Rainbow 100
Encyclopedia
The Rainbow 100 was a microcomputer
introduced by Digital Equipment Corporation
(DEC) in 1982. This desktop unit had the video-terminal display circuitry from the VT102, a video monitor similar to the VT220
in a dual-CPU
box with both Zilog Z80
and Intel 8088
CPUs.
The Rainbow 100 was a triple-use machine: VT102 mode, 8-bit
CP/M
mode (using the Z80), and 16-bit
CP/M-86
or MS-DOS
mode using the 8088.
The "100+" model was actually a marketing designation signifying that the system shipped with a hard drive installed; the "100+" and "B" models were identical in all other respects. When a hard-disk option was installed on the Rainbow, the kit included the 100+ emblem for the computer's case.
and the Intel 8088
respectively. The buses exchanged information via a shared memory.
When not executing 8-bit code, the was used for floppy disk access. The 8088 bus was used for control of all other subsystems, including graphics, hard disk access, and communications. While it may have been theoretically possible to load Z80 binary code into the Rainbow to execute alongside 8088 code, this procedure has never been demonstrated.
s were available from Digital Equipment Corporation
that could increase system memory with up to an additional .
. However, later versions of MS-DOS
and CP/M
allowed formatting of diskettes.
Of note was the single motor used to drive both disk drives via a common spindle, which were arranged one on top of the other. That meant that one disk went underneath the first but inserted upside-down. This earned the diskette drive the nickname "toaster". The unusual orientation confused many first-time users, who would complain that the machine would not read the disk.
produced a Winchester disk controller for the Rainbow capable of controlling hard disks compatible with the ST-506
interface. The controller, however, was limited to a single drive with up to and including and , limiting storage to a maximum of .
Third-party hard-disk controllers were also available.
The graphics option was a user-installable module that added graphics and color display capabilities to the Rainbow system. The Graphic module was based on a NEC 7220 graphic display controller (GDC) and a 8×64 KB DRAM video memory.
Due to the design of the graphics system, the Rainbow was capable of controlling two monitors simultaneously, one displaying graphics and another displaying text.
signal in monochrome mode. With the inclusion of the graphics option, the Rainbow could also output sync-on-green RGB video signals at TTL levels. The Rainbow was most often coupled with the 12-inch VR201 monochrome monitor or the 13-inch VR241 color monitor, both produced by Digital Equipment Corporation
.
keyboard used a new layout that made some ASR33
and VT100
users unhappy. However, the VT220 style of this keyboard can clearly be seen in the layout of the enhanced 101-key keyboard adopted by IBM in 1987.
(286) processor upgrade (Turbow-286), a 3.5-inch disk adapter kit (IDrive), and a battery-backed clock chip (ClikClok), all from Suitable Solutions.
In 1984, the first computer support for Native American languages began with the Rainbow 100. Rock Point Community School
on the Navajo reservation in Arizona commissioned a ROM chip for the Navajo language, enabling the school to create bilingual computer programs.
CP/M
software as users moved into the 16-bit
world of MS-DOS
. The disadvantages were that little DOS software was released on Rainbow media, and there were subtle differences between Rainbow's MS-DOS implementation and MS-DOS (or PC-DOS
) running on true IBM PC compatible
s. Towards the end of its life, Rainbow users were able to run IBM PC-compatible MS-DOS software using an emulation application called Code Blue.
MS-DOS compatibility was added late in the design, so hardware interrupts and MS-DOS software interrupts overlapped. One DEC documentation pack for developers included a listing of Microsoft assembly code to handle this. The theory was that hardware interrupts would interrupt again but software interrupts would only happen once.
DEC itself ported Microsoft
Windows 1.0
to the Rainbow. There was also a third-party upgrade that included a 286 processor board and a modified version of Windows 3.0
.
Microcomputer
A microcomputer is a computer with a microprocessor as its central processing unit. They are physically small compared to mainframe and minicomputers...
introduced by Digital Equipment Corporation
Digital Equipment Corporation
Digital Equipment Corporation was a major American company in the computer industry and a leading vendor of computer systems, software and peripherals from the 1960s to the 1990s...
(DEC) in 1982. This desktop unit had the video-terminal display circuitry from the VT102, a video monitor similar to the VT220
VT220
The VT220 was a terminal produced by Digital Equipment Corporation from 1983 to 1987.-Hardware:The VT220 improved on the earlier VT100 series of terminals with a redesigned keyboard, much smaller physical packaging, and a much faster microprocessor...
in a dual-CPU
Multiprocessing
Multiprocessing is the use of two or more central processing units within a single computer system. The term also refers to the ability of a system to support more than one processor and/or the ability to allocate tasks between them...
box with both Zilog Z80
Zilog Z80
The Zilog Z80 is an 8-bit microprocessor designed by Zilog and sold from July 1976 onwards. It was widely used both in desktop and embedded computer designs as well as for military purposes...
and Intel 8088
Intel 8088
The Intel 8088 microprocessor was a variant of the Intel 8086 and was introduced on July 1, 1979. It had an 8-bit external data bus instead of the 16-bit bus of the 8086. The 16-bit registers and the one megabyte address range were unchanged, however...
CPUs.
The Rainbow 100 was a triple-use machine: VT102 mode, 8-bit
8-bit
The first widely adopted 8-bit microprocessor was the Intel 8080, being used in many hobbyist computers of the late 1970s and early 1980s, often running the CP/M operating system. The Zilog Z80 and the Motorola 6800 were also used in similar computers...
CP/M
CP/M
CP/M was a mass-market operating system created for Intel 8080/85 based microcomputers by Gary Kildall of Digital Research, Inc...
mode (using the Z80), and 16-bit
16-bit
-16-bit architecture:The HP BPC, introduced in 1975, was the world's first 16-bit microprocessor. Prominent 16-bit processors include the PDP-11, Intel 8086, Intel 80286 and the WDC 65C816. The Intel 8088 was program-compatible with the Intel 8086, and was 16-bit in that its registers were 16...
CP/M-86
CP/M-86
CP/M-86 was a version of the CP/M operating system that Digital Research made for the Intel 8086 and Intel 8088. The commands are those of CP/M-80. Executable files used the relocatable .CMD file format...
or MS-DOS
MS-DOS
MS-DOS is an operating system for x86-based personal computers. It was the most commonly used member of the DOS family of operating systems, and was the main operating system for IBM PC compatible personal computers during the 1980s to the mid 1990s, until it was gradually superseded by operating...
mode using the 8088.
Models
The Rainbow came in three models, the 100A, 100B and 100+. The "A" model was the first released, followed later by the "B" model. The most noticeable differences between the two models were the firmware and slight hardware changes. The systems were referred to with model numbers PC-100A and PC-100B respectively; later were also designated PC-100B2.PC-100A
The "A" model was the first produced by Digital. The distinguishing characteristic of the "A" model from an end-user perspective was that the earlier firmware did not support booting from a hard disk. Other distinguishing hardware features included the three 2764 ROM chips holding the system firmware and the case fan/power supply combinations. Versions of the 100A shipped outside the USA included a user-changeable ROM chip in a special casing. The user changed the built-in ROM for this one to support their keyboard layout and language of the boot screen.PC-100B
The "B" model followed the "A" model, and introduced a number of changes. The "B" model featured the ability to boot from a hard disk (referred to as the Winchester drive) via the boot menu due to updated firmware. The hardware changes included bigger firmware stored on two and an improved case fan/power supply.The "100+" model was actually a marketing designation signifying that the system shipped with a hard drive installed; the "100+" and "B" models were identical in all other respects. When a hard-disk option was installed on the Rainbow, the kit included the 100+ emblem for the computer's case.
CPUs
The Rainbow contained two separate data buses controlled by the Zilog Z80Zilog Z80
The Zilog Z80 is an 8-bit microprocessor designed by Zilog and sold from July 1976 onwards. It was widely used both in desktop and embedded computer designs as well as for military purposes...
and the Intel 8088
Intel 8088
The Intel 8088 microprocessor was a variant of the Intel 8086 and was introduced on July 1, 1979. It had an 8-bit external data bus instead of the 16-bit bus of the 8086. The 16-bit registers and the one megabyte address range were unchanged, however...
respectively. The buses exchanged information via a shared memory.
When not executing 8-bit code, the was used for floppy disk access. The 8088 bus was used for control of all other subsystems, including graphics, hard disk access, and communications. While it may have been theoretically possible to load Z80 binary code into the Rainbow to execute alongside 8088 code, this procedure has never been demonstrated.
Memory
The 100A model shipped with memory on the motherboard, while the 100B had 128 KB memory on the motherboard. DaughterboardDaughterboard
A daughterboard, daughtercard or piggyback board is a circuit board meant to be an extension or "daughter" of a motherboard , or occasionally of another card...
s were available from Digital Equipment Corporation
Digital Equipment Corporation
Digital Equipment Corporation was a major American company in the computer industry and a leading vendor of computer systems, software and peripherals from the 1960s to the 1990s...
that could increase system memory with up to an additional .
Floppy disk drives
The floppy disk drives, known as the RX50, accepted single-sided, quad-density 5¼-inch diskettes. Initial versions of the operating systems on the Rainbow did not allow for low-level formatting, requiring users to purchase RX50 media from Digital Equipment CorporationDigital Equipment Corporation
Digital Equipment Corporation was a major American company in the computer industry and a leading vendor of computer systems, software and peripherals from the 1960s to the 1990s...
. However, later versions of MS-DOS
MS-DOS
MS-DOS is an operating system for x86-based personal computers. It was the most commonly used member of the DOS family of operating systems, and was the main operating system for IBM PC compatible personal computers during the 1980s to the mid 1990s, until it was gradually superseded by operating...
and CP/M
CP/M
CP/M was a mass-market operating system created for Intel 8080/85 based microcomputers by Gary Kildall of Digital Research, Inc...
allowed formatting of diskettes.
Of note was the single motor used to drive both disk drives via a common spindle, which were arranged one on top of the other. That meant that one disk went underneath the first but inserted upside-down. This earned the diskette drive the nickname "toaster". The unusual orientation confused many first-time users, who would complain that the machine would not read the disk.
Hard disks
Digital Equipment CorporationDigital Equipment Corporation
Digital Equipment Corporation was a major American company in the computer industry and a leading vendor of computer systems, software and peripherals from the 1960s to the 1990s...
produced a Winchester disk controller for the Rainbow capable of controlling hard disks compatible with the ST-506
ST-506
The ST-506 was the first 5.25 inch hard disk drive. Introduced in 1980 by Seagate Technology , it stored up to 5 megabytes after formatting and cost $1500. The similar 10 MB ST-412 was introduced in late 1981. Both used MFM encoding...
interface. The controller, however, was limited to a single drive with up to and including and , limiting storage to a maximum of .
Third-party hard-disk controllers were also available.
Graphics
The base Rainbow system was capable of displaying text in 80×24- or 132×24-character format in monochrome only. The system could apply attributes to text including bolding, double-width, and double-height-double-width.The graphics option was a user-installable module that added graphics and color display capabilities to the Rainbow system. The Graphic module was based on a NEC 7220 graphic display controller (GDC) and a 8×64 KB DRAM video memory.
Due to the design of the graphics system, the Rainbow was capable of controlling two monitors simultaneously, one displaying graphics and another displaying text.
Display
The base Rainbow system generates a TTL composite-videoComposite video
Composite video is the format of an analog television signal before it is combined with a sound signal and modulated onto an RF carrier. In contrast to component video it contains all required video information, including colors in a single line-level signal...
signal in monochrome mode. With the inclusion of the graphics option, the Rainbow could also output sync-on-green RGB video signals at TTL levels. The Rainbow was most often coupled with the 12-inch VR201 monochrome monitor or the 13-inch VR241 color monitor, both produced by Digital Equipment Corporation
Digital Equipment Corporation
Digital Equipment Corporation was a major American company in the computer industry and a leading vendor of computer systems, software and peripherals from the 1960s to the 1990s...
.
Keyboard
The Rainbow 100 and the other two microcomputers which DEC announced at the same time (DECmate II and Pro-350) had two quirks that annoyed conservative users. The LK201LK201
The LK201 was a detachable computer keyboard introduced by Digital Equipment Corporation of Maynard, Massachusetts in 1982. It was first used by Digital's VT220 ANSI/ASCII terminal and was subsequently used by the Rainbow-100, DECmate-II, and Pro-350 microcomputers and many of Digital's computer...
keyboard used a new layout that made some ASR33
ASR33
The Teletype Model ASR-33 was a very popular model of teleprinter. Introduced about 1963 by Teletype Corporation and designed for light-duty office use, it was less rugged and less expensive than earlier Teletype machines or its heavy-duty cousin, the Model 35-ASR.The Model 33's printing mechanism...
and VT100
VT100
The VT100 is a video terminal that was made by Digital Equipment Corporation . Its detailed attributes became the de facto standard for terminal emulators.-History:...
users unhappy. However, the VT220 style of this keyboard can clearly be seen in the layout of the enhanced 101-key keyboard adopted by IBM in 1987.
Third-party
Third-party upgrades were also available, including an 80286Intel 80286
The Intel 80286 , introduced on 1 February 1982, was a 16-bit x86 microprocessor with 134,000 transistors. Like its contemporary simpler cousin, the 80186, it could correctly execute most software written for the earlier Intel 8086 and 8088...
(286) processor upgrade (Turbow-286), a 3.5-inch disk adapter kit (IDrive), and a battery-backed clock chip (ClikClok), all from Suitable Solutions.
In 1984, the first computer support for Native American languages began with the Rainbow 100. Rock Point Community School
Rock Point Community School
Rock Point Community School is a school in Rock Point, Arizona. It is controlled by the community and contracted out to the Bureau of Indian Affairs under the Indian Self Determination and Education Assistance Act. It employs some 120 faculty members. It is split into elementary and secondary ...
on the Navajo reservation in Arizona commissioned a ROM chip for the Navajo language, enabling the school to create bilingual computer programs.
Software
A benefit of the Rainbow was that it could continue to run 8-bit8-bit
The first widely adopted 8-bit microprocessor was the Intel 8080, being used in many hobbyist computers of the late 1970s and early 1980s, often running the CP/M operating system. The Zilog Z80 and the Motorola 6800 were also used in similar computers...
CP/M
CP/M
CP/M was a mass-market operating system created for Intel 8080/85 based microcomputers by Gary Kildall of Digital Research, Inc...
software as users moved into the 16-bit
16-bit
-16-bit architecture:The HP BPC, introduced in 1975, was the world's first 16-bit microprocessor. Prominent 16-bit processors include the PDP-11, Intel 8086, Intel 80286 and the WDC 65C816. The Intel 8088 was program-compatible with the Intel 8086, and was 16-bit in that its registers were 16...
world of MS-DOS
MS-DOS
MS-DOS is an operating system for x86-based personal computers. It was the most commonly used member of the DOS family of operating systems, and was the main operating system for IBM PC compatible personal computers during the 1980s to the mid 1990s, until it was gradually superseded by operating...
. The disadvantages were that little DOS software was released on Rainbow media, and there were subtle differences between Rainbow's MS-DOS implementation and MS-DOS (or PC-DOS
PC-DOS
IBM PC DOS is a DOS system for the IBM Personal Computer and compatibles, manufactured and sold by IBM from the 1980s to the 2000s....
) running on true IBM PC compatible
IBM PC compatible
IBM PC compatible computers are those generally similar to the original IBM PC, XT, and AT. Such computers used to be referred to as PC clones, or IBM clones since they almost exactly duplicated all the significant features of the PC architecture, facilitated by various manufacturers' ability to...
s. Towards the end of its life, Rainbow users were able to run IBM PC-compatible MS-DOS software using an emulation application called Code Blue.
MS-DOS compatibility was added late in the design, so hardware interrupts and MS-DOS software interrupts overlapped. One DEC documentation pack for developers included a listing of Microsoft assembly code to handle this. The theory was that hardware interrupts would interrupt again but software interrupts would only happen once.
DEC itself ported Microsoft
Microsoft
Microsoft Corporation is an American public multinational corporation headquartered in Redmond, Washington, USA that develops, manufactures, licenses, and supports a wide range of products and services predominantly related to computing through its various product divisions...
Windows 1.0
Windows 1.0
Windows 1.0 is a 16-bit graphical operating environment, developed by Microsoft and released on 20 November 1985. It was Microsoft's first attempt to implement a multi-tasking graphical user interface-based operating environment on the PC platform. Windows 1.0 was the first version of Windows...
to the Rainbow. There was also a third-party upgrade that included a 286 processor board and a modified version of Windows 3.0
Windows 3.0
Windows 3.0, a graphical environment, is the third major release of Microsoft Windows, and was released on 22 May 1990. It became the first widely successful version of Windows and a rival to Apple Macintosh and the Commodore Amiga on the GUI front...
.
External links
- [ftp://ftp.update.uu.se/pub/rainbow/ Uppsala University Update Computer Club Rainbow archives]
- Vintage-Computer page on the DEC Rainbow 100
- Rainbow 100 Frequently Asked Questions