<< Chapter < Page Chapter >> Page >
IO devices and File systems

I/o device characteristics:


  • One character (8 bits of data or control function) is sent at a time, one interrupt per character.
  • 10-1800 characters per second.
  • Keyboard and display are independent in most systems (no automatic echo, full duplex).
  • Usually handled with one interrupt per character, but sometimes DMA nowadays.

Raster printers.

  • Bit mapped (one bit for each dot).
  • Typically about 300 to 1200 dots per inch.
  • Impact, ink jet, or laser printing.


  • 8mm wide by 750 feet long, or 1/2" wide by 2500 feet long..
  • Multi-track, helical, serpentine.
  • Variable length records.
  • Capacities go up to 70 GB/tape.
  • Densities of more than 30 KB/cm.
  • Inter-record gaps ofs about 10mm.
  • Transfer rates up to 5-500 MB/second.
  • Can read or write, but cannot write in middle. Can skip records.
  • Tapes are DMA devices, not one interrupt per character.


  • Draw picture of spindle, platters, read/write-arm.
  • Typically about 1024 cylinders, 20 tracks per cylinder, 32 sectors per track, 512 bytes per sector.
  • This is a total of about 1 GB per disk, or 500,000 double-spaced typewritten pages. Typically sectors are fixed length (512-4096 bytes arepopular sizes).
  • Sectors can be read and written individually, or in adjacent groups.
  • Seek time = 5-100 ms, latency is 0-15 ms (drive spins at 3600- 7200 RPM). This is the standard for medium term computer storage. Transfer timesare about 5-20 MB/second. These times depend on drive, controller, and interface standard (IDE, SCSI).


  • Current CD-ROMS's can hold up to 720 MB (650 MB is more typical) of data or 74 minutes of uncompressed audio. The data is organized in one (or afew) continuous spirals. The block size is 2K and "tracks" vary in size from 8 to 23 blocks There is extensive error correction information encoded with thedata.
  • Seek time = 100-300 ms. Transfer times are about .3-1.5 MB/second (for 2X-10X). 1X (150 KB/second) is needed for audio CD's.
  • Next generation CD (DVD) should store about 5-10 GB and be fully readable and writable. These drives will handle fully integrated data, audio,and video. There are currently several competing standards (ala the VHS vs. Beta competition of the 80's).

Disks and tapes read and write blocks of information rather than single bytes:

  • Storage efficiency: give example for tape. At 1600 bpi, 80-byte records use .05 inch, gaps use .6 inch, tape is all gap. However, 8000-byterecords use 5 inches so gaps are only about 11% of the tape. In the case of disks, there are a couple of thousand bits of leader at the beginning of eachsector used to identify the sector and to synchronize when reading. For 1000- byte sectors, 20% of the disk space is wasted.
  • Access efficiency: on disk it typically takes 25ms overhead before transfer begins. The actual transfer is only about 1 microsecond perbyte. Thus one-byte transfers take 25ms total time/byte, 1000-byte transfers take about 25 ms total time/byte. Re-iterate the importance of eliminatingseeks.

Two common I/O device access methods: DMA and CPU control

Questions & Answers

how to know photocatalytic properties of tio2 nanoparticles...what to do now
Akash Reply
it is a goid question and i want to know the answer as well
Do somebody tell me a best nano engineering book for beginners?
s. Reply
what is fullerene does it is used to make bukky balls
Devang Reply
are you nano engineer ?
fullerene is a bucky ball aka Carbon 60 molecule. It was name by the architect Fuller. He design the geodesic dome. it resembles a soccer ball.
what is the actual application of fullerenes nowadays?
That is a great question Damian. best way to answer that question is to Google it. there are hundreds of applications for buck minister fullerenes, from medical to aerospace. you can also find plenty of research papers that will give you great detail on the potential applications of fullerenes.
what is the Synthesis, properties,and applications of carbon nano chemistry
Abhijith Reply
Mostly, they use nano carbon for electronics and for materials to be strengthened.
is Bucky paper clear?
so some one know about replacing silicon atom with phosphorous in semiconductors device?
s. Reply
Yeah, it is a pain to say the least. You basically have to heat the substarte up to around 1000 degrees celcius then pass phosphene gas over top of it, which is explosive and toxic by the way, under very low pressure.
Do you know which machine is used to that process?
how to fabricate graphene ink ?
for screen printed electrodes ?
What is lattice structure?
s. Reply
of graphene you mean?
or in general
in general
Graphene has a hexagonal structure
On having this app for quite a bit time, Haven't realised there's a chat room in it.
what is biological synthesis of nanoparticles
Sanket Reply
what's the easiest and fastest way to the synthesize AgNP?
Damian Reply
types of nano material
abeetha Reply
I start with an easy one. carbon nanotubes woven into a long filament like a string
many many of nanotubes
what is the k.e before it land
what is the function of carbon nanotubes?
I'm interested in nanotube
what is nanomaterials​ and their applications of sensors.
Ramkumar Reply
what is nano technology
Sravani Reply
what is system testing?
preparation of nanomaterial
Victor Reply
Yes, Nanotechnology has a very fast field of applications and their is always something new to do with it...
Himanshu Reply
good afternoon madam
what is system testing
what is the application of nanotechnology?
In this morden time nanotechnology used in many field . 1-Electronics-manufacturad IC ,RAM,MRAM,solar panel etc 2-Helth and Medical-Nanomedicine,Drug Dilivery for cancer treatment etc 3- Atomobile -MEMS, Coating on car etc. and may other field for details you can check at Google
anybody can imagine what will be happen after 100 years from now in nano tech world
after 100 year this will be not nanotechnology maybe this technology name will be change . maybe aftet 100 year . we work on electron lable practically about its properties and behaviour by the different instruments
name doesn't matter , whatever it will be change... I'm taking about effect on circumstances of the microscopic world
how hard could it be to apply nanotechnology against viral infections such HIV or Ebola?
silver nanoparticles could handle the job?
not now but maybe in future only AgNP maybe any other nanomaterials
I'm interested in Nanotube
this technology will not going on for the long time , so I'm thinking about femtotechnology 10^-15
can nanotechnology change the direction of the face of the world
Prasenjit Reply
how did you get the value of 2000N.What calculations are needed to arrive at it
Smarajit Reply
Privacy Information Security Software Version 1.1a
Berger describes sociologists as concerned with
Mueller Reply
Got questions? Join the online conversation and get instant answers!
QuizOver.com Reply

Get the best Algebra and trigonometry course in your pocket!

Source:  OpenStax, Operating systems. OpenStax CNX. Aug 13, 2009 Download for free at http://cnx.org/content/col10785/1.2
Google Play and the Google Play logo are trademarks of Google Inc.

Notification Switch

Would you like to follow the 'Operating systems' conversation and receive update notifications?