Cad Guidebook: A Basic Manual for Understanding and Improving Computer-Aided Design (13 page)

Before these very high resolution printers, the plotters were often devices
called pen plotters. These devices mechanically moved pens across the paper, or
the pen slid in one direction and paper was rotated in another direction. This sort
of device created a very accurate drawing based on a fairly direct translation of
the data in the vector data file. As mentioned earlier the HPGL file, which was
developed for the Hewlett-Packard pen plotters, is still supported in some de-
vices. Indeed, some of the devices that would be considered printers (since they
can print bitmaps or text alone also) actually support the HPGL format via a
translator built into the printer. Many of these devices actually automatically de-
tect which kind of file has been sent to it (and translates accordingly). Another
very popular type of device for plotting (particularly for mainframe systems) was
the Calcomp®
plotter. This device also had its own file type that may still be
supported.

Printers (which generally handle bitmap data, but may have a translator to
handle the vector data) are usually based on laser printer technology or print jet
technology. As long as the resolution is high enough (perhaps at least 600 dpi),
the drawing image should be as clear and consistent as a plotter. The main con-
siderations are likely to be how big the paper output needs to be, how fast the
printer needs to go, and how expensive the ink cartridges are.

Of course, printer-type devices are the most appropriate for 3-D models.
Thus, a high quality printer can have the advantage of being able to handle both
the 2-D and 3-D image data. However, as mentioned previously, a printer for a 3-
D image needs to have the ability to handle a large amount of data, and it must be
able to produce a large number of colors to provide the shading illusion.

For many years, printers and plotters were attached to a minicomputer or
workstation directly. The printers often were connected to a Centronics®
parallel
port, and plotters were connected to an RS-232 serial port. This approach has
generally been replaced by connecting the hardcopy device directly to the com-
puter network. In this case, the files that need to be printed will be spooled or
queued on a designated computer that keeps track of the data being sent to the
devices on the network (print server activity). The hardcopy device, in turn, must
have a fairly large amount of memory to use as a temporary storage area for data

Computer Hardware Basics 41

awaiting printing on the device. This memory is generally referred to as RAM for
the hardcopy device. Obviously, a sufficient amount of this RAM must be in-
stalled in the device so that there is no bottleneck for the data. Since the 3-D
models tend to have the largest file size, even more RAM must be accounted for
if the printer is going to be used a great deal for 3-D model printing.

2.7.4 Pointing Devices

The next type of peripheral to discuss is the pointing device. This is a type of
device that can direct the user’s interaction with the graphical data being pre-
sented. This is in contrast with the keyboard which is used to just enter “charac-
ter” data (numbers, letter, special characters, etc.). The pointing device is an
essential part of the CAD system, since a large number of the functions that need
to be performed with the CAD software will be via the pointing device.

Some examples of pointing devices would be mice, trackballs, 3-D balls,
dial pads, and digitizing tablets. In each case, the user can control the cursor or a
pointer that is seen on the monitor. It allows for the selection or “picking” of
graphical entities (lines, dimensions, arcs, surfaces). These devices are usually
connected to a specially designated connector (or port) for the computer. Unlike
most standard computer software, CAD software often requires a 3-button
mouse. There are more commands than usual that need to be efficiently commu-
nicated between the user and the software.

Interacting with a 3-D model also produces greater demands on the point-
ing device. Most software uses a dial pad or a combination of the keys on the
keyboard with buttons on the mouse to generate the needed control of the
graphics interactivity. In order to interact with a 3-D model, the user will need
to deal with zoom in and out (the Z-direction degree of freedom), how to shift
left and right and/or up and down (panning in the X- and Y-direction), and how
to rotate the model in 3 different directions (X, Y, and Z). Furthermore, the user
will probably need to “clip” the model. This is a function to cut through or cut
into a 3-D model and see inside surfaces after cutting away part of the 3-D
model. In all these operations, the user should be able to indicate what degree
of freedom needs to be adjusted, and then be able to use the pointing device to
dynamically make that adjustment until the precise view is presented on the
monitor.

2.7.5 Keyboard

Not much needs to be said concerning the keyboard. It is a fairly standard periph-
eral that is attached to the computer via a special connector for the keyboard. It
allows for input of textual information. The function keys (or other “special” keys

42 Chapter 2

such as ctrl, shift, alt) on the keyboard may be used in conjunction with the point-
ing device to allow for the many operations need to manipulate 3-D models.

One difficulty that may arise with respect to keyboards is how they impact
different languages or nationalities. There often are special notations on letters
that are unique to specific languages or nations. If a single CAD system is going
to be specified for a variety of nations for a company, then the CAD system needs
to be able to handle these variations. As with the pointing device however, the
computer system and/or the CAD software is likely to have the ability to be cus-
tomized or adjusted to handle the differences.

2.7.6 Modems

Modems are devices that allow a computer to communicate across media such as
phone lines. These devices do not generally have any special impact on CAD
software. If a number of CAD software users need to share data, then generally
they are connected via a network, not via modem’s. If one is transferring CAD
data files across a modem, then particular attention must be made to the type of
file (ASCII versus binary) and the size of the file. In general, CAD data files are
compressed prior to transmission via modem.

2.7.7 Backup Devices

In Section 2.5 on storage systems, it was mentioned that the data in the storage
systems should be backed up regularly. This involves making a new copy of the
all the data on the daily-used devices (such as disk drives). These new copies are
then stored in a safe place (and often another copy kept off site), and these copies
can be used to reconstitute a system after a failure in the storage system or unde-
sired deletion of data by users.

Typical devices for “backups” would include tape drives and writeable CD
devices. These types of devices are expected to be able to store large amounts of
data, be physically stable (and thus able to keep the data stored and correct for
long periods of time), and easily managed for finding and retrieving data. The
speed with which the data is stored or retrieved is generally less important than
the long term reliability of the medium.

These devices may be connected to individual computer systems, or they
may be attached in some manner to the overall network. As stated above, the
most critical issue is that the data storage is reliable. All the CAD data on the
network should be backed up on one of these devices daily, and at regular inter-
vals as much of this data as possible should be duplicated for off-site storage (in
case the entire building or site is damaged or destroyed).

Computer Hardware Basics 43

2.8 ERGONOMICS AND DISABILITIES

The final issue with respect to computer hardware is to mention the requirements
for proper ergonomics and adaptive devices. For all users of a CAD system, the
computer hardware (particularly the keyboard, pointing device, and monitor)
must be arranged and physically accessed in a proper manner to avoid injury.
Standards or experts in the field of office ergonomics can be consulted.

For disabled users of a CAD system, there may be adaptive devices avail-
able. These devices should be researched and made available as needed or re-
quired by law. Although the capabilities of these special devices vary widely, and
the demands of the user interface of CAD systems keep expanding, some exciting
possibilities include natural language processing and intelligent pointing devices
that learn from their user based on the user’s physical capabilities.

2.9 CHAPTER EXERCISES

1. With permission, open up and study a computer system (following
standard electronic equipment safety procedures such as unplugging all units and
grounding oneself). Also refer to manufacturer’s documentation as needed. Lo-
cate the following:

2. The CPU. Record the manufacturer and the year of manufacture.

3. Storage system (disk drive). Record the manufacturer and determine
the access speed or I/O data rate.

4. Memory (main system RAM). Record the number of banks filled, the
number of chips per bank, and total amount of physical RAM (most likely all in
megabytes). Determine the access speed or I/O data rate.

5. Graphics Adapter (video card). Record the manufacturer and deter-
mine the amount of various kinds of RAM located on the circuit board.

6. If a computer network is used at one’s campus or company, determine
what IP addresses and node names are used for computers in the network.

2.10 CHAPTER REVIEW

1. Exactly how many bytes are in 1 kilobyte?

2. What system does the CPU communicate directly with—memory or

storage?

3. Which system is faster in manipulating data—memory or storage?
4. Which system is nonvolatile—memory or storage?

5. Which system would have CAD software installed on it perma-

nently—memory or storage?

44 Chapter 2

6. What is virtual memory?

7. What is the memory map?

8. If a graphics adapter supports a resolution of 1024 by 768 pixels, 8 bits

per color, and 2 frame buffers all in the graphics RAM area of the

memory map, how much Graphics RAM is required (to the nearest

megabyte)?

9. If a data file sent to a print device contains the X- and Y-values for the

endpoints of lines, does this file contain vector data or bitmap data?

3

Computer Software Basics

3.1 INTRODUCTION

The next step in building a foundation for understanding how CAD systems are
best employed is to present some basic information on computer software. As
with the Chapter 2 on computer hardware, the intent is not to present a thorough
discussion of computer software, which is an immense topic. Rather, there are
some important issues that are operating behind the scenes on the computer that
have a significant impact on CAD software and its users.

Recall from the previous chapter that the combination of computer hard-
ware and the basic software that controls that hardware is often referred to as a
platform. This chapter is going to present information on this controlling soft-
ware called the operating system (OS). However, keep in mind that some com-
puter hardware may only run one operating system, while other computer
hardware may run more than one. For example, the computer hardware built
around the Intel-based CPUs may run both the latest Windows software (as an
operating system) or a brand of Unix software. However, other manufacturers (so
called proprietary systems) may have their hardware run only their own individ-
ual operating systems. Fortunately, most of the features of these different operat-
ing systems are similar, so the discussion presented in this chapter will be