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.
SCSI
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.
ADB
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.
FireWire
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.
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.
FireWire: connection of the (near) future, MacTimes
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