1 The System Unit Lecture 2 CSCI 1405 Introduction to Computer Science Fall 2006

2 Overview This lecture covers: How the CPU, memory, and other components are arranged inside the system unit How the CPU works Strategies to speed up a computer and create faster computers

3 Inside the System Unit The system unit of a PC is the case that houses processing hardware and other hardware. All of the hardware contained within the system unit is connected to the system board or motherboard.

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5 CPU The CPU (central processing unit) does the vast majority of processing for a computer. CPUs contains a variety of circuitry and components and are connected to the motherboard. Also called the processor or microprocessor.

6 CPU, Cont’d. Processing speed (clock speed) is measured in megahertz (MHz) or gigahertz (GHz) and measures the number of clock ticks per second. A computer word is a group of bits or bytes that a CPU can manipulate at one time. Other factors that affect the speed of the computer include the amount of RAM and cache memory, bus width, and bus speed.

7 Memory: RAM RAM (random access memory) is the computer’s main memory and is used to temporarily storage programs and data with which it is working. RAM is volatile (erased when the power to the PC goes off). RAM comes in a variety of types, speeds, and size. Types of RAM include: DRAM SRAM SDRAM DDR SDRAM RDRAM DDR-II SDRAM

8 Memory: Other Types Cache memory—fast memory chips located on or close to the CPU chip (L1, L2, and L3). Registers—high speed memory built into the CPU. ROM (read-only memory)—non-volatile chips inside which data or programs are stored. Flash memory—non-volatile memory that can be erased and reused. Used both within the PC and for portable storage media (e.g digital cameras).

9 Buses Buses are electronic paths that data travels around on a computer system. Internal buses move data around within the CPU. Expansion buses establish links with peripheral devices. ISA, PCI, AGP, USB, FireWire.

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11 Expansion Slots and Cards Expansion for desktop PCs. Expansion cards can be inserted into expansion slots on the motherboard. Some external devices can be plugged into existing USB or FireWire ports without adding another expansion card. PC cards—used with notebook PCs. Expansion for handhelds and mobile devices—can have proprietary, PC card, or SDIO slot.

12 Ports Connectors to which devices can be attached. Common ports: Serial Parallel SCSI USB FireWire Network Keyboard Mouse Monitor Modem MIDI IrDA Game

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14 How the CPU Works The CPU is a collection of electronic circuits and components. Impulses from an input device passes through RAM and enters the CPU via a system bus. Within the CPU the impulses move through the circuits and components to create new impulses. Eventually, a set of electronic impulses leaves the CPU for an output device.

15 Typical CPU Components Arithmetic/logic unit (ALU) Control unit Registers Prefetch unit Decode unit Internal cache Bus interface unit

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17 The System Clock and the Machine Cycle The system clock synchronizes the computer’s operations. The machine cycle is the series of operations involved in the execution of a single, machine-level instruction. Fetch Decode Execute

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19 Making Computers Faster Now and in the Future Speeding up your system today. Add more memory. Perform system maintenance. Buy a larger or second hard drive. Upgrade your Internet connection. Upgrade your video card. Upgrade your CPU.

20 Making Computers Faster Now and in the Future Cont’d. Strategies for making faster computers. Moving circuits closer together. Faster and wider buses; faster memory. Improved materials (copper, SOI, new materials). Pipelining.

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22 Making Computers Faster Now and in the Future, Cont’d. Strategies for making faster computers, cont’d Multiprocessing (multiple CPUs, each working on a different job) and parallel processing (multiple CPUs working together to make one job finish sooner).

23 Summary Inside the system unit How the CPU works Making computers faster