Inside the Macintosh SE
By Gabriel Torres on February 6, 2013
Following the release of the original Macintosh (a.k.a. Macintosh 128K) in 1984, the Macintosh 512K in 1985, and the Macintosh Plus in 1986, in 1987, Apple released the Macintosh SE. Several versions of this computer were released. Let’s discuss this computer in detail.
The Macintosh SE was based on the same processor (Motorola 68000), had the same size, and used the same screen size and resolution (9-inch black-and-white with 512 x 342 pixels) as the previous Macintosh models (except the Macintosh SE/30, which used a Motorola 68030 processor). It inherited the external SCSI port, the 800 KB floppy disk drive (later upgraded to a 1.44 MB floppy, as we will discuss), and 1 MB of RAM using four SIMM-30 memory modules (allowing you to upgrade the memory to 4 MB) from the Macintosh Plus.
This computer, however, came with new features. The most important was the addition of an internal hard disk drive (20 MB or 40 MB) connected to a new internal SCSI port. This was the first Macintosh computer to feature an internal hard drive. (The dual drive model didn’t come with an internal hard drive.)
Another difference between the Macintosh SE and the previous models was the addition of a new bus for connection of peripherals such as keyboard and mouse, called ADB (Apple Desktop Bus).
The Macintosh SE was also the first Mac to feature an expansion slot, called the PDS (Processor Direct Slot). In fact, “SE” stands for “System Expansion.” Actually, the Macintosh II, which was released at the same time, also featured expansion slots. The Macintosh II was a full-sized desktop computer, unlike the SE and its predecessors, which were compact computers.
Another feature that was added with the SE was a cooling fan. Previous Apple computers didn’t feature a fan because Steve Jobs thought it was noisy and “inelegant.”
In Figure 1, you can see a Macintosh SE system with a keyboard and a mouse.
Nowadays, the first thing you will notice when looking at the Macintosh SE is how small it was. In Figure 2, we compare the Macintosh Plus to a 21-inch LCD monitor.
Unlike the previous models, the computer didn’t come with a keyboard; you had to buy one separately. At the time, two choices were available: the Apple Keyboard (model M0116), which was cheaper and thus more common (the one shown in Figures 1, 2, and 3) and the Apple Extended Keyboard (model M0115), which was bigger and more expensive. We show this keyboard in Figure 4. Since the Macintosh SE used an ADB port, any keyboard based on this connection could be used. For example, you could use the Apple IIgs keyboard or buy a keyboard manufactured by a different company.
The mouse that came with the Macintosh SE was different from the one that came with the previous Macintosh models, as you can see in Figure 5 (models A9M0331 or G5431). As with the keyboard, you could use any mouse based on the ADB connection.
In Figures 6 and 7, you have an overall look at the Macintosh SE. Similarly to the previous Macintosh models, the Macintosh SE had a brightness adjustment button on its front panel, below the Apple logo.
The Macintosh SE is easy to identify, as it has “Macintosh SE” written on its front panel and on its rear panel as well. However, four different versions of the Macintosh SE were released. On the next page, we address their differences and how to identify the exact model you may have.
A minor difference between the Macintosh SE and the previous models was the kind and location of the battery in charge of the computer’s real time clock. While in the previous models this battery was accessible through the rear panel, on the Macintosh SE this battery was installed on the motherboard.
As with the previous models, the Macintosh SE allowed you to install an anti-theft device that was a metallic tab for installing a steel cable to prevent people from stealing the computer, which was highly desirable in public spaces such as schools.
In Figure 9, you can see the connectors available at the rear panel of the Macintosh SE. The first two connectors were the ADB connectors for you to install the mouse and the keyboard. Next, there was a port for the installation of an external floppy disk drive. Then there was an external 25-pin SCSI port, which allowed you to install external SCSI devices (such as an external hard drive) to the computer.
There were two serial ports: one for a printer and one for an external modem, using the same kind of connector introduced with the Macintosh Plus. (The Macintosh 128K and the Macintosh 512K also had two serial ports, but with the Macintosh Plus, Apple changed the connector type used for them from DE-9 to DIN-8, which became the standard for future Apple computers.)
The last connector was a 3.5 mm connector for an external speaker (the computer had an internal speaker).
The following models of the Macintosh SE were released.
This model, also known as M5010, came with two 800 KB floppy disk drives, but it didn’t come with an internal hard drive. As the motherboard was the same as the standard model, you could install an internal hard drive. However, there was not enough space for two floppy disk drives and a hard disk drive, so you had to remove one of the floppy drives to install a hard drive. It is possible, however, to create a homemade bracket to install the two floppy drives and a hard drive simultaneously.
You can identify this model by the presence of two floppy disk drives as well as the model number M5010 and the phrase “Two 800K Drives” on its rear label.
The standard model came with one 800 KB floppy disk drive and either a 20 MB or 40 MB hard disk drive. It used the model number “M5011,” which is the same as the FDHD and the SuperDrive models. You can differentiate it from these other two models as they have the names “FDHD” or “SuperDrive” written on their front panel.
The Macintosh SE FDHD (Floppy Drive High Density) was a Macintosh SE with a 1.44 MB floppy disk drive instead of an 800 KB floppy disk drive. Its model number is the same as the standard model, but you can tell the two apart by the presence of the letters “FDHD” on the front panel. See Figure 12.
After a while, Apple renamed the Macintosh SE FDHD to “SuperDrive.” So, the Macintosh SE FDHD and the Macintosh SE SuperDrive are the same computer but with a different name. This model has the word “SuperDrive” written on its front panel.
The Macintosh SE/30, released in 1989, used a different motherboard that was based on the Motorola 68030 microprocessor (hence its name), which was more powerful than the 68000 processor used on other models. The “30” in the name had nothing to do with the size of the hard drive that came with the computer.
This model had a different model number: M5119. It came with a 1.44 MB floppy disk drive and could come with either a 40 MB or an 80 MB hard disk drive. Furthermore, it had either 1 MB or 4 MB of memory, which could be expanded up to 128 MB.
Another difference between the Macintosh SE/30 and the other Macintosh SE models was the type of expansion connector with which it came. While the expansion connector was generically called PDS (Processor Direct Slot) in both systems, the connector on the Macintosh SE had 96 contacts (three rows with 32 contacts each) and was called PDS 68000, while on the Macintosh SE/30 this connector had 120 contacts (three rows with 40 contacts each) and was called PDS 68030.
You could easily identify this model by the name it had on its front panel, “Macintosh SE/30,” or by the model number written on the label available on its back part. Interestingly, while on the other models the name “Macintosh SE” was written on the right-hand side of the front panel, on the Macintosh SE/30 its name was written on the left-hand side, near the Apple logo.
To avoid regular users from opening the Macintosh SE, Apple used Torx TT15 screws, a very unusual type of screw to be used on computers (especially at the time), which required a special TT15 screwdriver at least 9 inches (230 mm) long. The same applied to the previous Macintosh models.
Inside of the computer, you would find the most commented on (and hidden) feature of the computer: the signatures of all the members of the team that designed the Macintosh, including, of course, Steve Jobs. See Figure 15. These signatures were also present on the previous Macintosh models. The Macintosh Plus and the Macintosh SE were released after Steve Jobs left Apple, but for some reason, his signature was kept inside the computer, even though he was not related to the development of these computers – in particular, the Macintosh SE. Jobs would never have approved the addition of a cooling fan.
You will see several people selling old Macs on eBay saying “This Mac is so special that it has Steve Jobs’s signature” or “rare – signed by Steve Jobs.” Let’s make something clear. All early Macintoshes were signed by the whole team, so that is not a “special feature.” Since millions of these computers were sold, they are not rare.
In Figure 16, you can see how the Macintosh SE looked inside. It was comprised of two printed circuit boards. One contained the power supply and the electronics for the monitor; the other was the motherboard. These boards were different from the ones used on previous Macintosh models.
On the previous Macintosh models, the analog board had the electronics for the video monitor and the power supply. On the Macintosh SE, however, the power supply was available as a separate unit, although screwed to the analog board. See Figure 17. In Figure 18, you can see the video monitor board (officially called “Macintosh SE Analog”), part number 820-0206 or 630-0147, with the power supply removed. In Figure 19, you can see the power supply by itself.
As mentioned, the Macintosh SE was based on the Motorola 68000, which was a 32-bit microprocessor using a 16-bit data bus and a 24-bit address bus, allowing it to access up to 16 MB of memory. The Macintosh SE/30 was based on a different processor, the Motorola 68030. Because of that, we will discuss the motherboard used on this computer later.
The motherboard of the Macintosh SE, part number 820-0176 or 630-4125, had four SIMM-30 memory sockets, originally coming with four 256 KB memory modules installed. The four 256 KB memory modules could have been replaced with two 1 MB memory modules to have a computer with 2 MB of RAM. The alternative would have been to have four 1 MB memory modules to have a computer with 4 MB of RAM. Since the 68000 CPU used a 16-bit data bus, and each SIMM-30 memory module is an eight-bit entity, you would need two or four memory modules installed; you can’t install one or three memory modules.
In order to install memory modules with more than 256 KB, you need to cut one of the legs of the R35 resistor (labeled “256K BIT”). See Figure 21. On some revised motherboards you need to simply move the position of a jumper, instead of having to cut a resistor. See Figure 22. In this case, you must move the jumper to the “2/4M” position to enable 2 MB of memory. However, in order to enable 4 MB of memory, you must remove the jumper from the motherboard (and not place it at the “2/4M” position, as it would be logical to assume).
The Macintosh SE used the same NCR 5380 SCSI controller as the Macintosh Plus. It also used a 65C22, which was an upgraded version of the 6522 “Versatile Interface Adapter” used on the previous Macintosh models and in charge of mouse and keyboard communications. It also used the Z8530 serial communications controller, in charge of the two serial ports; and the custom-made IWM (Integrated Woz Machine), in charge of controlling the floppy disk drives.
On the FDHD and on the SuperDrive models, the IWM chip was replaced with the new SWIM (Super Woz Integrated Machine) chip, to support 1.44 MB floppy disk drives. For this reason, you couldn’t install 1.44 MB floppy disk drives into the standard Macintosh SE and the dual floppy Macintosh SE, as their control circuits didn’t support this kind of drive.
The Macintosh SE had two floppy disk drive ports on the motherboard instead of only one.
Two new custom-made chips were added to the Macintosh SE, replacing the six PAL (Programmable Array Logic) chips available in previous Macintosh models. These chips were called BBU (Bob Bailey Unit, a big chip manufactured by VLSI) and GLU (General Logic Unit).
Other features that were inherited from previous Macintosh models were the reset and interrupt buttons (seen at the top right corner in Figure 20), which were targeted to programmers. These buttons were normally not accessible from outside the computer. However, as these buttons were located in front of the side ventilation slits of the computer, programmers could buy a special “programmer's switch” that could be attached to this vent (located on the left-side of the computer) and, therefore, access them.
As previously mentioned, one of the new features of the Macintosh SE was its expansion connector, called PDS (Processor Direct Slot). This expansion connector allowed you to install expansion cards, such as accelerator and networking cards. Accelerator cards replaced the 68000 microprocessor with another more powerful CPU, usually a 68020, and frequently added more RAM, allowing you to have more than 4 MB.
The Macintosh Portable, the Macintosh SE/30, and the Macintosh IIfx also had a PDS connector. Although the PDS connector of the Macintosh Portable had the same number of contacts as the PDS slot of the Macintosh SE, it was not compatible with the connector available on the Macintosh SE. The Macintosh SE/30 and the Macintosh IIfx used a different model of the PDS connector, called PDS 68030, which was not compatible with the PDS connector available on the Macintosh SE.
To install an expansion card, you had to open the computer and remove the motherboard – a rather complicated process.
In Figure 24, you can see a Radius SE accelerator card installed on the Macintosh SE motherboard, which replaced the 68000 microprocessor with a 68020. In Figure 25, we show a different accelerator card that was available for the Macintosh SE, the Prodigy SE from Levco, which also replaced the microprocessor with a 68020 model and added 16 MB of RAM.
In Figures 26 and 27, you can see two different models of Ethernet cards.
The motherboard for the Macintosh SE/30 was completely different from the one used on the other models of the Macintosh SE.
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.