Why was USB 1.0 incredibly slow even for its time?

Question

USB 1.0 is from 1996 and has a transfer rate of up to 12 Mbps.

I think it's extremely slow even for its time. Because here are two similar standards from the same time which are much faster:

• IEEE 802.3u is the fast ethernet spec from 1995. Even though it is (a little) older than USB 1.0 and allows longer cables it has 100 Mbps. This is 8.3 times the speed of USB 1.0.

• Then there is IEEE 1394 from 1995 (FireWire 400). It has up to 400 Mbps. It's also a little older than USB 1.0 but its transfer rate is 33.3 times that of USB 1.0.

As you can see even for its time USB 1.0 was extremely slow.

Why?

Answer 1

USB was initially designed as a replacement for the 'legacy' ports including PS/2, serial and parallel ports. For those, up to 12 Mbit/s (or even only 1.5 Mbit/s, thx @lvd) seemed reasonable - USB was never envisioned as a high-end, top-notch interface but as a lower-cost alternative for the above ports.

USB wasn't intended for storage applications back then, but even its ~1 MB/s speed was competitive. Mind you, the still-popular floppy disks made just 30 KB/s and even quad-speed CD-ROMs a mere 600 KB/s.

ATA hard disks of the time could use up to PIO mode 2 with 8 MB/s.

Ethernet's 100 Mbit/s were considered back-bone speed in that period. Few people required that speed on a normal PC.

PS: For historical correctness, it's USB 1.1 that first gained wide popularity. Adoption of version 1.0 went rather slowly.

Answer 2

USB was very fast for its time and parts/cables cost.

It was intended to reduce the variety of specific cables and connectors needed for existing equipment, such as printers (huge Centronics, about 600 kbps max), serial ports (maybe 230,400 max), scanners, PS/2 ports (for keyboards and mice, <17 kbps and small power supply) and game controllers.

It was equally intended to support and encourage future peripherals. Many have since come along or become practical with USB speed increases, including USB storage sticks, digital cameras and mobile phones.

Its naming of Universal Serial Bus reflects that market. It wasn't aimed at being the Fastest All-round Serial Bus as that would have pushed its cost right up. Technology advances have let the speed increase over time while still keeping the prices down, with the now-cheap USB 2.x (480 Mbps) still plenty for many interfaces.

Ethernet adaptors etc of that day required much more expensive and powerful electronics to attain such speeds and distances. That shows in that a USB 2.0 Flash stick cost far less than an Ethernet card in, say, 2005 which is three years after USB 2.0 launched.

Answer 3

TL;DR: It's All About Use Case.

USB was intended as a low cost unified alternative and ultimate replacement of common peripheral device interfaces: serial, parallel and other custom variants of the time for tasks at the time (and still today). Intended use cases (devices to be connected via USB) were

• Keyboard
• Mouse
• Game Controllers (Joystick/-pad, wheels, FCS, etc.)
• Application Specific Keyboards (Numpads, Gamekeyboards, etc.)
• Generic Serial
• Modem (Internet)
• Printer
• Scanner
• Audio (Sound Card Control)
• Audio (Streaming Output)
• Photo transfer
• Video (low res, aka Webcam)
• External Media (Floppy, LS120, Zip drives)
• LAN Adaptors

All of them had, more or less specific connections while none of these run at speeds higher than what USB 1.1 can deliver. That's the area it was intended for.

At that time no-one even imagined solid-state storage that fast. Or any other of the things USB has grown into.

Equally if not more important than speed was cost: USB was intended to replace already cheap interfaces and lower the cost of devices considerably.

Bottom line: It was a perfect match for its target market ... and still is.

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Why was USB 1.0 incredibly slow even for its time?

Hint: It wasn't (see above)

USB 1.0 is from 1996 and has a transfer rate of up to 12 Mbps.

Not really, USB 1 had

• fixed symbol rate of
  • 1.5 MBd (low speed), or
  • 12 MBd (fill speed)

allowing a

• maximum transfer rate of ca.
  • 150 KiB/s (low) or
  • 1 MiB/s (high)

I think it's extremely slow even for its time. Because here are two similar standards from the same time which are much faster:

IEEE 802.3u is the fast ethernet spec from 1995. Even though it is (a little) older than USB 1.0 and allows longer cables it has 100 Mbps. This is 8.3 times the speed of USB 1.0.

• Ethernet is a network technology, not really for peripheral connection.
• It's a peer-to-peer network requiring complex and fast controllers running additional high level protocols on top of already complex network interaction.
• USB features a simple host/device structure with strict host control, making all interaction quite simple and deterministic.
• At the time 10Base-T was installed - if at all.
• NE1/2000 and Etherlink III were the (PC) network cards of the mid 1990s.
• Either of these cost (bulk price) ~50 USD for ISA or ~100 USD for PCI.
• USB 1 is quite capable of connecting to an external LAN adaptor running that.

It makes no business sense, neither on manufacturer's nor buyer's side, to raise the price of a PC by 50..100 USD to replace interfaces priced in single dollar range with a standard no devices exist for.

Then there is IEEE 1394 from 1995 (FireWire 400). It has up to 400 Mbps. It's also a little older than USB 1.0 but its transfer rate is 33.3 times that of USB 1.x.

Firewire was intended to replace SCSI - which at that time just introduced Fast-SCSI with a maximum of 10 MiB/s transfer rate. It also is, like Ethernet, a complex peer-to-peer network, requiring (for the time) high computing power to handle communication. A quite costly overhead, only justifiable for expensive high speed devices - or very special use cases.

As you can see even for its time USB 1.0 was extremely slow.

It wasn't slow. it was tailored to a specific use case: replacing all common interfaces of the time at low cost, or even saving money in production.

Answer 4

Like most things in the "silicon" specification world, the specification was based around a "minimally viable" VLSI implementation at the time of writing. When I was a grad student working on semiconductors, there was still a ½ micron design floating around for USB 1.0. I did a USB 1.1 core on 180nm (that's still used as far as I know). You save money in the hardware world by removing parts, and USB let you remove the two ICs and replace it with one. More than that, you could easily integrate it into the "winchip" idea at that time, which was to replace everything with software and remove hardware. It makes things cheap, and the PC world is completely driven by commodity hardware, and that's why everything is slow compared to when you put a few 00s behind the cost. (Best example is sapphire wafers over silicon where you get lower heat, and thereby increased speed due to the direct band-gap for the same process. 2k for a SI wafer but 20k for a sapphire wafer)

As a polled bus, USB is pretty great because it fails well. If you unplug something, you don't need to worry about the state. It's just sort of "gone" when you unplug it and you don't need to worry about the arbitration that exists on traditional buses. I have an implementation here in PIC assembly that I used once for a project. It took < 64 bytes in memory for a basic USB ↔ parallel IO board.

Answer 5

You're looking at it from the wrong end. Remember that one of the things USB had to be able to do was serve as a place to plug in a mouse and keyboard, and it was going to compete with existing mice and keyboard using "bus," serial, PS/2 and similar protocols.

Obviously a mouse that you had to plug into a wall power outlet, as well as your computer, was going to be a non-starter, and using cables any thicker than existing mouse cables would also be a problem. So USB had to run in some reasonable way across a thin cable that would keep a mouse still comfortable to move around on a desk. That limits both the amount of power you can send down the cable and the number of conductors you can use to send data in parallel. IEEE 1394 and twisted-pair Ethernet used four conductors for data; USB reduced this to two conductors. USB added two more conductors for ground and power, as IEEE 1394 also did in its 6-conductor configuration, but USB limited the power (in low-power configurations) to 100 mA at 5 V. (That makes a pretty big difference in wire size when considering small, flexible cables: a 0.22 mm solid wire can easily handle 100 mA; 1000 mA requires somewhere around 0.7 mm and these both become proportionally larger when you use stranded instead of solid wire.)

These power limitations already limit how much processing power (and thus potential networking speed) you can put into a USB mouse or keyboard, but of course a further limitation was cost: existing mice and keyboards used fairly cheap circuitry and USB was not going to fly if a mouse suddenly cost twice as much money.

Thus, the USB 1.0 transfer rate for keyboards and mice was even considerably slower than you suggest: just 1.5 Mbps. The higher speed 12 Mbps mode was never (even to this day, as far as I'm aware) used by mice or keyboards or the like, and how and what higher speeds you could add to USB beyond the essential 1.5 Mbps low-speed mode was limited by what the cheap, low-power, low-speed devices could still be compatible with. (The ability to negotiate connection speed itself requires circuitry and power draw.)

Answer 6

USB was mainly about replacing the legacy serial, parallel printer, and PS/2 ports – it had plenty of bandwidth for that. Furthermore, it is ultimately a point-to-point connection. With a virtual root hub, i.e. with each host port having its own controller, without an intervening physical hub, you could get 40–50 megabits/s sustained on a 4-port motherboard. Whether that was done depended mainly on the price and application area. Dedicated host port controllers were present on various industrial motherboards.

It's plenty adequate for many tasks even today. Not for high resolution video, but for audio, MIDI, various physical data acquisition systems – the bandwidths available are more than sufficient. There's plenty of industrial and research data acquisition where a few kHz of sampling rate is lots, since the physical processes monitored change way slower than that.

Answer 7

It's in the name: Universal Serial Bus.

A variety of serial bus interfaces were used to connect low and medium-speed peripherals like modems, keyboards, mice, scanners, protection dongles, and so on. Most manufacturers provided RS-232 or similar, but it was otherwise largely proprietary or platform-specific.

USB was to replace all of that nonsense. Use any mouse or keyboard with any PC or workstation. It accomplished that. It was also 10 - 100x faster than the busses it replaced, which opened up new possibilities, beyond the original scope. Hence USB 2.0.

Answer 8

Other answers refer to the connections USB is replacing, such as keyboards,
mice, serial ports, printers. However they leave out one important inspiration
and competitor: the Apple Desktop Bus.

The usage of ADB is very similar to USB: low speed user-interface devices: keyboards and mice, which can be daisy-chained. ADB's speed is reported to be "as high as 125 kbit/s" but usually at most half that. Compared to this, 12 Mbps is extremely fast, and even 1.5 Mbps is an order of magnitude faster. Everything is relative.

Answer 9

USB was intended to replace PS/2, Serial, and Parallel ports. Remember those parallel port scanners that were slow as hell and froze the PC while scanning? These were terrible.

In order to succeed in a commercial environment where every cent matters, USB had to meet stringent requirements:

For mice and keyboards, which were already very cheap devices at the time, it could not add any cost. This means it would have to be implemented inside the already dirt cheap microcontroller in the mouse/keyboard: pretty slow devices with as little RAM and ROM as possible, manufactured in a process that doesn't allow for anything fancy.

For more expensive peripherals like scanners, printers, USB storage, etc, the case is less clear cut: replacing the kludgy and expensive parallel port with much simpler and cheaper USB would already save costs, but then USB would have to be compatible with the microcontrollers used in these types of peripherals at the time, so a speed of 12Mbps seems adequate.

In addition, to get a wide adoption of the standard, motherboards must carry a lot of USB ports. At the time, during the transition, motherboards would offer both parallel/serial/PS2 and USB at the same time, so the cost per port must be very low in order for it to succeed. USB is usually implemented in the chipset, which is manufactured in processes allowing for much faster and more complex chips that a mouse microcontroller, but still, bleeding edge speed would add to the cost.

This drove the design of the entire protocol, which assumes an extremely dumb device that does what it's told.

Ethernet and FireWire are much more costly. On the software side, being actual networks (not master/slave like USB) they use rather complex protocols which require fast microcontrollers with lots of memory. It is possible to implement USB1 on a 8-bit micro with 64 bytes of RAM that costs cents, but for FireWire/Ethernet you would need 16-32 bit micro with 8-16k RAM at least, and much more ROM too. It's not economically feasible to implement these in a mouse.

On the hardware side, USB1 is dead simple due to being slow. Ethernet could have been made simpler and cheaper with a length restriction to ditch equalization, but there is still a lot of hardware complexity in the MAC/PHY. Plus it uses much more power due to being designed for long cables, which requires controlled impedance, etc. And FireWire is full duplex, so it needs two more wires! That will add cost to everything...

Basically for this type of standard to succeed, it needs wide adoption, and for that, cost matters a lot more than performance. Cost is the main reason why FireWire failed.