DISK ACCESS TIME DISK ACCESS TIME

1. Magnetic Disk
+ Magnetic disk storage is secondary, with two circular magnetic surfaces.
Drive + Motor drive disk of a disk drive at high speed (more or less than 60 rounds per second).
+ Read-write activity performed read-write head, which is placed above the plate. Read-write head is very sensitive to shocks that can cause the disk is damaged (bad sectors).
+ Record Room is divided into several tracks / paths and each path is divided again in a few sectors.
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This type of head divided into:
- Fixed-head disk occupy each track one head, thus speeding up the process of reading and recording.
- Moving-head disk has only one head on the move access from one track to another track.
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Some hard drive technology, among others:
»Shock Protection System (SPS)
»Self-Monitoring Analysis and Reporting (SMART)
»Solid State Disk (SSD)
»Magnetore-sistive (MR)» Partial Response Maximum Likelihood (PRML)
»Hot Swap
»Plug and Play ATA
»Environment Protection Agency (EPA)
»Error Correction Code (ECC)
»Auto Transfer
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2. Disk Usage
Access time is the time required by the read head to write or read the contents of the sector.
Consists of 4 components of time:
• Time search, time to achieve the desired cross-or cylinder.
• When steady, the time for literacy upstream to settle on a cross or a cylinder.
• Time latency, time to reach upstream literacy.
• Time salur, time to write or read the contents of the sector.
• As well as the combined time of inquiry time and time updating or replacement.
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- The formula to calculate the search time (t (n)) = t (n) = bn + s ket:
t (n) = time search
b = the time required to pass through a cross.
n = Number of traffic or the cylinder will be skipped.
s = Time steady upstream literacy.
- The formula for calculating the mean time look for:
T (rer) = w - 1. [S + b (w + 1)]
W 3
Ket:
w = Number of traffic on the disk or diskette.
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• The formula for calculating the mean latency time:
r - r
2 2m
ket:
r = rotation time.
m = Number of sectors perlintas.
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• At the time salur we know there are two time ie the time to read (r / m) and the time of writing (r).
The mean time of inquiry (read)
r (m +1)
2m
The mean time of update (write)
r (3m + 1)
2m