Classic Computer Magazine Archive CREATIVE COMPUTING VOL. 11, NO. 5 / MAY 1985 / PAGE 32

Compaq Deskpro versus IBM PC AT. (evaluation) Tom Badgett.

The Compaq Deskpro--affectionately called the "Texas AT" in some circles--provides heavy competition for the PC AT. This impressive hunk of iron isn't quite as high tech as the AT with its 80286 processor and 16-bit bus, but the Deskpro's 7 MHz 8086 and options give it good performance that stacksup especially well when the AT is unavailable.

The Deskpro is about a year old, and Compaq says sales are "superb." That wasn't the case in the fall when Compaq's thunder was muted by IBM's AT announcement. It seemed that even those users and dealers who hailed the Deskpro as a welcome addition to the PC compatible stable were wowed by the AT. The Deskpro fell on temporary hard times as the spotlight played on the AT.

Why AT?

There are at least four reasons for this attention. The first three are I, B, M. The fourth reason: the PC AT really is awesome. It is a big, fast, powerful micro with a lot of guts at an impressive price. The AT runs about two-and-a-half times as fast as the PC XT, thanks to its 6 MHz, true 16-bit, 80286 CPU. Hard disk storage can go to 40Mb. An improved keyboard, front panel keylock, up to 3Mb of RAM, and an onboard clock/calendar with battery backup round out the package.

The PC AT is offered in two basic configurations: The Model 68, a 256K floppy-based machine and the Model 99 with 512K, a 20Mb hard disk, and a serial/parallel I/O card. Options available from IBM include: memory expansion cards and chips, an additional 20Mb hard disk, 40-track floppy drive, math co-processor, various communications adapter cards, floor standing enclosure, and a tilt and swivel stand for the display monitor.

Or Deskpro?

The Deskpro specs are equally impressive. Its 16-bit 8086 processor normally runs at just over 7 MHz and executes most CPU-intensive tasks about twice as fast as standard IBM PC. The Deskpro comes in four basic configurations, each of which can be customized.

The model 1 is the basic unit, with 128K of RAM, a single disk drive, and either a green or amber 12" monitor.

The model 2 adds a second disk drive and 128K of RAM to the basic setup.

The model 3 has a 10Mb fixed disk and a clock/calendar/RS-232 board.

The model 4 adds a 10Mb tape cartridge backup unit and another 384K of RAM to the model 3.

You can expand any of the models to 640K of RAM on the motherboard. Other options include a clock/calendar/RS-232 board (standard on models 3 and 4), tilt-swivel monitor stand, and a 30Mb fixed disk. There are no official Compaq display adapter options because, like the earlier Portable, the Deskpro incorporates both graphics and text displays into the same card. Color attributes are displayed on the green or amber screen as shades of variable intnsity. Composite video, RF modulator, and RGB monitor outputs are standard equipment on all Deskpro models. Apparnelty, any third-party PC or PC/XT expansion card that works properly with the IBM machines will function wtih the Deskpro, expanding greatly the optional configurations possible with the machine. The Deskpro appears to be completely IBM compatible. All of the software we tried on it ran properly.

"We're more compatible with IBM than IBM," quipped Compaq spokesman Ken Price, apparently referring to compatibility problems some users are having with software and hardware products on the AT. In a few instances, products that don't "follow the rules" explicitly don't always run on the AT.

More Comparisons

Both Compaq and IBM have come up with winning successos to their basic machines. Both originals were winners, too. Some people chose the IBM PC for the name, the larger screen, or the keyboard. Others chose the Compaq for its size, protability, integrated text/graphics display, or keyboard. Similar choics are being made between the AT and the Deskpro.

Really, they are different machines, aimed at different audiences. The Deskpro is a faster, somewhat more powerful successor to the original Compaq Portable, and thus the PC and XT. The AT is that too, of course, but it also was conceived as a Xenix engine for multisuer and multitasking applications, and as a network server.

System Considerations

The 80286 CPU of the AT can address 16Mb of memory directly and one gigabyte of virtual memory using a built-in memory management capability. The CPU also has a built-in memory protection unit to keep mulit-users from interfering with one another.

To make use of the multi-user, multi-tasking abilities of the AT, IBM is depending on Xenix, a licensed derivation of AT&T's Unix distributed by Microsfot. This operating system is a multiuser, multitasking operating system tht fully exploits the 80286. Software applications from the Unix world apresumably could be brought up on the AT relatively easily. The real question is whether IBM will fully support the AT as a multiuser machine, and whether the user community is committed enough to Xenix to make it fly.

DOS 3.0 is the standard operating system for the AT. It is a patchwork upgrade of DOS 2.x--probably the last practical one without a major rewrite. It uses at least 12K more RAM than DOS 2.1, but it has some useful enhancements that obviously lean toward multiuser and network applications:

* Rudimentary file sharing.

* Block locking to restrict access to whole or portions of a file.

* Background printing that supports path and internal program calls.

* New DOS function calls for improved file management.

* VDISK program that uses RAM disk memory above IMb.

* Enhanced GRAPHICS screen dump utility for better printer support.

The 8086 CPU of the Deskpro lacks some of the sizzle of the 80286, but it is no slouch. It is a more powerful companion to the 8088 of the PC and XT. The difference between the two is that the 8088 can handle data in 8-bit chunks, while the 8086 can move things two bytes at a time. It is a true 16-bit processor. Both chips can address up to 1Mb of memory and could operate with a system clock speed of 8 MHz. IBM's PC, however, has a clock speed of 4.77 MHz. The Deskpro 8086 operates at 7.1 MHz. The faster system speed coupled with its ability to move data two bytes wide makes for a quick CPU. It isn't as fast in CPU-intensive operations as the AT, but the difference is small--about 25% according to Compaq. Tests with Basic timing loops and prime number generators support that claims.

Compaq says if both units have math coprocessors the DEskpro is faster than the AT. We didn't have access to the math chips to test that one. The Deskpro is more than twices as fast as the PC XT. A keyboard "soft switch" will slow down the system clock to a fully compatible 4.77 MHz to accommodate software that uses software timing loops or has other requirements for the IBM compatible clock. A front-panel LED glows red in this "common" or slowed down condition. When things are running at full speed, the LED is green.

Comparing operations that involve disk I/O is more difficult because of the many configuration variables on the Deskpro, and a slightly slower disk read/write routine in DOS 3.0 DOS 2.11 is standard with the Deskpro, and it has some custom Compaq enhancements to handle the tape backup chores. RAM-resident Microsoft GWBasic also is part of the package. The smaller 10Mb Compaq hard disk is slower than the 20Mb IBM unit with its 40ms access time. However, the Compaq 30Mb unit we tested is as fast or faster.


Computer keyboards always cause a great deal of end user comment. The ones with the AT and the Deskpro are no exception.

The AT keyboard is a winner. The large Enter and Shift keys are where they belong and have word labels as well as symbols. Several keys have been moved, but you probably won't notice the change until you look for the Escape key. It is above the number keypad on the right of the keyboard. Whether this is a curse or a blessing depends on whether you use the Esc key regularly, or merely stumble over it when you mean to press Tab. The most useful change is getting the Prtsc/key away from the right Shift and Enter keys where you can tap it by mistake and lock up your system. A SysReq key has been added to help future Xenir users choose multitasking modules.

Other keyboard enhancements include status indicators for the Num Lock, Caps Lock, and Scroll Lock keys. The action on the new keyboard is very much the same as the old keyboard with perhaps slightly less spring pressure.

The Deskpro keyboard sticks to the original PC layout, adding LED indicators on Caps Lock and Num Lock keys. The action is drastically different. With the Deskpro, Compaw switched to rubber dome technology, abandoning the controversial double spring, two-level keys of the Portable. To long-term PC and XT users, the Deskpro keyboard will seem impossible at first. It is absolutely quiet, for one thing, and it has a soft--very soft--feel. The difference between the Compaq portable and the Deskpro is less noticeable, and if you are a regular user of the new PCjr keyboard, as I am, you'll feel right at home. The technology is the same, and the feel quite similar. I found that after a few hours on the Deskpro, my typing speed seemed to increase over my old standby Portable.

It is a comfortable keyboard and easy to get used to, but it seems strange that Compaq kept the small Return and Shift keys of the original instead of making the same changes IBM did with the AT. It probably is just another example of Compaq's driving effort to remain IBM compatible. They apparently just didn't know about the AT--or didn't know enough about it--before the Deskpro was released. One user told me he liked the Deskpro better all around, except for the "incredible, cheesy, cheap, toy-like keyboard." He bought an AT because of that one complaint. To each his own.

Disk Drives

The PC AT can have up to three internal disk drives. They can be two floppies and one hard disk or two hard disks and one floppy. The Floppy disk drives come in two varieties. The standard is an 80-track, high density unit which can store 1.2Mb on special diskettes or 360K on regular media. Because this drive uses a recording head which is much smaller than that of a 40-track drive, no compatibility is claimed between the old and new drives. The slot below the high density floppy can hold a 40-track drive to allow reliable data transfer from the AT to other computers equipped with a similar drive. The hard disks are 20Mb units with an average access time of 40 ms.

The Deskpro does IBM one better with four external storage slots. Two 360K, 40-track floppies generally occupy the top two slots. In the model 4, a 10Mb tape backup unit is in the lower left position, and a 10Mb Winchester is in the lower right. With the current popular software and hardware configurations, this seems like a much more flexible arrangement. IBM apparently felt the 1.2Mb floppy would ease some of the backup problems always present with Winchester devices. But the fact is, the disk media are costly, and, for a 20Mb drive, you must still do a lot of disk swapping to get a good backup.

The Deskpro approach maintains complete media compatibility with existing software, while providing an easy backup solution with the 10Mb streaming tape unit. The tape must be formatted once before use. That takes about 16 minutes. After that you can back up an entire 10Mb disk in 20 minutes or less, depending on whether you do a file-by-file backup, or back up everything on the hard drive. Software utilities permit you to display a directory of the backup tape and restore from tape by named files if you wish. Even with all available options installed, the Deskpro has five UBM compatible expansion slots free.

The AT uses the standard IBM PC display adapter card, with two high-resolution, and equally high priced, options available. The Deskpro stays with the excellent quality combination unit of the Portable, but with a 12" screen in either amber or green. Either display gives excellent quality. And the crisp Compaq video on a 12" screen is truly a joy to use.

Making a Choice

The tendency is to compare the IBM PC AT head-to-head with the Compaq Deskpro. That is OK, because they stack up well against each other. In reality, however, they are totally different and should be considered that way when comparison shopping. The Deskpro is a bigger, better, faster PC or Compaq Portable, while the AT is a breed apart. It uses so much new technology--and design philosophy--that it is difficult to compare it with the Deskpro or the PC and XT.

Unless you just have to have the latest CPU technology, or multiuser and networking are musts, the AT may be more machine than you and your budget need. The Deskpro, on the other hand, with its easy expandability and relatively low price, makes an excellent choice for the single user office environment. With its 30Mb disk and other options, it could even be preferable to the AT, unless raw processor speed is the driving force behind your decision making. And that seems a narrow approach to computing, at best.

Products: Compaq Deskpro (computer)
IBM Personal Computer AT (Microcomputer)