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ermanent link page information cite this page get shortened url switch to legacy parser print export download as pdf printable version in other projects wikimedia commons wikidata item appearance move to sidebar hide from wikipedia the free encyclopedia hard disk drive seagate st506 5¼ inch hdd with cover removed 2 5 6495 mb ide drive next to a 5 25 full height 111 mb mfm drive the st 506 and st 412 sometimes written st506 and st412 1 were early hard disk drives introduced by seagate in 1980 and 1981 respectively 1 that later became construed as hard disk drive interfaces the st 506 disk interface and the st 412 disk interface introduced in 1980 the st 506 was the first 5 25 inch hdd its successor the st 412 was introduced in 1981 and implemented a refinement to the seek speed and increased the drive capacity from 5 mb to 10 mb but was otherwise highly similar 1 beginning with its selection as the hard drive subsystem for the original ibm xt 1 disk drive controllers supporting the st 412 interface grew to become ubiquitous in the personal computer industry 2 the st 412 interface and its variants were the de facto industry standard for personal computer hard disks until the advent and wider adoption of the ide or ata interface in the early 1990s history edit the st 506 hdd was the first 5 25 inch hard disk drive introduced in 1980 3 by shugart technology now seagate technology it stored up to 5 megabytes after formatting 153 cylinders 4 heads 32 sectors track 256 bytes sector 4 and cost us 1 500 equivalent to 5 861 in 2025 5 the similar 10 megabyte st 412 hdd was introduced in late 1981 with 306 cylinders the st225 was introduced shortly thereafter with 20 megabytes and half the height all three used mfm encoding a widely used coding scheme a subsequent extension of the st 412 interface the st 412hp used rll encoding for a 50 increase in capacity and bit rate the st 506 drive connected to a computer system through a disk controller the st 506 interface between the controller and drive was derived from the shugart associates sa1000 interface 6 which was in turn based upon the floppy disk drive interface 7 thereby making disk controller design relatively easy 3 the st 412 interface was adopted by numerous hdd manufacturers such that the interface became a de facto industry standard for disk drives 8 well into the 1990s the limitations of the st 412 interface are 5 million transitions per second maximum on data lines 16 heads 4 drive units and a 20 foot 6 1 m cable length the standard channel code for the st 412 and st 506 is mfm with one data bit per transition for a data rate of 5 mbit s the st 412hp rll variant averages 1 5 data bits per transition for a data rate of 7 5 mbit s interface to controller edit a 34 pin control cable and a 20 pin data cable for an st 412 drive connected to a controller card a 4 pin molex connector supplying power to the drive can not be seen in this image in the st 506 interface the drive connects to a controller card with two ribbon cables carrying signals while a third cable provides power the two signal cables are the wide 34 pin control cable and the narrow 20 pin data cable the control cable interface is very similar to the standard shugart floppy disk interface like that floppy disk interface it can support four drives the data cable carries two read write separate unidirectional rs 422 compatible differential signal pairs with 100ohm terminating resistors 9 20 as with floppy disk drives a flux reversal corresponds to a rising edge the positive line of the differential pair attaining a more positive voltage than the negative pair of a short pulse that is ended with a falling edge after a fixed timeout and thus a return to zero code even though the timing of these pulses and flux reversals is completely in the hands of the controller the system design was for mfm and user data bits were represented by the absence or the presence of these pulses at specific points in time while the controller was precisely synchronized to the flux reversal stream on the platter while up to four drives can share a control cable each drive has its own dedicated data cable connecting it to the hard disk controller hdc most hdcs supported only two drives the control card translates requests for a particular track and sector from the host system into a sequence of head positioning commands including setting the direction of head movement in or out and sending individual step commands to move four of the control cable pins hd slct 0 through hd slct 3 allow the selection among up to 16 heads although only four are available on the two platter st 506 the original st 506 st 412 interface defined only two hd slct lines providing supporting for only four heads but a third hd slct line was shortly added to the design a fourth was added a not much later by redefining the reduced write current signal needed only by very early drives as hd slct 3 once the heads are properly positioned and the appropriate head is selected data is read or written serially through a set of pins in the data cable the limited bandwidth of the data cable was not an issue at the time and is not the factor that limited the performance of the system however the unshielded cable can sometimes be susceptible to high levels of noise like a floppy drive interface st 506 moves the drive head one track at a time with a timed pulse which cannot occur faster than the stepper motor can move the head the st 412 disk drive among other improvements added buffered seek capability to the interface the controller sends the required step pulses to the drive as fast as it can receive them 10 the st506 disk drive without buffered seek averages 170 ms similar to a floppy drive or modern optical drive while the mechanically very similar st 412 disk drive with buffered seek averages 85 ms 9 by the late 1980s drives with an st 412 interface were capable of average seek times between 15 and 30 milliseconds the process of moving portions of the command interpretation off the controller card and onto the drive itself in order to improve performance is a common feature of later hard drive connection schemes notably scsi with its rich command set and the storage focused ide systems ide in effect is a system for extending the computer bus so the interface controller can be built into the drive unit rather than being plugged into the computer s backplane this allows a single controller card really just an interface card to communicate with multiple dissimilar drives while it also reduces latency and noise between the controller and drive hardware 11 effectively the roles are reversed instead of the controller doing almost all of the complex processing and the drive just transferring encoded data between the magnetic disks and the controller the drive does almost all of the complex processing and the controller just transfers decoded data between the drive and the host system in these systems the operational details of the drive like head selection and seeking are entirely hidden from the host and handled within the drive s dedicated controller these became known as smart drives while st 506 like devices retroactively became known as dumb while integrated controllers have many benefits they also have a disadvantage the mechanical drive called the head disk assembly or hda and the controller are effectively fused into a monolithic black box so that if something goes wrong with the drive it is nearly impossible to do anything about it the data is usually irretrievably lost with a separated controller and disk system like that of the st 506 interface sometimes the problem can be resolved by connecting the disk drive containing the actual perhaps very important data to another compatible controller furthermore an st 506 style interface makes it possible and easy not only to replace the controller without throwing away the data but to get access to the analog data signals from the disk drive and process them through a special data recovery system that may be able to reconstruct data that a normal controller cannot read such data recovery techniques are much more difficult to execute on integrated drives because the needed analog signals from the disk are not available at a standard interface and the internal data recording method sector format and disk organization of nearly every integrated drive model is different and secret compatible systems and developments edit western digital wd1006 many other companies quickly introduced drives using the same connectors and signals creating a hard drive standard based on the st 506 ibm chose to use it acquiring adapter cards for the pc xt from xebec 12 and for the pc at from western digital as a consequence of ibm s endorsement most of the drives in the 1980s were based on the st 506 however the complexity of the controller and cabling led to newer solutions like scsi and later ata ide a few early scsi drives were actually st 506 drives with a scsi to st 506 controller on the bottom of the drive 13 atari also used adaptec acb 4000a scsi to st 506 converter inside its own line of sh204 sh205 external acsi drives 14 likewise a few early ide drives were just drives with an st 412 interface attached to a controller board or chip ultimately all scsi and ata drives had built the controller into the drive thereby eliminating the st 506 412 interface in such models connector pinouts edit from st 506 st 412 oem manual 9 in the following tables denotes a negated active low signal control connector control connector pinout ground 1 2 hd slct 3 or reduced write current ground 3 4 hd slct 2 ground 5 6 write gate ground 7 8 seek cmplt ground 9 10 track 0 ground 11 12 write fault ground 13 14 hd slct 0 key no pin 15 16 reserved ground 17 18 hd slct 1 ground 19 20 index ground 21 22 ready ground 23 24 step ground 25 26 drv slct 0 ground 27 28 drv slct 1 ground 29 30 drv slct 2 ground 31 32 drv slct 3 ground 33 34 direction in data connector data connector pinout drv slctd 1 2 ground no connection 3 4 ground no connection 5 6 ground no connection 7 8 key no pin no connection 9 10 no connection ground 11 12 ground mfm write 13 14 mfm write ground 15 16 ground mfm read 17 18 mfm read ground 19 20 ground power connector pin 1 12 v dc pin 2 12 v return pin 3 5 v return pin 4 5 v dc references edit 1 2 3 4 beginnings mfm drives of the 1980s redhill com red hill technology n d retrieved 16 september 2020 note st 412 is correct you will often see st412 written in error changes to the st 506 st 412 interface retrieved 2019 05 27 1 2 disc storage innovations keep coming while manufacturers ponder user needs edn may 20 1980 p 59 st 506 microwinchester service manual page 3 may 1 1982 seagate ships one billionth hard drive archived 2012 10 11 at the wayback machine computerworld april 22 2008 the principal difference was that the data rate was increased from 4 34 to 5 00 mbit s simplify system design with a single controller for winchester floppy combo electronic design october 25 1979 pp 76 80 st506 st412 interface archived from the original on 2018 03 07 1 2 3 seagate st506 412 oem manual pdf archived from the original pdf on 2010 05 10 retrieved 2008 01 10 glass brett february 1989 hard disk interfaces byte pp 293 297 retrieved 2024 10 08 system architecture a look at hard drives archived from the original on 2006 05 08 retrieved 2008 07 25 ide drives on board controllers are configured to appear to the computer like standard st506 drives xebec lands key ibm controller pact computer system news november 29 1982 pp 1 29 adaptec acb 4000a scsi winchester disk drive controller for st506 412 drives the acsi is converted by adaptec acb4000 module to typical mfm st 506 standard external links edit wikimedia commons has media related to st 506 st506 microwinchester oem manual accessed 10 jan 2022 archived version st506 microwinchester oem manual accessed 03 sep 2020 v t e seagate technology people founders alan shugart tom mitchell doug mahon finis conner syed iftikar ceos tom mitchell 1983 1991 alan shugart 1991 1998 stephen j luczo 1998 2004 2009 2017 dave mosley since 2017 storage drives current barracuda firecuda ironwolf skyhawk exos x series e series nytro game drive series pc xbox playstation external series one touch ultra touch photo drive backup plus basic discontinued medalist u series cheetah momentus decathlon seagate st1 pulsar single models barracuda st3000dm001 external drives freeagent replica innov8 seagate seven technologies seashield early drives st 506 st 412 st 225 st 212 st 213 st 425 st 8100 hardware current lyve corvault jbod systems disk arrays discontinued goflex tv net home satellite nas blackarmor wss seagate nas nas pro business storage nas services lyve cloud lyve mobile seagate systems leasing software cortx seagate manager replica memeo seagate media sync seagate share blackarmor backup tappin nas os 4 acquisitions arcada software 1996 conner peripherals 1996 mirra inc 2005 maxtor 2006 metalincs 2007 lacie 2012 sandforce 2014 xyratex 2014 dot hill systems 2015 spin offs seagate software 2000 certance 2000 v t e technical and de facto standards for wired computer buses general system bus front side bus back side bus daisy chain control bus address bus bus contention bus mastering network on a chip plug and play double data rate quad data rate list of bus bandwidths standards ss 50 bus s 100 bus multibus unibus vaxbi mbus std bus smbus q bus europe card bus isa stebus zorro ii zorro iii camac fastbus lpc hp precision bus eisa vme vxi vxs vpx nubus turbochannel mca sbus vlb hp gsc bus infiniband ethernet upa pci pci extended pci x pxi pci express pcie agp compute express link cxl direct media interface dmi rapidio intel quickpath interconnect nvlink hypertransport infinity fabric intel ultra path interconnect coherent accelerator processor interface capi spacewire storage st 506 esdi sdi ipi smd floppy connector parallel ata pata bus and tag dssi hippi serial ata sata scsi parallel sas escon fibre channel ssa satae pci express via ahci or nvme logical device interface peripheral apple desktop bus atari sio dcb commodore bus hp il hil midi rs 232 rs 422 rs 423 rs 485 lightning dmx512 a ieee 488 gpib ieee 1284 parallel port ieee 1394 firewire uni o 1 wire i 2 c access bus pmbus smbus i3c spi d²b parallel scsi profibus usb camera link external pcie thunderbolt can bus audio adat lightpipe aes3 intel hd audio i 2 s madi mcasp s pdif toslink portable pc card expresscard embedded multidrop bus coreconnect amba axi wishbone slimbus interfaces are listed by their speed in the roughly ascending order so the interface at the end of each section should be the fastest category retrieved from https en wikipedia org w index php title st 506 st 412 oldid 1378334410 categories hard disk drives computer storage buses computer related introductions in 1980 computer related introductions in 1981 seagate technology hidden categories articles with shor...