Tech Jargon

Here's a listing of Hard Drive Abbreviations (Jargon) used in TheRef(tm)
Interface -- What does the Controller use to control the Hard Drive?

ST506/412 -- The original HD interface, in MFM or RLL flavors. Named after the first two drives that adapted it, the ST506, and the ST412. The controlling electronics were split between the drive and a seperate plug-in board.
ESDI -- Enhanced Small Device Interface. Tried to overcome many of the limitations of the "standard" ST506/412 interface by improving the transmission of the data to the drive, and increasing the amount of control over the drive.
SASI -- Shugart Associates Standard Interface. Forerunner to SCSI, and basically the same. It moved controler functions onto the Drive, and used an 8-bit parallel data stream.
SCSI -- Small Computer Systems Interface. SASI developed into SCSI while waiting for IEEE approval. It features improvements to SASI derived from the IPI interface. It has it's own language and command set, which has been added to with each subsequent proposal (SCSI-1, SCSI-2, & SCSI-3). SCSI-1 was subject to too many "optional" commands, which hurt interoperability. (Each Manufacturer was free to pick & choose which commands it wished to support, and to add non-standard additional commands... ie: the "OCS" or OMTI Command Set, as opposed to the "CCS" or Common Command Set.)
ATA & XTA -- AT Attachment & XT Attachment. Originally designed to provide a more cost effective interface than SCSI or ESDI by integrating all the drive control electronics on the drive and eliminating costly additional boards. It eliminated the costly translation & communication electronics of SCSI and provided a simple interface to the system.
IPI -- Integrated Peripheral Interface. A high speed interface normally used on Minicomputers and above.
SMD -- Storage Module Device Interface. Another Minicomputer and up interface. Enhanced versions are SMD-E and SMD-O/E.
PS/2 -- Personal System/2 drive interface. An ATA interface which combined the normal ATA with the Power cable.
SSA -- Serial Storage Architecture.
SCA -- Single Connector Attachment.
FC-AL -- Fiber Channel-Arbitrated Loop.
PCMCIA -- The ATA interface adapted for PC Card slots.

Capacity -- How many megabytes (MB) of storage are available on the drive after it is formatted?

Cylinders -- How many concentric data tracks are on each platter? If you link track#1 on each platter, you'll get what looks like a can or "cylinder".

Platters -- A hard drive consists of a number of round Aluminum or Ceramic disks, which are coated with a recordable media. These disks or "Platters" can be coated on one side or both sides, and anywhere from 1 to 20 may be stacked inside the drive.

R/W Heads -- How many Read/Write heads does the drive have?

Servo Heads -- In order to position the R/W heads correctly, drives with Voice Coil actuators (VC) need feedback on where they are. The first method of doing this was to dedicate a head & surface to this task. Later, with improved head technology, Mfrs. were able to Embed (E) this information in the area used for data, and this method is now the most common.

Sectors/Track -- Each Data Track is divided into Sectors (or Blocks) of 512 data bytes in length when the drive is Low Level Formatted. When the first drives were made, the surface was formatted in 17 pie-shaped sections running radially from the center of the disk to it's outer edge. This divided each track into 17 "Sectors" of 512 bytes each. While data near the center of the platter was cramped, data near the outer edge was spread over a large area, which wasted space. Changing to 26 Sectors, or even to 34 Sectors/track did not alleviate this problem. The answer was to divide the platter into "zones", so that each zone could be optimized for the best number of sectors. This technique is known as Multiple Zone Recording (MZR), and is used on most drives today.

PreCompensation -- see coverage of this in TechTalk.

Landing Zone -- Early drives required you to tell the controller via a CMOS setting what area was to be used to "Land" the heads when you turned off the computer. This was usually the last cylinder, or 1-2 cylinders past the last useable one. Drives today automatically park the heads.

PIO Modes -- Many ATA Interface drives use a method of data transfer called Programmed I/O, abbreviated as PIO (also sometimes referred to as "CPU Assisted I/O"). There are four modes of PIO transfer, usually labeled from 1 to 4. PIO Mode 4 is the fastest.

DMA Modes -- Newer, faster ATA Interface drives now support the Direct Memory Access method of Data Transfer, abbreviated as DMA. There are two modes of DMA transfer commonly used by today's ATA drives, labled 1 & 2. DMA Mode 2 is the fastest. I'm not sure what "mode" is used by the new "Ultra-33", or "Ultra-DMA" drives. Many claim to be "Bus-Mastering", but without true hardware support at both the drive and the controller, it's just "Slave DMA" with a specialized driver. (True "Bus Masters" use "1st Party DMA", which requires seperate, dedicated DMA controllers.) It's an example of trying to use software as a cheap substitute for hardware. While it gains a bit of ground in data transfer over Slave DMA alone, it forces the CPU to do more work, slowing down the System as a whole during transfers - not a brilliant engineering idea in today's multitasking environments. (But it IS a brilliant marketing ploy.)

Please excuse me here if you feel that I've unjustly criticized "Software Bus-Mastering"... as in the Laws of Physics, "There's No Such Thing As A Free Lunch" <Phhhhiiiitttt!!!!>

Transfer Rate -- If you're into specsmanship, Transfer Rate is about the most misused Specification in Hard Drive brochures today - to the point of being useless. I've decided to base this spec. on one thing... the speed of data flow from the Media in bits/sec. Since version 4.54 of TheRef(tm), I've tried to use a formula to get to a figure that could be compared from one drive to another. Since most drives today use MZR, they push a lot more bits through the heads when at the outer edge of the platters than near the center. Many Manufacturers now list both these extremes in their information. I add both figures, and divide by 2 to get an average rate, and this is listed in TheRef(tm). When Manufacturers only list one rate, I'm left to wonder how they arrived there, and hesitate to use it.

Head Activation -- What mechanism is used to position the heads over the platters? Early drives used a Stepper Motor (SM), which moved the head assembly in very small... steps. The motor transferred it's motion to the head assembly through a metal band. The heads swung over the platters with a motion akin to an arm in it's arc. Some later drives used a worm gear to push and pull the head assembly in a straight, linear motion from the edge to the middle of the platters. These still used a Stepper Motor, and I make no distinction in TheRef(tm) between the two. Stepper Motors were displaced by a new "stepperless" motor, which utilized Servo techniques to actually "read" where the heads were on the platters. This may seem like a mundane item to us today, but it was a revolution when it was introduced. These new motors were called "Voice Coil" or "Rotary Voice Coil" motors, because they resembled the "Voice Coils" in a speaker. The feedback for the servo-positioner was obtained by dedicating a platter surface & head, and writing positional information on that surface. Drives that use a dedicated Servo Head will be listed that way. Manufacturers soon found that they could embed the positional information between data, and most eliminated the wasteful dedicated servo in favor of an Embedded Servo. Drives that specifically mention using this technique show an "E" in the "Servo Heads" information, though almost all drives today use it.

M.T.B.F. -- Mean Time Before Failure... The Manufacturer's best guess as to how long the drive will spin (in hours) before it needs repair. If you could believe these figures, we'd never have to buy another hard drive, right?

Warranty -- How many years will the Manufacturer guarantee that the drive will work correctly. The astute will notice that the warranty bares no relationship to the MTBF, for some reason. (Since there's roughly 8.8K hours in a year, it's a little odd that a Manufacturer would rate its drive at 900K hours MTBF, but only warrant it for 26K hours... Hmmm)

Power -- How much power does the drive consume? Old "Full-Height" drives really used to suck up some power, and get pretty hot! We're talking 30 Watts or so. Put 3 or 4 of those in your computer and you'd be getting Christmas Cards from your local Utility Company! When those drives were in fashon, power supplies started approaching 300 watts, and even then the drives had to be stagger-started to avoid voltage starvation. These days, we're all "energy consious", right? With the advent of "Green" machines, and smaller profile drives, the amount of power used has decreased, and drives now list power consumption in different modes of operation. To accomodate this change, I now list these new drives using the power consumed in "Idle" mode. I signify this by using a lowercase "i" in the rating... as in "12Wi".

... To be continued...