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PAHI2= MASS EDN'sAll-Star PC incorporates several mass-storage devicesthat provide flexible information storage and easydata interchange among PCs. We frequently crossedthe thin linebetween the leading and the bleedingedges of data-storage.technologyaswe. tested variousstorage devices, host adapters, and peripheralcontrollers. What we learned applies to all typesof computersystems, notjust PCs. I nU's originalModel5151 PC provideddata stor- | l"g.onsingle-sided,160k-bytefloppydisksand I on audio cassettetapes. The floppy-disk-drive'r" capacitywas mediocre,even by early 1980sstan- vl' dards, and the 200 bytes/secaudio-cassette inter- . facewas a joke. Fortunately,mass-storage capacity t, ;:d:i,,l:'fii$i," ifiif, x'-'ili:'*a'"#TJ';, ry data, PC-compatible hard disks store hundreds and even thousands of megabytes, and tape drives store gigabytes. EDN's All-Star PC incorporateseight mass- --i t storage peripheral devicesmanaged by three con- troller or host-adapter cards (Fig 1). Each of these three mass-storagesubsystems- floppy disk, SCSI, and WORM (write- once, read-many)optical drive-has uniquecapabilities. The floppy-disksub- i systemsupports four floppy-diskdrives, which furnish convenient. removable data storage and permit standardized il STEVEN H LEIBSON, Senior Regional Editor data interchangewith other PCs. floppy-disk drive, the All-Star PC wastough because most PC floppy- The SCSI subsystemcontrols two would not be able to duplicate disk controllers manage only two 330M-bytehard disks for the com- floppy disks directly; it would have floppy-diskdrives. The All-Star PC putet's primary data-storageneeds to temporarily store the informa- would require a floppydisk control- and a 2.5Gbyte tape unit for archi- tion being copied on a hard disk ler card that could manage four val and backupstorage (Fis 2). Fi- while the source and destination floppy-disk drives and support the nally, the PC's opticalWORM drive disks were swappedin the floppy- PC's floppy-diskformats. The Com- provides indelible file storage on disk drive. Becauseof an idiosyn- paticard IV from MicroSolutions lG-byte cartridges. cratic aversionto 2-step floppy du- ComputerProducts met these re- Floppy-disk drives are the one plication, I decidedearly on that the quirements. common element in every PC's All-Star PC would incorporatefour Table I lists the PC floppy-disk mass-storage repertoire. IBM's floppy-disk drives: two 5%-in. and formats that the Compaticard IV floppy formats swept away the mi- two 3%-in.drives. supports. The Compaticard IV, crocomputerindustry's hundredsof Meetingthat 4-driverequirement alongwith one 5%-in.high-capacity 6%-in. floppy-disk formats devel- drive and one 8%-in. high-capacity oped for the CPAI{ operating sys- drive, can read any standard PC tem. However,even IBM's l60k- floppy-disk format. The Compati- byte disk format didn't last long. card IV also supports other types Microsoft,'sDOS 1.1 introduceda of floppy-disk drives, such as the 320k-byte, double-sided format. now archaic 8-in. units, and can DOS 2.0 added hierarchical file store 2.8M bytes on certain }L/t-in. structures to the disk, bumpedthe drives that accept a ne\Mtype of single-sidedfloppy-disk capacityto floppy disk basedon barium-ferite l80k bytes, and increasedthe dou- media. The All-Star PC incorpo- ble-sidedformat's capacity to 360k rates a 2.8M-byte floppy drive-an bytes. The 360k-byteformat's rapid FD-236I from Teac America Inc. proliferation consignedthe earlier This drive can read and write stan- PC floppy formats to oblivion. dard 720k-and 1.44M-bytePC disks The next mqjor change in PC and can also use barium-fenite floppydisk formats occured when disks. The All-Star PC incorporates IBM introduced its PC/AT with three other floppy-diskdrives from l.2M-byte, "high-density," llr-in. Teac-two FD-55GFR5%-in., high- floppy-disk drives. Then came 3%- density drives and one FD-235HF in. floppy-disk drives that stored gr/b-in. drive. Thus, the All-Star ?20k bytes, followed by the intro- PC's full complementof drives in- duction of IBM's PS/2 computers cludes two 5%-in. and two 3%-in. and 1.44M-byte, Srrh-in. drives. units. Over a 9-yearspan, the.PC, which had unified the industry's floppy- Twisted cablesmake it tough disk formats, evolvedits own collec- TWofactors in IbM's floppy-disk- tion of incompatibleformats. subsystem design complicated ef- The All-Star PC needed to ac- forts to put four floppy-disk drives commodate these various floppy in the All-Star PC. The first is a formats for maximumcompatibility very peculiar floppy-disk-driveca- with other PCs. It neededat least llcven mau-rtoragepcrlpheralr cram the All- ble for the PC. The cable includes two floppydisk drives: a irA-in., Strr PC'r l0 half-helghtdrlve bayr. hon top a twist that interchangesthe drive- l.ZM-byte drive and a Tr/z-in., to Dottom,the perlpheralrInclude a 2.5G-byte selectand motor-enablesignal lines tape drlve, tno 5.25-ln.and two 3.5-ln.flopry- 1.44M-byte drive. However, with dh& drlves, and tm 330M-bytehuddtrL betweenthe cable'stwo drive con- only one lVq-in. and one Tr/z-in. drlvee. nectors.firis cute schemesimplifies 108 EDN March29, 1990 9omprti.,rd tv 83li;,li?*"n-,;",ffrXlii s+,?,f,[f,gHi:]&lly],,.rr. eAi 6is).?rt'_l&6: system conflguration by allowing you to set all of the floppy-disk- drive selectjumpers to address 1, uz,riqi*$*r., but it negates the original floppy- disk-drivecable's ability to address four drives. Fig 3 illustrates how the Compaticard IV circumvents fffit'f**ilr"tr."',"* IBM's eccentric floppy-disk-drive cable limitations by splitting the four drives under its control into two pairs. Each pair of floppy-disk drives connects to the controller with a separate floppy-disk-drive cable. However, solving the hardware Compaticard IV and supplying a limitations of IBM's floppy-disk- loadable device driver for the extra subsystem design doesn't fix the two drives. The devicedriver adds This is not merely a hypothetical second problem-BlOS (basic I/O the extra floppy-disk drives onto problem. The All-Star PC includes system) limitations. Most PC the end of the existing drive-desig- a pair of enormoushard-disk drives mother-boardBIOS ROMs control nator chain. Thus, if your system and initially used Microsoft's DOS only two floppy-disk drives. Al- has four floppy-disk drives and two 3.3, which accommodates disk though the Compaticard IV man- hard drives, the first two floppy driveswith capacitiesto 32M bytes. ages as many as four floppy-disk designatorsare A and B, the hard- The AII-Star PC's hard-disk drives drives, IBM's original PC/AT com- drive designators are C and D, and have a formatted capacity of 330M puter did not. Consequently,com- the third and fourth floppy designa- bytes each. DOS 3.3's solution to puters and BIOS ROMs patterned tors are E and F. This scheme this mismatchwas to create l0logi- after the PC/AT support only two works for most PCs, but can cause cal drives out of eachphysical drive. floppy-disk drives. MicroSolutions problemsfor systemsthat useenor- As a result, the first hard-disk drive skirted this problem by incorporat- mous hard-disk drives and older transmuted into logical drives C ing a floppy BIOS ROM on the versionsof DOS. through L; the second hard-disk drive became drives M through V. The Compaticard IV therefore as- signed designators W and X to the €:d secondpair of floppies. DOS only handles26 logical drives (A through Z), leaving only two drive designa- tors for use with other storage de- *q vices.Because the All-Star PC was going to have an optical WORM disk drive, there was actually only one drive designator left to play with. ea Designator-relatedproblems arose with a disk-cachingprogram called PC-Cache,part of the PC ToolsDe- Sculptureby KathyJeffers/Sculpture Photog- raphy by Chrir Vincent.Photography by The Fig l-Three subsyrtemsprovide the All-StarPC's mass-storage capabilities: a floppy ruboyotem, PhotoWorks and StevenLeibson unless other- a SCSIsubsystem, and a WORM(write-once, read-many) optical-disk rubrystem, wire noted. EDN March 29, 1990 luxe software packagefrom Central fers. The All-Star PC could have audio tape) drive, but one wasn,t Point Software Inc (Beaverton, OR, used drives with larger capacities available in time for this project. (503)690-8090). PC-Cache improves (some 5%-in. SCSI hard-disk drives The EXB-8200stores 2.5G bytes on hard-disk performance, but it inter- such as Micropolis Corp's 1bg0 se- one 8-mm videotape cartridge, yet fered with the Compaticard IV's ries now have capacities in excess the entire unit, including an inte- floppy-disk device driver. After of lG byte), but we couldn't find gral formatter/controller, occupies loading the program, I could no any \Y+in. hard drives that were the space of a full-height, 5%-in. longer read or write from the two faster than the Wren Runners. For drive. It also employs helical-scan \r/z-in. floppy-disk drives, W and X. this project, speed reigned over ca- recording. Suspectingthat the program cache pacity, becausea pair of BBOM-byte The Wren Runners and the EXB- was inter{ering with the device drives seemedto provide all the ca- 8200 require a SCSI host adapter driver, I instructed PC-Cache to ig- pacity the All-Star PC required. for operation, but becauseof expe- nore drives W and X. It couldn't. No sane system integrator would diency (or perhaps becauseof a lack however,because it recognized only omit a way to back up 660M bytes of foresight), the PC's BIOS only the first 16 drive designators, A of on-line data.

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