<4 - 
plotting tables, CRT interactive displays, etc., can be readily 
obtained from manufacturers of computer and computer graphics devices, 
and incorporated into the system according to the particular needs 
arising from the desired performance of the system. 
2. HARDWARE AND SOFTWARE 
Theoretically all the potentials for the development of 
various methods and techniques are inherent in the basic design 
principle of analytical instruments. In practice the capabilities vary 
considerably with the properties of specific hardware components and 
basic software. Thus a review of the more significant characteristics 
of the hardware and the software of the new generation of analytical 
instruments will facilitate the analysis of their capabilities. Since 
an overall review of improvements and refinements will suffice for this 
purpose, a detailed description of any specific instrument is not neces- e 
sary. Naturally, all the features discussed are not necessarily 
included in every make or version of these instruments. 
2.1. Computers, Software Operating Systems and Peripherals 
The characteristics of dedicated computers and their software 
operating systems are by far the most important indicators of the capa- 
city and the capability of an analytical instrument. This is the logi- 
cal consequence of the definition of an analytical instrument that can 
be restated as follows: an analytical instrument is a general purpose 
digital computer that has an input-output peripheral for addressing a 
pair of photographs. The main drawbacks found in older types of 
analytical instruments were the low speed of the dedicated computers, 
the small capacity of their memory and the limitations related to the 
use of their external memory files. To alleviate the difficulties 
arising from these deficiencies when trying to meet the requirements 
for high frequency responses in real time operations, incremental 
computers were used in some instances as a support to the whole number 
computers [3]. Also, to minimize the disadvantages of inadequate soft- 
ware support and insufficient memory, two approaches were used, not so 
long ago, for handling of larger off-line programs. One was the incor- 
poration of analytical instruments into the time-sharing environment of 
a larger computer [4], and the other was the use of a magnetic tape 
unit for storage of programs that were partitioned in separately execu- 
table segments fitting the available memory [5]. But the most signifi- 
cant shortcoming was the necessity to write all the programs in machine 
language. The latter was the main reason for the relatively insignifi- 
cant use of analytical instruments in many photogrammetric disciplines, 
d spite the fact that the potential advantages were quite well recog- 
nized. 
The hardware and software characteristics of a number of 
present-day mini-computers virtually eliminated all these problems. 
Not only off-line programs but also the real-time programs may be 
almost exclusively written in higher languages. The only part of the 
real-time programs that normally cannot be handled by higher languages 
are the input-output instructions for the registers of the interface. 
But these commands once written as macro-commands can be used in con- 
junction with any real-time program, since the handling of values that 
are introduced into or read from these registers is always the same,