Improve and update comments.

FossilOrigin-Name: 2dc16d345bfb492b2ec69463b6130ff1b62fd291

manifest

@@ -1,5 +1,5 @@
-C Minimize\sthe\srequested\spermissions\swhen\sopening\sthe\svolume\son\sWindows\s7\sand\sVista.
-D 2017-01-18T19:06:41.323
+C Improve\sand\supdate\scomments.
+D 2017-01-18T19:36:10.754
 F Makefile.in 41bd4cad981487345c4a84081074bcdb876e4b2e
 F Makefile.linux-gcc 7bc79876b875010e8c8f9502eb935ca92aa3c434
 F Makefile.msc b8ca53350ae545e3562403d5da2a69cec79308da
@@ -374,7 +374,7 @@ F src/os.h 8e976e59eb4ca1c0fca6d35ee803e38951cb0343
 F src/os_common.h b2f4707a603e36811d9b1a13278bffd757857b85
 F src/os_setup.h 0dbaea40a7d36bf311613d31342e0b99e2536586
 F src/os_unix.c 30e2c43e4955db990e5b5a81e901f8aa74cc8820
-F src/os_win.c 2f6dd3eed5566b13e75569c18984fffb5a546241
+F src/os_win.c 2bd4caede7d9a916cc0a9be789f243a3c1ca6089
 F src/os_win.h 7b073010f1451abe501be30d12f6bc599824944a
 F src/pager.c 9dc72d23eebbdf992bd69f2ab954d0d3a27c7340
 F src/pager.h d1e944291030351f362a0a7da9b5c3e34e603e39
@@ -1545,7 +1545,7 @@ F vsixtest/vsixtest.tcl 6a9a6ab600c25a91a7acc6293828957a386a8a93
 F vsixtest/vsixtest.vcxproj.data 2ed517e100c66dc455b492e1a33350c1b20fbcdc
 F vsixtest/vsixtest.vcxproj.filters 37e51ffedcdb064aad6ff33b6148725226cd608e
 F vsixtest/vsixtest_TemporaryKey.pfx e5b1b036facdb453873e7084e1cae9102ccc67a0
-P cb9d1ab33d4109e0712d1a9dd2e51861e168e418
-R 2203396c1fcf2bc7c6ca68db070932df
+P 8d429a59cdad1693827b41369d642f9486c01155
+R 1d38fe74ce1d10707d97f6b91c77c8e9
 U mistachkin
-Z a4a51f21ac0fdade390d7b88237a4d72
+Z 19b1a1c98e5fbae99d5447129e998ccf

manifest.uuid

@@ -1 +1 @@
-8d429a59cdad1693827b41369d642f9486c01155
+2dc16d345bfb492b2ec69463b6130ff1b62fd291

src/os_win.c

@@ -454,15 +454,21 @@ const sqlite3_mem_methods *sqlite3MemGetWin32(void);
 #endif /* SQLITE_WIN32_MALLOC */
 
 /*
-** The following variable is (normally) set once and never changes
-** thereafter.  It records whether the operating system is Win9x
-** or WinNT.
+** The following variables are (normally) set once and never change
+** thereafter.  They record the major and minor OS version and whether
+** the operating system type is Win9x or WinNT.
 **
-** 0:   Operating system unknown.
-** 1:   Operating system is Win9x.
-** 2:   Operating system is WinNT.
+** sqlite3_os_type = 0:   Operating system type is unknown.
+** sqlite3_os_type = 1:   Operating system type is Win9x.
+** sqlite3_os_type = 2:   Operating system type is WinNT.
 **
-** In order to facilitate testing on a WinNT system, the test fixture
+** For the major and minor versions, the following are the "well-known"
+** operating system releases (i.e. the ones that are tested for):
+**
+** sqlite3_os_major.sqlite3_os_minor = 6.0 = Windows Vista
+** sqlite3_os_major.sqlite3_os_minor = 6.2 = Windows 8
+**
+** In order to facilitate testing on WinNT systems, the test fixture
 ** can manually set this value to 1 to emulate Win98 behavior.
 */
 #ifdef SQLITE_TEST
@@ -3627,6 +3633,14 @@ static int winFileControl(sqlite3_file *id, int op, void *pArg){
   return SQLITE_NOTFOUND;
 }
 
+/*
+** Same-volume determination for versions of Windows prior to Windows 8
+** is untested, undocumented, and unsupported.  All such code is omitted
+** unless the SQLITE_WIN32_VISTA_SECTOR_SIZE define is set at compile-time,
+** and that compile-time option is off by default and undocumented.  The
+** following code is for reference only.
+*/
+
 #if defined(SQLITE_WIN32_VISTA_SECTOR_SIZE) && \
     defined(_WIN32_WINNT) && _WIN32_WINNT >= _WIN32_WINNT_VISTA
 /*
@@ -3690,6 +3704,14 @@ static int winSectorSize(sqlite3_file *id){
   }
 #endif
 
+/*
+** Sector-size determination for versions of Windows prior to Windows 8
+** is untested, undocumented, and unsupported.  All such code is omitted
+** unless the SQLITE_WIN32_VISTA_SECTOR_SIZE define is set at compile-time,
+** and that compile-time option is off by default and undocumented.  The
+** following code is for reference only.
+*/
+
 #if defined(SQLITE_WIN32_VISTA_SECTOR_SIZE) && \
     defined(_WIN32_WINNT) && _WIN32_WINNT >= _WIN32_WINNT_VISTA
   if( osIsVistaPlus() ){