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The Mac Plus changed the Mac from a closed box to an
expandable computer system.
Macintosh 128K
On January 16, 1986, Apple introduced the Macintosh Plus. At first glance, it
didn't look much different from the original Macintosh
announced in January 1984, with its 128 KB of system memory, or the
Mac 512K "Fat Mac",
with four times as much system memory, released later that year.
Macintosh Plus
From the front, the biggest difference was that the new model said
"Macintosh Plus" whereas the original Mac was unique and didn't need a
nameplate.
Looks can be deceiving. Although from the front the Mac Plus looked
a lot like the 128K and 512K with its 9" display, 3.5" floppy drive,
and keyboard port, there were plenty of differences on the inside, on
the back, and even on the keyboard.
A New Paradigm: Expandability
Until 1986, the Macintosh was designed as a closed box. There was no
easy way to open up the computer, and there were no slots for upgrading
memory. What you bought was what you got. The only expansion options
were through external peripherals - a second floppy drive, an
ImageWriter printer, and later on a relatively slow hard drive that
connected to the Mac's floppy drive port.
With the Mac Plus, you got more to begin with. The Plus included an
800K double-sided floppy drive, giving it twice the capacity of the
400K single-sided drives used on the 1984 Macs. It shipped with
1 MB of system memory, twice as much as the 512K and 50% more than
IBM compatible MS-DOS PCs with their 640 KB
ceiling could access without special hardware.
Memory Expansion
30-pin 8-chip SIMM as used in Mac Plus.
But Apple went beyond simply giving it more memory and a higher
capacity floppy drive; Apple built the Mac Plus for expansion. That
megabyte of memory was installed as four 256 KB SIMMs, a new type of memory
module that made it much easier to install banks of memory. No more
fiddling with individual memory chips with their pesky, too easily bent
pins. One SIMM replaced 8 conventional RAM chips, and SIMMs used a
circuit board, making them easy to install.
AppleDesigned the Mac Plus so it could accept 1 MB SIMMs, allowing
memory expansion to a mind-boggling 4 MB. By replacing two 256 MB
modules, you had a 2.5 GB Mac. Replace all four for your 4 MB
maximum.
SCSI Expansion
Although the floppy drive port was fast enough for floppy drives, it
was excruciatingly slow for Apple's first Mac hard drive, the Apple Hard Disk 20
(also see Wikipedia), which had a
500 Kbps/62.5 KBps transfer rate. Several third-party vendors came to
the aid of early Mac users, but they were all hacks that required
special drivers, and many of them used one of the Mac's serial
ports.
Mac Plus with SCSI drive.
With the Mac Plus, Apple adopted SCSI as its peripheral
expansion bus. SCSI is an intelligent, buffered, peer-to-peer
interface, meaning that every SCSI device has some smarts, which places
less demands on the computer's processor. The SCSI bus on the Mac Plus
allowed connecting up to 7 devices - hard drives, tape drives,
scanners, and printers among the options.
So not only was SCSI a lot faster than the floppy drive port, it
also gave Mac Plus users a lot more expansion options. Although the
SCSI standard allowed for 5 MBps throughput and AppleDesigned its SCSI
interface to support 1.25 MBps, the Mac Plus has a 2.104 Mbps/263 KBps
ceiling, and you needed to use a system patch such as SCSI Accelerator 2.1 or SCSI Accelerator 7.0 to achieve maximum
throughput.
Despite limitations in the way SCSI was implemented on the Mac Plus,
it was over four times as fast as the old Hard Disk 20 connected to the
floppy port.
A New Disk Format
Mac Plus with floppy drive.
The Mac's original file system allowed for folders, but not for
folders within folders, which became a real nuisance with hard drives
and their enormous capacity (relative to floppies). What System 3,
introduced with the Mac Plus, Apple gave us HFS, a hierarchical file
system. The Mac got subfolders, and today's Macs use an updated version
of the filing system called HFS+.
Other Improvements
Steve Jobs, who had brought the Macintosh into the world, disdained the
"extra" keys found on most personal computers, so the original
Macintosh had used a minimalist keyboard that had just the keys you
needed. There were no arrow keys, no function keys, and numbers were on
the top row just like on a typewriter. In Jobs' mind, the mouse was the
proper way to navigate the screen.
However, Steve Jobs left Apple in
1985, opening the door for a more expandable Mac and a new keyboard
design. With the Mac Plus, Apple introduced that keyboard, adding
useful things like a numeric keypad and arrow keys.
Sound, mouse, floppy, SCSI, printer, and modem ports on the Mac
Plus.
The Mac Plus introduced a new connector for serial ports.
It used the small, round DIN-8 connector instead of the larger DB-9
port found on earlier Macs. The smaller ports freed up the space
necessary for adding a SCSI port.
The Mac Plus Legacy
The Macintosh Plus remained current until it was officially
discontinued on October 15, 1990 - the longest model run in Mac history
at 4 years, 10 months. For a lot of longtime Mac users, this is the
model we cut our teeth on, as it was one of the first with sufficient
power to handle Aldus PageMaker, the app that gave rise to the desktop
publishing revolution.
Two other factor came into play there: The Apple LaserWriter wasn't just a
high quality laser printer with Adobe Postscript, it was also very
expensive at nearly $7,000. Fortunately, it was also a networkable
laser printer, which meant that several Macs could share it. The second
factor is the built-in LocalTalk networking support that became
standard with the Mac Plus.
Although Apple moved to high-density floppy drives in 1989, Mac hard
drives remained compatible with 800K disks until Apple began to phase
out floppy drives in 1998. Likewise, SCSI and the DIN-8 serial ports
remained on Macs until 1998, when Apple began its switch to new
architecture with the first
iMac.
The Mac Plus is the oldest Mac to support System 7.0 and was
supported right through System 7.5.5. Like the Mac SE and Classic, both built around the
same 8 MHz 68000 CPU, it's no speed demon under System 7, but it
plods along reliably and provides real incentive for moving to a more
powerful model to properly support that more powerful operating
system.
For me, the Mac Plus was the first stepping stone along the Mac
path, and I used it until mid 1993, when I sold it to buy a far faster
Centris 610.
Dan Knight has been using Macs since 1986,
sold Macs for several years, supported them for many more years, and
has been publishing Low End Mac since April 1997. If you find Dan's articles helpful, please consider making a donation to his tip jar.
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The Mac Plus introduced a new connector for serial ports.
It used the small, round DIN-8 connector instead of the larger DB-9
port found on earlier Macs. The smaller ports freed up the space
necessary for adding a SCSI port.