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The Macintosh SE/30 Motherboard

The motherboard for the Macintosh SE/30 was completely different from the one used on the other models of the Macintosh SE.

Macintosh SE TutorialFigure 28: The Macintosh SE/30 motherboard

The Macintosh SE/30 used a different microprocessor, the 68030 (running at 16 MHz instead of 7.8 MHz as in the previous models). This is more powerful than the 68000 used by the previous versions of the Macintosh. It had an external 32-bit data bus (remember, the 68000 used an external 16-bit data bus, so when combining the higher clock rate with the higher number of bits to access the memory, the 68030 had four times more bandwidth for accessing memory than the 68000 used in previous models) and a 32-bit address bus, allowing the CPU to access up to 4 GB of RAM (in theory). It also had a 256-byte instruction cache and a 256-byte data cache, a feature not available in the 68000.

The SE/30 used a Motorola 68882 math co-processor. Previous Macintosh models didn’t have a math co-processor.

The motherboard of the Macintosh SE/30 had eight SIMM-30 sockets, allowing you to install up to 128 MB of RAM if eight 16 MB modules were used. The ROM of the computer was available in a SIMM-72 module.

Some chips used on the Macintosh SE/30 were the same used on the previous Macintosh models but were upgraded. The SCSI controller used was the 53C80, an upgraded version of the 5380 used on previous models. For controlling the two serial ports available (“Printer” and “Modem”), a Z8530 serial communications controller was still used but with the PLCC packaging instead of DIP, which occupies less space on the printed circuit board. For controlling the keyboard and mouse, it used two 65C22 chips (instead of only one as in the regular Macintosh SE), but this time it had the PLCC packaging instead of DIP. The SE/30 uses the SWIM (Super Woz Integrated Machine) chip to control the floppy disk drive, supporting 1.44 MB drives. Differently from the regular SE, the SE/30 had only one port for a single floppy disk drive. 

The Macintosh SE/30 uses a custom-made chip called GLUE (General Logic Unit), manufactured by VLSI, instead of the BBU chip present on the Macintosh SE or the PALs present on previous models.

There are two 256 kbit chips for the video memory, making 64 KB of dedicated video memory. On previous Macintosh models, part of the main RAM had to be used as video memory.

Audio was upgraded from the previous models, with the addition of a custom-chip called ASC (Apple Sound Chip) and two sound processing chips from Sony, providing stereo sound with up to four simultaneous voices. Previous models used a technique called PWM (Pulse Width Modulation) to generate audio, and only mono audio was available. Also, on previous models, the PWM circuit also controlled the speed for 400 KB floppy disk drives.

As with the Macintosh SE, the Macintosh SE/30 had a PDS expansion connector, called PDS 68030. This connector, however, was not the same one used on the Macintosh SE; therefore, you couldn’t install expansion cards developed for the Macintosh SE on the Macintosh SE/30.

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Gabriel Torres is a Brazilian best-selling ICT expert, with 24 books published. He started his online career in 1996, when he launched Clube do Hardware, which is one of the oldest and largest websites about technology in Brazil. He created Hardware Secrets in 1999 to expand his knowledge outside his home country.