Supplement on Personal Computers

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The Next and Linux Operating Systems

Intel PCs can run two operating systems that were not discussed by any of the presenters: the commercial Next OS and the free Linux OS. Both can be used as general purpose, multi-user server operating systems or as desktop single-user systems. Both are strongly influenced by unix, both provide a graphical user interface, and both are more likely to appeal to programmers than routine commercial business users. They are, however, quite robust and stable, and Linux, in particular, may well become of more interest commercially now that Oracle has announced plans to support it.


Future Trends for Computer Speed

Electrical signals travel at speeds of at most 300,000,000 meters/second (the speed of electromagnetic waves in a vacuum) within computer chips, on printed circuit boards, and in the wiring connecting peripheral devices. Typical speeds are about two-thirds to half that fast. High-end technical workstation systems, such as Digital's Alpha, are available with system clocks of up to 767 MHz, and even high-end mass-market personal computers exceed 300 MHz (e.g., the PowerMacintosh G3 at 333 MHz and Pentium II systems at 400 MHz). That means that during a single cycle of the system clock, taking between 1.3 and 3.3 billionths of a second, electrical signals travel between two-thirds and one-fifth of a meter. Because it is vital that all of the parts of a computer system be properly coordinated with each other, such a computer must have its two most distant points much less than one meter apart, measured along the length of the wires connecting them. We have already reached the point where further speed-ups in computer operation will place stringent limits on the physical size of the system.

We can therefore anticipate

Even so, it is becoming less likely that performance will continue to double every 18 months, as has been the historic trend for the last several decades.


Printer Choices

There are three printer types that are likely contenders for a small business: black-and-white laser, color ink-jet, and color laser.


Ink-jet printers


Monochrome laser printers


Color laser printers


System Unit vs. CPU vs. Hard Disk

The system unit of a modern PC will typically contain the CPU, the RAM, at least one disk drive, the user interface circuitry, and the network interface circuitry. The fact that printers, keyboards, mice, monitors, and sometimes modems are external to the system unit does not mean that the system unit should be spoken of as "the CPU" or as "the Hard Disk."


Power Sources

There are two issues here: having too much power and having too little.

First, in most parts of the country there is an extended season when thunderstorms are common. The electrical discharge of a lightening stroke does not just make noise; it also creates an electromagnetic pulse that can be picked up by any electrically conducting wire, including the power wiring, telephone wiring, data network wiring (excluding fiber-optic cable, which is glass or plastic and so does not conduct electricity), and the wiring that connects printers and other peripheral devices to a computer system. So-called "surge suppressors" or "spike eaters" are intended to remove or diminish the transmission of such pulses from the power wiring into the electronic devices connected to them. Many surge suppressors also include connections for telephone lines, to prevent the destruction of modems. Some surge suppressors are sold with a guarantee to pay for any damage to connected equipment.

Second, in most parts of the country, the majority of power failures are for a duration of less than five minutes, so a relatively modest "Uninterruptible Power Supply" (UPS) will prevent the loss of work-in-progress. A UPS will include

The UPS will have two critical performance ratings: the maximum load it can handle, usually expressed in Watts (typically a few hundred), and the duration of the power failure through which it can sustain that load. If a lesser load is placed on it, the duration it will handle is usually extended in proportion. Laser printers typically require 1,000 W to 1,500 W - about the same as a hair dryer or full-size microwave oven. They should not be connected to the UPS! You can always re-print your document, so long as it has been saved.


Software Selection

One criterion for selecting business software (such as billing, accounts payable, etc.) is the extent to which using that software would require modification of the processes already in use within the organization. As we will see in project 4, such changes in process are sometimes beneficial. When first computerizing, however, it is probably wise to choose software that the staff see as simplifying the accomplishment of their existing processes.


Bundled Software and Hardware

Often the marketing of computer hardware and software proceeds by "package deals" (known in this industry as "bundling") - "buy this and we'll throw this other in for free." Remember, TANSTAAFL, "There Ain't No Such Thing As A Free Lunch" (a phrase I first encountered in Robert Heinlein's novel, The Moon is a Harsh Mistress, although I do not know whether he originated it).


Virtual Memory

Virtual Memory is a method by which the part of the operating system that is responsible for allocating RAM manages to present to the rest of the operating system, and to the applications, and therefore to the user, the appearance of having more RAM than is physically installed in the machine. This is accomplished by swapping "pages" of memory between RAM and a dedicated portion of the hard disk.

Because RAM responds in 50 to 100 nanoseconds, but disk drives respond in 10 to 40 milliseconds (nearly a million times slower), virtual memory operation is often very slow. It does, however, permit the use of software that requires more RAM than the user can afford. Windows always has virtual memory turned on. Macintosh systems can run with it on or off. The older Macintoshes (with Motorola 680x0 CPU chips) usually run faster with virtual memory off, if there is enough RAM to accomplish the tasks at hand. PowerPC Macintosh systems' software is optimized for use with virtual memory, there is usually no perceptible speed penalty, except when switching between tasks, and even that is faster than shutting down one program and starting another would be. (It is possible to write software for the PowerPC Macintosh that works badly with virtual memory.)


"It's been obsolete for at least a week..."

Although that phrase was first applied to high fidelity equipement in about 1960 by Stan Freeburg, it catches the spirit of today's computer industry. The rapid pace of technological change in the computer industry means that we need to distinguish between items that are no longer "bleeding edge" and items that are so outdated that it is unreasonable to try to get useful work done with them. In between there is an extended period of transition, known as obsolescence.

It is often the case that it is reasonable to postpone retirement of a two- or three-year-old system by adding RAM, expanding the hard drive, or otherwise performing hardware upgrades. Furthermore, in a larger organization there are likely to be a range of computing needs, so that a "hand-me-down" cascade can result in one purchase of a high-end machine resulting in the upgrading of the machines in use by many people. Managers need to be careful to sustain the positive attitude of "This machine sure is nicer than the one I had," rather than the negative attitude of "Why do I always get the used machine?"


Scanners

Scanners measure the color of each pixel and report that information as a graphic representation of the scanned paged. The value recorded for each pixel may be one bit (black-and-white or monochrome), multi-bit grey-scale (monochrome) or multi-bit color. Current technology for moderately expensive units provides at least sixteen bits, and often more than twenty-four bits, at 600 or more pixels per inch. For comparison, FAX transmissions range from 75 to 200 pixels per inch, with one bit per pixel.


Optical Character Recognition

A scanned image of a photograph can be manipulated with standard graphical software. A scanned image of a written document will often need to be further revised. Before being able to use a word processor on such an image, the pixels' values must be processed by so-called "optical character recognition" software. Good quality OCR software analyzing a well-scanned image of cleanly printed text should be able to correctly recognize most of the characters - perhaps mis-identifying one character per line of text. Further proofreading and correction is nearly always needed, but that is often less work than human transcription would have been.

OCR software is very demanding on system computational capabilities, RAM, and I/O throughput. High-end PowerPC and Pentium systems can often be justified by the need to do OCR.


Personal Digital Assistants

The Achilles heel of PDAs is the trade-off between cramped keyboards and the continuing difficulty of programmed handwriting recognition. Like the dancing bear, what is impressive is not how well it works, but that it works at all. It is conceivable that within a few more years the growth in CPU horsepower and software sophistication will combine to provide good real-time handwriting recognition. I do not regard it as a sure thing. Even now, OCR for printed text is still no simple matter on desktop machines.


SX vs. DX

The 80386 and 80486 series of CPU chips were routinely manufactured in two varieties: those with (DX) and those without (SX) the built-in capacity to perform arithmetic directly on floating-point numbers (decimal fractions). Those without that ability built-in get the job done by executing small sub-programs that do the calculation one step at a time using integer arithmetic, just as people do for example, long division with paper and pencil. Typically, the SX machines will be much slower on spreadsheet recalculation, and somewhat slower on word processing with proportionally spaced fonts.


DX2

Many CPU chips operate at an internal clock speed that is double, triple, or quadruple the external clock speed of the primary system bus. For CPU-intensive operations involving data and instructions within a compact range of RAM addresses, such systems will be faster, because they will be able to obtain their data from the internal (L1) cache at the higher internal clock speed. On a realistic range of tasks their speed advantage will be much less than one might hope for based on the internal clock speed, because they will so often have to wait for data from RAM, which will arrive at the slower system bus speed.


MMX Technology

The latest versions of Intel's Pentium chip include new machine language instructions that provide for a single instruction to result in the calculation of what was previously a multi-step arithmetic result. The particular arithmetic combinations that have been chosen are those that are widely used in data compression algorithms. This permits acceptable performance on those tasks (such as display of JPEG-encoded images) with a cheaper total system cost than would otherwise be the case.


I-Drive

Using an internet-connected file-server instead of a hard drive may well reduce initial system costs. On the other hand, once you buy a regular disk drive, you have essentially no further operating costs, while the internet-connected file-server approach costs for server operation and for connection to the network. The Iomega JAZ drive, for example, has cartridge costs of less than 13 cents per MB, and hard drives are available for perhaps 6 cents per MB, so in the long run a local disk drive will be cheaper, unless the I-drive storage costs were lower than are currently being discussed.

As we will see in Project 2, there are also major performance and security issues that would need to be confronted, especially for those whose internet connections are by dial-up.


Operating System Internals

Operating systems can be designed as a giant software package, composed of many subprograms that are all "peers." A more effective alternative for a multi-user operating system, and in many cases also for a multi-tasking operating system, is a formally organized ("architected") design, in which a central core portion of the operating system is responsible for CPU scheduling, other resource allocation, and system integrity, with the user interface and many utility programs being outside of this core, using the services that it provides. This central core is sometimes referred to as the "kernel." A significant advantage of kernel-based operating system design is that the kernel can be small enough that critical system functions are actually implemented bug-free. Furthermore, by having defined interfaces ("APIs") between the kernel and the rest of the operating system, the programmers are more likely to work with sufficient discipline to produce robust code and therefore a stable working environment for application programmers and end-users.


Serial and Parallel Ports

Keyboards, mice, and modems are routinely connected through wiring that provides a single wire carrying the signal to the computer (and, in the case of a modem, another single wire carrying the signal from the computer). Such connections are referred to as "serial ports" because the bits of each byte are sent in sequence.

Printers and other specialized devices are routinely connected through wiring that provides multiple wires carrying information from the computer (and, in the case of disk drives, for example, multiple wires carrying information to the computer). Such connections are referred to as "parallel ports" because the bits of each byte are sent at the same time on the several wires.


SCSI Ports

The Small Computer Systems Interface (SCSI, pronounced "skuzzy") is a high-speed parallel connection designed for disk drives, scanners, and other peripherals. SCSI connections are daisy-chained, with up to seven peripheral devices (three bits are used to identify the device, providing eight possibilities, the eighth device is the computer).

In order to function correctly, the electonic signals must not be reflected from the last device in the chain; such reflections are prevented by "terminators," which may be internal to the device or may be small connectors that plug in to the connector that would be used for a cable to the next device. Internal terminators on other devices than the first and last must be switchable to be disconnected, since they would otherwise absorb too much of the signal.

SCSI was introduced to the mass market by the Macintosh in the mid-1980s. Since that time, SCSI has evolved to include variants

Fast SCSI and Fast Wide SCSI system configurations are often difficult because the fast electronics are more sensitive to reflected signals, even with proper termination, and problems with relections are always exacerbated by longer cables. This justifies the extra expense of FWD (four wheel drive? no, fast, wide, differential) SCSI, giving the mechanical designer more room to use, and giving the consumer more flexibility in locating the external devices.

The primary advantage of SCSI is that it provides a relatively easy method for plug-and-play attachment of high-performance, external, add-on, disk drives and scanners by the consumer. The primary disadvantage is that it is a slightly more expensive approach than, for example, the IDE standard for disk drive interface electronics and cabling.

Universal Serial Bus connections are slower and cheaper than SCSI, but still fast enough for scanners and many other peripherals.


Mac and Windows Compatible Software

Many businesses will discover that some people need a different platform than the bulk of the staff, because of critical software for their particular job functions. In such cases, there are advantages to choosing general purpose software (word processor, spreadsheet, etc.) for which there are versions on both platforms. That way, because the Macintosh can read and write PC diskettes and ZIP cartridges, it will be easy to share the document data files. Be alert in buying suites and "works" packages: the Macintosh and Windows versions may not encompass fully equivalent sets of features. Microsoft Office has looked good on these grounds, with Office 98 being released on the PowerMac before it was released on Windows.


Sequence for Purchase Decisions

People often put the cart before the horse, presuming that a Pentium system running Windows 95 or Windows NT is the best platform. In many cases it is the right choice, but that will only be known after a process of the following nature:

  1. Identify tasks and the people who perform them.

  2. Identify software types that will assist in performing those tasks.

  3. Identify possible software packages of those types.

  4. Select platform (hardware and operating system) knowing the requirements of the various packages.

  5. Choose specific packages of each required type.

  6. Buy the hardware and software.

The purchase should be postponed until the last stage, because one often has choices about the "bundled" software when the hardware is purchased.


Works Packages vs Suites vs best-of-breed

Under DOS, works packages were especially adventageous, because they were the only software that provided consistent commands for multiple activities. Typical works packages provide basic capabilities for each application. Under Windows, it is common to find suites of full-function applications that provide quite consistent user interfaces. On Windows, and even more so, on the Macintosh, applications provided by different vendors are often sufficiently consistent that it is effective to choose, for example, the best spreadsheet, the best word processor, and so on, without restricting your choices to those of a single vendor.


O/S to optimize application programmers' effectiveness

The true primary function of the operating system is to optimize the application programmer's effectiveness. By providing subprograms with defined usage (Application Programming Interface, known as "API") for many commonly ocurring tasks, the application programmer does not have to re-invent the wheel. For example, a file selection dialog need not be written from scratch, but can instead simply call the standard routine in the operating system, with inputs (default file type, etc.) appropriate to the specific application.

This simplification of the application programmer's job has the fortunate side-effect that many different software packages written for use on any one operating system are likely to present virtually identical appearances to the user for most common tasks. Thus, in addition to being easier to write, the software is easier to use! This advantage was not evident with DOS, leading to the all-too-common difficulty of learning a new package, because DOS was a minimal operating system that did not provide very many useful subprograms. The Macintosh, and now Windows, were much more complete operating systems, providing the tools needed by application programmers wanting to write software with graphical user interfaces.

The inclusion of so many more standardized subprograms and software tools within the operating system has lead to software bloat, which has been accepted only because of the continuing decline in prices for RAM. DOS was introduced when 64 KBytes was a lot of RAM, and was designed to use in systems that would have at most 10 times that much. Now, of course, sixteen years later, it is quite common to have personal systems that sport 64 MBytes of RAM, 1,000 times as much!


Mail-order shipping costs

Overnight or second day shipping for a complete PC system, including monitor and printer, typically exceeds $100. Sometimes you will be able to convince the vendor that you do not want the system shipped that way, thereby saving money. This is obviously especially attractive when a dozen or more systems are purchased at the same time.

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Dick Piccard revised this file (http://oak.cats.ohiou.edu/~piccard/mis300/pcextra.htm) on September 24, 1998.

Please E-Mail comments or suggestions to "piccard@ohio.edu".

© Copyright 1998 Richard D. Piccard