The Leading Edge Model D was an IBM clone computer first released by Leading Edge Hardware in July 1985. It was initially priced at $1,495 configured with dual 5.25" floppy drives, 256 KB of RAM, and a monochrome monitor. It was manufactured by South Korean conglomerate Daewoo and distributed by Canton, Massachusetts-based Leading Edge.[1] Engineer Stephen Kahng spent about four months designing the Model D[2] at a cost of $200,000.[3] Kahng later became CEO of Macintosh clone maker Power Computing.
In August 1986, Leading Edge cut the price of the base model by $200, to $1,295, and increased the base memory of the machine to 512 KB.[4]
The Model D was an immediate success, selling 100,000 units in its first year of production. It continued to sell well for several years, until a dispute with its dealers forced Leading Edge into bankruptcy in 1989.[5]
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The Model D initially featured an Intel 8088 microprocessor at 4.77 MHz, although later models had a switch in the back to run at 4.77 MHz (normal) or 7.16 MHz (high). Earlier models had no turbo switch and ran only at 4.77 MHz, while a few of the later ones (seemingly very rare) were 7.16 MHz only. Three models are known: DC-2011, DC-2010E, and DC-2011E. The "E" seems to correlate with the capability of running at 7.16 MHz.
Unlike the IBM PC and IBM PC/XT, the Model D integrated video, the disk controller, a battery backed clock, serial and parallel ports directly onto the motherboard rather than putting them on plug-in cards. This allowed the Model D to be half the size of IBM's models.[5]
The motherboard came in eight different revisions: Revision 1, 5, 7, 8, CC1, CC2, WC1, and WC2. A list of motherboard part numbers and revision numbers can be found here. Revisions 1 through 7 were usually found in model DC-2011, with revisions 8 through WC2 being either in 2010E or 2011E. WC1 (presumably also WC2) is 7.16 MHz only. Due to its tight integration, the Model D motherboard was a nonstandard form factor, so replacing the motherboard with an off-the-shelf upgrade was not possible.
They came preinstalled with 256, 512, or 640 KB of RAM. Lower-capacity machines were user upgradeable to 640 KB.[6] Motherboard revisions 7, 8, WC1 and WC2 came with 768 KB of RAM installed (640 KB available to the user).
Some models featured a monochrome/CGA selection switch, with a single port used for both modes. Some models had both a Monochrome and a CGA port, also with a switch to change modes (and ports).[6]
The Model D computers supported a special extended graphics mode: 640x200.
The buyer had the choice between a floppy disk model and a fixed disk (hard disk) model. The floppy disk model had one or two 360 KB drives, so that the user could run MS-DOS programs on the primary drive and work with files on the secondary drive, if equipped.[6] The fixed disk model had one 360 KiB floppy drive and either a 10 MB, 20 MB, or 30 MB hard disk. The model with the 20 MB fixed disk was initially released in February 1986 at a cost of $1,895.[7] Leading Edge dealers had difficulty keeping the 20MB model in stock.[7] At the time, a Tandy 1200 equipped with a 10MB drive sold for $1999.
The buyer also had a choice between an amber or a green monochrome CRT monitor.
The unit came with MS-DOS 2.11 or later,[1] and a special edition of GW-BASIC to support the extended graphics mode.
It also came with a diagnostics disk. This disk contained a diagnostics program, and PARK.COM, a utility used to park the hard drive heads when the computer was to be moved. Most models also came with a word processing program developed by Leading Edge titled Leading Edge Word Processor, commonly referred to by its acronym 'LEWP'.
The computer supports the Microsoft Windows operating system up to version 3.0, as it is the last version of Windows to support Real Mode.
The Model D, along with the Tandy 1000 and Epson Equity series, was one of the first IBM PC Compatible computers to become popular for home use, due to its low price and good reviews. Previously, MS-DOS and IBM Compatibles were almost exclusively used in businesses, with the home computer market dominated by Commodore, Apple and Atari. For years afterward, many home-oriented software packages for the PC specifically cited the Model D along with the Tandy and Epson models as compatible hardware.
Leading Edge was Phoenix Technologies' first customer for its IBM-compatible BIOS, and the Model D was one of the first PCs on the market to use the Phoenix BIOS.[8] Although advertised as 100% IBM compatible, numerous letters published in the January 13, 1986 issue of InfoWorld identified compatibility issues with several popular software packages and aftermarket hard drives. Syndicated newspaper columnists T.R. Reid and Michael Schrage, writing in April 1986, predicted that the popularity of the Model D would lead to hardware and software vendors specifically testing for compatibility. In spite of these early reports, the Model D continued to sell well. In early 1987, Daewoo was producing 13,000 units per month and failing to keep up with demand. As a result, buyers waited 2–8 weeks before taking delivery.[9]
The Model D also has the distinction of being the first Korean-made PC to be sold in the United States, and at the time of its introduction, it undercut the price of similar IBM PC compatibles by $500.[10]
The Model D received 4 out of 5 stars from InfoWorld, and a positive review in Popular Mechanics cited its low price and the quality of its keyboard.[11] It received good reviews in other computer magazines and Consumer Reports magazine.[5]