Information Technology Reference
In-Depth Information
Fig. 7.22
Simple layered
model of a computer system
to as the host system, and the system being emulated is referred to as the target
system. Emulators can emulate a whole computer hardware system (see Fig.
7.22
for a simple model of a computer system) including CPU and peripheral hardware
(graphics, disk etc). This means that they can run operating systems and software
that used to run on the target system on any newer hardware even if the instruction
set of the new system is different.
The concept of emulation for running old software on newer systems has been
around for nearly as long as the modern digital computer. The IBM 709 computer
system build in 1958 contained hardware that emulated the older legacy IBM 704
system built in 1954 and enabled it to run software from the old 704 system [
81
].
The main purpose of Emulation techniques has been to run older, legacy, software
on new hardware. Usually this has been to extend the life of software and systems
such that the transition to newer systems can be done at a more leisurely and cost
effective pace. During this time, new software can be written as a replacement and
also data can be migrated. Another factor that makes emulation useful is it gives
time to train people to use the newer systems and software. Usually emulation is
only a short term, stop gap, solution when moving to a new hardware/software sys-
tem. Only recently has emulation been suggested [
82
] as a long-term preservation
strategy for software.
It has been proposed for the preservation of digitally encoded documents by pre-
serving the ability to render those digital objects, ignoring the semantics of the
