IN DESCRIBING the tape transport of

Apparatus For Magnetc Storage on Three-Inch Wde Tapes R. B. LAWRANCE R. E. WILKINS R. A. PENDLETON IN DESCRIBING the tape transport of the DATAmatc 1, t s perhaps well to begn by revewng the nfluental system features and ther resultng requrements n the followng sectons: Informaton Rate The central processor communcates wth the magnetc fle unts through the nput and output buffers at the steady average rate of a quarter of a mllon bts per second. Wth any presently practcable tape speed and recordng densty, ths requres a tape wdth greater than the conventonal half nch or so. DATAmatc-lOOO tape has a nomnal wdth of 3 nches (actually 3.56), carres 31 channels of nformaton and 5 channels of prewrtten magnetc block marks, s trans ported n ether drecton at a speed of 1 nches per second, and utlzes bt denstes per channel of 32 and 16 bts per nch. magnetcally nspected and put n servce; these block marks are never altered thereafter. As shown n Fgs. 1 and 2, nformaton space and stop-start space are alternated n an nterlaced pattern wth an over-all length of 1.23 nches. The tape, approxmately 2,6 feet long, contans 5, blocks, of whch 25, belong to the so called "frst half," normally scanned n the physcal forward drecton, and 25, to the "second half," normally scanned n the physcal reverse drecton. On scannng the frst half, the nterlaced second-half nformaton space serves for stop-start space (somewhat over.6 nch) and smlarly, for scannng the second-half nformaton space, the frsthalf nformaton space s avalable for stoppng and startng. Apart from the mproved effcency of tape utlzaton, ths has the consderable advantage that no separate rewnd operaton s requred. Readng and Wrtng physcal reverse for second half blocks. Playback however, can be done n ether drecton. The tape mechansm s thus requred to scan nformaton n ether drecton under a varety of contnuous. moton and stop-start-reversal condtons hence the stoppng, acceleraton to nomnal speed, accuracy of nomnal speed, and trackng all must satsfy certan rather strngent condtons. In addton to the system requrements outlned brefly n the foregong, varous. other requrements must be met by the tape mechansm. Of prme mportance s the requrement that no normal operaton: or concevable malfuncton of the tape mechansm shall result n deteroraton or destructon of the tape or ts nformaton content. MIDDLE OF TAPE Organzaton of Words and Channels As mentoned earler by J. E. Smthl 48 nformaton bts and 4 checkng bts are grouped together n each word. In wrtng or readng, all the bts of a word are fed sequentally to a sngle channel so that characters and words are organzed completely longtudnally rather than across the tape. In recordng, a tmng relatonshp does exst between bts beng wrtten n the varous nformaton channels, but ths s only ncdental and a matter of convenence; n playback there need be no nterchannel tmng relatonshp at all. Transfer of nformaton from a tape nto the nput buffer or output converter s asynchronous. There s no synchronous channel and no requrement for smultaneous sensng of bts n the nformaton channels. The major potental source of trouble from skew s thus elmnated. Organzaton of Words Into Blocks The locatons on tape nto whch nformaton s wrtten are pre-establshed and marked by magnetc block marks, whch are placed on the tape before t s The same magnetc head assembly s used for wrtng and readng. Because of the pre-establshed nformaton spaces and block mark pattern, and because of the nature of the recordng system, t s possble to alter nformaton, when requred, smply by wrtng new nformaton over the old, n as few or as many channels as desred. It s thus requred of the tape mechansm that at the tme of rerecordng, the relatonshp of head and tape must be closely controlled both laterally and longtudnally to be essentally the same as when the orgnal recordng was made. Snce t s a feature of the DATAmatc-lOOO system that tapes recorded on any ndvdual tape drve may be played back or rerecorded on any other tape drve, the channel locatons on the magnetc heads and the trackng of the tape must be held to wthn a very few thousands of an nch. Ablty to Scan Informaton In Ether Drecton In the DATAmatc 1, recordng of nformaton s alway done wth the tape movng n the logcl forward drecton, physcal forward forrst half blocks and Fg. 1. Alternatng frst-half and second-half nformaton spaces on D-1 magnetc tape The tape employed has a specal constructon shown n Fg. 3. The magnetc head does not come n contact wth the magnetc recordng oxde but s separated from t by a.5-ml layer of Mylar. In manufacturng, the oxde layer, \Yhose thckness s also.5 ml, s deposted on ths Mylar overlayer so that the oxde surface nearest the head gap has the smoothness characterstc of the :Mylar sheet rather than the less perfect surface characterstcs of the ar -dred mxture of oxde and bnder. A lamnatng adhesve whose thckness s approxmately 1/4 ml s then used to attach the composte oxde and Mylar sheet to a base of 2.-ml Mylar. The result s a tape whch produces much less wear on the magnetc head than do drect contact tapes; furthermore, the nformaton-carryng oxde s protected from abrason, scratch- R. B. LAWRANCE, R. E. WILKINS, and R. A. PENDLETON are wth the DATAmatc Corporaton, Newton Hghlands, Mass. 84 Lawr(1nce, Wlkns, Pendleton-Magnetc Storage on Wde Tapes

MOTION OF TAPE: Fg. 2 (left). Organzaton of nformaton spaces and block mark channels RECORDING SIDE / ON SCANNING FIRST HALF, THE INTERLACED SECOND HALF 'INFORMATION SPACE SERVES FOR STOP-START SPACE. ON SCANNING SECOND HALF, VCE VERSA. Fg. 3 (rght). Enlarged secton D-1 magnetc tape ng, flakng, embedment of dust, mosture, and other forms of deteroraton. Fg. 4 shows two magnetc head assembles, one of whch s shown unmounted and the other mounted n ts cylndrcal cartrdge. The heads are of staggered gap constructon and have the followng sgnfcant dmensons and specfcatons: Number of channels: 36 Offset of alternate channels (stagger):.2 nch on centers Gap wdth: 1 ml (.1 nch) Gap shm: 1 ml beryllum copper Channel wdth: 6 mls Gap heght: 2 mls Spacng of channels on centers: 82 mls Tolerance on channel locatons: ± 1,5 mls Radus of curvature of head and cartrdge: 2 nches Magnetc materal: 3 ml mu-metallamnatons Number of turns: 1 Voltage output on normal playback; 1 mllvolts peak-to-peak Tape Transport Mechansm The appearance of nformaton recorded on tape s shown n Fg. 5. For clarty, only the locatons of nformaton pertanng to frst-half record spaces are shown; those pertanng to second-half nformaton would be nterlaced n accordance wth Fg. 2. The alternatng pattern due to the staggered gap constructon s evdent from Fg. 5, although for smplcty t was not shown n Fgs. 1 and 2. In the enlarged porton of the fgure s shown the appearance of a porton of a typcal word as t would be made vsble by magnetc development wth collodal Fe 34. The vertcal lnes correspond to pole concentratons, alternately north and south, produced by _ reversal of the head current. It wll be notced that the spacngs of pole concentratons have two characterstc values, approxmately 3. and 6. mls (3 and 6 J,Lsec) as wrtten on tape. A 3 J,Lsec nterval between head current reversals represents a zero bt and a 6 J,Lsec nterval represents a one bt. It s possble wth a lttle practce to read vsually the bts of a word when the magnetc mage s carefully developed and vewed under a medum power mcroscope. The attanment of the hgh bt denstes quoted above, wth the relatvely wde head gap and the unusually large.5-ml separaton between the pole face and the magnetc oxde, s due to the characterstcs of the recordng and playback system, whch represents a radcal departure from present practce. Space does not permt further descrpton of these features n the present paper. As ndcated n the openng secton of ths paper a consderable part of the flexblty of the DATAmatc-lOOO system results from the use of unnumbered but accurately located nformaton spaces -specfed by the permanently placed magnetc block marks. The acton of the tape handlng equpment n deceleratng, reversng, and acceleratng tape must accordngly be fast and reproducble under all condtons of moton. In one mportant mode of moton the tape moves contnuoesly; ths mode s so smple that t does not requre further dscusson. In stop-start moton, when the tape s nstructed to stop after scannng a block t must come to rest well wthn the allotted space before the next nformaton space. Upon restartng n ether drecton t must reach full speed and be n steady moton by the tme the next nformaton space s entered, as ndcated by sensng the begnnng block mark. In order to fulfll these requrements, consderable care has gone nto the evoluton of the assembly shown n Fg. 6, whch shows a closeup of the capstan, brake, head mountng, valve, and actuator assembly, wth the tape draped n poston. The contour of the tape and the relatve locatons of the surfaces wth whch t comes n contact are shown n more detal n Fg. 7. Two contnuously counter-rotatng capstans of approxmately lo-nch crcumference are used, and these are drven at approxmately 1 revolutons per second by a synchronous motor. To move the tape n a desred dre,cton, the slotted Fg. 4. Two magnetc head assembles, rght: head mounted n cylndrcal cartrdge; left: head unmounted Lawrance, Wlkns, Pendleton-Magnetc Storage on Wde Tapes 85

BLOCK MARKS: \ SECOND HALF FIRST HAL, [ ) I [ TAPE MAGNETIC HEAD CARTRIDGE FIXED BRAKE COUNTER-ROTATING CAPSTANS: SURFACE SPEED 1 INCHES SEC. 15 INFORMATIO CHANNELS CARRY A COMPLETE INSURANCE POLICY RECORD AS AN EXAMPLE I "'IdMIIMfjjjjjjj!!!jjj11.",rJ::::1r;:::::::;:;::::,;,!r l U M M"J:::1::::rJ::r:::::::: MftM ldnlbllum!'!dm jlumrm!!mmmm!ffl "w':m:::;:oo _JIIN',,::l"!!. Mrl r:= DYNAMIC STIFFE.NING WORKING AIR PASSAGES Fg. 5. Informaton on tape, showng channel stagger TO LOOP CHAMBERS surface of the approprate capstan s communcated (through an nternal commutator, a hollow shaft, and a fast-actng electro-pneumatc valve) to a reservor contanng ar at reduced pressure. Atmospherc pressure then presses the tape nto contact wth a porton of the surface of the chosen capstan. For arrestng the moton of the tape a statonary brake surface of smlar slotted Fg. 7. constructon s used. The brake s located closely adjacent to tbe magnetc head assembly and surrounds t on botb sdes. Ths has the desrable effect that wben tape moton s arrested by engagng the tape to the brake surface tbere s a mnmum of lateral or longtudnal dsplacement relatve to the head. Upon Capstan, brake, and head assembly subsequent resumpton of tape moton n etber drecton, the tape n contact wth tbe head needs to make essentally no trackng adjustment before t s agan runnng true. The contour of tbe brake and ts loca. ton relatve to.the magnetc head are such that the tape has a slght wrap Fg. 8. Capstan assembly, wth valve and actuator assembly Fg. 6. Capstan assembly, showng tape n poston removed. Note slotted surfaces of capstan 86 Lawrance, Wlkns, Pendleton-Magnetc Storage on Wde Tapes

\&.I a: en en \&.I en a: \&.1\&.1 a::c CLCL \&.len... 1 en aa Z cr- PRESSURE AT CAPSTAN SURFACE r,/ I ' I ' \,... _- COMPRESSED AIR RESERVOIR PRE SSURE PRESSURE AT BRAKE SURFACE SUCTION RESERVOIR PRESSURE o ---r-------+-------------------=time DRIVING DRIVING------- "BRAKE"/ COMMAND VALV E OPERATION EFFECTED IIDRIVE FORWARD" COMMAND VALVE OPERATION EFFEC TED Fg. 9. Capstan, showng nternal commutator Fg. 1. Approxmate pressure wave Forms durng a drve-brakedrve cycle around the head, thus assurng good contact for readng and wrtng. The spacng between brake and head s several tmes as wde as the thckness of the tape however, so that edgewse nserton of the tape s very easy. Edge gudes mounted on the brake provde accurate trackng of the tape n the vcnty of the head. Adjacent to and beneath each capstan there s, mounted a long flat nclned plate whch s also equpped wth edge gudes. The top end of the plate s adjacent to the capstan and asssts n separatng the tape from the capstan. Snce the plate s closely adjacent to the normal path of the tape t serves as a dynamc stffener and oscllaton damper for the tape n the vcnty of the capstan assembly. Fg. 8 s a closeup vew smlar to Fg. 6 but wth the valve and actuator assembly removed, and wth the tape removed from the capstans so as to show the slotted surfaces whch connect nternally to the workng ar passages. The entrances to the two capstan ar passages are vsble as 1/4 nch dameter a-rng sealed apertures on the front of the valve mountng plate. A smlar aperture leadng to the brake s mdway between the two capstan apertures. The medum sze aperture exposed at the bottom s the lne carryng compressed ar to the valve and actuator assembly, and the larger hole mmedately above s the connecton to the vacuum reservor. A closeup vew of a capstan and ts nternal commutator s shown n Fg. 9. The purpose of the commutator s to communcate vacuum to only that porton of the capstan about whch the tape s wrapped. The crcumference of the capstan s accordngly dvded nto segments each of whch s connected to one passage on the commutator, and the number of commutator segments connected to the vacuum lne at anyone tme vares between two and three as the capstan rotates. Snce a vacuum system s used for controllng tape moton and snce compressed ar s used n the valvng arrangement, t s a smple matter to provde ar lubrcaton for those capstan surfaces not n engagement wth the tape. By ths means frcton, tape wear, and the generaton of Mylar dust are greatly reduced. There s stll another way n whch controlled selectve njecton of compressed ar nto the capstan and brake s of great beneft. Consder the vacuum to be appled to the rght-hand (clock-wse rotatng) capstan so that the tape s movng to the rght, n the forward drecton. If t s now desred to stop, the vacuum s shfted to the brake member and dsconnected from the rght-hand capstan. In order to dsengage the tape rapdly and affrmatvely from the capstan a short puff of medum pressure ar s blown nto the rght-hand capstan mmedately followng dsconnecton of the vacuum supply. Ths puff reaches the capstan and dsengages the tape at essentally the same tme as the vacuum newly appled to the brake causes the tape to be attracted to the brake. Transfer of the tape from engagement wth the movng capstan to engagement wth the statonary brake s thereby quckly accomplshed wthout subjectng the tape to a tug-of-war between these two surfaces. Tape abrason and the maxmum stresses n the tape are accordngly greatly reduced. Fg. 1 shows a typcal cycle of operatng pressures n a drve capstan and n the brake, as a brakng operaton and a subsequent start n the same drecton are performed. Smlar consderatons apply to a brakng operaton followed by acceleraton n the opposte drecton. Ar/vacuum connectons to the two capstans and the brake are controlled by three ndvdual dentcal assembles, each of whch conssts of two electrcal actuators and a control valve. A schematc of one of these electro-pneumatc valves s shown n Fg. 11. Compressed ar at approxmately 35 pounds per square nch (gauge) s contaned n a chamber wth two compressed ar ext ports, each of whch s normally closed by the armature of an electromagnet. On the control valve sdes these two apertures are adjacent to the two faces of a control vane, whch teeters about a reslent fulcrum whch also acts as a pressure sealng 'barrer. On the other sde of the control vane a large passage equpped wth a seal communcates to the vacuum reservor, and another passage equpped wth a seal at one end bypasses the sealng fulcrum barrer. A lttle consderaton shows that two stable postons of the control vane are possble, wth the holdng force beng suppled by the vacuum reservor n both nstances. Snce the two postons of the control vane are stable, the valve s a mechancal non-bnary flp-flop, and only a short puff of hgh-pressure ar on the proper surface s requred to effect a transton. These puffs of ar are ntated by a short burst of current n the approprate electromagnet, whose armature uncovers the aperture and allows ar to escape from the compressed ar chamber and mpnge on the control vane. Immedately after the vacuum s dsconnected from a passage by drvng actuator A' the partally spent compressed ar s drected nto the workng ar passage and thence to the capstan (or brake) provdng the pressure blow off Lawrance, Wlkns, Pendleton-Magnetc Storage on Wde Tapes 87

Fg. 11. Schematc of electro-pneumatc valve Fg. 12. Valve and actuator mechansm descrbed above. Spent ar from actuator B' s conserved by leadng t to the reservor of low pressure ar used for lubrcaton; the pressure of ar n ths chamber s regulated by a feather vane whch controls the exhaust to atmosphere. The prncpal components of the valve and actuator mechansm are shown n Fg. 12. The control vane s made of surface-hardened alumnum and fts nto the cavty wth a clearance of approxmately 2 mls. Both n the mountng of the control vane and n the mountng of the relay armatures use s made of reslent pvots held n compresson. Valve seats are of slcone rubber to avod stckng when fast operaton s requred after a long nterval of tght closure. The entre valve and actuator assembly can be removed from the capstan by unscrewng four easly accessble machne screws, and the chamber contanng the actuators s smlarly easly dsassembled. Passages from the vacuum reservor and the compressed ar lne are cast nto the heavy alumnum housng, whch serves both to contan the medum pressure compressed ar and to sheld the nearby magnetc heads and tape from the magnetc felds generated by the actuators. Snce the actuators are drven n pars the actuator connectons are arranged o that the external felds n the vcnty of the head substantally cancel each other and cause no dffculty. The power handlng capacty of the actuator cols n ths applcaton s greater than ordnary snce the cols are effectvely cooled by the flow of compressed ar whch they control. Fg. 13 shows a typcal curve of velocty and dstance, measured at the head, as a functon of the tme elapsed from the ssung of a brake command. Current from a low mpedance hard-tube drver starts to flow wthn a few,usecs of the command and bulds up wth a tme constant on the order of.7 mllsecond. The actuator armature starts to move, uncoverng the compressed ar ext port, n slghtly under.3 mllsecond and the control vane s flpped to ts new poston n about 1. 7 mllseconds. In rather less than 3 mllseconds the pressure at the under surface of the tape has changed suffcently to start engagement (vacuum) or dsengagement (pressure puff), and a bref perod of tape deceleraton ensues. As seen from the curve the tape comes completely to rest after havng traveled a lttle over.3 'nch from ts locaton at the tme the brake command was ssued. A smlar record of the tape acceleraton characterstcs s gven n Fg. 14, whch also partcularly shows the velocty of the tape at the tme when a begnnng block mark s normally encountered. In stoppng, the tape comes to rest somewhat beyond the center of the avalable stopstart space. The avalable dstance for acceleraton s thus less when the orgnal drecton of tape moton s resumed, as shown n ths fgure; approxmately.2 nch more s avalable f the tape restarts n the opposte drecton. It wll be noted that the mplementaton s such that t s not necessary for a brakng operaton to be completed before a reverse drecton or restart command can be accepted and acted upon. Detaled dscusson of the actuator, valve, and tape moton as a functon of the nterval between brake and drve commands s, however, beyond the scope of ths paper. In preparng tape for use on DATA matc 1 a complete nspecton procedure s followed, usng an equpment called the tape certfer, whch s shown n Fg. 15. After layng down all of the block marks, ncludng specal block marks dentfyng the "end" and the "mddle" of the tape (as ndcated n Fg. 1) the block marks and the entre nfonnaton space are nspected for playback adequacy and freedom from any mperfectons whch would prevent full and accurate recovery of recorded nformaton. Block marks whch are substandard or whch surround nformaton regons contanng tape defects are magnetcally erased so that at no tme does the DA T Amatc 1 attempt to depost nformaton onto any tape locaton except those known to be fully up to standard. By ths means, and wthout requrng any addtonal equpment n magnetc fle unts or central processor, a small defect rate n the manufactured tape can be tolerated, all defects beng detected and 88 Lawrance, Wlkns, Pendleton-Magnetc Storage on Wde Tapes

U III U) III % U >-..J III > 1 5 DISTANCES TRAVELED SINCE BRAKE COMMAND ( FINAL REST POINT \ / AT.31 INCHES).3\,, 2 3 4 5 6 TIME IN MILLISECONDS FROM ISSUING -BRAKE" COMMAND Fg. 13. Typcal curve of velocty and dstance versus tme durng brakng operaton, c z o 1 U) 1&.1 % U 5 DISTANCES MOVED FROM INITIAL POSITION -LL-4-... o 2 3 4 5 6 7 8 9 1 I I 12 TIME IN MILLISECONDS FROM ISSUING "DRIVE" COMMAND Fg. 14. Typcal curve of velocty and dstance versus tme durng a drve operaton completely avoded n the fnshed "certfed" tape. The nherent economes are obvous and mportant. Space permts only a bref descrpton of the remanng features of the tape handlng mechansm. In conventonal fashon pneumatc loop chambers are nterposed between the capstan assembly and the tape supply and takeup reels. An nnovaton s the control of the reel servo motors by pneumatc contactors whch derve ther motve force from the loop chamber sucton. Not only are the complcatons and tme delays of electrcal contactor arrangements thereby avoded, but because of the large vscous dampng any contact bounce s automatcally suppressed. In addton, fal-safe de- sgn guards aganst tape damage from loss of sucton. The tape mechansm sts adjacent to a companon unt contanng preamplfers swtchng relays and auxlary gear, and the combnaton of the two unts s referred to as a sngle magnetc fle unt. All mechansms n an nstallaton are Fg. 15. Tape ce,rtfer suppled wth hgh-pressure ar and subatmospherc ar from a common pumpng and manfold system. The enclosures of the tape handlng mechansms are acoustcally treated. Gasketed double doors of transparent plastc provde vsual observaton and attenuaton of the sound felds generated by the tape mechansm. Reference 1. PROCEEDINGS OF THE EASTERN JOINT COM PUTER CONFERENCE' AlEE Specal Publcaton T-92 "A New Large-Scale Data-Handlng System, DATAmatc 1," J. Ernest Smth. May, 1957, pp. 22-28. ---------------------------------------------+---------------------------------------------- Dscusson W. A. Farrand (Autonetcs Dvson of North Amercan Avaton): What s the land area between channels? Why s ths partcular recordng code used? Dr. Lawrance: As gven n the tabulaton the channel wdth s 6 mls; the center to center spacng of channels s 82 mls and the land between channels s 22 mls. The recordng system used, s beleved to be capable of very hgh fdelty n both the readng and the wrtng processes, because of the tme modulaton features of the system. H. L. Gross (Natonal Cash Regster Company): Can one read or wrte successve blocks of nformaton contnuously wthout stoppng and startng the tape after each block? Dr. Lawrance: Yes, n fact, successve blocks of nformaton are generally wrtten or read contnuously wthout any nterrupton of tape moton. R. M. Gordon (Electrodata): May the tape be searched for a specfc block? If the. answer s yes, descrbe brefly the search procedure. Dr. Lawrance: A channel of each block of nformaton s devoted specfcally to nformaton that enables searchng to be performed readly. The search procedure nvolves hgh-speed comparsons of the Lawrance, Wlkns, Pendleton-Magnetc Storage on Wde Tapes 89

dentfcaton ot key nformaton wth the tape n contnuous moton; n fact, ths search may proceed smultaneously on ten tapes wth all tapes n contnuous moton. R. A. Frontero (Internatonal Busness Machnes Corporaton): Does the DATAmatc system allow fle searchng and/or record searchng wthn a fle wthout readng all precedng fles or records on the tape reel? If so, what method s used? Dr. Lawrance: Only a small fracton of the nformaton n each record, namely, the dentfcaton key, need be read n the search process. All satellte nformaton s passed over wthout readng untl the desred record has been reached. N. Dean (Ramo-Woolrdge): Is t possble to record selectvely on the tape,.e., wrte only selected blocks? Is t possble to read and wrte on the same tape on the same pass? Dr. Lawrance: Selectve recordng on the tape s possble and, n fact, desrable n many DATAmatc-1 applcatons. Consecutve ntervals of readng and wrtng durng a sngle pass of a gven tape s defntely a permtted procedure n ths system. B. Scheff (Massachusetts Insttute of Technology): Have there been any problems wth tape stretchng? If so, how have they been remeded? Dr. Lawrance: There have been no problems wth tape stretchng due to operaton of the capstans, brake, or reel servos. Even though the acceleratons produced by the capstan and brake are of the order of 25 g, the mass of tape accelerated s so small that we reman safely below the elastc lmt. The reel servo control setup has been desgned to be essentally fal- safe:, so that a trple falure s requred before any danger of tape stretchng s encountered. Furthermore, n the event of such a falure, a puff of compressed ar s suppled to both capstans and to the brake, so that the tape s completely free to move through the capstan assembly. J. K. Lews (Department of Defense, Washngton, D. C.): What s the thckness of the mylar cover flm, and the thckness of oxde. Is t correct to assume that the head s n contact wth the mylar cover flm? Who makes the tape? Dr. Lawrance: The thckness of the mylar overlayer s 1/2 ml, and the thckness of the oxde s also 1/2 ml. The lamnatng adhesve between the undersde of the oxde and the 2-ml bottom layer of mylar s about.2 mls thck. Ths makes an overall thckness of approxmately 3.2 mls. The head s, ndeed, n contact wth the top surface of the flm. The tape s made for us by sp'ecal arrangement wth Mnnesota Mnng and Manufacturng Company. H. H. Sten (Ferrant Electrc-Canada): Are two channels used for block marks n order to elmnate erroneous readout of a mark due to nose or other tape defect? Is there ever a need fqr splces and, f so, do tape splces produce sgnals n the blockmark read amplfers, whch may be read as marks? Dr. Lawrance: The double blockmark channels are employed n a specal crosscheckng functon to verfy the poston of nformaton on the tape. The need for splcng should be very rare, but splces do not nduce spurous sgnals nto the blockmark sgnals. M. B. Stad (Remngton-Rand Corporaton): How does ths sandwch tape compare n cost to "ordnary" coated tape? Do you have stretch problems or edge wrnklng due to 3 nches wdth? Dr. Lawrance: The DATAmatc-1 tape s more expensve ntally than ordnary coated tape because of the more complex lamnar constructon. Each roll of tape released by DAT Amatc must satsfactorly pass an exactng nspecton process, such that the tape s certfed to be error-free n all recordng areas. No, the 3 nch wdth gves us no dffculty wth stretchng or edge wrnklng. M. E. Montjo (Rado Corporaton of Amerca): Why was the electrostatc clutch prncple n your mechansm abandoned? Dr. Lawrance: At the stage progressed wth the electrostatc clutch development, magnetc tape lfe was as yet too short to satsfy the performance standards of the DATAmatc-1 system. H. E. Van Wmkle (Internatonal Busness Machnes Corporaton): What type of reel servo s used? Dr. Lawrance: The type reel servos used are 4 watt, 2 phase servo motors wth two dfferent gradatons of dynamc brakng. Sensng of the tape poston s done by pneumatc elements whch control the motor crcuts drectly. M. Sten (Natonal Bureau of Standards): Does the tape ever move faster than 1 nch per second durng the frst 8 mllseconds or shortly after whle the servos are settlng down? Dr. Lawrance: Detaled evdence such as shown n Fg. 14 shows that over-speedng of the tape n the vcnty of the head s lmted to a fgure well wthn the capabltes of the read-wrte system. Synch!onzaton of a J. KIELSOHN IN COMPUTER DESIGN the problem of communcaton between the central computer and the outsde world s always present.,ths paper descrbes how ths problem was solved for the Cambrdge computer wth a new type of shft regster employng the Ferractor*, the magnetc core developed by Remngton Rand Unvac. The computer and the magnetc amplfers whch t uses were descrbed n some detal n other papers. The shft regster tself has many unque features, however, and the desgn and applcaton mert a separate dscusson. The Cambrdge computer s a magnetc devce n the sense that all of the normal amplfyng functons are performed wth Magnetc Computer G. SMOLIAR Ferractors. Germanum dodes are used for the logcal operatons of gatng and buffng. Pulse shapng and delay are accomplshed by the magnetc amplfers, and therefore separate components are not needed to perform these functons. The synchronzer of a computer must act as a lnk n both drectons between the essentally unform pulses crculatng n the computer and the nput and output pulses occurrng at random. The Cambrdge computer, although relatvely restrcted n nput-output functons, stll has many external communcaton paths. There are data lnks for real-tme operaton, an n-and-out paper-tape punch and reader, and a modfed typewrter for nput and output. Consderaton of the typewrter only, however, wll nvolve all of the fundamental prncples of synchronzer operaton. Transfer of data from the typewrter s made through a shft regster, ro, n whch the ten characters of a computer word are assembled. The dgts comng from the typewrter occur at random and n reverse order wth respect to the sequence n whch they are carred n the computer. In other words, an operator types the most-sgnfcant dgt frst, whle the word s carred n the computer wth the least-sgnfcant dgt frst, for the usual reason that the result of a carry may be recorded after the carry. The J. KJELSOHN and G. SMOLIAR are wth Remngton Rand Unvac, Dvson of Sperry Rand Corporaton, Phladelpha, Pa. The work reported here was sponsored by the Ar Force Cambrdge Research Center under contract AF 3(62)-155. * Trade-mark, Sperry Rand Corporaton. 9 Kelsohn, Smolar-Synchronzaton of a Magnetc Computer