Btec National - COMPUTER Systems 1 Computer Systems Week 1 The Basics – System Unit Components

Btec National - COMPUTER Systems 2 Aims Discussion into what will be covered in this Unit Understand the basic principles Gain an understanding into the system components A knowledge of Buses

Btec National - COMPUTER Systems 3 What is covered in this Unit? Computer systems –System Unit components –Peripherals –Computer selection (complete systems) Operating systems –Operating system functions –Computer operations (i.e. files structures, tailoring of interface (user need))

Btec National - COMPUTER Systems 4 What is covered in this Unit? – Cont. Design a computer system –Selection (i.e. processor, memory, storage) –User needs (Costs, particular requirements)

Btec National - COMPUTER Systems 5 Basic principles – Computer configuration CPU Central Processing Unit Input device Output device keyboard mouse microphone screen printer speaker Can you name any other input and output devices?

Btec National - COMPUTER Systems 6 Basic principles – Cont. Input devices CPU Central Processing Unit Input device Output device Input devices Capture information from the real world Send data to the CPU

Btec National - COMPUTER Systems 7 Basic principles – Cont. Output devices CPU Central Processing Unit Input device Output device Output devices Are sent data by the CPU Convert the data to an understandable form, e.g. images on screen, sounds, printed text

Btec National - COMPUTER Systems 8 Basic principles – Cont. What is data –Data is unorganised facts, numbers, letters and symbols represented in a formalised manner suitable for communication, interpretation and processing by computers. (Binary code) What is information? –Information is data which has been assigned a commonly understood meaning. (Human understanding)

Btec National - COMPUTER Systems 9 Basic principles – Cont. Where is data stored CPU Central Processing Unit Input deviceOutput device Main memory Backing store Hard disk USB device CD DVD RAM

Btec National - COMPUTER Systems 10 Basic principles – Cont. How is data stored –All computer data is stored as binary patterns. –Binary patterns are combinations of 1s and 0s, e.g –Each 1 or 0 is known as a bit. –Binary patterns are usually stored in groups of 8, 16, 24, 32 or 64 bits.

Btec National - COMPUTER Systems 11 System Components Have a go at the online test – Before we move on (Quiz-Hardware-Parts)

Btec National - COMPUTER Systems 12 System Components – Cont. The main system unit components are: –CPU (Central processing unit) –Cache Memory –Internal Memory: RAM – Random Access Memory, ROM – Read Only Memory –Hard disk –Motherboard

Btec National - COMPUTER Systems 13 System Components – Cont. CPU (Central Processing Unit) –Controls the transmission of data from input devices to memory –Processes the data held in main memory –Controls the transmission of information from main memory to output devices

Btec National - COMPUTER Systems 14 System Components – Cont. CPU – How it works A CPU - also known as a microprocessor - is a complete computation engine that is fabricated on a single chip.

Btec National - COMPUTER Systems 15 System Components – Cont. The CPU uses its ALU (Arithmetic Logic Unit) to enable it to perform mathematical operations like addition, subtraction, multiplication and division. Modern CPUs contain complete floating point processors that can perform extremely sophisticated operations on large floating point numbers. A CPU can move data from one memory location to another. A CPU can make decisions and jump to a new set of instructions based on those decisions.

Btec National - COMPUTER Systems 16 System Components – Cont. CPU – fetch-decode execute cycle –The fundamental operation of most CPUs, regardless of the physical form they take, is to execute a sequence of stored instructions called a program. This is achieved by using the fetch-decode and execute cycle.

Btec National - COMPUTER Systems 17 System Components – Cont. CPU – fetch-decode execute cycle –Fetch involves retrieving an instruction from program memory. The location in program memory is determined by a program counter (PC), the program counter keeps track of the CPU's place in the current program. Often the instruction to be fetched must be retrieved from relatively slow memory, causing the CPU to stall while waiting for the instruction to be returned. This issue is largely addressed in modern processors by caches.

Btec National - COMPUTER Systems 18 System Components – Cont. CPU – fetch-decode execute cycle –Decode The instruction that the CPU fetches from memory is used to determine what the CPU is to do. In the decode step, the instruction is broken up into parts that have significance to other portions of the CPU. The way in which the numerical instruction value is interpreted is defined by the CPU's instruction set architecture (ISA). Often, one group of numbers in the instruction, called the opcode, indicates which operation to perform. The remaining parts of the number usually provide information required for that instruction, such as operands for an addition operation.

Btec National - COMPUTER Systems 19 System Components – Cont. CPU – fetch-decode execute cycle –Execute During this step, various portions of the CPU are connected so they can perform the desired operation. If, for instance, an addition operation was requested, an arithmetic logic unit (ALU) will be connected to a set of inputs and a set of outputs. The inputs provide the numbers to be added, and the outputs will contain the final sum.

Btec National - COMPUTER Systems 20 System Components – Cont. CPU – Clock Speed –To synchronize the steps of the fetch-decode execute cycle, all processors have an internal clock which generates regularly timed pulses. –All activities of the fetch-decode-execute cycle must begin on a clock pulse.(megahertz (MHz) or gigahertz (GHz).)

Btec National - COMPUTER Systems 21 System Components – Cont. CPU – Word Size –A word is simply a fixed-sized group of bits that are handled together by the CPU. –The word size is the number of bits that the CPU can process simultaneously. –Normally groups of 8, 16, 32, 64, 128 bit words are processed as a unit during input, output and logic instructions.

Btec National - COMPUTER Systems 22 System Components – Cont. CPU – Cache Memory –high-speed memory used as a temporary store for recently processed instructions and data, or those which the CPU predicts will be processed soon –Much quicker to access instructions and data from cache memory than requesting it from normal RAM Two types of cache exist, Level 2 (L2) and Level 1 (L1) –L2 cache can be on the motherboard, located between the CPU and RAM –L1 cache is part of the CPU itself. Cache memory is typically very expensive, so would be prohibitive in great quantities.

Btec National - COMPUTER Systems 23 System Components – Cont. Internal Memory –RAM (Random Access Memory) –ROM (Read Only Memory)

Btec National - COMPUTER Systems 24 System Components – Cont. RAM –RAM can be altered; it is the main memory used in the system to store data and programs whilst the computer is running. Its contents are lost when power is removed (volatile storage).

Btec National - COMPUTER Systems 25 System Components – Cont. RAM - exists in many different formats –SRAM – Static Random Access Memory More expensive memory, normally reserved for cache memory; fast because its data doesn’t need to be refreshed electronically. –DRAM – Dynamic Random Access Memory Cheaper and slower than SRAM because its data needs to be periodically refreshed. –SDRAM – Synchronous Dynamic Random Access Memory All the features of DRAM but faster as it can access multiple data addresses at the same time. Its primary advantage is that its speed is synchronised to the speed of the processor.

Btec National - COMPUTER Systems 26 System Components – Cont. ROM –Read-only memory is a class of storage media used in computers and other electronic devices. Because data stored in ROM it cannot be modified (at least not very quickly or easily), it is mainly used to by firmware (i.e. BIOS – Basic Input Output System used to identify and initialize system component hardware such as the video display card, hard disk etc)

Btec National - COMPUTER Systems 27 System Components – Cont. Hard disk - Commonly either: –PATA (IDE - Integrated Drive Electronics interface) – older parallel technology which has 2 channels, each supporting a slave and master device –SATA (IDE - Integrated Drive Electronics interface) – newer serial technology (hot swapping) –Hard drives provide permanent storage of data and programs which would otherwise be lost from a computer’s RAM when power is removed (non- volatile storage).

Btec National - COMPUTER Systems 28 System Components – Cont. Motherboard – –This is the main circuit board that all of the other internal components connect to. – –The CPU and memory are usually on the motherboard. Other systems may be found directly on the motherboard or connected to it through a secondary connection. – ) –For example, a sound card can be built into the motherboard or connected through PCI (Peripheral Component Interface) or a graphics card connected via the AGP (Accelerated Graphics Port)

Btec National - COMPUTER Systems 29 System Components – Cont. Motherboard media.arstechnica.com

Btec National - COMPUTER Systems 30 Buses Buses –A bus is a collection of parallel data tracks on the motherboard used to permit data flow between subsystems. –Common examples include the data bus, address bus, control bus and the processor bus.

Btec National - COMPUTER Systems 31 Buses Data bus –The data bus is used to transmit the actual data to the different components on the motherboard –The width of a data bus determines how many bits can be transmitted simultaneously and the maximum address which can be referenced.

Btec National - COMPUTER Systems 32 Buses Address bus –An address bus is a computer bus, controlled by the CPU for specifying the physical addresses of computer memory elements that the requesting unit wants to access (read or write).

Btec National - COMPUTER Systems 33 Buses Control bus –A control bus is (part of) a computer bus, used by CPU for communicating with other devices within the computer. While the address bus carries the information on which device the CPU is communicating with and the data bus carries the actual data being processed, the control bus carries commands from the CPU and returns status signals from the devices, for example if the data is being read or written to the device the appropriate line (read or write) will be active.

Btec National - COMPUTER Systems 34 Buses Processor bus –This is also called the front side bus (FSB). It is the bidirectional link between the motherboard and the processor itself. –The Front Side Bus (FSB) is the data transfer bus that carries information between the CPU and the Northbridge of the Motherboard.

Btec National - COMPUTER Systems 35 Conclusion We discussed the Unit outcomes Looked into the basic principles of a computer system Discussed the system unit components Acquired a knowledge of system buses