Apple introduced the PowerBook Duo 270c on October 21, 1993. It stayed in production until May 1, 1994 when it was replaced by the PowerBook Duo 280c. PowerBook Duos are subnotebooks that have almost no ports and no internal floppy disk drive. Duos must use a dock like a MiniDock or Duo Dock in order to expand capabilities and give them access to standard Macintosh and PowerBook ports. The PowerBook Duo 270c originally cost $3100 to $3600 depending on the configuration. We acquired our PowerBook Duo 270c in 2008 for $25.

The PowerBook Duo 270c uses 33 MHz 68030 processor with an integrated 68882 math coprocessor (FPU or floating point unit). The 270c uses a redesigned Duo 230 motherboard, which does not have an FPU. If the 270c is inserted into a Duo Dock II, the system turns off the Dock's coprocessor. Apple offered two standard configurations:

• $3100, 4 MB RAM, 240 MB hard drive
  
  
• $3600, 12 MB RAM, 240 MB hard drive, Express Modem Card
  
  

The 270c has 4 MB of built-in RAM and one RAM slot that uses 70 ns Duo RAM. It can address up to 32 MB RAM. If the 270c has a 32 MB RAM card installed, it cannot address the 4 MB built into the motherboard. Our 270c has 24 MB RAM. The 270c originally shipped with Mac OS 7.1 and it supports up to Mac OS 7.6.1. It is advisable to have at least 16 MB RAM installed if you intend to run for Mac OS 7.5 to Mac OS 7.6.1. Our 270c is currently using Mac OS 7.5.

The 270c shipped with a 240 MB internal SCSI hard drive. Duos like the 270c do not have a built-in floppy disk drive and have few ports. Connectivity and expansion requires the use of a docking device or adapter. The 270c does have a single expansion slot for an internal modem (RJ-11). Our 270c has the optional internal PowerBook Express Modem installed. It sends and receives data at 14,400 bps and sends and receives faxes at 9,600 bps. Apple included Express Fax software with the card.

The Duo 270c has few built-in ports. The only standard ports on the Duo 270c are one optional internal modem port (RJ-11) and a serial port (RS-422) for a printer or external modem. The 270c also has a tiny built-in speaker residing in the monitor casing.

The largest port on the Duo 270c is a 152-pin Processor Direct Slot (PDS) located on the back. The slot is used to plug the Duo 270c into a dock that provides additional connectivity. Apple sold two primary types of docks: a MiniDock and a full-sized Duo Dock desktop system. Apple also sold a Duo Floppy Adapter, which allows for the connection of an external HDI-20 floppy disk drive and an ADB keyboard and mouse.

The MiniDock adds a variety of ports, including: one HDI-20 floppy drive port, one HDI-30 SCSI port, one DB-15 monitor port, one serial external modem port, one serial printer port, one sound-in jack, one sound-out jack, one ADB port, and one modem port (RJ-11).

The Duo Dock has most of the same ports as the MiniDock (the Duo Dock does not have an HDI-20 port), but it includes a PowerLatch slider mechanism that pulls the PowerBook Duo inside the chassis, similar to a VHS tape being pulled into a VCR (Video Cassette Recorder). The Duo 270c is compatible with the Duo Dock II and Duo Dock Plus. It is not compatible with the original Duo Dock because the compartment that holds the subnotebook is too narrow, designed for use with earlier Duos that have grayscale displays. To accommodate the thicker color screen (the 270c is 1.5 inches high, compared with 1.4 inches for the grayscale Duos), Apple introduced the Duo Dock II, an upgraded version of the original Duo Dock with a hinged door. Apple sold a $69 upgrade for the original Duo Dock to allow it to accommodate the thicker color Duos.

Apple introduced a later Duo Dock called the Duo Dock Plus in 1995 to make it more compatible with the PowerPC-based PowerBook Duo 2300c and the 68LC040-based PowerBook Duo 280 and 280c. The Duo Dock Plus was designed to be fully compatible with all Duos even though it lacks the FPU found on the Dock II. Because the Duo Dock II has a built-in FPU, it is recommended for use with all Duos except the 280, 280c, and 2300, but in the case of the 270c, the lack of an FPU in the Plus doesn't affect performance because the 270c has a built-in FPU.

The Duo Dock II or Plus turns the PowerBook Duo 270c into a full desktop system. Other than the array of ports the Duo Dock adds to the subnotebook, it also offers additional video RAM (VRAM), a built-in floppy disk drive, two NuBus expansion slots, and room for an optional internal hard drive. An external monitor is required because the PowerBook Duo 270c has to be folded up and inserted into the Duo Dock in order to make the connection.

The 270c has an 8.4-inch (94 dpi) color active matrix LCD capable of 16-bit color depth (thousands of colors) at 640 x 400 and 8-bit color depth (256 colors) at 640 x 480. Although the capability to display 16-bit color depth is an improvement over older 8-bit displays, you don't actually see all the 32,768 colors available on CRT monitors, because the LCD used on the 270c doesn't have the tonal range of contemporary CRTs. In the 16-bit, 640 x 400 mode, the image is centered on the screen with a black band at the top and bottom, similar to the look of a letterboxed movie.

The brightness of the display is controlled by two buttons located under the speaker grill on the right side of the display. When attached to the Duo Dock, the resolution of the display and its color depth depends partially on the external monitor being used. The Duo Dock II and Plus have 1 MB of built-in VRAM.

The 270c shipped with the Nickel Metal Hydride (NiMH) Type II battery capable of two to four hours of continuous use on a single charge. Although the battery will drive a grayscale Duo for two and a half to five hours, the 270c's color LCD display draws more power. The battery alone sold for $85 and it will work with all earlier Duos. Later Duos like the Duo 2300 shipped with the Duo NiMH Type III battery. We tested this battery on the 270c and noted no issues. Apple produced three types of Duo batteries: Type I, II, and III. Type I batteries came installed in Duo 210 and 230 systems, Type II batteries came installed in Duo 250, 270c, and 280 systems, and Type III batteries were installed in the Duo 280c and 2300. It is possible to use both Type II and Type III batteries in Duo 210 and 230 systems with the addition of appropriate battery management software. Type I batteries can be used in newer Duo systems, but battery life is significantly reduced. The 270c uses the same power adapter as all other Duos.

Despite modest sales of the earlier PowerBook Duo 210 and 230, Apple hoped to generate new interest in the product line with the release of the color 270c. The 270c, introduced along with a grayscale counterpart, the PowerBook Duo 250, featured improved displays, improved battery technology, and in the case of the 270c, a built-in math coprocessor and more RAM capacity. It was also hoped that these improvements, along with a flurry of new third-party docking station introductions, would convince skeptics that the Duo line represented flexibility that was unmatched among laptops.

By 1997, miniaturization had begun to reach the point where consumers just couldn't justify buying a pricey dock to use with a pricey subnotebook that had almost no ports and no built-in floppy or CD drive of its own. The Duo Dock concept was unique to Apple Computer. It was an attempt to overcome the shortcomings of early laptops that offered portability but suffered from limited capabilities (connectivity, processing power, and video) in comparison to traditional desktop systems. The Duo line took advantage of advances in systems networking in order to free the laptop from the need to house media drives like a floppy disk drive or CD-ROM drive. This gave the Duos unmatched portability, but consumers for the most part just didn't get it. By in large, potential laptop consumers did not see the lack of an internal floppy disk drive or the need to use docking devices as an equal exchange for increased portability.