=20
<p>
=20
<a href=3D"https://web.archive.org/web/20151004202005/http://du=
artes.org/gustavo/blog/post/how-computers-boot-up/" title=3D"Previous Post:=
How Computers Boot Up" _pageexpand_=3D"204">=C2=AB How Computers Boot Up</=
a>
=20
=20
<a style=3D"float:right" href=3D"https://web.archive.org/web/20=
151004202005/http://duartes.org/gustavo/blog/post/lucky-to-be-a-programmer/=
" title=3D"Next Post: Lucky to be a Programmer" _pageexpand_=3D"208">Lucky =
to be a Programmer =C2=BB</a>
=20
</p>
</footer>
</article>
=20
</div>
<aside class=3D"sidebar col-lg-2">
=20
<section class=3D"panel panel-default titleFont">
<div class=3D"panel-heading">
<h3 class=3D"panel-title">Recent Posts</h3>
</div>
<div id=3D"recent_posts" class=3D"list-group">
=20
<a class=3D"list-group-item " href=3D"https://web.archive.org/web/20151=
004202005/http://duartes.org/gustavo/blog/post/home-row-computing-on-mac/" =
_pageexpand_=3D"40">Home Row Computing on Macs</a>
=20
<a class=3D"list-group-item " href=3D"https://web.archive.org/web/20151=
004202005/http://duartes.org/gustavo/blog/post/system-calls/" _pageexpand_=
=3D"44">System Calls Make the World Go Round</a>
=20
<a class=3D"list-group-item " href=3D"https://web.archive.org/web/20151=
004202005/http://duartes.org/gustavo/blog/post/what-does-an-idle-cpu-do/" _=
pageexpand_=3D"48">What Does an Idle CPU Do?</a>
=20
<a class=3D"list-group-item " href=3D"https://web.archive.org/web/20151=
004202005/http://duartes.org/gustavo/blog/post/when-does-your-os-run/" _pag=
eexpand_=3D"52">When Does Your OS Run?</a>
=20
<a class=3D"list-group-item " href=3D"https://web.archive.org/web/20151=
004202005/http://duartes.org/gustavo/blog/post/closures-objects-heap/" _pag=
eexpand_=3D"56">Closures, Objects, and the Fauna of the Heap</a>
=20
</div>
</section>
<div>
<a href=3D"https://web.archive.org/web/20151004202005/http://duartes.or=
g/gustavo/blog/about/" title=3D"about" _pageexpand_=3D"36">
<img src=3D"https://web.archive.org/web/20151004202005im_/http://du=
artes.org/gustavo/blog/images/circleChai120px.png" alt=3D"Author and his do=
g Chai" style=3D"display: block;margin:40px auto" _pageexpand_=3D"60">
</a>
</div>
<div class=3D"socialNav">
<ul class=3D"socialNav">
<li style=3D"float:left">
<a href=3D"https://web.archive.org/web/20151004202005/http://tw=
itter.com/food4hackers" title=3D"follow me" _pageexpand_=3D"212">
<img src=3D"https://web.archive.org/web/20151004202005im_/h=
ttp://duartes.org/gustavo/blog/images/twitter.png" _pageexpand_=3D"260">
</a>
</li>
<li style=3D"float:right">
<a href=3D"https://web.archive.org/web/20151004202005/mailto:fo=
od4hackers@duartes.org" title=3D"email me" _pageexpand_=3D"216">
<img src=3D"https://web.archive.org/web/20151004202005im_/h=
ttp://duartes.org/gustavo/blog/images/email.png" _pageexpand_=3D"264">
</a>
</li>
<li>
<a href=3D"https://web.archive.org/web/20151004202005/http://fe=
eds.feedburner.com/GustavoDuarte" rel=3D"subscribe-rss" title=3D"subscribe =
via RSS" _pageexpand_=3D"220">
<img src=3D"https://web.archive.org/web/20151004202005im_/h=
ttp://duartes.org/gustavo/blog/images/rss.png" _pageexpand_=3D"268">
</a>
</li>
</ul>
</div>
=20
</aside>
</div>
</div>
</div>
<div id=3D"footer" role=3D"contentinfo">
<div class=3D"container">
<p>
Copyright =C2=A9 2008-2014 Gustavo Duarte -
<span class=3D"credit">Powered by <a href=3D"https://web.archive.=
org/web/20151004202005/http://octopress.org/" _pageexpand_=3D"12">Octopress=
</a></span>
</p>
</div>
</div>
<!-- HTML5 shim and Respond.js for IE8 support of HTML5 elements and medi=
a queries -->
<!-- WARNING: Respond.js doesn't work if you view the page via file:// -->
<!--[if lt IE 9]>
<script src=3D"https://oss.maxcdn.com/html5shiv/3.7.2/html5shiv.min.js"=
></script>
<script src=3D"https://oss.maxcdn.com/respond/1.4.2/respond.min.js"></s=
cript>
<![endif]-->
<div id=3D"pt-ext-root" flashstop-shadow=3D"true" flashstopped=3D"true"><te=
mplate shadowmode=3D"open"><div></div><div></div></template></div><textarea=
id=3D"BFI_DATA" style=3D"width: 1px; height: 1px; display: none;"></textar=
ea><title> </title><div id=3D"WidgetFloaterPanels" translate=3D"no" style=
=3D"display: none; text-align: left; direction: ltr; visibility: hidden;" c=
lass=3D"LTRStyle"> <div id=3D"WidgetFloater" style=3D"display: none"> <div =
id=3D"WidgetLogoPanel"> <span id=3D"WidgetTranslateWithSpan"><span>TRANSLAT=
E with </span><img id=3D"FloaterLogo" _pageexpand_=3D"316"></span> <span id=
=3D"WidgetCloseButton" title=3D"Exit Translation">x</span></div> <div id=3D=
"LanguageMenuPanel"> <div class=3D"DDStyle_outer"><input name=3D"LanguageMe=
nu_svid" type=3D"text" id=3D"LanguageMenu_svid" style=3D"display:none;" aut=
ocomplete=3D"on" value=3D"en"> <input name=3D"LanguageMenu_textid" type=3D"=
text" id=3D"LanguageMenu_textid" style=3D"display:none;" autocomplete=3D"on=
"> <span tabindex=3D"0" class=3D"DDStyle" id=3D"__LanguageMenu_header">Engl=
ish</span> <div style=3D"position:relative;text-align:left;left:0;"><div st=
yle=3D"position:absolute;width:;left:0px;"><div class=3D"DDStyle" style=3D"=
display:none;" id=3D"__LanguageMenu_popup"> <table id=3D"LanguageMenu" bord=
er=3D"0"> <tbody><tr> <td><a tabindex=3D"-1" href=3D"https://web.archive.or=
g/web/20151004202005/http://duartes.org/gustavo/blog/post/kernel-boot-proce=
ss/#ar" _pageexpand_=3D"376">Arabic</a></td><td><a tabindex=3D"-1" href=3D"=
https://web.archive.org/web/20151004202005/http://duartes.org/gustavo/blog/=
post/kernel-boot-process/#he" _pageexpand_=3D"380">Hebrew</a></td><td><a ta=
bindex=3D"-1" href=3D"https://web.archive.org/web/20151004202005/http://dua=
rtes.org/gustavo/blog/post/kernel-boot-process/#pl" _pageexpand_=3D"384">Po=
lish</a></td> </tr><tr> <td><a tabindex=3D"-1" href=3D"https://web.archive.=
org/web/20151004202005/http://duartes.org/gustavo/blog/post/kernel-boot-pro=
cess/#bg" _pageexpand_=3D"388">Bulgarian</a></td><td><a tabindex=3D"-1" hre=
f=3D"https://web.archive.org/web/20151004202005/http://duartes.org/gustavo/=
blog/post/kernel-boot-process/#hi" _pageexpand_=3D"392">Hindi</a></td><td><=
a tabindex=3D"-1" href=3D"https://web.archive.org/web/20151004202005/http:/=
/duartes.org/gustavo/blog/post/kernel-boot-process/#pt" _pageexpand_=3D"396=
">Portuguese</a></td> </tr><tr> <td><a tabindex=3D"-1" href=3D"https://web.=
archive.org/web/20151004202005/http://duartes.org/gustavo/blog/post/kernel-=
boot-process/#ca" _pageexpand_=3D"400">Catalan</a></td><td><a tabindex=3D"-=
1" href=3D"https://web.archive.org/web/20151004202005/http://duartes.org/gu=
stavo/blog/post/kernel-boot-process/#mww" _pageexpand_=3D"404">Hmong Daw</a=
></td><td><a tabindex=3D"-1" href=3D"https://web.archive.org/web/2015100420=
2005/http://duartes.org/gustavo/blog/post/kernel-boot-process/#ro" _pageexp=
and_=3D"408">Romanian</a></td> </tr><tr> <td><a tabindex=3D"-1" href=3D"htt=
ps://web.archive.org/web/20151004202005/http://duartes.org/gustavo/blog/pos=
t/kernel-boot-process/#zh-CHS" _pageexpand_=3D"412">Chinese Simplified</a><=
/td><td><a tabindex=3D"-1" href=3D"https://web.archive.org/web/201510042020=
05/http://duartes.org/gustavo/blog/post/kernel-boot-process/#hu" _pageexpan=
d_=3D"416">Hungarian</a></td><td><a tabindex=3D"-1" href=3D"https://web.arc=
hive.org/web/20151004202005/http://duartes.org/gustavo/blog/post/kernel-boo=
t-process/#ru" _pageexpand_=3D"420">Russian</a></td> </tr><tr> <td><a tabin=
dex=3D"-1" href=3D"https://web.archive.org/web/20151004202005/http://duarte=
s.org/gustavo/blog/post/kernel-boot-process/#zh-CHT" _pageexpand_=3D"424">C=
hinese Traditional</a></td><td><a tabindex=3D"-1" href=3D"https://web.archi=
ve.org/web/20151004202005/http://duartes.org/gustavo/blog/post/kernel-boot-=
process/#id" _pageexpand_=3D"428">Indonesian</a></td><td><a tabindex=3D"-1"=
href=3D"https://web.archive.org/web/20151004202005/http://duartes.org/gust=
avo/blog/post/kernel-boot-process/#sk" _pageexpand_=3D"432">Slovak</a></td>=
</tr><tr> <td><a tabindex=3D"-1" href=3D"https://web.archive.org/web/20151=
004202005/http://duartes.org/gustavo/blog/post/kernel-boot-process/#cs" _pa=
geexpand_=3D"436">Czech</a></td><td><a tabindex=3D"-1" href=3D"https://web.=
archive.org/web/20151004202005/http://duartes.org/gustavo/blog/post/kernel-=
boot-process/#it" _pageexpand_=3D"440">Italian</a></td><td><a tabindex=3D"-=
1" href=3D"https://web.archive.org/web/20151004202005/http://duartes.org/gu=
stavo/blog/post/kernel-boot-process/#sl" _pageexpand_=3D"444">Slovenian</a>=
</td> </tr><tr> <td><a tabindex=3D"-1" href=3D"https://web.archive.org/web/=
20151004202005/http://duartes.org/gustavo/blog/post/kernel-boot-process/#da=
" _pageexpand_=3D"448">Danish</a></td><td><a tabindex=3D"-1" href=3D"https:=
//web.archive.org/web/20151004202005/http://duartes.org/gustavo/blog/post/k=
ernel-boot-process/#ja" _pageexpand_=3D"452">Japanese</a></td><td><a tabind=
ex=3D"-1" href=3D"https://web.archive.org/web/20151004202005/http://duartes=
.org/gustavo/blog/post/kernel-boot-process/#es" _pageexpand_=3D"456">Spanis=
h</a></td> </tr><tr> <td><a tabindex=3D"-1" href=3D"https://web.archive.org=
/web/20151004202005/http://duartes.org/gustavo/blog/post/kernel-boot-proces=
s/#nl" _pageexpand_=3D"460">Dutch</a></td><td><a tabindex=3D"-1" href=3D"ht=
tps://web.archive.org/web/20151004202005/http://duartes.org/gustavo/blog/po=
st/kernel-boot-process/#tlh" _pageexpand_=3D"464">Klingon</a></td><td><a ta=
bindex=3D"-1" href=3D"https://web.archive.org/web/20151004202005/http://dua=
rtes.org/gustavo/blog/post/kernel-boot-process/#sv" _pageexpand_=3D"468">Sw=
edish</a></td> </tr><tr> <td><a tabindex=3D"-1" href=3D"https://web.archive=
.org/web/20151004202005/http://duartes.org/gustavo/blog/post/kernel-boot-pr=
ocess/#en" _pageexpand_=3D"472">English</a></td><td><a tabindex=3D"-1" href=
=3D"https://web.archive.org/web/20151004202005/http://duartes.org/gustavo/b=
log/post/kernel-boot-process/#ko" _pageexpand_=3D"476">Korean</a></td><td><=
a tabindex=3D"-1" href=3D"https://web.archive.org/web/20151004202005/http:/=
/duartes.org/gustavo/blog/post/kernel-boot-process/#th" _pageexpand_=3D"480=
">Thai</a></td> </tr><tr> <td><a tabindex=3D"-1" href=3D"https://web.archiv=
e.org/web/20151004202005/http://duartes.org/gustavo/blog/post/kernel-boot-p=
rocess/#et" _pageexpand_=3D"484">Estonian</a></td><td><a tabindex=3D"-1" hr=
ef=3D"https://web.archive.org/web/20151004202005/http://duartes.org/gustavo=
/blog/post/kernel-boot-process/#lv" _pageexpand_=3D"488">Latvian</a></td><t=
d><a tabindex=3D"-1" href=3D"https://web.archive.org/web/20151004202005/htt=
p://duartes.org/gustavo/blog/post/kernel-boot-process/#tr" _pageexpand_=3D"=
492">Turkish</a></td> </tr><tr> <td><a tabindex=3D"-1" href=3D"https://web.=
archive.org/web/20151004202005/http://duartes.org/gustavo/blog/post/kernel-=
boot-process/#fi" _pageexpand_=3D"496">Finnish</a></td><td><a tabindex=3D"-=
1" href=3D"https://web.archive.org/web/20151004202005/http://duartes.org/gu=
stavo/blog/post/kernel-boot-process/#lt" _pageexpand_=3D"500">Lithuanian</a=
></td><td><a tabindex=3D"-1" href=3D"https://web.archive.org/web/2015100420=
2005/http://duartes.org/gustavo/blog/post/kernel-boot-process/#uk" _pageexp=
and_=3D"504">Ukrainian</a></td> </tr><tr> <td><a tabindex=3D"-1" href=3D"ht=
tps://web.archive.org/web/20151004202005/http://duartes.org/gustavo/blog/po=
st/kernel-boot-process/#fr" _pageexpand_=3D"508">French</a></td><td><a tabi=
ndex=3D"-1" href=3D"https://web.archive.org/web/20151004202005/http://duart=
es.org/gustavo/blog/post/kernel-boot-process/#ms" _pageexpand_=3D"512">Mala=
y</a></td><td><a tabindex=3D"-1" href=3D"https://web.archive.org/web/201510=
04202005/http://duartes.org/gustavo/blog/post/kernel-boot-process/#ur" _pag=
eexpand_=3D"516">Urdu</a></td> </tr><tr> <td><a tabindex=3D"-1" href=3D"htt=
ps://web.archive.org/web/20151004202005/http://duartes.org/gustavo/blog/pos=
t/kernel-boot-process/#de" _pageexpand_=3D"520">German</a></td><td><a tabin=
dex=3D"-1" href=3D"https://web.archive.org/web/20151004202005/http://duarte=
s.org/gustavo/blog/post/kernel-boot-process/#mt" _pageexpand_=3D"524">Malte=
se</a></td><td><a tabindex=3D"-1" href=3D"https://web.archive.org/web/20151=
004202005/http://duartes.org/gustavo/blog/post/kernel-boot-process/#vi" _pa=
geexpand_=3D"528">Vietnamese</a></td> </tr><tr> <td><a tabindex=3D"-1" href=
=3D"https://web.archive.org/web/20151004202005/http://duartes.org/gustavo/b=
log/post/kernel-boot-process/#el" _pageexpand_=3D"532">Greek</a></td><td><a=