Tandy 1000

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The Tandy 1000 was the first in a line of more-or-less IBM PC compatible home computer systems produced by the Tandy Corporation for sale in its RadioShack chain of stores.

Overview

Released in November 1984,[1] the Tandy 1000 was designed as a PC compatible with enhancements compatible with the IBM PCjr.[2][ 1] It was followed by a series of models which appended two or three letters to the name, after a space (e.g. Tandy 1000 EX, Tandy 1000 HX, Tandy 1000 SX, Tandy 1000 TX, Tandy 1000 RL, Tandy 1000 RLX). In a few instances, after these letters a slash was appended, followed by either a number or additional letters (e.g. Tandy 1000 TL/2, Tandy 1000 RL/HD).

The machine was primarily aimed at the home and educational markets, and it copied the PCjr's 16-color graphics (PCjr's graphics were an extension of CGA video) and 3-voice sound, but didn't use the PCjr ROM cartridge ports. As the Tandy 1000 line outlasted the PCjr by many years (and in fact did not make it to market until shortly before IBM announced the discontinuation of the PCjr) these graphics and sound standards became known as "Tandy-compatible" or (for the graphics) "TGA" (standing for Tandy Graphics Adapter).

Software companies of the era advertised their support for Tandy 1000 graphics.[3] 28 of 66 games that Computer Gaming World tested in 1989 supported Tandy graphics.[4]

Design and Architecture

Tandy 1000 computers were some of the first IBM PC clones to incorporate a complete set of basic peripherals on the motherboard using proprietary ASICs, the forerunner of the chipset. All Tandy 1000 computers featured built-in Tandy video hardware with color graphics (CGA compatible with enhancements), enhanced sound (based on one of several variants of the Texas Instruments SN76496 sound generator), game ports compatible with those on the TRS-80 Color Computer, an IBM-standard floppy disk controller supporting two drives, and a parallel printer port, all integrated into the motherboard. This is in addition to the hardware standard on the IBM PC, PC/XT, and PC/AT motherboards: keyboard interface, expansion slots, memory subsystem, DMA, interrupt controller, and math coprocessor socket. (Hard disks were high end, not standard, equipment for home computers until the late years of the Tandy 1000 line, explaining the absence of an integrated hard disk controller from most Tandy 1000 motherboards.) An IBM PC, XT or AT would require at least 4 expansion cards for similar hardware: one video graphics adapter card, one floppy disk controller (FDC) card, one serial and parallel port card, and one sound card with a joystick port. (A third-party multi-IO card might merge the ports and FDC onto one card.) Therefore, the 5 XT slots of the original Tandy 1000, 1000 TX, 1000 SX, and similar models remained available for other hardware, making them equivalent or better than the 8 slots in IBM's XT and AT models (which had 8 slots because the original PC's 5 proved inadequate.)

The earlier models of the Tandy 1000 had a composite video output, and could be used with a color or monochrome composite monitor, or a TV with an RF modulator. The original 1000 and SX had a light-pen port. Unlike most PC clones, several Tandy 1000 computers had MS-DOS built into ROM and could boot in a few seconds. Tandy bundled DeskMate, a graphical suite of consumer-oriented applications, with various Tandy 1000 models.

The original line was equipped with the Intel 8088 CPU, which was later extended to faster clock speeds and also the 8086, 80286 and toward the end of the line with the RSX, 80386SX processors. Tandy 1000s (at least all early models) used Phoenix BIOS. Common models of the machine included the Tandy 1000, 1000 EX, 1000 HX, 1000 SX, 1000 TX, 1000 SL, 1000 RL, and 1000 TL.

Hard disk drives

Due to their cost and status as a high-performance item, Tandy 1000 computers did not feature integrated hard disk controllers until the release of the Tandy 1000 TL/2, which featured an on-board XT IDE controller. However, it was possible to add a hard drive to most Tandy 1000 computers. Most of the desktop-type Tandy 1000 units could accept regular 8-bit ISA bus MFM, RLL and SCSI controllers like typical XT class machines; however, care had to be taken when configuring the cards so that they do not cause conflicts with the onboard Tandy-designed peripherals.

For most Tandy 1000 models other than the compact EX and HX that did not come already equipped with a hard drive, Tandy offered hard disk options in the form of "hardcards" that were installed in one of the computer's expansion slots and consisted of a controller and drive (typically a 3.5" MFM or RLL unit with a Western Digital controller) mounted together on a metal bracket. Although this arrangement provided a neat physical coupling between the controller and the disk, single-sector internal transfers and dependence on the speed of the host machine to transfer data to memory meant that a trial-and-error approach was still needed to set the disk interleave correctly to ensure optimum transfer rates. Even then, transfer rates could be as low as 40kB/s for 8088 and 8086 machines.

Starting with the Tandy 1000 TL/2, XT IDE controllers were integrated onto the motherboard. However, these are unable to support common AT IDE hard drives. The TL/2, TL/3, RL and RLX all used the XT IDE interface, where the later (and significantly upgraded) RSX was the first and only Tandy 1000 model computer to use a standard AT IDE interface.

Retirement

By 1993, changes in the market made it increasingly difficult for Tandy Corporation to make a profit on its computer line. Tandy Corporation sold its computer manufacturing business to AST Computers, and all Tandy computer lines were terminated. RadioShack stores then began selling computers made by other manufacturers, such as Compaq.

Reception

BYTE in August 1985 called the original Tandy 1000 "a good, reasonably priced IBM PC clone that has most of the best features of the IBM PC and PCjr ... at current prices it is a very good alternative". It noted the high level of PC-software compatibility and the good keyboard, but stated that DeskMate was "fairly good ... but a little extra programming work could have turned [it] into a much better program", noting that—for example—the word processor did not have a Move command. The review also advised customers of the computer's inability to use full-length PC expansion cards.[5] PC Magazine also noted the short slots and criticized the Tandy 1000's fit and finish, but acknowledged the computer's low price.[6]

Selected Tandy 1000 Models

Tandy 1000

The original Tandy 1000 was a large computer almost the size of the IBM PC, though with a plastic case over an aluminium lower chassis to reduce weight. The original Tandy 1000 featured a proprietary keyboard port (using an 8-pin DIN connector) along with 2 joystick ports (using 6-pin DIN connectors) on the front of the case. The rear featured a RGB monitor connector (a standard 9-pin female D-shell compatible with CGA/EGA monitors), an RCA-style composite video-out connector, a single RCA-style monophonic line-level audio connector, a light pen port, and an edge-card connector used to attach a parallel printer. The printer port followed the old Centronics standard and was not fully compatible with the parallel port found on PCs. The original Tandy 1000 came standard with one internal 5.25" double density floppy disk drive, with an additional exposed internal bay usable for the installation of a second 5.25" disk drive (available as a kit from RadioShack). The floppy drives used the old-fashioned method of selecting the drive number with jumpers instead of the IBM cable twist. 128 kB of memory was standard, with the computer accepting up to 640 kB of total memory with the addition of expansion cards.

MS-DOS 2.11, DeskMate 1.0, and a keyboard with the same layout as the Tandy 2000's were included with the computer. Like the PCjr. DMA was not supplied on the motherboard, but unlike the IBM system, DMA was added by a memory expansion board. While the Tandy 1000 had three XT-compatible expansion slots, early Tandy memory upgrade boards took up two of the slots to get to 640 kB. Because the slots were 11 1/2 inches in length instead of the PC's 13 inches, full-length cards did not fit.[ 1]

A later revision of the original Tandy 1000 model was the Tandy 1000A. This revision fixed bugs, scanned expansion cards for bootable ROMs, and added a socket for a math coprocessor.

Tandy 1000 HD

The original Tandy 1000 (and many other models), like most home computers sold at the time, did not have a hard disk drive. The Tandy 1000 HD was essentially an original Tandy 1000 with a hard disk option factory installed. The factory hard disk had a capacity on the order of 10 or 20 MB.

Tandy 1000 EX

Tandy 1000 EX

The Tandy 1000 EX was designed as an entry-level IBM compatible personal computer. The EX was a compact computer that had the keyboard and 5.25" floppy drive built into the computer casing. The 5.25" drive was accessible on the right-hand side of the computer. The EX was marketed as a starter system for people new to computing, and sold for US $1000.00 from RadioShack in December 1986. The EX and HX would be among the most popular of the Tandy 1000 line because of their (relatively) low price.

The EX had a 7.16 MHz 8088 (capable of clocking down to 4.77 MHz) and one internal 5.25" floppy drive. An external drive could be connected to a port on the back. A useful feature for the EX and later systems is the ability to boot off either drive, as the drives can be logically swapped when the system boots, so that the drive that is normally drive B: becomes drive A:, and vice versa, and the drives remain swapped until the system is powered off or reset.

Tandy 1000 HX

The Tandy 1000 HX was the bigger brother of the EX. It was mostly the same machine, but had a 3.5" floppy instead of a 5.25" one, and also had DOS 2.11 in ROM, which could be accessed by starting the computer with no bootable disk present. Like the EX, the clock speed of its 8088 CPU was increased to 7.16 MHz, providing a large performance benefit; it could clock down to 4.77 MHz for compatibility with older applications. (4.77 MHz was the speed of the 8088 in the IBM PC and PC/XT models and so was the de facto standard speed for an 8088 in an IBM-compatible.)

A Tandy 1000 HX, with a Tandy RGB monitor, an external 5.25 disk drive, joystick, and a Tandy DMP-133 dot matrix printer.

The computer's memory could be expanded to 640 kB. This would be accomplished by placing a memory expansion card, which came with 128 kB, in the expansion slot and adding another 256 kB (for a total of 384) kilobytes in memory chips to this board. The cards for the 1000 HX (and 1000 EX) were ISA electrically, but used a pin header rather than an edge connector. Called "PLUS cards", their connector design allowed them to be smaller (and cheaper) than standard ISA cards and to stack, rather than connecting to separate motherboard connectors; both of these aspects of the design saved space and allowed up to three cards to be installed in a small card compartment of the compact integrated system case. RadioShack eventually sold an adapter card that allowed the installation of a "Plus Card" into a standard ISA slot, such as those in the larger Tandy 1000 models. On the back of the machine there was a port which allowed a user to connect an external 360 kB 5.25" or 720 kB 3.5" floppy disk drive unit, available from Tandy.

The 1000 HX did not come with a hard drive, nor was it available from Tandy as an option, although a number of third party vendors sold them. The design of the EX and HX did not make it easy to add a hard drive, however.

The settings on the computer could be changed so that instead of looking in ROM for DOS at bootup that it would go to the floppy drive instead. Most versions of MS-DOS worked with the 1000 HX, including DOS 3.x, and some later versions. There was a quirk in the DOS 4.0 environment that prevented that version of DOS from working with Tandy 1000 HX computers.

Tandy 1000 TX and Tandy 1000 SX

The Tandy 1000 TX was very similar to the Tandy 1000, having an external keyboard and similar casing. The major difference was the use of an 80286 CPU; otherwise, it was nearly identical to the Tandy 1000, including the unique parallel port edge connector. Despite the 80286 processor, it was still an XT-class PC, not an AT-class PC, as it adapted the 80286 to operate over the same 8-bit data bus as previous Tandy 1000 models, and had 8-bit XT-style expansion slots. As such, it could not operate in 80286 protected mode or perform 16-bit memory or I/O transfers in one bus cycle, but it did benefit from the higher speed of the 80286 and its other added instructions in real mode. The TX had a 3.5" internal floppy disk drive, with an optional additional internal 5.25" floppy disk drive. It contained ports for two joysticks in the front along with the keyboard, and included a volume control with a 1/8" headphone jack on the front. The back had all of the same ports as the Tandy 1000, except that the light pen port was replaced with an RS-232 serial port. The memory size was 640k (upgradable to 768 kB, with the added 128 kB devoted to video[7]) and the computer came bundled with DeskMate.

The Tandy 1000 SX was the lower-end sibling of the TX, and was essentially an upgraded reissue of the original Tandy 1000. It used a 7.16 MHz 8088-2 processor, had 384k of memory (upgradeable to 640 kB on the motherboard), came with either one or two 5.25" internal floppy disk drives, had the light pen port (not a serial port) like the original Tandy 1000, and lacked the volume control and headphone jack of the TX (also like the original 1000). The Tandy AX was a Tandy SX rebadged for sale in Wal-Mart stores.

The 1000 SX came with MS-DOS 3.2 and Deskmate 2 on 5.25" 360 kB diskettes. The MS-DOS was a version specialized for and only bootable on the Tandy 1000, as it would announce on the screen of any other PC-compatible one tried to boot with it; it included a version of BASICA (Microsoft's Advanced GW-BASIC) with support for the enhanced CGA graphics modes (a.k.a. Tandy Graphics or TGA) and three-voice sound hardware of the Tandy 1000.

All original Tandy-provided internal floppy disk drives for the 1000 SX and TX were double-density drives. The Tandy 1000 SX and TX were the first models in the Tandy 1000 line to have a built-in DMA controller. The earlier 1000/1000A, 1000 HD, 1000 EX and 1000 HX models, like the IBM PCjr, did not have a DMA controller, but could be upgraded with one. The DMA controller chip was included on the PLUS-type memory expansion board for the EX and HX, and on regular ISA memory expansion cards sold by Tandy and other companies for the 1000, 1000A, and 1000HD. Adding the DMA chip improved the speed and IBM PC-compatibility of these earlier Tandy 1000 models.

Tandy 1000 SL, SL/2, TL, TL/2, TL/3

The Tandy SL and TL series of computers were updates of the SX and TX respectively. In addition to having a redesigned case and a more integrated motherboard, the SL and TL each offered improved video hardware capable of 640 × 200 × 16 graphics, on-board Hercules Graphics Card compatible monochrome video offering 720 × 350 resolution, and an improved sound circuit featuring an 8-bit mono DAC/ADC. The composite video output was also dropped. The ADC/DAC, which became known as the "Tandy DAC" in games that supported it, was broadly similar in function to sound devices which connected to the parallel port (such as the Disney Sound Source), but unlike those devices it was integrated onto the motherboard, supported DMA transfers and could sample at frequencies up to 48 kHz. While the Tandy DAC's features were comparable to those offered by Creative's 8-bit Sound Blaster audio cards, unlike the Sound Blaster or the Tandy's PCjr-compatible audio the DAC never saw widespread adoption by software developers. The 640 × 200 × 16 graphics mode was rarely used either, as it was not supported by the BIOS. The TL line also allowed the onboard floppy controller, parallel port, and joystick ports to be disabled, which the earlier models did not.

The Tandy 1000 SL and SL/2 feature an Intel 8086 processor running at 8 MHz. Thanks to the 8086 processor's 16-bit bus and slightly higher clock speed, the SL series enjoyed a modest yet appreciable increase in performance over the earlier 8088-based Tandy 1000's. The SL came with 384 kB of RAM preinstalled, whereas the SL/2 offered 512 kB. Both machines can be expanded to 640 kB, although only 576 kB could be used by the operating system.

The Tandy 1000 TL and TL/2 use 8 MHz Intel 80286 processors, whereas the TL/3 uses a 10 MHz 80286. These computers had 640 kilobytes of memory preinstalled, with an option for an extra 128 kilobytes to be installed for use as video memory for the onboard video hardware. It is therefore impractical to expand the onboard memory beyond 640 kB if a VGA graphics card is installed. Notably, the TL/3 had a high-density floppy controller for the first time, although it only shipped with a double-density 3.5" drive. Also, the TL/2 and TL/3 feature on-board 8-bit XT IDE ports, which were not compatible with common AT IDE hard drives.

Since the TL series are XT-class machines, it is impossible to install or use extended memory(XMS), although expanded memory (EMS) can be used with an 8-bit LIM EMS memory card for software that supports expanded memory.

The SL and TL were also shipped with MS-DOS 3.3 and DeskMate 3 in ROM, and featured an EEPROM memory chip to store BIOS settings (which enabled similar functionality to today's CMOS NVRAMs, so that startup options could be saved). (Earlier Tandy 1000 models, like IBM PC and PC/XT systems, used DIP switches for startup configuration settings.) The machines could also run 'normal' MS-DOS 3.x, 5, and 6 and Windows 2 and 3.0, albeit in real mode. In common with many PC clones of the era, MS-DOS 4 was problematic and generally avoided.

Tandy 1000 RL, RL/HD, RLX, RSX

The Tandy 1000 RL/RLX/RSX series were slim-line desktop home computers. The RL and RL/HD featured a 9.56 MHz 8086 processor, 512 kB of RAM (expandable to 768 kB to provide 128 kB for video), smaller keyboard and mouse ports (which were similar to the PS/2's ports but not directly compatible), a bidirectional parallel port instead of the edge-connector ports, and the SL's enhanced graphics and sound. The RL/HD also included a built-in XT IDE hard drive.

The RLX was the 'mid-range' offering of the RL line. It had a 10 MHz 286, and unlike other 286-based Tandy 1000s, it supported up to 384 kB of extended memory. However, it was not a full AT-class machine, as it still had an 8-bit ISA bus and only 8 IRQs. While the 3-voice sound chip and DAC were still present, Tandy video was dropped. The RLX had VGA instead, offering 256 kB of video memory and a maximum 640x480x16 (or 320x480x256) graphics resolution. Also, the RLX featured a high-density, 1.44 MB 3.5" disk drive. The RLX offered 512 kB of memory preinstalled, which could be expanded to 1 MB. (The hard disk version came with 1 MB preinstalled.)

The RSX offered a 25 MHz 80386SX processor, two 16-bit ISA slots, AcuMos SVGA video, an AT compatible IDE interface and standard PS/2 keyboard and mouse ports. It was a full 386-class PC, and could use up to 9 MB of memory. The RSX still retained the 3-voice sound hardware and DAC, though the I/O address for the 3-voice sound chip was moved, rendering many games previously compatible with it unable to play music unless modified. The DAC could be used to emulate the Covox Speech Thing via MS-DOS device drivers for limited sound support in MS-DOS based software. This works with "Chuck Yeager's Air Combat" video game.

Windows 3.xx sound device drivers were available that works in Windows 95 (with full 9MB RAM) on Tandy 1000 RSX. The ACUMOS VGA graphics could be software updated with Cirrus Logic BIOS (via MS-DOS driver) to allow VESA/SVGA to function in Windows 95, as the Windows 3.xx Tandy VGA drivers were insufficient for Windows 95.

References

  1. ↑ "BRIEFS". InfoWorld. 1985-02-12. p. 23. Retrieved February 27, 2011. 
  2. ↑ Anderson, John J. (December 1984). "Tandy Model 1000; junior meets his match". Creative Computing. p. 44. Retrieved February 26, 2013. 
  3. ↑ "Electrifying Software For Today's PC". Compute! (advertisement). June 1988. p. 23. Retrieved 10 November 2013. 
  4. ↑ "The Owner's Guid to Tandy 16 Color". Computer Gaming World. August 1989. p. 14. 
  5. ↑ Malloy, Rich (August 1985). "The Tandy 1000". BYTE (review). p. 266. Retrieved 27 October 2013. 
  6. ↑ Rosch, Winn L. (1985-10-15). "Cost-Conscious Computing". PC Magazine. p. 113. Retrieved 29 October 2013. 
  7. ↑ Because the Tandy 1000 was originally designed to be compatible with the IBM PCjr, and the IBM PCjr used part of its main memory as video memory, so did the Tandy 1000 series (except for the VGA-equipped RLX and RSX). In this respect, the Tandy 1000 and PCjr are unlike the IBM PC, PC/XT, PC AT, and all 100% compatibles, which used display adapters with separate, dedicated video memory. Expanding the memory of the Tandy 1000 TX to 768K ensured that more memory would be available in the 640 kB of the memory space allocated by IBM for main memory (for programs and their general data).

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