Major components of Disk Drive

• Platters

• Read /Write Heads 
• Actuator assembly

• Spindle motor

Patter -- 
They are made up of glass or aluminium  substrate . It is rigid thin flat and smooth . All platters are attached to common shaft (spindle).

Hard Drive Platter: In computing, particularly in the context of hard disk drives (HDDs), a platter refers to one of the round, flat disks coated with a magnetic substance where data is stored. Multiple platters are stacked on a spindle inside the hard drive enclosure, and data is written and read from these platters using read/write heads.
Read/Write Head -- 
Each platter surface has  its  own read/write head .Head  flies above the platter surface It is attached to  acutator assembly  .Read/Write head never touch platter .If they touch it is termed as   "Head Crash " 

Actuator  --

All headsare connected to single actuator  they move at same time . Actuators are responsible for head movement 

An actuator is a mechanical or electromechanical device that is responsible for moving or controlling a mechanism or system. Actuators are commonly used in various applications across different industries, including robotics, automotive, aerospace, HVAC (heating, ventilation, and air conditioning), and manufacturing.There are different types of actuators, including:

1. Electric Actuators: These use electrical energy to create motion. Examples include solenoids, stepper motors, and servo motors.
2. Hydraulic Actuators: These use hydraulic pressure to create linear or rotary motion. They are commonly found in heavy machinery and industrial applications.
3. Pneumatic Actuators: These use compressed air to create motion. They are often used in applications where electricity is not feasible or where precise control is not required.
4. Mechanical Actuators: These use mechanical force to create motion, such as rack and pinion systems or screw mechanisms.

Spindle --

All platters are mounted on single spindle  Each platter move at same speed 

A "spindle" refers to a rod or shaft, typically with a pointed end, that rotates within a bearing. Spindles are commonly found in various mechanical systems where rotational motion is required. They serve several purposes across different industries and applications:

1. Machining: In machining processes like milling, drilling, or grinding, spindles are used to hold and rotate cutting tools such as end mills, drills, or grinding wheels. The rotation of the spindle allows for the precise shaping or removal of material from a workpiece.
2. Textile Industry: In textile manufacturing, spindles are used in spinning machines to twist fibers together to form yarn or thread. These spinning spindles rotate at high speeds to produce the desired twist in the fibers.
3. Automotive: Spindles are integral components in automotive systems, particularly in the suspension and steering systems. They are used to support the wheel hubs and allow them to rotate smoothly.
4. Woodworking: In woodworking, spindles are used in machines such as lathes and routers to hold and rotate wood pieces while they are being shaped or carved.
5. Electronic Devices: Spindles are also found in various electronic devices, such as hard disk drives (HDDs), where they support and rotate the disks on which data is stored.

Data Organization and Formatting

• consists of Tracks 
• Tracks divided into Sectors
• Minimum block size is one sector

• Individual Tracks and Sectors are addressable

Note - Each track in a zone has same number of sectors 

Capacity of Disk Drive 

Capacity of Disk Drive is maximum number of bits that can be stored

Capacity is determined by following technology factors

• Recording Density ( bits/inch)---  Number of bits that can be stored into one inch  segment of a track
• Track Density (tracks/inch) --Number of tracks that can be stored into  one inch  radial segment
• Areal Density ( bits/inch^2) - It is product of recording and track density 

Note --

 Capacity is generally expressed in Giga bytes 

 1 GB = 10^9 Byte 

Modern disk drives have more than 1 tera bit of areal density

Numerical

Compute capacity of disk having 

-512  bytes/sector

-300 sectors/track

- 20,000 tracks /surface

- 2 surfaces/platter

-5 platters/disk

Solution

formula -

(bytes/sector)*(sector/track)*(track/surface)*(surface/platter)*(platter/disk)

=  512*300*20000*2*5 

= 3072*10^7 Byte 

= 30.72 GB    ( 1 GB = 10^9  Byte )

What are parameters to to measure performance of DiskDrive 

- Seek  Time 

-  Rotational  latency 

- Input /Output operations per seconds

- Mega Bytes per second a disk drive can perform 

Seek Time

"Seek time" is a term primarily associated with computer storage devices, particularly hard disk drives (HDDs). It refers to the time it takes for the read/write heads of the drive to move to the correct location on the disk to access a specific piece of data. Seek time is a critical factor in determining the overall performance and speed of a storage device.There are typically two types of seek times:

1. Average Seek Time: This is the average time it takes for the read/write heads to move from one track to another on the disk. It is often measured in milliseconds (ms). Lower average seek times indicate faster performance.
2. Track-to-Track Seek Time: This is the time it takes for the read/write heads to move between adjacent tracks on the disk. Since the read/write heads are already positioned over the correct cylinder, this seek time is typically shorter than average seek time.

Reducing seek time is important for improving the overall performance and efficiency of storage devices, especially in systems where there are frequent requests for data retrieval or storage. Advances in technology, such as the use of faster actuators and improved disk controller algorithms, have contributed to reducing seek times in modern storage devices.

Rotational Latency

Rotational latency, also known as rotational delay, is a term used in computer storage systems, particularly in hard disk drives (HDDs). It refers to the delay or latency experienced while waiting for the desired sector of a disk to rotate into position under the read/write head.HDDs consist of rotating disks (platters) coated with magnetic material, and read/write heads that move across the surface of these disks to read or write data. When data is requested, the read/write head must wait for the desired sector to rotate under it before it can access the data. This delay due to the rotation of the disk is called rotational latency.Rotational latency is affected by several factors:

1. Rotational Speed: The rotational speed of the disk, typically measured in revolutions per minute (RPM), affects the latency. Higher RPM drives have shorter rotational latencies because they rotate faster, allowing the desired sector to arrive under the read/write head more quickly.
2. Distance to Travel: The distance the read/write head must travel across the disk to reach the desired sector also affects rotational latency. Sectors located closer to the current position of the read/write head will have shorter latencies compared to sectors farther away.
3. Starting Position: The starting position of the read/write head when the request for data is made also impacts rotational latency. If the head is already positioned over or near the desired sector, the latency will be shorter compared to when the head needs to move a significant distance across the disk.

Reducing rotational latency is essential for improving the overall performance of HDDs, especially in scenarios where there are frequent requests for data access. However, rotational latency is a fundamental limitation of HDD technology and cannot be entirely eliminated, unlike seek times in solid-state drives (SSDs).

Input output operations

Input/output (I/O) operations refer to the communication between a computer's central processing unit (CPU) and external devices, such as storage drives, network interfaces, displays, and peripherals. These operations involve transferring data to and from these devices, enabling the computer to interact with its environment.I/O operations can be categorized into two main types:

1. Input Operations: Input operations involve receiving data from external devices and transferring it into the computer's memory or CPU for processing. Examples of input devices include keyboards, mice, scanners, cameras, microphones, and sensors. Data from these devices are transmitted to the computer system for processing, manipulation, and storage.
2. Output Operations: Output operations involve sending data from the computer's memory or CPU to external devices for display, storage, or interaction. Examples of output devices include monitors, printers, speakers, storage drives, and actuators. Data processed by the computer system are transmitted to these devices for presentation, recording, or control purposes.

I/O operations are critical for the functioning of computer systems, as they enable users to interact with software applications and for software applications to interact with the physical world. The efficiency and performance of I/O operations can significantly impact the overall responsiveness and throughput of a computer system.In modern computing systems, various techniques are employed to optimize I/O operations, such as buffering, caching, asynchronous I/O, and I/O multiplexing. Additionally, advancements in hardware technology, such as faster storage devices (e.g., solid-state drives) and high-speed interfaces (e.g., USB 3.0, Thunderbolt), contribute to improving the speed and efficiency of I/O operations.

Mega bytes per second disk drive perform

The performance of a disk drive, typically measured in megabytes per second (MB/s), depends on several factors, including the type of drive (e.g., HDD or SSD), its specifications, and the specific workload it is handling. Here's a brief overview of the performance expectations for different types of disk drives:

1. Hard Disk Drives (HDDs):
   • HDDs typically have lower sequential read and write speeds compared to solid-state drives (SSDs). The average sequential read/write speeds for consumer-grade HDDs might range from 100 MB/s to 200 MB/s.
   • The performance of HDDs can vary based on factors such as the rotational speed (RPM), data density, interface (e.g., SATA, SAS), and cache size.
   • Random read/write speeds, which are more relevant for real-world usage scenarios, tend to be lower than sequential speeds, often ranging from a few MB/s to tens of MB/s.
2. Solid-State Drives (SSDs):
   • SSDs offer significantly higher performance compared to HDDs due to their lack of moving parts and use of flash memory.
   • Consumer-grade SATA SSDs typically offer sequential read/write speeds ranging from 500 MB/s to 600 MB/s, although higher-end models can achieve speeds of over 3000 MB/s.
   • NVMe (Non-Volatile Memory Express) SSDs, which use the PCIe interface, can achieve even higher speeds, often exceeding 3000 MB/s for both sequential read and write operations.
3. External and Portable Drives:
   • External HDDs and SSDs connected via USB interfaces (e.g., USB 3.0, USB-C) can exhibit varying performance based on the specific drive and the USB connection speed.
   • USB 3.0, for example, has a theoretical maximum transfer rate of 5 Gbps (gigabits per second), which translates to approximately 625 MB/s in ideal conditions. However, real-world transfer rates are typically lower due to overhead and other factors.