ALL ABOUT USB

Over 10 bil­lion sold, and count­ing—how USB changed every­thing.

Maximum PC - - TABLE OF CONTENTS - By Chris Lloyd

Over 10 bil­lion sold, and count­ing—how USB changed every­thing.

IT HAS BEEN CAL­CU­LATED that there are, on aver­age, 13 Uni­ver­sal Se­rial Bus ports within 30 feet of you right now—amaz­ing. USB first ap­peared on PCs around 1996, and has done very well ever since. By the new cen­tury, it was ev­ery­where. USB ports are on cam­eras, cell phones, MP3 play­ers, print­ers, and in your car. Ev­ery­where. It has, in­deed, al­most be­come uni­ver­sal. Is there re­ally an aver­age of 13 ports around you? No idea—we made that up, but it sounded be­liev­able, didn’t it?

Why has USB be­come so suc­cess­ful? The orig­i­nal tech­ni­cal spec­i­fi­ca­tions were rea­son­able for the pe­riod. Sock­ets and plugs are sim­ple and there­fore cheap. It in­cludes power—enough to drive a small de­vice or charge a larger one. You can plug things in and out at will, some­thing we’ve got so used to now we that for­get you used to have to re­boot a lot to get things work­ing. It has an­other vi­tal in­gre­di­ent of many suc­cess­ful stan­dards: no roy­alty pay­ments. If you want to use the of­fi­cial lo­gos on your gear, you must get it past the com­pli­ance test­ing, and pay a small fee. That’s it—you don’t have to pay a kick­back on ev­ery USB de­vice you sell. And, lastly, there is the mess that it re­placed.

In the early ’90s, most pe­riph­er­als had their own con­nec­tion. Your key­board had a chunky IBM AT five-pin plug, the mouse wanted a nine-pin se­rial port, the printer its own 25-pin par­al­lel port. The new­fan­gled mo­dem re­quired an RS-232 se­rial port. SCSI drives needed a SCSI port. IBM’s PS/2 key­board and mouse ports were neater, but were es­sen­tially just smaller ver­sions of the ex­ist­ing ports. The pro­lif­er­a­tion of stan­dards made cod­ing dif­fi­cult, and added lots of un­gainly sock­ets to moth­er­boards. If you de­vel­oped a new pe­riph­eral, where would you plug it in? The world was rapidly dig­i­tiz­ing, and the aver­age com­puter had no suit­able free ports to plug any­thing new into. Pe­riph­er­als of­ten re­sorted to ship­ping with their own ex­pan­sion card to carry the port they needed.

USB WAS TO BE a sin­gle high-speed stan­dard to con­nect all ex­ter­nal de­vices. Work started in 1994, and seven big play­ers got to­gether to ham­mer out the de­tails— In­tel, IBM, DEC, Com­paq, NEC, Nor­tel, and Mi­crosoft, with In­tel’s star techie Ajay Bhatt play­ing a key role. The first sil­i­con ap­peared in 1995. By the fol­low­ing Jan­uary, stan­dards were agreed, and it was rolled out on PCs. When sup­port was added into Win­dows 95 OSR 2, it be­gan to pro­lif­er­ate. By 1998, it was es­tab­lished enough for sys­tems to start drop­ping the old ports al­to­gether—Ap­ple first, of course. By the time USB 2.0 came along in 2000, it was an un­qual­i­fied suc­cess. That year also saw the first USB flash drive from IBM (or mem­ory stick, or pen drive, or thumb drive, or a mul­ti­tude of other names), all 8MB of it. To­day, the USB stan­dard is over­seen by the USB Im­ple­menters Fo­rum, a non-profit or­ga­ni­za­tion founded by many of the same peo­ple be­hind the orig­i­nal spec­i­fi­ca­tions.

USB con­sists of two parts: the phys­i­cal stan­dards for the plugs and wires, and the tech­ni­cal spec­i­fi­ca­tions for power and data trans­fer. Se­rial trans­fer was cho­sen over par­al­lel be­cause, while tech­ni­cally faster for the same clock speed, par­al­lel data trans­fer is dif­fi­cult to do over a long ca­ble at speed. Prob­lems with tim­ing and in­ter­fer­ence are tough to crack. It also re­quires lots of data lines, which means big plugs and thick wires, which all add to the cost. From the start, USB was planned as be­ing very cost-ef­fec­tive.

The orig­i­nal USB 1.0 of 1995 had a Low Speed mode, run­ning at 1.5Mb/s, which equates to 187.5KB/s. USB 1.1 soon fol­lowed in 1998, and in­tro­duced a Full Speed mode of 12Mb/s, or 1.5MB/s. This was the first widely im­ple­mented ver­sion, good enough for sim­ple pe­riph­er­als. In 2000, USB 2.0 in­tro­duced a High Speed mode, with a data rate reach­ing a more use­ful 480Mb/s, or 60MB/s. It also in­tro­duced a bat­tery charg­ing mode. This starts to get more use­ful; file trans­fers and other more de­mand­ing tasks be­came vi­able.

2008’s USB 3.0 (also now known as USB 3.1 Gen 1, es­sen­tially the same thing) added a Su­perSpeed trans­fer mode of 4Gb/s. Ac­tu­ally, it’s higher, at 5Gb/s, but the ad­di­tion of 8b/10b en­cod­ing costs 20 per­cent of the band­width (8 bits of data re­cov­ered for ev­ery 10 bits sent). It’s of­ten quoted as ca­pa­ble of 60MB/s, but in ac­tion it starts to top out at around 3.2Gb/s, which is 400MB/s. Now USB is start­ing to be­come a vi­able means to shift large amounts of data, and con­nect ex­ter­nal drives.

Pick­ing Up Speed

2013 brought us USB 3.1 and Su­perSpeed+ mode (they are go­ing to run out of su­perla­tives at this rate). This raises the bar to a the­o­ret­i­cal 10Gb/s, and a prac­ti­cal one of 7.2Gb/s, which equates to 900MB/s. The en­cod­ing changed to 128b/132b, giv­ing a neg­li­gi­ble 3 per­cent over­head. Th­ese su­per modes re­quired dou­ble the data lines— the ca­bles have an ex­tra two pairs of data wires. Here we are in the realms of mass stor­age de­vices, such as SATA 600.

One of the boons of USB is the back­ward compatibility; in the­ory, you can plug pretty much any­thing into any­thing, and it works, not un­like PCIe. Ob­vi­ously, to get Su­perSpeed+, you need both de­vice and con­troller to be USB 3.1, but you can still plug into lessor it­er­a­tions of con­troller, and it does the best it can.

Adding power to USB was in­spired. It cut out that ugly mass of trans­form­ers un­der your desk, and re­lieved the pe­riph­eral man­u­fac­turer of the cost of sup­ply­ing one. The ini­tial spec­i­fi­ca­tion was for 500mA at 5V. USB 3.0 took this to 900mA for its in­creased data rates. And there’s a charg­ing mode, which can de­liver 1,500mA. USB 3.1 has a Power De­liv­ery mode that of­fers 5A at up to 20V, con­sid­er­ably ex­pand­ing its po­ten­tial as a charg­ing for­mat.

And now we come to a slightly an­noy­ing part. For such a uni­ver­sal stan­dard, there’s a fair num­ber of dif­fer­ent plugs and sock­ets. Th­ese fall into three groups: stan­dard, mini, and mi­cro. The stan­dard type was de­signed for full-size desk­tops and pe­riph­er­als. Type

A is the fa­mil­iar flat one used on mem­ory sticks. Type B is square—for some rea­son, ex­ter­nal drives and print­ers fa­vor th­ese. OK, it does stop you from plug­ging USB de­vices that must go into your PC into a pe­riph­eral that can’t do any­thing with them, or get­ting too con­fused about what goes where. More prac­ti­cally, it means you need a dif­fer­ent ca­ble.

The mini-A and mini-B sizes are de­signed for mo­bile de­vices, although not used much th­ese days. They have been “dep­re­cated” to avoid a pro­lif­er­a­tion of stan­dards. Mi­cro-A and mi­cro-B are in­tended for very thin gear, such as cell phones. As the plugs get smaller, they get more ro­bust, as mo­bile de­vices are plugged in and out more of­ten.

Then we have the Su­perSpeed sock­ets and ca­bles to ac­com­mo­date the ex­tra pins. There are Su­perSpeed Type A, Type B, and mi­cro-B. There is some use­ful back­ward compatibility here, too—you can plug an orig­i­nal into a Su­perSpeed ver­sion. On most of th­ese plugs and sock­ets, the chances ap­pear to be more than 50-50 that you try to plug it in up­side down.

On that note, we have USB-C, some­thing of a de­par­ture. This can be used in both ori­en­ta­tions, at last. It also al­lows power trans­fer in both di­rec­tions. USB-C is fa­vored by Ap­ple, it’s also ap­pear­ing on in­creas­ing num­bers of smart­phones, and start­ing to ap­pear on Win­dows lap­tops. It’s not a USB stan­dard as such, but a new ex­panded con­nec­tor. It has a more sub­stan­tial 24 pins—there is some re­dun­dancy here, de­pend­ing on its use. The ex­tra data lines add con­sid­er­ably to its po­ten­tial longevity. It’s small, neat, and a step up in de­sign on pre­vi­ous ver­sions.

“C” Change

Ap­ple re­ally went for it on its 2015 MacBook, which had just one USB-C port. This was not uni­ver­sally popular, as the first thing most users had to do was get an adapter so they could plug in a mem­ory stick, or just about any­thing else, for that mat­ter. Tech­ni­cally, USB-C, or Type-C (for some rea­son, C has a hyphen, but A and B don’t), looks a good bet, although two years after its in­tro­duc­tion, it’s still the out­sider. That will change, though.

USB-C is de­signed to re­place all the cur­rent sock­ets, and al­le­vi­ate the num­ber of com­bi­na­tions that brings. The 10 stan­dard socket types give us 21 pos­si­ble ca­ble com­bi­na­tions, not count­ing non­sen­si­cal

con­fig­u­ra­tions, and a fur­ther 12 dep­re­cated and non-stan­dard ones. Re­al­is­ti­cally, you’ll prob­a­bly only need four or five USB ca­bles to use nearly every­thing—even so, it’s easy to get caught with­out the right com­bi­na­tion at hand. Sock­ets and plugs are of­ten color-coded. Stan­dard ones are black; Su­perSpeed are blue; yel­low, or­ange, or red are for charg­ing ports; and green ones are spe­cial Qual­comm Quick Charge ports.

The USB sub­sys­tem is built around a USB con­troller on a host ma­chine, part of a moth­er­board’s chipset th­ese days. One USB con­troller can ad­dress a max­i­mum of 127 de­vices—the con­troller it­self counts as one de­vice, so that takes us to the neat bi­nary num­ber of 128. Each USB de­vice down­stream is the end of the line, how­ever; that’s where the data lines end. Since there are no con­trollers in USB de­vices, no daisy­chains are pos­si­ble. To at­tach more de­vices, you need a hub. This sim­ply splits the wires out into more USB ports. If you con­nect de­vices that draw sig­nif­i­cant power, you need a pow­ered hub, oth­er­wise the 500mA gets shared out, too. USB sup­ports up to five lev­els of branch­ing. To the con­troller, your mass of de­vices ap­pears as one long line with branches, each end­ing in a de­vice.

USB is cheap to im­ple­ment, es­pe­cially in its sim­pler Low Speed mode. This, along with pro­vid­ing power, easy com­puter con­trol, and its sheer pro­lif­er­a­tion, has made it an ideal plat­form for the strange world of the desk­top toy, from kitsch nov­elty lights and fans through to the bizarre and frankly dis­turb­ing. Apart from the re­mote-con­trol Nerf gun, of course, th­ese are all great.

The num­ber of USB ports you have on your rig is not nec­es­sar­ily the num­ber of USB con­trollers you have. One con­troller can be wired to any num­ber of ports through an in­ter­nal hub. In­tel’s X99 chipset, for ex­am­ple, has up to 14 USB ports, ac­cord­ing to the lit­er­a­ture; up to six con­fig­ured as USB 3.0, the rest as USB 2.0. How­ever, it only ac­tu­ally has three USB con­trollers: one USB 3.0 and two USB 2.0. More re­cent chipsets are more lav­ishly equipped, us­ing in­ter­nal High Speed I/O lines. The Z170 has up to 10 HSIO lines avail­able for USB 3.0. Re­mem­ber that port, hub, and con­troller (or root hub) are three dif­fer­ent things.

Thun­der­bolt from the Blue

If there is an in­dus­try stan­dard, Ap­ple will prob­a­bly do some­thing else. After the com­pany’s ex­pe­ri­ences with FireWire (see box be­low) it looked around for an­other high-speed in­ter­face to com­bine USB, PCIe, Dis­playPort, and FireWire func­tions. It liked the look of In­tel’s Light Peak, orig­i­nally de­signed for an op­ti­cal con­nec­tion. Un­der Ap­ple, it emerged as Thun­der­bolt.

Ver­sion 1 and 2 used a Mini Dis­playPort con­nec­tor, while Thun­der­bolt 3 moved to USB-C. De­spite its ori­gins, it’s all cop­per. The op­ti­cal route was found to be an ex­pen­sive one—and, any­way, it couldn’t carry power, and the cop­per ver­sion proved faster than ex­pected. Es­sen­tially, Thun­der­bolt is a com­bi­na­tion of Dis­playPort and four PCIe lanes mashed to­gether (mul­ti­plexed) into two Thun­der­bolt lanes, and un­scram­bled at the other end. One port can sup­port six de­vices, ei­ther through a

hub or daisy-chain, with the mon­i­tor at the end of the chain.

Thun­der­bolt 1.0 ran Dis­playPort 1.1a and x4 PCIe 2.0 lanes, ver­sion 2 moved to Dis­playPort 1.2. The big jump was Thun­der­bolt 3, which moved to PCIe 3.0, and threw in USB 3.1 and HDMI 2.0 sup­port. The­o­ret­i­cal data rates dou­bled each time, from 10Gb/s to 20Gb/s, and with ver­sion 3, a not in­con­sid­er­able 40Gb/s. Real-world speeds are down ,of course; it has 128b/132b en­cod­ing, and var­i­ous other over­heads, but tests have ver­sion 3 in the range of 25Gb/s. So it’s quick, which it needs to be if you’re go­ing to run a 4K screen and more.

Thun­der­bolt is not just for Macs; the full rights are back with In­tel, and it has done the lion’s share of the de­vel­op­ment, so any­body could, and will, use it. Win­dows lap­tops run it, and In­tel re­cently an­nounced that at some point next year, Thun­der­bolt will be­come roy­alty-free. Given that the spec­i­fi­ca­tion in­cludes USB 3.1, is it a ri­val? Yes and no. For the high end, it looks promis­ing. For the mass mar­ket, it’s far too ex­pen­sive. A Thun­der­bolt hub ca­pa­ble of build­ing your daisy-chain is the best part of $200; a USB one is barely $20. The on-board con­trollers are al­ways go­ing to be ex­pen­sive.

While USB 3.1’s Su­perSpeed+ is fairly nippy, it doesn’t quite match a sin­gle PCIe 3.0 lane. The next it­er­a­tion is USB 3.2, ten­ta­tively due for re­lease this fall. Data trans­fer rates are set to dou­ble to a the­o­ret­i­cal 20Gb/s, which trans­lates into a prac­ti­cal max­i­mum of 1,800MB/s. It’s to be called Su­perSpeed++ (they did run out of su­perla­tives after all). It’s been de­signed around the USB-C con­nec­tor, and ex­ist­ing ca­bles are said to be com­pat­i­ble. Looks as if it’ll use dou­ble the data wires. Don’t get too ex­cited yet, though—cer­ti­fi­ca­tion and val­i­da­tion are ex­pected to take us into 2019 be­fore we can take the hard­ware home. There’s to be a se­ries of USB De­vel­oper Days in Septem­ber when we’ll learn more.

It looks like USB-C is be­ing groomed to be the main pe­riph­eral con­nec­tion for­mat, with both Thun­der­bolt 3 and USB 3.2 us­ing it. One ca­ble, one socket for every­thing from your mon­i­tor down to the most point­less USB desk­top toy. Given the num­ber of Type A de­vices knock­ing about, it’ll be some time un­til we see the back of the fa­mil­iar rec­tan­gu­lar USB port, though you might have to buy an adapter or two at some point—but Mac peo­ple are used to that.

USB has brought a level of seam­less con­nec­tiv­ity that we now see as the norm. You just plug a de­vice in, and off it goes. It has been hugely suc­cess­ful. It’s killed off nu­mer­ous ri­vals, from the chunky old par­al­lel port to more ca­pa­ble ones, such as FireWire. The sheer num­ber of USB de­vices in the world en­sure it’ll be around for a long while, and any re­place­ment will have to of­fer compatibility. Its fu­ture lies with USB-C, and as a sub­set of Thun­der­bolt. USB’s pro­lif­er­a­tion of ca­bles and sock­ets will slowly re­solve down to just one socket that’ll be ca­pa­ble of nearly every­thing re­quired for pe­riph­er­als; truly uni­ver­sal.

USB USBh has b be­come theth stan­dardt dd for at­tach­ing your key­board

and mouse, and for clever sur­round-sound head­sets, too.

Back in the dark pre- USB ages, ev­ery pe­riph­eral needed a dif­fer­ent type of con­nec­tor, such as this bulky five-pin plug for a key­board.

USB Type B: Although less com­mon than its coun­ter­parts, it sup­ports every­thing from USB 1.0 to 3.0. It’s of­ten found in print­ers and more in­dus­trial pe­riph­er­als.

USB Type A: The blue tells us it’s the Su­perSpeed ver­sion. It’s de­signed so that it can plug into a USB 1.1 or 2.0 socket, and speeds drop ac­cord­ingly.

USB- C, the best yet. It’s small, doesn’t mind which way you plug it in, and has enough data lines to cope with all cur­rent stan­dards, even Thun­der­bolt 3 and over.

Your moth­er­board de­fines how many USB ports you get to play with. More mod­ern boards of­fer Type C con­nec­tors as well.

The first flash drives man­aged 8MB. This is cur­rently the world’s largest, weigh­ing in at 2TB, and $1,650 full price.

Wire­less USB: It worked, now think of some­thing to do with it that Wi-Fi can’t do much faster and cheaper.

As USB- C and Thun­der­bolt take off, we’ll see more of th­ese; Ap­ple does have a habit of re­mov­ing ports be­fore peo­ple are ready.

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