Compaq Portable 386
| Company type | Public |
|---|---|
| Industry | Computer hardware |
| Founded | February 16, 1982 |
| Founder | Rod Canion, Jim Harris, Bill Murto |
| Headquarters | Houston, Texas , United States |
| Products | Personal computers, portable computers |
The Compaq Portable 386 was introduced by Compaq Computer Corporation in 1987, equipped with an Intel 80386 processor. It came standard with RAM, ROM, a floppy disk drive, and offered options for a hard disk, priced between $7,999 and $9,999. A notable feature was its unique 10-inch amber gas-plasma screen.
Early versions maintained the chassis and branding of the Compaq Portable III, with the only visible modification being a "386/20" label on the bezel surrounding the display.
Network General released a specialized iteration of this model named the "Sniffer" Network Analyzer, designed specifically for network diagnostic purposes.
Processor and Math Coprocessor
The Portable 386 derives its name from the socketed Intel 386DX CPU operating at 20MHz. An optional socket for a 20MHz 387 FPU was available but not part of the standard package. Because the system bus speed matches the CPU frequency, upgrading to a faster 386DX does not improve performance unless using the uncommon Cyrix 486DRx2 20/40, which doubles the clock speed while remaining compatible with the 386 socket.
Memory
The motherboard accommodates up to four proprietary 512KB SC-RAM SIMM modules. Memory capacity can be increased beyond the base 2MB by utilizing an internal expansion slot designed for a 32bit Memory-/Modem board expansion. This expansion provides sockets for two additional RAM cards of 4MB each. These memory modules were available through Compaq as well as third-party vendors like Kingston Technology.
Video hardware
The graphics adapter supports configurable modes emulating both CGA and MDA. CGA mode is required for running Microsoft's Windows Compaq Plasma Driver and general graphical applications. The display resolution reaches up to 640x400 pixels with 2-bit monochrome depth, exceeding IBM's original CGA vertical resolution while maintaining compatibility. The internal gas plasma display renders 640x400 pixels with up to sixteen shades of gray using a proprietary interface. Although users could connect enhanced graphics cards via the Compaq Expansion Unit, these external cards could not output to the built-in monitor.
Storage
The Portable features two half-height 5.25" drive bays: one dedicated to a hard disk and one housing an internal floppy disk drive. Compaq provided hard drives in capacities of 40MB and 100MB. The BIOS supports only certain predefined hard disk types (e.g., Type 17 corresponds to 40MB, Type 42 supports up to 504MB), imposing a maximum drive size limit of 504MB due to standard CHS geometry constraints. The table below summarizes supported hard disk configurations:
COMPAQ PORTABLE 386 HARD DRIVE TYPES
Type | Cylinders | Heads | Sectors | Write Precompensation | Landing Zone -----|-----------|-------|---------|-----------------------|-------------- 1 | 306 | 4 | 17 | 128 | 305 2 | 615 | 4 | 17 | 128 | 638 … (additional types omitted for brevity) 42 | 1023 | 16 | 63 | -1 | 1023
These specifications illustrate inherent limitations affecting storage expansion on the Portable 386 system.
Floppy Drive
The default configuration included a single internal 5.25" floppy drive capable of reading and writing at 1.2MB alongside a 40MB hard disk drive. Alternatively, customers could opt for a less expensive setup replacing the hard disk with a second internal 5.25" floppy drive supporting only 360KB capacity. The standard floppy connector and BIOS support allowed users to swap out the original drive for a more modern internal 3.5" floppy disk drive with a capacity of up to 1.44MB.
Options for External Expansion
To boost its functionality as a professional office computer, Compaq provided several external expansion modules that could be attached to the back of the Portable when it was powered down.
- Compaq Expansion Unit
- This accessory introduced two full-length 16-bit ISA slots. Compaq highlighted ISA cards such as the COMPAQ-VG-Controller card, which supported enhanced display modes including 720×400 text and 640×480 graphics with up to 256 colors simultaneously on an external Compaq VG display.
- Compaq Expansion Unit with 40MB Tape Drive
- A variation designed specifically to accommodate a 40MB tape drive, this unit resembled the ISA expansion physically but contained only the tape drive bay.
Options for Internal Expansion
The Portable 386 supported various internal expansion cards installed inside its main chassis, requiring the system to be turned off before installation or removal.
- 32-bit Memory/Modem Carrier Board
- Serving as a foundation for additional expansions, this carrier board also integrated a 2400 baud modem.
- 1-2MB Memory Expansion
- Mounted on the carrier board, this module provided 1MB of RAM along with two SC-RAM slots (each supporting 1MB). It was incompatible with the 4MB memory expansions due to connector constraints.
- 4MB Memory Expansion
- Also dependent on the carrier board, this card supplied 4MB of built-in RAM.
- Additional 4MB Memory Expansion
- Installed above the initial 4MB module, it added another 4MB, bringing total supported memory up to 10MB.
- Asynchronous Connection Extension
- Offered an RS232 port but could not be used simultaneously with the carrier board.
- 1200/2400 Baud Modem Kit
- Available in North America, this kit included a Hayes-compatible modem (operating at either 1200 or 2400 baud), its own carrier board, a housing cover featuring a modem connector, and a telephone cable.
BIOS
The BIOS configuration utility was not embedded in an EPROM chip but was instead supplied on a single floppy disk. Archived disk images can be found at archive.org/details/CompaqPortableDiagnosticDisk:
- 3.5" 720 KB edition: SP0308.EXE / SP0308.ZIP
- 5.25" 360 KB edition: SP0316.EXE / SP0316.ZIP
Software
The Portable 386 came preloaded with Compaq-DOS version 3.31, a custom variant of MS-DOS 3.2 that supported FAT16 and hard disk partitions exceeding 32 MB. An OEM release of Windows 2.01 utilized the advanced memory management capabilities of the 386 processor. The User Programs disk included utilities for managing memory and adjusting CPU speeds (6, 8, and 20 MHz):
- ADAPT.COM – a TSR utility for dynamic configuration of CGA/MDA character sets
- CACHE.EXE – Compaq Disk Cache software, functioning similarly to SmartDrive found in later MS-DOS versions
- CEMM.EXE (for 386 CPUs) / CEMMP.EXE (for 286 CPUs) – Compaq Expanded Memory Manager, incompatible with Windows 3.x
- CHARSET.COM – installs the THINUS font to enhance text rendering on the internal gas plasma display
- CLOCK.SYS – driver supporting the real-time clock of the Portable 386
- MODE.COM – replaces the standard MS-DOS MODE.COM, enabling commands such as "MODE SEL MDA", "MODE SEL CGA", "MODE SPEED HIGH", and "MODE SPEED LOW" to switch between graphics modes and CPU frequencies
- VDISK.SYS – virtual disk driver that uses RAM as storage