ITT Xtra XP; the power of an AT for the price of an XT. (evaluation) Joe Desposito.
To paraphrase the Wendy's commercial, "Where's the Xtra?" was a legitimate comment on ITT's first microcomputer. Not so the second time around. The ITT Xtra XP abounds with extra features that make it one of the most powerful machines on the market a very competitive price.
Basically, what ITT has tried to accomplish is to design a PC with the performance of an IBM AT (i.e., very fast) at the price of an IBM XT. The machine we reviewed had 1.64Mb of RAM, a 20Mb hard disk, and a color monitor. The standard configuration, however, includes a 10Mb hard disk, 512K RAM, and a monochrome display at a suggested retail price of $4365.
What makes it so fast?
When you first start using the ITT XP, it is immediately evident that the machine is very, very fast. One reason is that it uses Intel's high performance 80286 microprocessor, which runs at 6MHz. But there are other reasons, too. A hardware reason is that it uses 512K of onboard, 16-bit, zero-wait-state DRAM (expandable on board to 640K). A software reason is something called FXP automatic I/O management.
FXP is a sophisticated enhancement to DOS 2.11. It both establishes a disk cache for the hard disk and provides a print buffer. Both the cache and buffer are alotted a dedicated area of system memory. FXP monitors the activity of the hard disk. When a program requests information from the disk, FXP checks the RAM cache first. If it is there, the information is passed directly to the program--no disk access is made. This significantly reduces the access time of the disk. Of course, if information is not in the cache, things slow down. An entire track containing the information is loaded into the cache, and the relevant data are then passed to the program. And since the XP does not use the AT's high performance drives, access time is about double that of the XT. But depending on the application, overall access time can be less than with an AT.
FXP also tries to correct some of the disk writing limitations of DOS. Even for small files, DOS moves the disk head many times to access a file. FXP, on the other hand, automatically starts writing modified tracks in the cache to the disk. It uses a technique called "elevator" writes to do this. This means that the track nearest the current position of the head is written first, followed by the next nearest, and so on, until all modified tracks are updated.
This elevator technique is analogous to what happens in a real elevator. Though people press numbers at random, the electronics of the elevator sort them out and deliver people to their floors in sequence. On the XP, this enables FXP to access files on the disk more quickly. Thus FXP increases disk access speed in two ways. It keeps frequently used files in RAM, and it writes all files back to disk in an optimum way.
The print buffer also increases system performance. Whenever you need to print a document, FXP sends the information from the program to an area of memory at high speed and then sends the information to the printer from this buffer area. In most cases, you don't have to wait for the printer to finish its work before you can resume using a particular program. But when a document exceeds the buffer size, you must wait until some of the information is printed.
More About the XP
The ITT Xtra XP system unit is fairly compact. At the front we find a 10- or 20Mb half-height hard disk drive and a 360K half-height floppy drive stacked one on top of the other. The keyboard connects to the rear with a 6' coiled cord. Also at the rear are connectors for RS-232 serial and Centronics parallel ports. Inside the unit are five full-size PC XT compatible expansion slots.
The display we used was an ITT color monitor with a 14" diagonal CRT. A non-glare etched surface and .31mm dot pitch give the monitor good readability in text mode. The monitor is mounted on a base that can be swiveled and tilted for easy viewing.
There are more software enhancements, too. VDISK gives you a way to create one or more RAM disks. And for users concerned about compatibility problems due to faster processor speed, the speed can be reduced to 4.77MHz by
a CTRL-ALT- command.
Memory can be expanded beyond 640K with a proprietary expansion board from ITT. The board is available with 512K onboard and room for an additional 512K. The board can be used with FXP for cache and print buffering, with VDISK as a RAM disk, or via a software switch, as expansion memory for programs that take advantage of the Protected Virtual Address mode of the 80286.
A Keyboard with a Twist
The XP has an 84-key keyboard that is almost identical to that found on the IBM PC. However, there is one difference that touch typists will welcome. The lefthand SHIFT key has been interchanged with the backslash key. This is great for first-time users, but somewhat frustrating for those who have accustomed themselves to the IBM PC layout. The other changes is that the RETURN key is horizontal instead of vertical, with the open single quote key removed to a position over the right half of the RETURN key. An improvement over the IBM keyboard is the inclusion of a small light emitting diode (LED) in the CAPS LOCK key.
Comments and Conclusions
We used the ITT Xtra XP for several weeks and were thoroughly impressed with its exceptional performance. A database application (Pfs:File) ran particularly fast on the XP. For example, an initial search of the database is performed at high speed due to the faster processor speed and the hard disk. If a desired record happens to reside in the cache, it appears instantaneously when requested. Then, if you need to print a record or group of records, you are returned almost immediately to the program as the print buffer does its job. What it all adds up to is much greater productivity.
There are also some drawbacks to the machine. The main one is with the disk drive. Some of the high performance drives for the IBM AT automatically park the hard disk heads when power is interrupted, which makes a disk crash unlikely. With the ITT, however, you must invoke a command called SPINDISK to park the heads. This means that a careless bump could spell disaster if you neglect to park the heads after using the machine.
Overall, I was really pleased with the performance of the XP. In some applications it even delivers the instantaneous response that users crave from a PC, and many prospective compatible buyers will find this machine an attractive alternative to the IBM AT. Although suggested retail price quotes can sometimes be deceiving, it appears that the ITT Xtra XP has lived up to its goal of providing AT performance at XT prices.
Products: ITT Xtra XP (computer)