Tandy TRS-80 Model IV
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The TRS-80 was Tandy Corporation's desktop microcomputer model line, sold through Tandy's Radio Shack stores in the late 1970s and early 1980s.
The successor to the Model III was the Model 4 (April 1983, with "4" written as an Arabic numeral), which included the capability to run CP/M.
Running CP/M had previously only been possible via a hardware modification that remapped the BASIC ROMs away from memory address zero, such as the third-party add-on sold as the Omikron Mapper board, or by running a version of CP/M modified to run at a starting address other than zero. However, this also required modified applications, since the area of memory at zero contained the vectors for applications to access CP/M itself. The Model 4 also added an 80 column by 24 line video display mode required for CP/M compatibility.
The Model 4 shipped with TRSDOS 6, an enhanced version of LDOS by Logical Systems and a vastly superior operating system to Tandy's earlier TRSDOS offerings. When the Model 4 booted into TRSDOS 6 the video display switched into 80×24 mode and the entire 64KB address space was mapped as RAM. The Model 4 was also capable of running all Model 3 software when a Model 3 operating system disk was detected and loaded during bootup with a 64×16 video mode and Model 3 ROMs mapped from address zero.
The Model 4 also had the ability to display 640×240 or 512×192 high-resolution monochrome graphics with an optional board. A "luggable" version known as the Model 4P (1983) was a self-contained unit with a case design similar to that of a portable sewing machine.
Early versions of the Model 4 mainboard were designed to accept a Zilog Z8000 16 bit CPU upgrade board to replace the Z80 8 bit CPU but this option was never released.
Our Model IV was very kindly donated by Edward Gladstone together with his vast collection of Tandy hardware, software and manuals.
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This exhibit has a reference ID of CH15780. Please quote this reference ID in any communication with the Centre for Computing History.
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