Hard Drive Operations and Characteristics

Mass Storage

• Disks provide long-term data storage when the computer is off, functioning as secondary storage
• The Operating System manages storage allocation, free space, disk scheduling, and data I/O
• Optical storage (DVD/CD) and magnetic tape are other types of storage devices

Mass Storage Management

• Data transfer to disk or other storage devices is slower than other computer operations
• Registers are level 1 storage, characterized by < 1KB typical size, 0.25 - 0.5 access, and compiler management
• Cache memory lies at level 2, featuring < 16MB typical size, 0.5-25 access, and hardware management
• Main memory is level 3, with < 64GB typical, 80-250 access, and operating system management.
• Solid state disks at level 4, exhibit < 1TB, 25,000-50,000 access, and operating system management
• Magnetic disks are level 5, possessing < 10TB, 5,000,000 access, and operating system management

Caching

• Data flows from the hard disk to the CPU through main memory and cache
• When an application opens, a large number of instructions flow from disk to RAM to cache
• The cache stores the processor's next instruction, preventing delays from slower main memory retrieval

Hard Drive Structure

• Hard disk drives are the most widely used mass storage media
  • They provide high storage capacities
  • They are moderately inexpensive
• Hard disk drives come in physical sizes of 1.8, 2.5, and 3.5 inches.
• Available platter rotation speeds includes 4200 RPM up to 15,000 RPM depending on usage

Hard Disk Structure

• Hard drives consist of platters coated with magnetic media
• All platters are mounted on a common spindle, rotating together
• Hard disks are divided into Tracks and Sectors
• A track is a circular ring on a platter with concentric tracks.
• A cylinder groups the same track on all platters
• The head reads/writes data to a track in a sector
• A cluster is a group of sectors used to store files

Hard Disk Structure: Sectors

• A sector is the basic unit of storage
• Each track is divided into sectors and can store 512 bytes of data
• Older hard drives had pie-shaped sectors
• A standard was set at 17 sectors per track, with the same number of sectors on each track
• Track 0 is at the disk's outer edge with tracks there being longer than inner tracks

Hard Disk Structure: Magnetic Media

• The hard disk surface is a magnetic medium
• The head is a small electromagnet
• An electric current sent to the head creates a magnetic field that magnetizes the disk
• Data bits are written as small magnetic areas with North-South and South-North fields
• The drive controller changes the electric current direction to change data from 0 to 1

Hard Disk Structure: Zoned Bit Recording

• Zoned Bit Recording (ZBR) enables having more sectors on outer rings for increased data storage
• Tracks group into zones based on distance from the disk's center
• Each zone is assigned a number of sectors per track
• Sectors stay constant in size/length
• Outer disk zones has more sectors per track than inner ones

Hard Drive Structure: Addressing

• Disk drives are addressed as physical blocks
• Low-level formatting creates physical blocks numbered sequentially from 0 to N
• A physical block has a disk address by Drive, cylinder head, and sector
• Mapping proceeds from track to cylinder, then outermost to innermost cylinder

Disk Scheduling

• Time delays always occur when data is transferred due to moving parts
• Transfer rate is the rate of data between the drive and the systems
• Positioning time (random access time)is the drive's needed time of positioning, factoring in Seek Time & Rotational Latency
• Seek Time is the time to move the head to the correct cylinder
• Rotational Latency is the time to rotate the platter to place the correct sector under the head

Disk Scheduling Algorithms

• Queuing and scheduling of disk access requests is needed to allow for processes to be handled
• An operating system uses disk scheduling to meet these requirements
• First Come First Served (FCFS) utilizes a first-in-first-out queue to fulfill the requests it receives
  • This can be inefficient given the erratic movement of disk heads
• Shortest Seek Time First (SSTF) re-orders disk access requests based on the current head position
  • It yields less head movement and faster data read/write, and may delay some processes over others.

Disk Scheduling Algorithms cont'd

• SCAN (Elevator Algorithm) starts at the disk's outer edge
  • It moves towards the inside, servicing requests in order
  • Then moves from inside to outside to service disk requests
  • This head movement is efficient with the possibility of introducing delays to edge requests
• C-SCAN follows SCAN concept, servicing requests while moving from one disk edge to the other
  • Upon reaching the far edge, the head returns to the start without handling requests, then begins a new servicing pass
  • Extra head movement results in less wait times
• LOOK and C-LOOK operate by servicing all pending requests and return to the start
  • They only travels over the disk far to service all pending requests
  • Both improve upon SCAN and C-SCAN by means of not moving the head as far

File System Types

• Operating systems accommodate multiple types of file systems
• Each file system type defines the number of files, storage bytes, and file metadata
• Windows file system types include FAT, FAT16, FAT32, exFAT, NTFS, and RFS
• Linux file system types are ext3, ext4, xfs, etc
• Specialized types such as zfs for SAN (Storage Area Network) devices also exists

File Allocation

• Files are written to a track in a sector
• Multiple sectors are grouped into a cluster (file allocation unit)
• Cluster size depends on the file system/hard disk size
  • Sizes ranges from 4,096 to 16,384 bytes.
• Files are assigned clusters upon being written
• if a file has 99 bytes of data, the complete cluster is dedicated to that file, with the rest unavailable

File Allocation cont'd

• Free'd clusters become available for other files to be written to the disk
• Disk writes access the first available cluster
• Deleting and writing many files could lead to spreading large files across several clusters, causing fragmentation
• Fragmentation decreases the ability of the drive to complete requests

File Allocation Methods

• To allocate disk blocks to a file system, there are 3 main methods
• Contiguous places all files in contiguous blocks, and results in no fragmentation
• Linked scatters files anywhere on disk. Each allocation unit points to start of next unit.
• Indexed lists each allocation unit orderly in an index file

File Allocation Methods cont'd

• Contiguous allocation places all files in contiguous blocks, requiring minimal head movement for reading/writing
  • With fragmented disk space, contiguity draws back in trying to find a contiguous space for a new file
• Linked allocation stores files as lists of blocks that contain address of next file block
  • Though each block can be anywhere and not contiguous, it uses disk space efficiently at the cost of head movement

File Allocation Table

• A table with the number of the file's first block and a list of where the next blocks are that the file is
• A null pointer indicates the file's last block For example, beginning at block 217 can go to 618, lastly to 399
• Reading the FAT and other data blocks will require the head to move to the volume's start.

Indexed File Allocation

• Each file utilizes its own array of disk block addresses
• The file directory holds location of the index block
• The index contains all of the different disk blocks where something can be located
• The needed disk space to do this is a drawback
• Each file (no matter what size) must have the same amount of space that is set aside for the index block
• Even small files will require a block to store this index
• NTFS is a file system type that make use of indexes

Indexed File Allocation Cont'd

• The directory entry for a file links to an index block, which in turn links to an index table that links to the file blocks
• The index entries are sequenced according to the order of the data in the file blocks
• Utilizing this approach, NTFS has a Master File Table (MFT) with directory information

File Allocation Table - FAT

• Originally designed for use with floppy disks in 1977
• Still utilized on solid state memory devices like digital camera's and USB memory drives
• FAT 16 comes with a 16-bit address space, allowing a maximum of 65,535 clusters per volume
• FAT 32 comes standard on most USB's, but each file maximum reaches 4 GB.
  • The 32 bits set aside for the file size field, equates to the "4GB" total
  • With 28 bits made for the cluster number, space reaches 2 terabytes supporting 268 million clusters

NTFS: New Technology File System

• Developed by Microsoft for WinNT 3.1, it is a filesystem improving FAT32 with more support for file metadata
  • Includes information on file, owner, date created, and permissions
  • Additional security with file permissions (DACLS)
• Journaling
• Its volume can get up to 16 terabytes dependent on a 4 KB default cluster size.
• Its volume can get up to 256 terabytes dependent on a 64 KB cluster size.

Journaled File Systems

• Many file systems use transaction logs, i.e. journals, to protect integrity if there's an unexpected error
• Should this occur, any incomplete transaction is playable from the journal for the file system to be usable
• In files, the structure of data is the only thing journaling protects
• Ext3, ext4, xfs, and NTFS utilize journaling services

Disk Management

• A disk needs to be configured so it is usable by an operating system
• Performed by its manufacturer, its low-level formatting sets up track and sector layouts
• The operating system has to record its own data structures on the disk
• A partition has to be formatted for the disk in order to partition it for its file system
• The file system's directory is made upon the disk when doing logical level formatting.

Disk Management cont'd

• A disk can be distributed into different partitions of logical disks/groups
• The system below has 2 labeled disks
  • Disk 0-Online Size 60 GB
  • Disk 1-Online Size 10 GB

Disk Management - Bootable Disk

• Setting up a bootable disk means a primary partition for the operating system has to be set up
• The Master Boot Record is located inside track 0, side (head) 0, and sector 1.
• The Partition Table data for the small executable code is in the Master Boot Record
• BIOS checks occur after the computer's power goes on and the commands load from ROM into memory
• The necessary hardware gets checked via POST, loading all the basic I/O kernels like video/keyboard
• Instructions to locate the operating system occurs after POST finishes the check, loading the O/S

Master Boot Record

• Created when the disk is partitioned, the MBR stores the most important data structure, and the MBR contains:
  • a minimal amount of code (master boot)
  • the disk's signature
  • its partition table

MBR program

• Program determines, when master the boot code gets executed, what partition with the right type of operating system should be branches too

MBR & Boot Sector

• A “boot sector” is a region (typically first in this order - 512 bytes)
• In a hard drive, a boot sector includes information that "boots" an operating system stored in that segment
• The boot sector often correlates to the MBR which occupies the first part of an HDD
• The MBR's function is to determine the operating system for finding, and copying it from storage into the memory

Partition Table

• Contains the first section of a partitioned drive. This partition also entails the volume boot record which contains basic information needed by the system to boot correctly
• The boot sector is the first section of everything on the hard disk; it includes the sections stored in every partition
• Provides information about both primary, and secondary partitions on the disk

Partition Table Data

• Includes a 64-byte data field that indicates partition layouts.
• Conforms to standard layouts not depended to O.S.
• There is a 16-byte limit for each entry, permitting a maximum of 4 initial partition names.
• Only 1 external partition, and 3 main partitions can exist on a disc drive
• Logical drives may be separated within the extended partition

Windows Disk

• A segment on every Windows disk gets assigned to the preliminary partition and will be set through the drive letter
• "C:" is usually in first partition
• A goal to get partitions configured by the O.S. has to have certain types of organizational uses

Windows Disk Boot Sector

• Before Win7, a partition's letters all had the system settings under the first.
• A recent release of BitLock's full encryptor will have hidden file boot disks not as much
• No letters

Partition Table Sizes

• A size of 60 GB has previously been the standard for disk drives
  • To work as a source to boot partitions

DISKPART> select disk 0
Disk 0 can now be selected
DISKPART> list partition
Partition ### Type Size Offset
Partition 1 Primary 59 GB 1024 KB

Partition Table & File System

• Size up to 60GB and NTFS file system settings

C:\Windows\system32>diskpart
Microsoft DiskPart version 10.0.15063.0
Copyright (C) Microsoft Corporation.
On computer: DESKTOP-VJU9DF6
DISKPART> list disk
Disk ### Status Size Free Dyn Gpt
- ------- ---------- ------- ------- --- ---
Disk 0 Online 60 GB 0 B
Disk 1 Online 10 GB 10 GB
DISKPART> list volume
Volume ### Ltr Label Fs Type Size Status Info---------- ------ ----------- ----- ---------- ------- --------- --------
Volume 0 D DVD-ROM 0 B No Media
Volume 1 C NTFS Partition 59 GB Healthy System
DISKPART>

Storage Type & Partition Letters

• Format different partitions with multiple file systems on one hard drive

• Formatting one way to create a way to see the storage, assigning a letter, and drive

  • Each volume was formatted this way

DISKPART>list volume
Volume ### Ltr Label Fs Type Size Status Info---------- ------ ----------- ----- ---------- ------- --------- --------
Volume 0 D DVD-ROM 0 B No Media
Volume 1 C NTFS Partition 59 GB Healthy System
Volume 2 F NTFS Partition 2048 MB Healthy
Volume 3 G FAT32 Partition 4096 MB Healthy
Volume 4 H FAT Partition 1024 MB Healthy

Globally Unique Identifier Partition Table (GPT)

• GPT is the new partitioning standard
• As part of the( UEFI) Unified Extensible Firmware Interface
• Which is both a replacement for BIOS (Basic Input/Output System) -As well as a replacement to existing Master Boot Record -GPT allows for a huge number of partitions each with 18 exabytes -Whereas MBR is limited by the size of 2 TB and smaller

Dual Boot Windows and Linux

• Dual Booting means that both disk drives can be split between O.S. with an "operating system"
• In the O.S., and at it's start or setup
• The basic input will choose where it operates

Dual Boot Setup

• Windows installs a loading setup so each O.S., to allow to choose what boots the user wanted for

Hard Drive Interfaces

• Computer hard drives contain data with technologies which hold attachments, SCSI, or fiber channels
• ATA (attachment) is a standardised type of transmission
• Data transmission speed for higher serial ports

Hard Drive Interfaces: SCSI

• SCSI is similar to bus ports, connecting devices for the computer
• Up tp 8 of them can stay in the device

Format command & Low Level

• The format is not fully cleared out for high standard.
• Tracks can stay where the O.S. sets them -High level formatting needs the same for "Done by disc Manufacturer"

Safe Disc Destruction

• Wiping hard drives becomes required to sell a surplus computer.
• Software overwrites to clean the drive for future sectors.

Data security

• Wiping a program has the windows washers' ability to reset and erase all
• Some systems will still have traces left for binary files.
• Use Windows command lines with a cleaner program
• Erasers do GUI to wipe. -Write three times

File Security

• Total BitLocker encryption will remain
• Windows page and the setup folder of other pages, will remain

File security

• Flip flop circuits contain info like this, power removal from the drive is required.
• Solid state has no magnetic data

Explore the multifaceted responsibilities of operating systems in managing hard drives. Understand data transfer speeds, cache memory's role, and differences between desktop and server drives. Learn about magnetic media, tracks and cylinders, and logical block mapping.