Microsoft Windows - Computer Busses - page 564

providing virtual device drivers (VDDs). These detect a call to hardware and communicate
with the NT 32-bit device driver.
Windows NT communicates with hardware through device drivers. These drivers have a
.sys file extension. An example listing of these is

Directory of C:\WINNT\system32\drivers
afd.sys atapi.sys atdisk.sys beep.sys
cdaudio.sys cdfs.sys cdrom.sys changer.sys
cirrus.sys disk.sys diskdump.sys diskperf.sys
fastfat.sys floppy.sys ftdisk.sys hpscan16.sys
i8042prt.sys kbdclass.sys ksecdd.sys modem.sys
mouclass.sys msfs.sys mup.sys ndis.sys
netdtect.sys npfs.sys ntfs.sys null.sys
parallel.sys parport.sys parvdm.sys pcmcia.sys
scsiport.sys scsiprnt.sys scsiscan.sys serial.sys
sfloppy.sys streams.sys tape.sys tdi.sys
vga.sys videoprt.sys

With this, virtual memory applications can have access to the full available memory but NT
then maps this to a private memory range (called a virtual memory space). It maps physical
memory to virtual memory in 4 KB blocks (called pages). This was previously illustrated in
Figure H.6. The driver used to perform the page file access is Pagefile.sys (which is normally
found in the top-level directory).
Windows NT has 32 levels of priority (0 to 31). Levels 0 to 15 are used for dynamic ap-
plications (such as non-critical operations) and 16 to 31 are used for real-time applications
(such as Kernel operations). NT provides a virtual memory by paging file(s) onto the hard
disk. Priority levels 0 to 15 can be paged, but levels 16 to 31 cannot.
A summary of the system32 directory is shown below. The wowdeb.exe and wowexec.exe
files allow Windows 3. x programs to run in a 32-bit environment.

Directory of C:\winnt\system32
ansi.sys append.exe at.exe atsvc.exe
attrib.exe autoexec.nt backup.exe bootok.exe
bootvrfy.exe cacls.exe chcp.com chkdsk.exe
clipsrv.exe comm.drv command.com comp.exe
compact.exe config.nt control.exe convert.exe
country.sys csrss.exe dcomcnfg.exe ddeshare.exe
ddhelp.exe ebug.exe diskcomp.com diskcopy.com
diskperf.exe doskey.exe dosx.exe DRIVERS
edit.com exe2bin.exe expand.exe fastopen.exe
fc.exe find.exe findstr.exe finger.exe
fontview.exe forcedos.exe format.com ftp.exe
gdi.exe graftabl.com graphics.com grpconv.exe
help.exe himem.sys inetins.exe internat.exe
kb16.com keyb.com keyboard.drv keyboard.sys
krnl386.exe label.exe lights.exe lodctr.exe
mem.exe mode.com more.com mpnotify.exe
mscdexnt.exe nddeagnt.exe nddeapir.exe net.exe
nlsfunc.exe notepad.exe ntdos.sys ntio.sys
ntvdm.exe os2ss.exe pax.exe pentnt.exe
ping.exe portuas.exe posix.exe print.exe
psxss.exe rdisk.exe recover.exe redir.exe
replace.exe restore.exe rpcss.exe rundll32.exe
runonce.exe savedump.exe setup.exe setver.exe
share.exe shmgrate.exe skeys.exe smss.exe
sort.exe SPOOL sprestrt.exe subst.exe
syncapp.exe sysedit.exe systray.exe taskman.exe