11 * or aborts suspends * ******************************************************* P C C O M P A T I B L E S R B B S ******************************************************* HARDDISK TECHNOLOGY ---------------------- The computer magazines are filled with ads advertising 10 mg drives for as little as $495.00. Whether you should rush out and purchase one of these drives, or wait and save a few more dollars for the a "Second Generation" drive is the purpose of this bulletin. I'll supply reasons why some of you should, and why a few should not, snap up these bargains. STORAGE MEDIA SURFACES ---------------------- A "hard disk" refers to the storage medium used, usually aluminum platters coated with a magnetic substance. A magnetic layer is created by coating the aluminum substrate with a paste containing gammaferric oxide particles. The paste is then cured and polished. Next, a protective layer is added and burnished smooth. The particles in this magnetic layer (about 30 microinches thick) can now be polarized by More (Y),N,NS? ns the read/write head to accept the data input. This procedure for creating storage media has been used since 1955. Most of the low cost drives available today are MULTIPLE OXIDE COATED PLATTERS - easier and cheaper to manufacture than the newer "Second Generation" drives which use one of two newer methods for coating the platters. Another medium coating that has been around for a while is the METALLIC THIN-FILM PLATED disks. The aluminum substrates (platters) are immersed in a series of chemical baths that coat the substrate with layers of metallic film. The final layer is about three microinches of a cobalt alloy that accepts the data input. Finally, the newest form of media plating is METALLIC THIN-FILM SPUTTERED disks created by coating the aluminum substrate with a nickel phosphorus layer. Next, a continuous vacuum deposition process called SPUTTERING is begun. During this process, magnetic layers as thin as two microinches are deposited on the disk similar to the way wafers are coated with metallic films in the semiconductor industry. The sputtering technique is then used to lay down a DIAMOND HARD one-microinch protective carbon coating. This drive surface will hold up better than most and allow a denser format - greater storage capacity. OK Monty, all this is very interesting but do I really need to know this technical crap? If you wish to be a smart shopper, you bet you should know. What storage medium is used is very important to ensure a reliable and trouble free drive in your particular application. The storage medium used is important because the read/write head doesn't touch the surface of the disk, it flies over it at high speeds only microinches away from the dreaded "head crash" - the head crashes onto the surface and wipes out all those lovely files you treasure so dearly. The thinner the surface of the disk, the better. Although the surface of an OXIDE COATED disk may appear smooth, under an electron microscope hills and valleys appear. Therefore, the head must travel at a greater height. With the head farther away from the disk surface, a less densely packed magnetic field must be used yielding a lower storage capacity ( 5 & 10 mgs). Also, with more hills and valleys present in this type of plated media, more head crashes occur. To increase capacity you add more platters and you get full height drives in the 5 1/4 inch size. A METALLIC THIN-FILM platted disk is being used in the new 3 1/2 inch drives. The surfaces of this platter contain magnetic layers as thin as two microinches - a much smoother surface, thus allowing the head to fly closer to the disk surface. With the head closer, the density of the magnetic field can be increased to provide greater storage capacity. The head can fly over the surface as closely as eight micro inches. Moreover, the increased intensity of the magnetic field provides the higher signal amplitudes needed for good signal-to-noise performance. This translates into increased storage capacity in a smaller area , fewer head crashes , and a drive that will give you many months of trouble free use. Now that we understand hard disk surfaces, let's explore the devices used to read and write data onto the magnetic fields these surfaces contain. HEAD/ARM ASSEMBLY (Read/Write Heads) ----------------- It is the read/write head that transfers the data from the disk to the drive electronics. The most commonly used head mechanism is a WINCHESTYER CONTROLLER ARM with a FERRITE HEAD. A more advanced head being used today is a tiny electronic magnet called a THIN-FILM HEAD used with a WHITNEY CONTROLLER ARM. Thin-Film heads can read/write data in denser patterns on the disks surface. Besides higher recording densities, Thin-Film Heads tend to be more reliable and lighter than Ferrite Heads. WHITNEY is the name commonly associated with the "second generation" winchester technology. The Whitney arm is more streamlined than the Winchester. The arm improves read/write signal reliability by improving "flying height stability" and tracking accuracy , and reducing interfering signals from adjacent tracks (this yields a higher signal to noise ratio). Manufacturing cost for the Whitney Arm & Thin-film head are higher then the Winchester Ferrite head assembly so I suspect the Winchester type will continue to be used in the lower capacity, cheaper drives. So when you see that 10 mg drive listed for a mere $495, you'll know that it is an Oxide Platter with a Winchester/Ferrite Open-Loop Stepper Motor assembly, right? You will also know that you can expect very slow access times. DRIVE PERFORMANCE (Average Access Times) ----------------- All of you have no doubt heard the term Average Access Time (AAT) - The mean time needed to reposition the read/write head from one data record to another and includes average latency - the rotational delay of the spinning disk. The drive in your IBM XT may have an AAT of 85 milliseconds, while the drive in an IBM AT will produce AAT's of 39 milliseconds. The speed difference is usually associated with what type of positioning mechanism is being used. The low-cost, low-capacity drive with an AAT of 85 MS uses an OPEN-LOOP STEPPER MOTOR to move the head from track to track. Once a command to seek a particular track is given, the stepper motor shaft clicks off the desired number of steps. This system relies on the mechanical accuracy of the motor to bring the heads to the correct location. Since this is a purely mechanical system, parts wear out and cause failures and longer access times. A more accurate (and more expensive) way to position the read/write head is with a CLOSED LOOP ROTARY VOICE COIL. This system employs electrical feedback to find the desired location on the disk. The information needed by the positioning mechanism to determine its distance from a specified location is contained either on a dedicated servo surface (DSS), which is one of the hard disk surfaces, or embedded in all of the recorded gaps on every track. All this results in faster access times and more accurate head placement. That drive on the IBM AT mentioned earlier uses this type of head positioning device. A few of TANDON'S new hard disks use what is termed a PSEUDO CLOSED-LOOP HEAD positioner. With this method, servo positioning information is embedded in the microscopic index wedge located on each data track. The drive checks its location during each revolution and corrects its position if necessary. This method is a nice compromise - More accurate than an Open-Loop System, yet less expensive than a Closed-Loop System.. Access times are not faster, but because this is used on a 3 1/2 inch drive, the AAT is a respectable 65 milliseconds. The TANDON 775 drive will use this head positioner method with a Whitney Head/Arm assembly and Metallic Thin-Film Spattered disks. This 20 mg drive is a good buy at about $500-700 mail order and is highly recommended. This bulletin is getting rather long, so I'll close with a few recommendations for the best PRICE/PERFORMANCE drives on the market. I hope you've found this bulletin informative. If you're in the market for an inexpensive 10 or 20 MG drive, check out the new 3 1/2 inch drives or pickup one of the older tech drives at bargain basement prices. Which one to buy? Well, if your computer use is light to moderate, the older drives should serve you well. If your computer use is heavy and you need a reliable drive that will last, check out the new technology drives. Spending that extra one or two hundred dollars may payoff in the long run. FOR THE IBM PC & AT...Compatibles --------------------------------- TANDON & MINISCRIBE ARE ABOUT TO SHIP THEIR NEW 3 1/2 INCH DRIVES. BOTH COMPANIES OFFER A QUALITY PRODUCT WITH VARYING DRIVE SPEEDS. RECOMMENDED 5 1/4 inch Drives ----------------------------- RODIME 33 MG (Internal- Full Height) Average Access Times are 45 milliseconds. The performance should satisfy any IBM PC user. For the IBM AT, if you aren't using your AT in a Multi-User environment, the speeds should handle your needs. I doubt whether many of you could tell the difference between this drive and the one that comes with the AT. List Price $1695. This drive can be had mail order for as little as $995 with controller card and for $850 without controller. An EXCELLENT drive. PRIAM 43 MG (Internal-Full Height) Average Access Times are 29 milliseconds. This is the drive for the AT user who needs speed and reliability. Priam has experience with mainframe disk systems and their expertise is unmatched by any other drive manufacture. This could be the finest drive available for the AT, or any micro for that matter. List Price is $2195 Contact Priam for a dealer: PRIAM 20 W. MONTAGUE EXPRESSWAY SAN JOSE, CA 95134 (408) 946-4600 40 min left Bulletin # 1 thru 14, L)ist, C/R continues? lJOSE, CA 95134 (408) 946-4600 40 min left Bulletin # 1 thru 14,