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.