dard, and this, together with clock speeds of up to 750 MHz, results in a faster computing capability.
Their memory size (above) now exceeds that of earlier mini- and mainframe computers and they can be
linked together into micro-networks (LANs) based in one or covering several laboratories. The disk
operating system (DOS) of a microcomputer, e.g. MS-DOS, is now loaded from a hard disk on startup
(booting the system) rather than being resident on a ROM chip. This enables the system to be upgraded
easily or even another DOS altogether to be employed. One further distinguishing feature of the
microcomputer is the use of a microprocessor-based CPU (see below). Many analytical instrument
manufacturers now offer their instruments complete with a dedicated microcomputer and supporting
software packages to perform appropriate instrument control tasks, data processing and display and/or
printout of results; the provision of high-resolution (1760 × 1280 pixels) colour graphics software to
display such things as chromatograms and spectra on a VDU screen has become an important feature.
These and more general applications software packages frequently run in a windows environment and
multicolour (up to 16.7 million colours) display mode. This gives great flexibility to the user allowing
information in the form of option menus, help screens, data tables, spectra, chromatograms editing and
file-handling routines, expanded scale graphical displays, etc., to be temporarily superimposed on an
existing screen within a series of rectangular frames (windows) that can be enlarged, moved or instantly
erased when no longer required. The use of a computer mouse as an alternative to entering commands
and parameters at the keyboard greatly speeds up the use of this type of software. Maximum flexibility
for the user is achieved by offering a high-level programming language (usually BASIC or VISUAL BASIC) for
editing existing programs or for writing entirely new ones.
Microprocessors
A microprocessor is a miniaturized CPU which is all on one integrated circuit chip and occupies only a
few square centimetres in area. Many analytical instruments are now microprocessor controlled, the
control programs for setting and monitoring instrumental parameters, for diagnostic routines and for
some data processing (sometimes called data reduction) being stored on ROM chips. Some RAM may
also be available to enable the user to write and store sets of method parameters for particular routine
analyses and to perform a degree of additional data processing. Microprocessors are also at the centre of
every microcomputer on the market. The layout of a typical microprocessor system is shown in Figure
13.3. Clock frequencies, which determine the rate of computation, have risen steadily from below 10
MHz to well over 500 MHz as new processors have been developed. The fastest currently available is a
pentium processor with a clock speed of 750 MHz enabling multitasking and realtime data processing
to be readily accomplished.