Macintosh Makes the Connection
Dan Knight - December 1997
Surprising to many, the first Macs didn't have SCSI. The Apple design team created a compact, closed box with a disk drive, CPU, monitor, 128KB of RAM, keyboard and mouse ports, a floppy drive port, and two serial ports. The serial ports were the secret - they could support a 230.4Kbps network and be used for system expansion. Apple called the latter their high speed serial bus.
It never caught on.
In 1986 Apple released the Mac Plus. Not only did it come with 1 MB of RAM (expandable to 4 MB!), there was a new hard drive connector called SCSI. This was far, far faster than the older serial hard drive. And SCSI allowed adding one, two, up to seven devices to the Mac in a single chain.
Over time Apple improved their SCSI implementation. The Plus topped out at 2,104kbps, but the 1987 Mac II and SE offered improved throughput of 11,200kbps and 5,248kbps, respectively. Over the years, both Apple and third-party vendors offered Fast SCSI, Wide SCSI, Fast-Wide SCSI, and Ultra-SCSI.
But SCSI is running out of steam in the era of digital video. For a more detailed overview of SCSI, read SCSI Throughput.
With the Mac II and SE, Apple eliminated the dedicated keyboard and mouse connectors of the past for a new peripheral bus. Like SCSI, you can daisy-chain devices on the ADB bus. The earliest ADB Macs came with two ports, although Apple reduced that to one over the years.
- Time to make a personal plug for the MicroSpeed KB101M keyboard. Not only does it provide identical layout the Apple's extended keyboard with superior components to the current keyboard, but it has 4 ADB ports. One ties the keyboard to the computer; others can be used for a mouse, a trackball, or some other ADB device. Highly recommended.
For a time, ADB was so cool that someone even made an ADB modem. There was enough spare bandwidth to comfortably support 2400bps. But over time the 10Kbps throughput of ADB became a bottleneck. Enough for a mouse or keyboard, it's insufficient for touch tablets and modems.
The next hot technology from Apple is IEEE 1394, commonly known as FireWire. Faster and more flexible than SCSI, FireWire offers several advantages.
- 100Mbps minimum bandwidth, with 400 available today and 1Gbps by 2000
- devices negotiate fastest mutually supported data transfer speed
- capable of supporting 63 devices (v. SCSI's seven)
- can be used between computers, not just peripherals (should put ethernet to shame)
- devices can be hot plugged, eliminating need to power down CPU and peripherals
- high speed serial protocol requires just 6 wires, allowing small connectors and thin, flexible cabling
- can provide up to 60 watts of power to peripherals, often eliminating need for separate power
- auto configuration eliminates need to set device IDs
Sony has already adopted FireWire on their digital video cameras. Musicians are discovering FireWire as an option for wiring together electronic instruments, making it a replacement for MIDI.
For hard drives, digital video, high speed networking, and scanning, FireWire will eventually supplant SCSI.
USB, the Universal Serial Bus
This standard came from the other side of the tracks, Microsoft and Intel. USB has become common in the Wintel world and is well on the way to becoming the de facto keyboard and mouse port. But with a bandwidth of 12Mbps and typical speeds of 6-8Mbps, it's also fast enough for digital audio and modems. It is especially in the latter realm that USB is promising.
Mac serial ports have limited throughput, especially if LocalTalk is active (see Macintosh Serial Throughput). With DSL and cable modems just around the corner promising 1Mbps and higher throughput, we need another way to connect them. One option is the 10Mbps ethernet port. Another is using a PCI-based modem on a card, just like the Wintel world has done for years with internal modems.
USB provides sufficient throughput for ADSL, CDSL, and cable modems. It should be much less expensive to implement than FireWire, especially if it replaces ADB for mouse and keyboard connection.
For more on USB, read USB, okay for the low end.
While SCSI and ADB were adequate a few years ago, they are showing their age. Over the coming years, expect FireWire and USB or some similar technology to replace both.
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