IB Computer Science Topic 2 1 1 By

IB Computer Science Topic 2. 1. 1 By: Mr. A. Lawson

IB Computer Science Topic 2. 1. 1 Outline the architecture of a central processing unit (CPU) and the functions of the arithmetic logic unit (ALU) and the control unit (CU) and the registers within the CPU. Key Terms: • CPU = Central Processing Unit • ALU = Arithmetic Logic Unit • CU = Control Unit • Registers = small temporary storage spaces inside the CPU

IB Computer Science Topic 2. 1. 1 Central Processing Unit Video: How are CPUs made CPU definition: The key component of a computer system, which contains the circuitry necessary to interpret and execute programing instructions for the computer device. CPU

IB Computer Science Topic 2. 1. 1 Examples of ALU’s & CU’s Function of the ALU • Part of the CPU that does all the arithmetic (+/-) and logical (AND/OR) calculations • Sometimes an ALU is referred to a “core”, hence computers with dual core technology have two ALU’s to process two calculations simultaneously.

IB Computer Science Topic 2. 1. 1 Two functions of the CU: It handles the loading of new commands into the CPU and the decoding of these commands. Also, it directs the data flow and the operation of the ALU. Computer Architecture: • In 1945, a scientist called Von Neumann suggested that a computer system be slip into a processor module (where the instructions are calculated) and a memory module (where instructions and data are stored). • We still use this model today: CPU and Primary Memory

IB Computer Science Topic 2. 1. 1 Special relationship between CPU & RAM CPU needs it’s own “memory” • Registers: they are small, very fast circuits that store intermediate values from calculations or instructions inside the CPU. • There are many small units, but the four most important ones are the following: 1. MAR 2. MDR 3. Accumulator 4. Program Counter

IB Computer Science Topic 2. 1. 1 Program Counter & Accumulator • Program Counter holds the memory address of the next instruction. • Accumulator holds the intermediate results of the currently running instructions. MAR (Memory Address Register) • MAR is connected to the address bus. • MAR contains a memory address. • MAR’s sole function contains the RAM address of the instruction the CPU wants next.

IB Computer Science Topic 2. 1. 1 MDR ( Memory Data Register) • MDR is connected to the data bus. • MDR holds data that will be written to the RAM or that was read from RAM. • Relationship between MAR & MDR: The MAR gives the address the data of the MDR will be read from or written to.

IB Computer Science Topic 2. 1. 2 Describe the Primary Memory.

IB Computer Science Topic 2. 1. 2 RAM = Random Access Memory • Contains the data and instructions the computer has loaded since starting up and everything the user has opened or loaded. • Is volatile = loses its contents if the power is lost • Has a special link to the CPU ROM = Read Only Memory • Originally its contents were static (“read only”) and could not be changed – not true any more (“flash upgrades”). • Non-volatile = does not lose its contents if the power is lost • Stores the BIOS (Basic Input Output System) – a small program that allows the computer to know what to do to find the operating system to “boot” the computer after power is restored. RAM ROM Volatile Non-Volatile Contains user’s programs and data that has been loaded since “booting up” Contains the BIOS Usually measured in Gigabytes (common capacities are 1 GB, 2 GB or 4 GB) Usually measured in Kilobytes (much smaller than RAM)

IB Computer Science Topic 2. 1. 2 Connections between RAM & CPU • Control Bus (bi directional) • Address Bus (uni directional-from CPU to RAM only) • Data Bus (bi directional) • Bus = a set of wires that connect two components in a computer system IB Computer Science Topic 2. 1. 3 Explain the use of cache memory.

IB Computer Science Topic 2. 1. 3 Memory Primary RAM Secondary HDDs ROM Flash Cache Definition: Cache A type of small, high-speed memory inside the CPU used to hold frequently used data, so that the CPU needs to access the much slower RAM less frequently

IB Computer Science Topic 2. 1. 3 IB Computer Science Topic 2. 1. 4 Explain the machine instruction cycle. Simplified model:

IB Computer Science Topic 2. 1. 4 Simple Model #2 Video's Tutorials to explain Video 1: Video 2: IB Computer Science Topic 2. 1. 5 Identify the need for persistent storage

IB Computer Science Topic 2. 1. 5 Why do we need “storage”? Processing done in CPU * Has no storage Stores results / data in RAM * HDD/SSD Types of storage * RAM is volatile (looses contents if power is lost) Needs to be stored on persistent storage

IB Computer Science Topic 2. 1. 6 Describe the main functions of an operating system Hierarchy of Software Operating System Software Utilities Drivers / Libraries Application Software Games Word processor Productivity Spread sheet Specialist Browser

IB Computer Science Topic 2. 1. 6 Functions of an operating system A. Provides a user interface B. Does memory management C. Does peripheral management D. Allows multi-tasking E. Provides security A. User interface • OS has to provide a link between the user and the computer hardware. • Types of user interfaces: ü Graphical User Interfaces (GUIs) that have menus and icons, graphics, desktop style. ü Command Line Interfaces (CLIs) where the user types in codes, data entry style. ü Natural Language Interface (NLIs) where the user speaks to the interface. ü Menu Based Interface (MBIs) which gives the user a selection of options.

IB Computer Science Topic 2. 1. 6 Examples of user interfaces GUI CLI NLI MBI B. Memory Management • • Memory management is done by keeping track of storage devices (like HDD) and controlling which application has access to which area of memory (RAM). Each location in memory can be read, modified, and written to by the OS. When the memory location is full the OS sends a confirmation message. Similarly, the OS provides file management services by sorting out where data is stored on the disk drives and memory. The OS allows users to organize files in folders as well as to copy and delete files. Examples of memory management File manager for managing files on HDD Memory manager for RAM to make sure programs don’t use same memory space

IB Computer Science Topic 2. 1. 6 C. Peripheral management • • • The OS coordinates the basic input and output systems (the BIOS). Keyboard, mouse, monitor and printers are controlled through device drivers. A device driver is a software program which allows hardware devices to be used by the OS. They act as translators between the devices and the computer system. Peripheral management example