CompTIA A+ Cert Exam Guide Ch. 11 - Hard Drive Technologies Flashcards
What does a traditional hard drive consist of?
Individual disks, or platters, with read/write heads on actuator arms controlled by a servo motor-all contained within an airtight case.
What is a flux?
A small magnetic field on the hard drive disk used for the storage of data. The polarity of the field can be switched between north and south polarity.
What is flux reversal?
The process of shifting the magnetic field of a flux from north to south or vice versa.
What is a run?
A group of fluxes read by a HDD
What is Run Limited Length?
RLL; An encoding system of any combination of ones and zeros stored in a preset combination of about 15 runs on a HDD
What is Partial Response Maximum Likelihood encoding?
PRML; Powerful, intelligent circuitry used to analyze flux reversal to make a “best guess” as to what type of flux reversal it has just read. The maximum run length is up to 16-20 fluxes vs. the 7 of RLL.
What is perpendicular recording?
The vertical storage of fluxes on a HDD vs. storing them longitudinally. This allows for a much more densely packed HDD.
What are actuator arms/head actuators?
The piece(s) that are attached to the read/write heads that allow them to move across the platters
What are the two types of motors used to move the actuator arms?
- Stepper motor
* Voice coil/linear motor
How does the stepper motor function?
It moved the arms in fixed increments or steps across the platters.
What were the limitations of the stepper motor?
- It required minimal slippage to maintain accuracy. Over time, the position of the arms could change with wear, causing data transfer errors
- Heat deformation created problems with stepper motors
- The stepper motor needed to be parked when off. If the read/write heads were not parked when handling the drive, they could cause damage to the platters.
How does the linear motor function?
Voice Coil Motor; Uses a permanent magnet surrounding a coil on the actuator arm. When an electrical current passes, the coil generates a magnetic field that moves the actuator arm. The direction of the movement depends on the polarity of the electrical current.
What are the advantages of the linear motor over the stepper motor?
- Because the coil and the actuator arm never touch, there is no degradation of positional accuracy
- The linear motor automatically parks the read/write heads
What is the geometry of a disk?
The magnetized pattern in which a hard drive disk stores data. Ever model (brand?) of HDD uses a different pattern.
The geometry is describes with a set of numbers representing 3 things: heads, cylinders, and sectors per track
What are heads?
The read/write heads used to store data. Every platter requires two.
What is a cylinder?
A group of tracks with the same diameter
What are sectors per track?
The number of sectors per track on a HDD
What is a sector?
A specific piece of track on a HDD platter.
What is the write precompensation cylinder?
Older drives had trouble reconciling the smaller sectors towards the inside of the platter. To compensate for this, the drive would spread data on the inside of the platter a bit farther apart. The drive would need to know where this began.
What is a landing zone?
An unused cylinder used as a “parking space” for the read/write heads. When not in use, the read/write heads were parked in the landing zone so as to prevent damage to the platters when the disk was moved.
How is the speed of a drive measured?
The speed of a drive is measured in revolutions per minute (RPM). Common drive speeds are 5400, 7200, 10,000, and 15,000 RPM. Faster drives means better performance, but also the possibility of overheating your computer.
What is a Solid State Drive?
SSD; A hard drive that uses a series of memory chips rather than platters, etc. to store data. As a result, SSDs have no moving parts. Instead, they use current flow and negative/positive electron charges to store and retrieve data.
Some facts:
• Form factors - 1.8-inch, 2.5-inch, and 3.5-inch
• Can be PATA, SATA, eSATA, SCSI, or USB
• SSDs that use SDRAM will lose data when powered off. SSDs that use nonvolatile memory, such as NAND, retain data when powered off
• Less expensive SSDs utility multi-level cell (MLC) memory technology whereas more expensive SSDs use single-level cell (SLC) technology
ATA
Advanced Technology Attachment
IDE
Integrated Drive Electronics; Any hdd with a built-in controller is considered an IDE hdd.