Platter storage(HDD)
Background information
Platter based storage or as it's more commonly known, a hard drive. It stored data in a binary format on a magnetized disk (platter),
which is written or read to by moving a magnet over the area on the platter and changing the polarity of the magnetic charge of that area of the platter
to either a positive or negative, which is treated as either a 0 or a 1 and used as binary to store data on the platter.
In order to access different parts of the platter, the platter can be spun 360 degrees by a motor, which the magnet attached to an arm which move across the
platter by a magnetic coil which can either attracts or repel a magnet located on the arm to move the arm. Platters are often stacked between 4 and 6 platters high
allowing greater storage space without much extra space being used.
Hard drives are made up of two main sections.
Electronics
- Logical block addressing(LRA)-Addresses data blocks in a linear fashion(1,2,3)instead of an older CHS geometry which was more complex
- Partion table management-Manages partitions on the disk through the use of the master boot record(MBR) or the GUID partition table(GPT)
- Disk scheduling algorithms-Determines the order that input/output(I/O) requests are processed, see(FCFS, SSTF, SCAN, CLOOK) algorithms
- Read and Write buffers(R/W)-temporarily stores data while the respective read and or write processes are being conducted ,
- prefetching-Predictes what data is likely to be accessed and loads it into the cache
- Caching-Stores frequently accessed data in order to reduce access times
- Disk Firmware (Microcontroller, DMA Engine)- Handles communications between the hard drive and the OS (like a data air traffic control)
- Error Correction (CRC, Reed-Solomon Codes)- Checks for errors through algorithms such as Cyclic Redundancy check(CRC) then corrects errors using
algorithms such as Reed-Solomon codes - Bad Sector Remapping (SMART)-Detects any failing/failed sectors and moves any data worth moving("valid") data to spare sectors which replaces the failed sectors
Typically through Self-monitoring, Analysis and Reporting Technology (SMART) - Data Caching - Stores frequently accesses data to RAM to improve speeds and reduces drive uses (not related to caching in Disk management layer, except in principle)
- Data Encoding/Decoding - Turns data into magnetic signals so they can be encoded onto the platter itself and vice versa when it comes to decoding
- Communication protocols(SATA, SAS, IDE, SCSI) - Defines how the HDD communicates with the device as a whole, modern devices use SATA and SAS while older but still common drives
Use IDE and SCSI - command Queues (Native Command Queuing for SATA(NCQ) - Organizes and optimizes the order Read and write commands are handled to reduce the distance the R/W head as to travel
this speeds up data access or writing as the head can grab two pieces of data next to each other rather than grabbing one, going to the other side of the disk then coming back for the second one - Power management-Improves power efficiency and useable by disabling unused platters or returning the head to idle when not in use.
Disk management layer
Hard Disk Controller Layer
Physical drive interface layer
mechanical
-
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- Platters (Magnetic Disks coated with Magnetic Material)(stores the data)- Typically made up of a Ferris (magnetic) metal such as aluminium with an extremely thin magnetic coating that is used to encode data
as either positive or negative polarities, which can be converted into binary 1s and 0s later. - Read/Write Heads (Magneto resistive Heads)- Altars areas on the platter to either be positive or negative through electromagnetism in the case of writing data or
reads the polarities in the case of reading data - Actuator Arm (Positions the Heads over Tracks)- Moves the R/W heads to the right place on the right platter.
- Spindle Motor (Typically spins the platters between 5400-15000 RPM)- Spins the platters at different rates in order to achieve the most efficient (often fastest) data transfer and access rates
- Data Storage Geometry (how it's stored)-
- Sectors-The smallest addressable (editable) unit of storage on the platter, it sits on a track
- Tracks-Made up of sectors, the rings on the platter itself
- Cylinders-Aligns the tracks on the platter, so the actuator arm doesn't have to move to read the same data that is split across multiple platters
- Head Disk Assembly (HDA)(Holds the head on the arm-Holds the R/W head on the actuator arm
- Voice Coil Motor (VCM) (moves actuator arm)- A electromagnet that moves the Actuator arm to where it is required to go.
Physical hard drive layer
Flow chart of order of operations
Insert a flow chart of steps and actions for each task (create using diagram)
Related Topics
Topics such as desoldering to chip off or firmware dumping for disk PCB repairs
Further reading
External references in wiki references can just be cited through the keyword link
- Reference 1: Source details
- Reference 2: Source details