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Clusters, Sectors, and Wastage. More File Storage Details CSCI 325. Recap - Definitions. Sector sector size determined by HDD manufacturer size is almost always 512 bytes commonly 63 sectors per track hence, a common track size is 31.5 KB Cluster a group of sectors

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clusters sectors and wastage

Clusters, Sectors, and Wastage

More File Storage Details

CSCI 325

recap definitions
Recap - Definitions
  • Sector
    • sector size determined by HDD manufacturer
    • size is almost always 512 bytes
    • commonly 63 sectors per track
      • hence, a common track size is 31.5 KB
  • Cluster
    • a group of sectors
    • the smallest unit of disk space manageable by the Operating System
    • files use whole clusters
      • hence, some wastage; hence today's lecture
recap effect of cluster sizes
Recap -Effect of Cluster Sizes
  • NTFS
    • NTFS-5 handles max 264 clusters
    • Max Disk Size
      • with 4K clusters = 16 TB
      • with 64K clusters = 256 TB
  • FAT32
    • Max Disk Size
      • with 32K clusters = 8TB
      • with .5K clusters = 2TB
common cluster sizes
Common Cluster Sizes
  • Cluster sizes (sectors per cluster) are always powers of 2.
  • Cluster size is fixed at disk format time.
  • Default cluster sizes for NTFS:

http://support.microsoft.com/kb/140365

wastage example 1
Example Stolen from

Dr. Foster's CSCI325 Course Notes

Wastage - Example 1

File Size = 100,000 bytes

Cluster Size = 8 sectors

100000 bytes

clusters needed = -------------------------------------

8 sectors/cluster * 512 bytes/sectors

100000B

--------------- = 24.41 clusters = 25 clusters

4096B/cluster

Allocated Space = 25 clusters * 4096B/cluster = 102400Bytes

not used 2400B

Percent Wastage = --------- = ------- = 2.34%

allocated 102400B

wastage example 2
Wastage - Example 2

File Size = 100,000 bytes

Cluster Size = 1 sector

100000B

clusters needed = ------------ = 195.31 = 196 clusters

512B/cluster

Allocated Space = 196 clusters * 512B/cluster = 100352Bytes

352B

Percent Wastage = --------- = 0.35%

100352B

wastage example 3
Example Stolen from

Dr. Foster's CSCI325 Course Notes

Wastage - Example 3

File Size = 30 bytes

Cluster Size = 8 sectors

30B

clusters needed = --------------- = 1 cluster

4096B/cluster

Allocated Space = 1 cluster * 4096B/cluster = 4096Bytes

4066B

Percent Wastage = -------- = 99.27%

4096B

Small Files in Big Clusters = Lots of Wasted Space

wastage example 4
Wastage - Example 4

File Size = 30 bytes

Cluster Size = 1 sector

30B

clusters needed = -------------- = 1 cluster

512B/cluster

Allocated Space = 1 cluster * 512B/cluster = 512Bytes

482B

Percent Wastage = -------- = 94.14%

512B

wastage example 5
Wastage - Example 5

Size of this PowerPoint file = 92,817 bytes

Cluster Size on my office's WindowsXP = 4KB (8 sectors)

92817B

clusters needed = --------------- = 22.66 = 23 clusters

4096B/cluster

Allocated Space = 23 cluster * 4096B/cluster = 94208Bytes

1391B

Percent Wastage = -------- = 1.48%

94208B

See Next Page

file properties
File Properties
  • Usage = 90.6KB / 92.0KB = 98.48%
  • Wastage = 100% - 98.48% = 1.52%
  • More Accurate: Usage = 92817/94208 = 98.52%
  • Waste = 1.48%

Size

Allocated Space

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