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TITLE: Product Preview: Compaq's Deskpro 386


                   The Compaq Deskpro 386

A high-performance PC AT-compatible system based on Intel's 80386

                 by Dennis Allen & Tom Thompson

About a year ago, Intel began selling samples of its latest-
generation microprocessor, the 80386 (see the November 1985 BYTE,
page 9). After much anticipation this processor has finally made
its way into the design of several new microcomputer systems.
Compaq, the Houston-based manufacturer widely known for its IBM-
compatible computers, has introduced one of the first such
systems, the Compaq Deskpro 386. The new Compaq machine was
designed to be compatible with 80286-based systems, such as the

IBM PC AT, yet take advantage of the 80386's processing power for
better performance. Like the PC AT, the Deskpro 386 was also
designed to run much of the existing software written for the
older 8086/8088 Intel microprocessors.


System Description

From the outside, the Deskpro 386 is spartan in design. The
system is housed in an IBM PC AT-style box with indicator lights,
a security key, and space for up to four half-height disk drives
or other storage devices. The back panel of the system unit has a
9-pin serial port and a 25-pin parallel printer port.  The system
comes with your choice of a standard 84-key PC keyboard or the
Compaq Enhanced Keyboard, an IBM RT PC-style 101-key keyboard.
   The standard configuration, called the Model 40, sells for
$6499 and includes 1 megabyte of RAM, a 1.2-megabyte floppy disk
drive, and a 40-megabyte hard disk. Compaq also offers a system
configured with a 130-megabyte hard disk (instead of the 40-
megabyte hard disk) called the Model 130, which sells for $8799.

   Because no production machines were available at press time,
we examined a preproduction Model 40 that had an additional
megabyte of RAM (for a total of 2 megabytes), 360K floppy disk
drive, 40-megabyte tape cartridge unit, and  color graphics
adapter. The system used MS-DOS 3.1.
   Inside the machine is a 192-watt power supply, a fan, and a
single motherboard. The motherboard contains a real-time clock
with  battery backup, seven expansion slots, the CPU, and a 32-
bit slot occupied by the System Memory Board.  Four of the
expansion slots are full-size 8-/16-bit slots, and three are 8-
bit slots, two of which are full size and one half size.
Compaq's multipurpose disk controller, which is included with the
base system, occupies one of the full-size 8-/16-bit expansion
slots.  The disk controller supports two 1.2-megabyte floppy disk
drives, a 40-megabyte hard disk, and either a second 40-megabyte
hard disk or a 40-megabyte tape backup unit.  The Model 130
requires an additional drive controller in one of the full-size
8-/16-bit expansion slots for the 130-megabyte hard disk.















Unleashing the 80386

The CPU is a version B1 80386 microprocessor running at 16 MHz.
The 80386 has built-in memory management and supports a numeric
coprocessor, but the motherboard has a socket for only a 4- or 8-
MHz 80287 -- not an 80387. The 80386 uses two separate 32-bit
buses for addressing and data. The processor can dynamically size
its data bus to handle 32-bit or 16-bit data bus operations.

Also, the address bus can be pipelined: that is, the processor
can perform address decoding for the next bus operation during
the previous bus cycle, allowing for overlap of bus activity.
   To tap the performance potential of the 80386, Compaq designed
a high bandwidth CPU bus and memory bus. The CPU bus is a 32-bit
non-multiplexed address and data bus. This bus provides signals
for interfacing to both the 32-bit memory bus and the 8-/16-bit
expansion bus. In the event of bus contention between the memory
bus and the expansion bus, the memory bus has priority. The
expansion bus is electrically compatible with existing plug-in
cards for the  PC AT. However, we did not test any plug-in cards
in the system.
   The memory bus provides the bandwidth necessary to take
advantage of the 80386's speed and bus pipelining. It uses a
paged memory architecture to improve access times. The memory bus
does not include I/O status or control signals, and it is not
intended to be used as a general-purpose bus. The maximum
physical memory this bus can address is 16 megabytes.  However,
using Compaq options, you can expand the system only to 10
megabytes of RAM on the 32-bit bus.



Faster Memory

Naturally, a faster memory bus requires faster memory. For this,
the System Memory Board is equipped with 36 256K-bit static-
column RAM chips soldered directly to the board, for a total of 1
megabyte of memory with 4 bits for parity. Using this arrangement
with 100-nanosecond RAM reduces the number of wait states
required for memory access in the paged mode to nearly 0. Memory
cells within the same physical page can be rapidly accessed by
keeping the row address of the RAM constant while modifying the
column address.  For such consecutive memory fetches within a
page, access times can be as low 50 nanoseconds. During nonpaged
operations, access times are about 100 nanoseconds. A PC AT, on
the other hand, is equipped with 150-ns RAM.
   The System Memory Board has sockets for another megabyte of
RAM chips, which cost $549. Additional memory must be added in 1-
megabyte increments. When upgrading memory, you must change a set
of 9-pin jumpers on the memory board. You can also set the

jumpers to reduce the 640K-byte base memory of the system to 512K
or 256K.
   A special expansion board can be piggybacked on the System
Memory Board to bring the total memory to 4 megabytes using 256K-
bit chips. Compaq also offers a piggyback board with 4 megabytes












of RAM using 1-megabit chips for $2999. This board has sockets
for another 4 megabytes of RAM ($2699), again using the 1-megabit
chips. A fully populated System Memory Board (2 megabytes) and

expansion board using 1-megabit chips (8 megabytes) give you a
total of 10 megabytes of 32-bit high-speed memory. You could also
use two 16-bit boards configured with 2 megabytes each to bring
the Deskpro 386 to a maximum of 14 megabytes using Compaq
options. In doing so, however, you would lose the speed advantage
of the 32-bit memory bus.


The Virtual Machine

An important feature of the 80386 CPU is its virtual mode. This
mode, combined with memory paging, allows a real mode environment
(64K-byte segments, 1 megabyte of physical address space, no
memory protection) to be emulated anywhere within the 80386's
physical address space of 4 gigabytes. The virtual mode also
features I/O protection so that the host operating system can
imitate various I/O ports. Compaq claims to have successfully
"virtualized" an 8086 machine in the Deskpro 386.  In other
words, MS-DOS programs should run on the Deskpro 386 with little
or no modification. More importantly, ill-behaved programs --

that is, programs that read or write directly to hardware I/O
ports rather than using DOS functions -- should operate properly.
   To access memory beyond the 640K of base memory under MS-DOS
control, the Deskpro 386 uses a proprietary software driver
called the Compaq Extended Memory Manager (CEMM). The CEMM takes
advantage of the 80386's memory paging features to emulate the
Lotus-Intel-Microsoft (LIM) expanded memory specifications in the
Deskpro 386's 32-bit memory system.  In effect, it virtualizes an
Intel AboveBoard.  You can install the CEMM and define the memory
size (up to the 8-megabyte LIM limit) using the MS-DOS
configuration file, CONFIG.SYS.  Using the CEMM with the Deskpro
386's 32-bit memory should result in favorable speeds compared to
using the LIM specifications with a 16-bit memory board.

This virtual machine arrangement promises to resolve possible
software compatibility problems with existing 8086/8088 and 80286
real mode programs, at least in the single-user mode. In fact,
the 80386's virtual mode will allow copies of different operating
systems to execute real mode applications concurrently with
memory protection and privilege control. But, for now at least,

Compaq does not support host software that allows different
operating systems to run concurrently.


System Speed Control

Another obstacle to software compatibility are programs using
time-dependent code that relies on the computer system to be
operating at a particular speed. Copy-protection schemes and
certain program displays (typically games) fall in this category.
Compaq's answer to this problem is the Deskpro 386's simulated
System Speed Control.
   The speed control is accomplished by lengthening the refresh
cycles on the system bus, effectively slowing the CPU. However,
lengthening of the refresh cycles is done in a way that does not
interfere with direct memory access transfers or the bus
bandwidth. The Deskpro 386 normally operates in an automatic mode
where the CPU speed is reduced to 8 MHz -- essentially mimicking
a PC AT -- each time a program accesses a floppy disk drive. The
system resumes its high-speed operation as soon as the disk I/O

is finished.
Performance is not degraded, since the system must wait on the
slower disk drive.
   An MS-DOS command, MODE, allows you to manually select a
system speed. You can select 4-MHz 8088, 6- or 8-MHz 80286, or
16-MHz 80386 system speeds using this command. The speed remains
the same (even through a keyboard reboot) until you alter the
setting, or a power-on reset occurs.


Fast Disk Drives

To complement the Deskpro 386's data processing performance,
Compaq selected high-speed disk drives for the system.  The 40-
megabyte hard disk has an average access time of under 30
milliseconds, and the 130-megabyte hard disk's average access
time is under 25 milliseconds.  In contrast, the PC AT's 20-
megabyte hard disk has an average access time of 40 milliseconds.
Data transfer rates are 5 megabits per second (same as the PC
AT's 20-megabyte hard disk), and 10 megabits per second,

respectively.
   For hard disk backups, the 40-megabyte tape drive has a
transfer rate of 500 kilobits per second, which is about twice
the speed of the drive previously offered for the Deskpro line of
computers. The tape drive uses a new DC2000 tape cartridge,
unlike its predecessors, which used the DC1000. However, the
Deskpro 386 can read, but not write to, the older tape
cartridges.


Display Adapters

The system we examined was equipped with Compaq's new Enhanced
Color Graphics Board ($599), which also made use of the system's
virtual mode. The graphics board provides 640 by 350 resolution
with 16 simultaneous colors, and it is also compatible with IBM's
EGA. Although the graphics board has only an 8-bit data path, the
system cleverly relocates the board's ROM to the 32-bit RAM area.
As a result, Compaq claims, graphics execution speed is increased
by about four times.  (The system also relocates the contents of

its 16-bit ROMs to the 32-bit RAM area for speed improvement.)
To go with the color board, Compaq offers a 13-inch RGB color
monitor for $799.
   In a departure from previous Compaq systems, the Deskpro 386
does not include a monochrome display controller. Instead, the
company sells its Video Display Controller Board separately for
$199. It provides the same video control as that found in other
Compaq systems and is compatible with IBM's Color Graphics
Adapter. The controller board can be used with either an RGB
monitor (such as Compaq's), a composite color monitor, or
Compaq's Dual-Mode Monitor, a monochrome monitor that sells for
$255.


Compatibility and Performance

The 80386 CPU is object-compatible with 8086/8088 and 80286 code.
To examine how well Compaq implemented this capability, we first
ran several programs that we considered thorough in their use of
memory and I/O operations.  The BASICA on the machine accepted

and ran the IBM PC tokenized versions of two BYTE benchmark
programs (SIEVE and CALC) without problems. The programs
conveniently provided us with a performance estimate.
   The results of these preliminary benchmarks are impressive
when compared to a 6-MHz PC AT.  Generally, the Deskpro 386 ran
about three to four times faster.  We also compared the Deskpro
386's times to those of a PC AT specially equipped with 100-ns
memory running at 11.5 MHz, and the Deskpro 386 was about twice
as fast.
   Next, we compiled several small C programs with Manx's Aztec
C, version 3.20C, using the small memory model. We used the two
floppy disk drives to compile and link the programs without any
problems.  Not only did these programs run flawlessly; they ran
quicker than we had ever seen before.
   We then ran two programs that are considered ill-behaved in
their use of DOS: the XyWrite editor, version 3.05, with
SideKick, version 1.52A, resident. The XyWrite editor responded
correctly to the cursor and function keys, and SideKick responded
properly when invoked.


   Admittedly, these tests were less than comprehensive.  But
they do indicate a high level of software compatibility.
   Unfortunately, the only operating system offered for the
Deskpro 386 at press time was MS-DOS. Only a true 32-bit
operating system could push the machine to its limits. Compaq did
say that it would offer Microsoft's XENIX System V/386 during the
first quarter of 1987. [And Microsoft said a software-development
toolkit for XENIX 386 is ready now.] According to Compaq, the new
XENIX will be demand paged and allow multitasking operations. We
did not, however, see even a preliminary version of the package.















For a Select Few

A number of folks might benefit from using the Deskpro 386.
First, there are those who need the raw processing power to run
very large spreadsheets or simulations. The linear address space
provided by the 80386 combined with the Deskpro 386's processing
speeds not only make such work possible but also bearable. And
large complicated programs, such as expert systems, should run
with respectable performance on this machine.  There are also
software developers who need a high-performance machine to
shorten their development cycle.  Here, the fast storage devices
are particularly helpful.  Moreover, the system's 80386 CPU
allows developers to begin writing the next generation of
software.  And for others, the large storage capacity of the
Model 130 and its claimed compatibility with networking software
should make it a high-powered file server.

   But like any new system, the Deskpro 386 is not without some
disappointments.  Although CAD and desktop publishing are likely
candidates for development on the machine, with no I/O signals on
the memory bus and the CPU's 32-bit bandwidth to peripherals
effectively halved by the expansion bus, we don't see the Deskpro
386 as a serious threat in the high-speed graphics workstation
arena.  Also, the Deskpro 386 seems like overkill in single-user
mode. Certainly, a multitasking 32-bit operating system would put
the system to fuller use.
   Surely, more powerful 32-bit peripherals and operating systems
are coming for the 80386-based systems.  For now, the Deskpro 386
appears to be a well-engineered bridge to a new generation of
those machines.



[Dennis Allen and Tom Thompson are technical editors at BYTE.]
its predecessors, which used the DC1000. However, the
Deskpro 386 can read, but not write to, the older tape
cartridges.


Display Adapters

The system we examined was equipped with Compaq's new Enhanced
Color Graphics Board ($599), which also made use of the system's
virtual mode. The graphics board provides 640 by 350 resolution
with 16 simultaneous colors, and it is also compatible with IBM's
EGA. Although the graphics board has only an 8-bit data path, the
system cleverly relocates the board's ROM to the 32-bit RAM area.
As a result, Compaq claims, graphics execution speed is increased
by about four times.  (The system also relocates the contents of

its 16-bit ROMs to the 32-bit RAM area for speed improvement.)
To go with the color board, Compaq offers a 13-