Modern Operating Systems by Herbert Bos ...
Modern_Operating_Systems_by_Herbert_Bos_and_Andrew_S._Tanenbaum_4th_Ed.pdf-M ODERN O PERATING S YSTEMS
Showing 60 out of 1137
Modern Operating Systems by Herbert Bos and Andrew...
Modern_Operating_Systems_by_Herbert_Bos_and_Andrew_S._Tanenbaum_4th_Ed.pdf-M ODERN O PERATING S YSTEMS
Modern Operating Systems by Herbert...
Modern_Operating_Systems_by_Herbert_Bos_and_Andrew_S._Tanenbaum_4th_Ed.pdf-M ODERN O PERATING S YSTEMS
Page 60
SEC. 1.3
read sector 11,206 from disk 2.
The controller then has to convert this linear sector
number to a cylinder, sector, and head. This conversion may be complicated by the
fact that outer cylinders have more sectors than inner ones and that some bad sec-
tors have been remapped onto other ones. Then the controller has to determine
which cylinder the disk arm is on and give it a command to move in or out the req-
uisite number of cylinders. It has to wait until the proper sector has rotated under
the head and then start reading and storing the bits as they come off the drive,
removing the preamble and computing the checksum. Finally, it has to assemble
the incoming bits into words and store them in memory.
To do all this work, con-
trollers often contain small embedded computers that are programmed to do their
The other piece is the actual device itself. Devices have fairly simple inter-
faces, both because they cannot do much and to make them standard.
The latter is
needed so that any SAT A disk controller can handle any SAT A disk, for example.
stands for
Serial ATA
in turn stands for
AT Attachment
. In case
you are curious what AT stands for, this was IBM’s second generation ‘‘Personal
Computer Advanced Technology’’ built around the then-extremely-potent 6-MHz
80286 processor that the company introduced in 1984.
What we learn from this is
that the computer industry has a habit of continuously enhancing existing acro-
nyms with new prefixes and suffixes. We also learned that an adjective like ‘‘ad-
vanced’’ should be used with great care, or you will look silly thirty years down the
SATA is currently the standard type of disk on many computers. Since the ac-
tual device interface is hidden behind the controller, all that the operating system
sees is the interface to the controller, which may be quite different from the inter-
face to the device.
Because each type of controller is different, different software is needed to
control each one. The software that talks to a controller, giving it commands and
accepting responses, is called a
device driver
Each controller manufacturer has to
supply a driver for each operating system it supports. Thus a scanner may come
with drivers for OS X, Windows 7, Windows 8, and Linux, for example.
To be used, the driver has to be put into the operating system so it can run in
kernel mode.
Drivers can actually run outside the kernel, and operating systems
like Linux and Windows nowadays do offer some support for doing so.
The vast
majority of the drivers still run below the kernel boundary. Only very few current
systems, such as MINIX 3, run all drivers in user space. Drivers in user space must
be allowed to access the device in a controlled way, which is not straightforward.
There are three ways the driver can be put into the kernel. The first way is to
relink the kernel with the new driver and then reboot the system. Many older UNIX
systems work like this. The second way is to make an entry in an operating system
file telling it that it needs the driver and then reboot the system.
At boot time, the
operating system goes and finds the drivers it needs and loads them.
works this way. The third way is for the operating system to be able to accept new

Ace your assessments! Get Better Grades
Browse thousands of Study Materials & Solutions from your Favorite Schools
Concordia University
Great resource for chem class. Had all the past labs and assignments
Leland P.
Santa Clara University
Introducing Study Plan
Using AI Tools to Help you understand and remember your course concepts better and faster than any other resource.
Find the best videos to learn every concept in that course from Youtube and Tiktok without searching.
Save All Relavent Videos & Materials and access anytime and anywhere
Prepare Smart and Guarantee better grades

Students also viewed documents