SQA Computing Science and S3 Broad General Education.
Higher – Low-level Operations and Computer Architecture (Revision)
Virtual Machines: an emulation of a complete computer system which can be used to run alternative operating systems, or several copies of a single operating system
Emulators: software which duplicates the function of one computer system in another
Mobile Devices: features which require different types of software from conventional desktop systems eg touchscreen, pinch
Binary Representation of:
Integers – 163: 1 0 1 0 0 0 1 1
Negative Integers – -93: 1 0 1 0 0 0 1 1
Real numbers – 16.25: Mantissa & Exponent
Stored using a mantissa (Larger = greater accuarcy) and an exponent (Larger = greater range)
Characters
ASCII (American Standard Code for Information Interchange) stores each letter, number or symbol using a number code from 0 to 127; ASCII uses eight bits (1s and 0s) to store each character
UNICODE 16bits, larger pool of characters
Instructions – represented by machine code as 0s and 1s
Vector Graphics – stored as a collection of mathematically determined shapes or objects; each object in the picture has properties such as width, height, fill colour, line colour eg
<rect height=”96” width=”128” y=”3” x=”90” stroke-width=”6” stroke=”#cc0000” fill=”#ffcc33” id=”yellowrectangle”>
Bitmap Graphics – made up of a grid of pixels and stored in memory as a bit pattern of ones and zeros (calculations are mentioned later in this booklet)
Sound – sample rate (the number of times the value of the signal is recorded) and its bit depth (the number of bits used to store the sample)
Video – storing video requires both images and sound to be stored together; files will be very large as a result so compression is always used unless the video is being recorded for editing later; each frame in an MPEG video is compressed as a JPEG; the data that stays the same in successive frames is then removed
Processor: consists of several different parts:
the Arithmetic and Logic Unit which performs calculations;
the Control Unit which loads, decodes and executes instructions,
Registers which are small memory locations used by the processor
Cache: a faster kind of memory which stores copies of the data from frequently used main memory locations
Read Only Memory: Permanent memory; data is not lost when power switched off; this memory is very important and is used to store programs, like the operating system, for a long time
Random Access Memory: used to hold all data required for an active program or application to run; data is transferred from backing storage to RAM and held there until it is no longer required by the processor
Address Bus: identify the address of the location in cache or main memory that is to be read from or written to; uni-directional
Data Bus: will transfer data to/from the address that is held on the address bus; bi-directional; the amount of data that can be carried by the data bus depends on the word size (width of the data bus)
Interfaces: used to allow peripheral devices and hardware to connect to a computer system; allow for differences in speed and the way that data is handled by each peripheral device; an example is a USB; responsible for voltage conversion, status signals, data format conversion
