[SIGCIS-Members] FC: Oral history of USB

Joly MacFie joly at punkcast.com
Sat Jun 1 00:03:35 PDT 2019

Fast Company interview with Ajay Bhatt, Bala Cadambi and Jim Pappas of Intel



AB: Good question. We had looked at it, but the whole goal here was to make
it very inexpensive, and at that point, we were trying to solve all the USB
problems with two wires. At that point, if you added wires to make things
flippable, you have to add wires, and you also have to add a lot of
silicon. Wires and pins cost real money, so we decided to keep it as cheap
as possible. With serial port and parallel port, there were versions that
were 25 pins and 36 pins and so on and so forth. The cables were very thick
and expensive. We were trying to solve all the problems. We went in favor
of fewer wires. In hindsight, a flippable connector would have been better.

AB: Our goal was to say that this interface should be such that it should
work on a mouse and it should also work on a high-end printer or on digital
cameras. That’s what we were looking at, the range of products. At one end,
we wanted it simple enough, so there could be very low costs. At the other
end, we wanted to make sure that it could be scaled and, just as we speak
today, we’re running the USB at tens of gigs. The original one was running
at 12 megs. We’ve come a long way in scaling.

JP: One of the people we met at Microsoft was Betsy Tanner, and at the
time, she was the engineering manager for the mouse. I talked to Betsy and
said, “if there ever comes a day that you’re not going to use USB for your
next Microsoft mouse, I need to know.” And she says, “okay, that’s a fair

We were designing USB—originally, it was supposed to be a five
megabit-per-second bus, which at the time was faster than anything else
that normally would come at the back of the PC. It’s not fast by today’s
standards, but at the time, it seemed fast. And the reason we wanted high
speed was so you could fan it out through hubs, and basically, however many
devices would be attached to that single port would be sharing that
bandwidth—not necessarily all being used simultaneously, but we wanted it
to be fairly robust. Well, Betsy called me one day and said, “Jim, you
asked me to call you if we’re not going to be using USB for the mouse. I’m
calling you to tell you we’re not going to be able to do it because we have
a problem.”

And I said, “what’s the problem?” She says, “Well, 5 megabits is just too

I said, “For a mouse, we don’t need that much bandwidth, and secondly, I’m
really afraid of whether we can pass the electrical magnetic interference
specifications. Signals going through a wire become an antennae. Am I going
to have too much EMI radiation coming off creating digital noise?”

She said, “we could solve it by putting a shield around it, but it adds 4
cents per foot to the cost of a cable. If I’ve got a six foot cable that
adds 24 cents. So I can’t do that. Secondly, if I put a shield on it, a
mouse needs to have a simple cable. The cable can’t affect the movement of
the mouse, and I’m afraid that if I put a shield, it becomes too stiff.”

So I said, “Betsy, what could you live with?” She said, “We’d be
comfortable with two megabits per second.”

And I said, “Damn, that’s just as slow. Give me a week, can you do that?”

She said yes. I came back to the team, and we discussed Microsoft’s
problem, and that’s where we actually split it, where we had a high speed
and a low speed in the bus. At the high speeds, we brought it up to 12
megabits per second. And then we made the slow speed down to one and a half
megabits per second, which was three quarters of the speed that was her

We saved Microsoft, we saved the mouse. And I think that that call from
Betsy saved the program. One of the reasons why USB was so successful is
because it hit the cost point that was required. It didn’t add any
significant cost to the PC. You can even make the argument that it reduced
the cost, over time.


Joly MacFie  218 565 9365 Skype:punkcast
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.sigcis.org/pipermail/members-sigcis.org/attachments/20190601/d1a3092a/attachment.htm>

More information about the Members mailing list