Vintage PC pages
Home -> Vintage PCs -> Compaq Portable II

The Compaq Portable II


Hardware-wise, the Portable II is very similar to the original Portable, though smaller. Instead of being XT-compatible like the Portable, it's AT-compatible, with a 286 processor, a real time clock, a 16-bit ISA bus, and so forth.

According to the service manual, there are two versions of the motherboard. They are functionally equivalent but the second is physically smaller. There is a socket on the underside of the motherboard for a memory expansion board; alternatively, memory can be expanded by plugging in an ISA card.

The video card has the same capabilities as the one in the Portable and Deskpro, though it's a later version of the design (Assembly no. 000525).

As with the Deskpro, the video card can can be made to display text attributes like an MDA does (ie, you only get bright and underlined) rather than in 15 shades of green. This feature only applies in the high-resolution mode, and it's selected by setting bit 7 of the CGA control register (port 03D8h).


The keyboard controller is most likely the same 106436-001 as used in the Portable III (documented here). If so, then it will support XT and AT keyboard types, auto-sensing the protocol used.

The keyboard controller supports the following Compaq-specific commands (for more details see table P0401 in the Interrupt List, file PORTS.A):

Set 6MHz speed
Set 8MHz speed
Set 16MHz speed
Toggle CPU speed
Special read (get keyboard type and other values). In the value returned:
	Bit    5 set for XT keyboard, clear for AT.
	Bits 2,3 give CPU speed.
		 Bits 2 and 3 set:  8 MHz
		 Bit  2 set:       16 MHz
		 Else:              6 MHz (if available; see below).
Set CPU speed limit. Followed by one byte giving the new limit (0 or 1).

On some motherboards(?), port 86h also seems to be involved in CPU speed switching. When read:

	If bits 6 and 7 are set, CPU speed is 16MHz, slowing to 8MHz during 
                              floppy access.
	If bit 3 is set,   8MHz and 16MHz are available.
		    clear, 6MHz, 8MHz and 16MHz are available.

When the CPU speed is being set, this port is used if the value read had bit 3 set. Various permuations of bits 5,6,7 are then used to select the speed.


There are two drive bays. The upper one holds an ATA hard drive. On my Portable II, this is actually a Miniscribe MFM hard drive with an ATA-to-MFM bridgeboard bolted to its underside. The lower bay holds a slimline 5.25" floppy drive (mine has a 360k one, but the service manual also has part numbers for 1.2M and 1.4M drives). There are two types of 5.25" drive; "flip door" and "push button".

The physical arrangement of the drive enclosure also allows a twin-floppy configuration, with a second floppy drive in the upper bay.

The following hard drive types are supported by the BIOS. Any others would need a drive overlay to be installed:

TypeCylindersHeadsSectorsCapacityLanding zoneWrite precompensationControl byte
130641710.2 M3051280x00
261541720.4 M6381280x00
361561730.6 M6151280x00
4102481768.0 M10235120x00
594061746.8 M9395120x00
669751728.9 M6961280x00
746281730.7 M5112560x00
892551738.4 M9241280x00
99001517112.1 M899-10x08
1098051740.7 M980-10x00
1192571753.7 M9241280x00
1292591769.1 M9241280x08
1361281740.6 M6112560x00
1498041732.5 M9801280x00
150000.0 M000x00
1661241720.3 M61200x00
1798051740.7 M9801280x00
1896651740.1 M9661280x00
19754111768.8 M753-10x08
2073351730.4 M7322560x00
2173371742.6 M7322560x00
2280561740.1 M805-10x00
2392481761.4 M924-10x00
249661417112.3 M966-10x08
259661617128.3 M966-10x08
2610231417118.9 M1023-10x08
27966101780.2 M966-10x08
28748161799.3 M748-10x08
2980562661.3 M805-10x00
3061542530.0 M6151280x00
3161582560.1 M6151280x00
3290592599.4 M9051280x08
3374883499.3 M748-10x00
34966734112.3 M966-10x00
35966834128.3 M966-10x00
36966934144.3 M966-10x08
3796653480.2 M966-10x00
386111663300.7 M611-10x08
3910231133181.3 M1023-10x08
4010231534254.8 M1023-10x08
4110231533247.3 M1023-10x08
4210231663503.5 M1023-10x08
4380542640.9 M805-10x00
4480522620.4 M805-10x00
4574883396.4 M748-10x00
4674863372.3 M748-10x00
4796652559.0 M9661280x00


The Portable II has 32k of BIOS in two 16k chips.

John Elliott 16 May 2009.