The Compaq Portable 386 is a computer released by Compaq Computer Corporation in 1987.  It was equipped with a 20 MHz Intel 80386 CPU, 1 MB RAM, 16 KB ROM, 1.2 MB 5¼-inch floppy, 40 or 100 MB hard disk drive, priced at US$7,999 or 9,999 respectively, and a 10" amber gas-plasma display.  
 Early versions of the Compaq Portable 386 were sold with the Compaq Portable III case and badges. A differing screen bezel stating "386/20" was the only externally visible change.
 Network General resold a customized version of the Compaq Portable 386 as the "Sniffer" Network Analyzer.
 The Portable 386 got its name due to the socketed Intel 386DX CPU with 20MHz. There is also an additional socket for a 20MHz 387 FPU option, which was not included in the basic configuration of the Portable. Since the whole system bus runs with CPU frequency, there is no way to improve the CPU performance by installing a 386DX CPU with more than 20MHz other than the rare Cyrix 486DRx2 20/40 which has a multiplicator of 2 for the frequency while being still pinout compatible with the 386 socket.
 The mainboard can take up to four proprietary 512KB SIMMs which were called SC-RAM in the Portable manual. Additionally, there was an expansion slot inside the Portable which allowed to expand the memory by another 8MB alongside the 2MB on the mainboard by:
 Installing the so-called 32bit Memory-/Modem board expansion offers a socket for another expansion card which has 4MB (8×512 KB 80 ns) of memory and another expansion socket installed on which the user can install a 3rd expansion card with another 4MB (again 8×512 KB 80 ns) of RAM. These RAM expansion cards were available through Compaq or third party manufacturers, such as Kingston Technology.
 The graphics card can be configured between CGA and MDA emulation mode whereas the CGA mode is mandatory for using Microsoft Windows' Compaq Plasma Driver and graphic capabilities in general. The internal CGA graphics card is able to display a resolution up to 640x400 pixels with a color depth of 2 bits (monochrome), which was first seen in the AT&T 6300 built by Olivetti, surpassing the original IBM standard by 200 pixels in height while remaining fully CGA compatible elsewhere. 
 The internal gas plasma display is able to display 640x400 pixels with up to 16 shades of gray and is connected to the graphics card via a proprietary connector. Users can install a better graphics card via the Compaq Expansion Unit (See below), but the factory-installed monitor was unable to take advantage of it.
 The Portable offers two drive bays for 5.25" half-height drives where one is reserved for the hard disk and the other one for the internal floppy disk drive. Compaq originally offered a 40MB and 100MB hard disk option. Quite common back in the days, the BIOS of the Compaq only offers to select preconfigured hard disk configurations like Type 17 for 40MB or 42 for 504MB. There is no detailed information about the underlying CHS configuration of these types, but some basic information on the drive numbers and their specs is available (See table). The device suffers from the wide-spread CHS barrier, not allowing hard disk drives greater than 504MB.
 COMPAQ PORTABLE 386 HARD DRIVE TYPES 
 In its basic configuration, Compaq offered only a single 5.25" 1.2MB floppy disk drive aside of the 40MB hard disk drive, but there was also a cheaper option for a secondary 5.25" 360KB floppy disk drive instead of the hard disk. Giving the fact that the Portable uses a standard floppy drive connector and has built-in support in the BIOS, one can easily replace the 5.25" with a 3.5" 1.44MB drive.
 In order to better position the Portable as a professional office computer, Compaq also offered multiple external expansion which can be installed on the back of the Portable while the device is turned off.
 Compaq offered multiple expansion cards for the Portable 386, which can be installed inside the main housing. Similar to the external expansions, these internal expansion cards cannot be exchanged while the device is turned on.
 The BIOS setup utility is not preinstalled in an EPROM chip, but comes on a single floppy disk. If a user is no longer owning such a disk, it can be still easily found at archive.org/details/CompaqPortableDiagnosticDisk
 Compaq bundled Compaq-DOS in version 3.31 with the Portable 386, a variant of MS-DOS 3.2 which already offered support for FAT16 and hard disk partitions with more than 32MB. A Windows 2.01 OEM version was also available which makes use of the 386 memory management. There was also a User Programs disk bundled with the Portable which offers tools for memory management and adapting the CPU speed (between 6, 8 and 20MHz):
 
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