The Hard-Disk Explosion High-Powered Mass Storage for Your Personal Computer Tom Manuel 1208 Apollo Way, Suite 502 Sunnyvale CA 94086 High-performance, high-quality, new small sizes-200 mm (7.87 inch) drives, especially where multiple and large-capacity hard-disk drives or 210 mm (8.27 inch) diameter-and drives would normally be neces­ are now a low-cost reality for your one new drive uses 130 mm (5.12 sary to obtain enough storage. personal-computer system. Most inch) platters. Even so, their data For example, instead of adding hard disks use Winchester media, capacities are significantly larger than more floppy drives to increase head technology, and other modern floppy-disk drives of the same ap­ the storage capacity of a system, techniques to achieve high density proximate size. one set of dual floppy-disk drives and high performance in a small The latest disk drives can be divid­ might be replaced with an 8-inch space. One side effect is low power ed into two general categories: hard-disk drive that fits in the consumption. Some of the drives suit­ same space. This improves the able for personal computers use the • low-cost, relatively low­ storage capacity and system per­ older 14-inch standard diameter plat­ performance drives that will formance dramatically. These ters. Many new drives use one of two eventually replace floppy-disk low-end disk products will com­ pete on a cost-per-drive basis. • high-capacity, top-performance drives that must compete on a cost-per-byte basis. The 8-inch or smaller versions will likely (at least at first) be more costly per byte than the 14-inch models. However, their advantages of small size, light weight, low noise, and low power re­ quirements make them very at­ tractive for desktop and personal computers as well as small business systems. The Winchester disk-drive tech­ nology developed by IBM provided expensive, large-capacity, high-per­ formance, and low cost-per-byte disk subsystems (ie: the IBM 3350 and 3370 disk-drive systems) for large, ex­ pensive computer systems. This technology and development in other areas of disk-drive performance are now being applied to the develop­ ment of products suitable for smaller systems. The tremendous growth of Photo 1: The Memorex Model 101 hard-disk drive. (Photo courtesy of Memorex') microcomputers has created a de- 58 August 1960 © BYTE Publications Inc mand for small, compact disk drives. What Is Winchester T echnology7 • thinner magnetic coating: 44 The industry has responded and is be­ Three disk technologies have micro inches versus 185 micro­ ginning to produce them. A evolved, all pioneered by IBM. Other inches in the 2314 disk drive Winchester disk drive for your per­ manufacturers have refined the • lubricated disk surfaces sonal computer is now, or soon will designs. These technologies are usual­ • heads resting on disk surface be, a possibility. However, it may ly referred to by the model numbers when drive is stopped-they take still cost you five to ten times the of the original IBM product employ­ off and fly low when motion price of your processor to get a com­ ing the technology: "2314" starts (normal take-off and land­ plete small hard-disk subsystem with technology (in the 1960s), "3330" ing are done on an area reserved drive, controller, interface, power technology (late 1960s, early 1970s), for that purpose) supply, and packaging. and 'Winchester" technology (1973). • light loading force (10 g) and Disk storage, being a special type lighter heads. of add-on memory, can directly affect a computer system's performance, These characteristics permit many throughput, and reliability. Because performance improvements: very low of this crucial role, the principal flying heights (19 to 20 microinches), design objectives for disks are large improved reliability, and a dramatic capacity, fast access time, absolute reduction in head crashes are possible reliability, and low cost. because of the clean environment, Each of the three advances has new head and loading designs, and brought a significant increase in lubrication. Data densities are in­ storage density. One way to increase creased because of lower flying height density is to reduce the flying height and thinner platter coating. The of the heads over the disk surface. higher densities improve throughput Each reduction in height allows an in­ performance directly. More bits per crease in: tpi (tracks per inch) and bpi inch allow more data to pass under (bits per inch) (see figure 1). Ad­ the heads per unit time. More tracks vances in head design and positioning per inch mean that track-to-track ac­ mechanisms have also contributed to cess times are shorter. The lighter increases in tpi and bpi. heads and head mounts have less in­ Head flying heights have evolved ertia and can be positioned faster. as shown in table 1. Throughput performance can be im­ Photo 2: Close-up of a Winchester-type Just prior to 1973, disk-drive proved by increasing the rotational read/ write head. (Photo courtesy of Kennedy Company.) technology approached some limits. speed, up to a point-the aero­ The flying height had been reduced to dynamic characteristics of the flying 31 microinches. Without further head put some constraints on the reduction, significant improvement in rotational speed. The reliability of the data density was difficult. At lower Winchester drives surpassed that of flying heights, a single smoke parti­ any moving-head disk drive that was cle, whose diameter may be up to ten previously available. times the distance between the head Improvements and refinements and disk surface, can damage the disk have continued from many manufac­ and data. Therefore, cleaner condi­ turers. The costs of many of the most tions were required. Also, the disk expensive elements in a disk (the platters and magnetic surfaces were motor, head actuator, and control inadequate for large increases in track electronics) are relatively indepen­ and bit densities. dent of the capacity of the disk plat­ The 3340 Winchester disk drive, in­ ters. It is, therefore, cost-effective to troduced by IBM in 1973, was the increase the density of the platters first breakthrough. Storage and the number of platters. The in­ Technology Corporation announced centive has been to add capacity by a similar disk drive around the same any conceivable means, and trends time: the STC 8800 superdisk. have been toward more platters per spindle and greater bpi and tpi den­ Winchester Characteristics sities (data density has gone from Photo 3: The remarkable Shugart Winchester disk drives have the about 1000 bpi on early 2314s to over Technology Model ST506 hard-disk following characteristics: 8600 bpi on some of the recent disks, drive, offering 6 megabytes of mass and tpi density has gone from 200 tpi storage in a 3.5-pound package that fits in • sealed disk, head, and position­ on 2314s to over 600 tpi on new pro­ the ' same space as a 5-inch floppy-disk ducts). Cost effectiveness has also drive. (Shugart Technology is a new com­ ing assemblies pany located in Scotts Valley, California, • new trimaran head design-two been enhanced by reducing the access and is not affiliated with either Shugart outriggers supporting a narrower time and increasing the data flow; the Associates or Xerox. Photo courtesy of inner hull containing the economic payoff is increased Shugart Technology.) read/write head (see photo 2) throughput and efficiency of the total 60 August 1980 © BYTE Publications Inc system. In applications where disk come from RPS (rotational postion­ because twice the amount of data can storage is a key element, the pro­ ing sensing), which frees the disk con­ be read or written without moving cessor is often disk-IIO-bound. Pro­ troller and 110 (input! output) chan­ the heads. gram execution speed depends on nel for other work during seek time disk speed. Every increase in (head actuator movement) and dur­ Comparing the New Hard Disks throughput will improve the total ing part of the rotational delay time. to Floppy-Disk Drives performance. Improvements have also included The current trends toward multi­ Other improvements in throughput new automatic error detection, cor­ terminal ' systems, real-time transac­ performance in disk subsystems have rection, and recovery capabilities tion oriented systems, small business built into disk controllers. systems, and more powerful personal Voice-coil actuators, described in computers for a great variety of ap­ the next section, are common on plications have created a demand for high-performance disk drives. There more on-line data storage. Floppy­ are both linear and rotary voice-coil disk drives and tape cassettes often do positioners. Rotary voice coils not have the required performance typically take up less space, require (access times, throughput, etc), less power, and generate less heat reliability, or capacities. Thus, the than linear voice coils. Stepper need for secondary storage is being motors with band actuators are filled by new, inexpensive, high­ usually used in lower-performance, performance, highly reliable small­ lower-cost disk drives. Many of the disk drives with capacities, speeds, new small drives use brushless DC and reliability close to the very ex­ (direct current) motors with direct pensive drives. These new drives are drive on the platters. Designed as part physically much smaller and more of the spindles, these motors are com­ reliable than 14-inch cartridge or pact (about 1 inch high), maintain disk-pack drives. They are aimed in­ speed more accurately, use less itially at a gap between floppy drives power, and require simpler power and 14-inch drives (eg: Winchester, supplies than AC (alternating cur­ 5440 cartridges and 3330 type packs). rent) motors with belt drives.