Pumping Up the Parallel Port

An alternative to high-speed serial is sitting right in your PC

The Centronics-style parallel port, says Larry Stein, president of Farpoint Systems (Jersey City, NJ), ``became an industry standard the day IBM introduced the personal computer with a parallel port on it.'' At that time, a screamingly fast peripheral was a 240-character-per-second dot-matrix printer, which received its data in ASCII. Today, you're more likely to be hooked up to an 8-page-per-minute laser printer, pumping down megabyte-size color graphics files. Yet if you own a newer PC, the parallel port on the back of it is identical in performance to the 1981 model whose speed tops out at around 150 KBps. Maintaining even that rate is processor-intensive--your CPU has to oversee moving data to and from the port, including all the hands haking between the computer and peripheral.

The 150-KBps parallel port is woefully slow for many new printers, which can accept data at much higher speeds, as well as for other peripherals such as tape drives. It is inadequate for even the slowest of single-spin CD-ROM drives. It's obvious that the parallel port needs major pumping up if it's going to survive on the multimedia desktop.

The IEEE 1284 standard defines a newer, faster, and better parallel port with some major muscle in it. The good news is that 1284 ports are backward-compatible with existing parallel ports; the Hewlett-Packard DeskJet will plug right in, using existing cable and connector. Even better news is that, for only the cost of a new cable, a 1284 parallel port can inject new life into your old printers.

Current parallel connections are notoriously flaky at distances of more than 10 feet. ``With 1284,'' says Stein, who is also chairman of the 1284 committee, ``we wanted to go a minimum of 10 meters. It's important t o realize that, in some cases, 1284 has the parallel port going 100 to 200 times faster than it was meant to originally. You can't do that using $2 cables, so the 1284 standard defines the cable as well. Now we can guarantee that when a user buys a 1284 port, a 1284-capable product, and a 1284 cable, it'll work at 2 feet, 10 feet, or 30 feet.''

IEEE 1284 actually defines four different modes for the new parallel port: nibble, byte, ECP (Enhanced Capabilities Port), and EPP (Enhanced Parallel Port). All modes have at least some bidirectional ability, allowing the printer to talk back to your computer. Data passing from the peripheral to the host is called back-channel communication.

The first two modes, nibble and byte, provide for relatively slow back-channel communication, 4 and 8 bits at a time, respectively. ECP, intended mainly for host-to-printer connections, can achieve data rates of up to 4 MBps in both directions. The maximum speed depends on the peripheral and host computer.

EPP allows you to attach devices such as CD-ROM and hard drives, which would normally plug into the internal bus, to the parallel port. In addition to high data speeds, EPP allows the system to regard the parallel port as an extension of the system bus. Although not as sophisticated as FireWire, EPP lets you hang multiple peripherals off a single port.

All 1284-compliant devices can identify themselves and their capabilities to the host computer, letting the system know whether to speak in EPP, ECP, nibbles, or plain old Centronics. Microsoft has announced support for ECP-compliant devices within Chicago, the next version of Windows. Chicago will use the ID string returned by ECP-compliant peripherals to automatically install the proper drivers.

An EPP can even drive your existing printers much faster. Copy some graphics files to your plain-Jane, non-1284 printer today, comments Stein, and you'll get throughput ranging from 6 to 14 KBps. With an EPP port and a new 1284 cable, however, you could get as much as 500 KBps. ``By the end of the year,'' Stein says, ``you should see ECP printers capable of 400 KBps to 2 MBps.''

And the 1284 port has one thing going for it that none of the proposed serial standards do: an installed base of millions on millions of parallel-port-equipped devices, all of which will plug right in.

But there's still a serious question about how well these new parallel ports will work when you add in all the extra baggage needed to allow them to compete with the new serial buses. To me, this technology stinks of death. The more I read about it and how much work goes into tweaking parallel ports to run 100 times faster than what was intended--with special cables, strict capacitance rules, and so on--the more convinced I am that the serial-port solutions are going to take over pretty quick.