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Disk Drives and Cylinders

post #1 of 4
Thread Starter 
Hey guys,

Studying for an exam and looking at Disk Drives and Cylinders in them, can't seem to find any good examples so I was wondering if anyone would care to help me?

An example question (Taken from a previous exam) is: Example Question (Click to show)
Suppose that a mini-disk drive has 30 cylinders, numbered 0 to 29. The drive
is currently serving a request at cylinder 10. The queue of pending requests, in
FIFO order, is
8, 14, 9, 20, 0
Starting from the current read/write head position, what is the total distance
(in cylinders) that the disk arm moves to satisfy all the pending requests, for
the SCAN disk scheduling algorithms (the read/write head moves toward
cylinder 0 first)?
(A) 29
(B) 30
(C) 31
(D) 32
(E) None of the above

Basically what would the answer be and how do you get it? smile.gif

EDIT: Think I get it now after eventually finding a guide on Google. from here

Basically:

10 - 7 = 3
7 - 13 = 6
13 - 8 = 5
8 - 19 = 11
19 - 0 = 19

3 + 6 + 4 + 11 + 19 = 44

Adding all of those "cylinder changes" together gives us 44 which isn't on the list of options therefore the answer is E.
Edited by Matt-Matt - 6/4/13 at 8:11am
 
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post #2 of 4
You got there, but your math looks wrong.

10 to 8 = 2 steps
8 to 14 = 6 steps
14 to 9 = 5 steps
9 to 20 = 11 steps
20 to 0 = 20 steps
 
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post #3 of 4
Thread Starter 
Quote:
Originally Posted by ramicio View Post

You got there, but your math looks wrong.

10 to 8 = 2 steps
8 to 14 = 6 steps
14 to 9 = 5 steps
9 to 20 = 11 steps
20 to 0 = 20 steps

Yep, I actually changed the question so I wouldn't get in any form of trouble for copyright.. awkward moment when I write down the answer to what was the question tongue.gif

Great though, thanks so much! +Rep
 
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Samsung 840 Evo Seagate Barracuda 2TB Western Digital Green 2TB Samsung Spinpoint 1TB 
Hard DriveOptical DriveCoolingCooling
Western Digital Green 640GB 2x OEM DVD Drives Heatkiller Rev 3.0 XSPC RX360 
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Hard DriveHard DriveHard DriveHard Drive
Samsung 840 Evo Seagate Barracuda 2TB Western Digital Green 2TB Samsung Spinpoint 1TB 
Hard DriveOptical DriveCoolingCooling
Western Digital Green 640GB 2x OEM DVD Drives Heatkiller Rev 3.0 XSPC RX360 
CoolingCoolingCoolingOS
Laing D5 + XSPC Res Primochill Bloodshed Red Tubing Koolance Fullcover R9 290x Block Windows 10 Pro x64 
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post #4 of 4
Gotcha thumb.gif
 
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i5-2500k ASUS P8Z68-M Pro 16 GB (4 x 4GB) Mushkin Enhanced Silverline DDR... 64GB Kingston SSD 
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Blu-ray reader and DVD/CD burner combo drive Scythe Big Shuriken 2 Rev. B Windows 7 Ultimate x64 1440x900 old LG LCD with anti-glare film peeled... 
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CPUMotherboardGraphicsRAM
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Hard DriveHard DriveCoolingOS
Hitachi Deskstar 2TB 32GB Patriot SSD Scythe Big Shuriken 2 Rev. B Ubuntu Server 
PowerCaseOtherOther
COOLMAX 700 watt modular Norco RPC-3216 Areca ARC-1222 w/ BBU 4 SFF-8087 Cables 
CPUMotherboardRAMHard Drive
i5-2500k ASUS P8Z68-M Pro 16 GB (4 x 4GB) Mushkin Enhanced Silverline DDR... 64GB Kingston SSD 
Optical DriveCoolingOSMonitor
Blu-ray reader and DVD/CD burner combo drive Scythe Big Shuriken 2 Rev. B Windows 7 Ultimate x64 1440x900 old LG LCD with anti-glare film peeled... 
KeyboardPowerCaseMouse
Dusty old Dell PS/2 Seasonic 560 watt modular Lian-li PC-V354B Some generic one from Best Buy 
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