1. Arsitektur

Menyimpan Data dan Mengatur Penyimpanan Data Harddisk

A. Structure of a hard disk

*. Hard disk consists of a number of platters

The platters rotate at a very high speed (5400 RPM to 10,000 RPM) Disk (read/write) heads move over the platter surface to read and write (magnetize) data bits

*. The disk head can read or write data only when the desired disk surface area is under the disk head.

Internal operation of a hard disk:

B. Data access time of data on disk consists of:

  1. Seek time (get to the right track)
  2. Latency (wait for the right sector to rotate under the disk head)
  3. Transfer time (actual reading of the data)

C. Each platter is logically divided into a number of tracks

D. Each track is logically divided into a number of sectors:

Each sector is uniquely identified by its sector number

Disk sectors are usually 512 bytes in size.

E. To facilitate data access (larger chuncks) a number of sectors are logically groups into a disk block

Disk blocks are usually 4K or 8 K bytes in size.
  • Each disk block contains a number of sections
  • Each disk block is uniquely identified by its block number
  • There is a mapping defined between disk block numbers and sector numbers
  • Sectors of a disk block need not be located “contiguously” on the platter (for speedier access, sectors are usually interspersed)
E.g., the sectors (4, 5, 6, 7) of this block is interspersed:

2. File Organization of a Hard Disk

A. Each computer system has a (built-in) file system

  • File systems used by Microsoft Windows are: FAT (File Access Table), FAT32 and NTFS
  • File systems used by Solaris UNIX are: UFS (UFS File System) and ZFS (ZFS File System)

B. The file system always reserve a number of disk blocks (directory disk blocks) to store information about the files on the disk:

C. The directory disk blocks contains a large number of directory entries

D. The structure of a directory entry looks something like this:

  • A file name
  • Zero or more block number

3. Accessing data stored in Files on a Hard Disk

A. A file is uniquely identified by its file name

B. A (non-empty) file takes up one or more disk blocks

The content of the file are stored in the disk blocks of the file

C. Users can access a file by providing its file name in an “open file” operation.

This operation locates the directory entry of the file and obtain the disk blocks of the file.

The directory entry is stored in the Operating System area.

The Operating System manages the resourses of the computer.

Examples of Operating Systems: Microsoft Windows, UNIX

The disk blocks in the directory entry identify the sectors of the disk where the data of the file are stored.

Subsequent file read/write operations can find the exact location to access the data store in the file:

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