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Tandy 2000
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== Compatibility issues == The Tandy 2000 was nominally BIOS-compatible with the IBM XT, so well-behaved DOS software ran on both platforms. However, most DOS software of the time bypassed the operating system and BIOS and directly accessed the hardware (especially video and external ports) to achieve higher performance. This rendered such software incompatible with the Tandy 2000. === Graphics === The base-model Tandy 2000 supported only a text-mode display in monochrome.<ref name=":0">{{Cite news |last=JENNINGS |first=MARK S. |date=December 1984 |title=SYSTEM RE VIEW - The Tandy Model 2000 |url=https://www.tech-insider.org/personal-computers/research/acrobat/8412-b.pdf |work=BYTE |pages=239 - 248}}</ref> The Tandy VM-1 monitor used the 8-pin [[DIN connector|DIN]] video port on the computer's rear panel. The text-mode address space was in a different location but third-party memory-resident software hacks remedied this by copying the PC-compatible text-mode memory to the Tandy 2000's text space at a rate of 5–10 times per second. This sometimes caused some choppiness in the display. It produced a fast text display rate—often too fast to read—but the 'HOLD' key on the keyboard could be used to pause text output. The bit pattern for each text character's raster image was maintained in RAM and could be modified by the user. With clever programming the display's ability to present fine lines provided by the 640x400 screen resolution could be accessed in text mode even without the optional graphics board. ==== Tandy 2000 Graphics Adapter ==== [[File:Tandy 2000 Color Graphics Option 640x400x8 ar corrected.png|thumb|Tandy 2000 Color Graphics Option 640 × 400 x 8 colors]] The display was upgradable to support pixel-addressable graphics via the Tandy 2000 Graphics Adapter, a circuit board that fit into an expansion slot.<ref name=":0" /> It had its own connector for the monochrome VM-1 monitor; the video connector in the rear-panel cabinet was disabled when this expansion board was installed. The graphics resolution was 640x400 and supported high intensity pixels. Color capability was provided by the Color Graphics Option,<ref name=":0" /> which was a set of chips that were inserted into the empty sockets on the monochrome Graphics Adapter provided for this purpose.<ref group="note">The Color chipset comprises 16 readily-available chips: eight 4416-15 DRAMs, four 74F245s, and four 25LS22 chips. A trace cut on the graphics board was also required.</ref><ref>{{cite web|title=Model 2000 Color Graphics Option Kit Installation Instructions|url=http://www.classiccmp.org/cini/pdf/Tandy/Tandy%202000%20Color%20Chip%20Kit%20Install%20Manual.pdf|website=ClassicCMP|accessdate=May 23, 2016}}</ref> Resolution for the color board was the same 640x400, non-interlaced, and eight colors out of a palette of sixteen available colors were displayable on the Tandy CM-1 monitor (~$799).<ref name=":0" /> This was a particularly high-resolution and colorful display for its day. The CM-1 monitor accepted, as input from the color graphics board, [[List of monochrome and RGB color formats#4-bit RGBI|digital RGBI signals]] (indicating separate Red, Green, and Blue signals with a Intensity bit).<ref name=":1">{{Cite book |url=https://github.com/Tandy2K/Tandy2000/blob/master/Hardware/Technical%20Reference%2026-5404.pdf |title=Tandy Model 2000 Technical Reference Manual |date=1984 |publisher=Tandy Corporation |publication-date= |pages=278}}</ref> [[Color Graphics Adapter|CGA]] compatibility was hit-or-miss. {| class="wikitable sortable" |+Tandy 2000 Graphics Adapter Color Graphics Option hardware palette on CM-1 monitor <ref name=":1" /> !Color !I !R !G !B !Color !I !R !G !B |- |Black |0 |0 |0 |0 |Black |1 |0 |0 |0 |- |Dark Blue |0 |0 |0 |1 |Blue |1 |0 |0 |1 |- |Dark Green |0 |0 |1 |0 |Green |1 |0 |1 |0 |- |Dark Cyan |0 |0 |1 |1 |Cyan |1 |0 |1 |1 |- |Dark Red |0 |1 |0 |0 |Red |1 |1 |0 |0 |- |Dark Magenta |0 |1 |0 |1 |Magenta |1 |1 |0 |1 |- |Dark Yellow |0 |1 |1 |0 |Yellow |1 |1 |1 |0 |- |Gray |0 |1 |1 |1 |White |1 |1 |1 |1 |} There were only three non-Tandy monitors that worked with the Tandy 2000 graphics card, all of which are long out of production. These were the original (1986–88) Mitsubishi Diamond Scan, and the [[NEC]] Multisync and Multisync GS (grayscale).<ref>{{cite web|title=Tandy 2000 FAQ|url=http://www.classiccmp.org/cini/docs/t2kfaq.txt|website=Classiccmp.org|publisher=Classic Computer, Jeff Hellige|accessdate=May 23, 2016}}</ref> The required horizontal scan frequency for the Tandy 2000 is 26.4 kHz. Modern flat-panel multisync computer monitors cannot sync at frequencies below 30 kHz. The CM-1 monitor is also digital RGB; all modern CRT monitors are analog-only. === Media === The Tandy 2000 used quad-density 5.25" floppy disks formatted at 720k. This format (80-track disks at the double-density bitrate) was not used by PC-compatibles, although some CP/M machines and the [[Commodore 8050]]/8250 drives had them. Normal PCs of the time had 40-track double-density floppy drives and could not read quad-density due to the drive heads being too wide to read the narrower tracks. 1.2 MB 5.25" drives (introduced on the IBM AT) could read quad-density disks because they were 80-track and had thinner heads. Various utility programs for DOS existed that could read nonstandard formats such as the Tandy 2000's disks. Much like 1.2 MB drives, the Tandy 2000 had problems reliably writing 360k PC disks due to the smaller heads not completely erasing the tracks and causing 40-track drives to become confused by residual magnetic signals on the outer edge of the track. Tandy distributed the computer with a utility called PC-Maker that would read and format 40-track disks in the 2000s 80-track drives, and were readable in drives on ordinary PCs. The floppy controller on the Tandy 2000 is compatible with 3.5" double-density 720 KB floppy drives. As of May 2019, there is an abandonware site (winworldpc.com) that has available for download a disk image for the latest version of MS-DOS for the Tandy 2000. It includes instructions for using the IBM 1.2 MB 5.25" disk drive (80-track) to create a system disk bootable in the Tandy 2000 5.25" drive.<ref>{{cite web|title=Microsoft MS-DOS 2.11 [Tandy 2000 OEM] (02.02.00) (5.25-DSQD 720k)|url=https://winworldpc.com/download/40e280b9-7b22-18c3-9a11-c3a4e284a2ef|website=WinWorld|accessdate=December 28, 2017}}</ref> This procedure can also be used to create a bootable 3.5-inch system disk using an ordinary 720 KB 3.5-inch PC drive; this will boot a Tandy 2000 if its 5.25" boot drive has been replaced with a double-density 720 KB 3.5 inch PC drive. === Keyboard === The keyboard was a new design made for the Tandy 2000. It would later be the same keyboard shipped with the [[Tandy 1000]] and its successors. The arrangement of the function keys was changed from that of the IBM PC/XT, which had ten on the left side of the keyboard in two columns of five. Tandy was among the first PC manufacturers to change this to the modern arrangement of twelve function keys arranged horizontally across the top. IBM gave a nod to the new standard by using this arrangement for the [[Model M keyboard]]. === Serial port === The serial port hardware was completely different from the PC/XT's. PC-compatible terminal emulation software had to either access the serial hardware strictly through BIOS or use a [[FOSSIL]] driver, a software wrapper that virtualized the serial hardware (see also [[DEC Rainbow]]), to run on a wider variety of hardware. Several terminal programs were available for the Tandy 2000, making it possible to log in on [[Bulletin board system|BBS]]es, e-mail, and other remote systems. === Operating system === The Tandy 2000 required a specific version of [[MS-DOS]] that would run only on this machine. Standard MS-DOS or [[PC DOS]] (for generic IBM-compatibles) would not run on a Tandy 2000. It was standard practice and Microsoft's expectation at the time that a customized version of MS-DOS would be prepared for each different machine, with I/O drivers designed for the hardware of that model. The highest version of DOS that Tandy Corporation released for the Tandy 2000 was 2.11.03, with a few minor third-party patches after the fact. A modified version of [[Windows 1.0]] was able to run on the Tandy 2000. MS-DOS for the Tandy 2000 resided entirely in RAM, unlike on IBM PCs where the BIOS portion of the OS resided in ROM. The complete MS-DOS system (BIOS and BDOS) occupied about 53 KB of RAM.<ref>{{cite web |last1=Harrell |first1=John B. |title=80 Micro, November 1984, page 174, column 2000 PLUS, Memory Management on the Tandy 2000 |url=https://archive.org/details/80-microcomputing-magazine-1984-11/page/n175/mode/2up |website=www.archive dot org |date=November 1984 |publisher=CW Communications |accessdate=July 15, 2020}}</ref><ref>{{cite web|title=Byte review of Tandy 2000|url=http://tech-insider.org/personal-computers/research/acrobat/8412-b.pdf|website=tech-insider dot org|accessdate=May 25, 2016}}</ref> This means that the RAM required to run applications on the Tandy 2000 was a little greater. However, the Tandy 2000 fared better in comparison to the later IBM PC-AT in that the AT was required to run MS-DOS version 3.x in order to operate its 1.2 MB floppy drives and hard drive. Version 3 of MS-DOS was rather larger than Version 2.x running on the Tandy 2000. It also proved advantageous that the Tandy 2000's OS resided entirely in RAM and therefore could be updated and hacked with rather less effort. The Microsoft BASIC interpreter was supplied with the computer. It was highly customized for the Tandy 2000 hardware, particularly its high-resolution color graphics. Although IBM produced the Enhanced Graphics Adapter a little more than a year later (October 1984), the Microsoft BASIC interpreter would not support its greater color and resolution capabilities until 1988. Tandy/Radio Shack produced print advertising featuring [[Bill Gates]] of Microsoft extolling the superior performance of the Tandy 2000 and how it was advantageous in Microsoft's development of Windows 1.0.<ref>{{cite magazine|title=Radio Shack print ad with Bill Gates and Tandy 2000|url=https://books.google.com/books?id=oC4EAAAAMBAJ&dq=bill%20gates%20tandy%202000&pg=PA1|magazine=InfoWorld |page=1 |type=Ad |volume=6 |issue=45|access-date=May 23, 2016|date = 5 November 1984}}</ref>
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