Ch. 11 Hard Drive Technologies
ATA interfaces
- Advanced Technology Attachment - Called IDE's : Integrated Drive Electronics
External SCSI Devices
- Concected to external connections of host adapter. - May have two connections in the back to allow daisy chaining. - SCSI chain can connect 15 devices, plus the host adapter.
Run Length Limited
- Data is stored using "runs" that are unique patterns of ones and zeroes. - Runs can be about 7 fluxes.
Internal SCSI Devices
- Installed inside the PC and connect to the host adapter through the internal connector. - 68-pin ribbon cable - Cables can be connected to multiple devices.
Spindle Speed
- Measured in (RPM) revolutions per minute. ie. 5400, 7200, 15,000 - Faster rotational speed produces more heat.
Benefits of SATA
- Narrow cables = better airflow and cable control - Max cable length = 1 meter - Hot-Swappable - No drive limit
Flash-based SSDs
- Pure flash drives for portables - Advantages: low power usage and heat generation; No moving parts = fast; rugged = nothing to break. - Disadvantages: $$$ HDD's 2.5% of the cost of SSD per GB
SCSI IDs
- Unique value of ID numbers range from 0 -15 - No two devices connected to a single host adapter can share the same ID
Geometry
- Used to determine the location of the data on the hard drive. - Previously required to know to enter manually into CMOS. Now stored on hard drive; BIOS can query the hard drive for data.
Stepper Motor Technology
- Used to with the voice coil technology to move the head actuator. - Moves the arms in fixed increments or steps.
Voice Coil Technology
- Uses a permanent magnet surrounding the coild on the head actuator to move the arm. - Automatically "parks" drive over non-data area when power removed.
Solid-state drives
- Uses no moving parts. - DRAM and flash-based drives - Technology in hard drives, memory cards, and more.
Partial Response Maximum Likelihood
- Uses powerful, intelligent circuitry to analyze each flux reversal. - Runs of about 16 to 20 fluxes. - Significant increase in capacity - up too 1 TB
LBA
- logical block addressing - Higher Capacity: Added more sectors/track on the outside tracks
eSATA
A modern type of connector for attaching external hard disks
Hard Disk Drive
A traditional hard disk drive (HDD) is composed of individual disks, or platters that are coated in a magnetic medium, with read/write heads on actuator arms controlled by a servo motor—all contained in a sealed case that prevents contamination by outside air
SATA bridge
Adapter that allows PATA devices to be connected to a SATA controller.
AHCI
Advanced Host Controller Interface
Advanced Host Controller Interface
An interface specification for enabling advanced SATA features is called:
ATAPI
An interface standard- part if the IDE/ATA standards- that allow tape drives, CD-ROM drives, and other drives to be treated like an IDE hard drive by the system
Tracks
Concentric circles on platters where data is stored.
Serial ATA
Creates a point-to-point connection between the device and the controller or host bus adapter.
Sectors
Date is stored on the platters in sectors or slices in the hard drive. 512 bytes per sector.
Small Computer System Interface
Fast communications bus that allows you to connect multiple devices to the computer, reliable, works on most systems, must be configured to specific computer, has limited BIOS support, and no common software interface. SCSI stands for...
Cylinders
Group of tracks of the same diameter going completely through the drive.
HDD
Hard Disk Drive
HBA
Host Bus Adapter
Disk Mirroring
Install a hard drive controller that reads and writes data to two hard drives simultaneously. The data on each drive would always be identical. One drive would be the primary drive and the other drive, called the mirror drive, would not be used unless the primary drive failed.
Point-to-point
No intermediary chips or devices
PATA
Parallel Advanced Technology Attachment
PRML
Partial Response Maximum Likelihood
Disk Striping
Provides no redundancy. If you save a small Microsoft Word file, for example, the file is split into multiple pieces; half of the pieces go on one drive and half on the other.
RLL
Run Length Limited
SATA
Serial Advanced Technology Attachment
SCSI Chains
Series of SCSI devices working together through a host adapter. ( internal and external)
SCSI
Small Computer System Interface
SSD
Solid-state Drives
Flux Reversal
The process through which the flux switches back and forth.The Hard Drive reads these flux reversals at a very high speed when accessing or writing data.
Head Actuator
The read/write heads move across the platter on the ends of these.
Fluxes
Tiny magnetic fields where Hard Drives store data
Duplexing Drives
Two drives, each on a separate controller, the system will continue to operate even if the primary drive's controller stops working.
"Heads" in a hard drive
Two tiny read/write heads service each platter, one to read the top and the other to read the bottom of the platter
Terminators
Used to prevent a signal reflection that can corrupt the signal. Only the ends of the SCSI chains should be terminated. Today most manufacturers build SCSI devices that self-terminate.