Chapter 4 The Central Processing Unit: What goes on Inside the Computer

Components of the CPU Control Unit (CU) Directs system operations Communicates with the ALU and memory Arithmetic Logic Unit (ALU) Performs calculations

ALU Operations Arithmetic operations Addition (+) Subtraction(-) Multiplication (×) Division (÷) Logical operations Equal-to (=) Less-than (<) Greater-than (>)

Components of the CPU Registers Temporary storage High speed Not part of memory System clock Controls speed of processing Does not keep date/time

Instruction Execution Machine cycle: Fetch – get an instruction Decode – interpret, then get data from memory Execute – perform the instruction Store – move the result to memory or a register

Data Representation Bit (Binary Digit) ON (1) OFF (0) Byte 8 bits Stores one character Word Number of bits processed at one time The size of a register 32 or 64 bits for PCs

Coding Schemes Assigns a number to each characters ASCII – 1 byte per character Used on PCs and larger computers 256 possible characters EBCDIC – 1 byte per character Used on IBM mainframes 256 possible characters

Coding Schemes Unicode – 2 bytes per character Allows characters from languages other than English Used by Java, a programming language for the web 65,536 possible characters

Memory Types RAM Random Access Memory Volatile – lost if the power goes off Often called main memory ROM Read Only Memory Non-volatile Required for booting the computer

Memory Types CMOS RAM Stores info about computer hardware Requires battery power

Memory Each location has unique address Fast access regardless of location Programmers use names instead of address numbers

Memory and Storage Capacities Kilobyte (KB or K) – approx. one thousand bytes Exactly 1024 bytes Megabyte (MB) – approx. one million bytes Gigabyte (GB) - One billion bytes Terabyte - One trillion bytes

System Unit the box or case that houses the electronic components of the computer Inside the system unit you find: CPU Memory Motherboard Power supply And much more

System Unit’s Motherboard CPU Memory Expansion slots Connections to other components

Microprocessors Intel Pentium Celeron Xeon, Itanium Intel-compatible Cyrix, AMD Non-Intel PowerPC Alpha

System Bus Copper lines on the motherboard For example, from memory to CPU Transports data and instructions Bus width Bus speed

Expansion Buses Expansion boards Ports Serial ports Parallel ports Universal Serial Bus (USB) PC Card Bus

Measuring Computer Time Millisecond—one thousandth of a second Microsecond—one millionth of a second Nanosecond—one billionth of a second Picosecond—one trillionth of a second

Computer Processor “Speed” The frequency of pulses from the system clock MHz – megahertz, one million pulses (ticks) per second GHz – gigahertz, one billion pulses per second The higher the number, the faster the CPU can process instructions.

PC Processor “Speed” Common processor frequencies 1.53 Gigahertz ( 1,530,000,000 ticks per second ) 1.8 GHz 2.2 GHz 2.8 GHz

Cache Very fast memory Stores frequently used instructions Level 1 - Built into the processor chip Level 2 - Separate chips Usually 256 KB or 512 KB Cheaper than level 1 Most PCs have Level 2 cache

Flash Memory Nonvolatile RAM Uses Cellular phones Digital cameras Handheld computers

Some of the factors affecting overall speed of a computer CPU speed Amount and speed of RAM Speed and size of bus lines Amount and speed of L1 and L2 cache Register size (Word size)

Shopping for a Computer 1. Decide what software you will need. What do you want to do with the computer? ?Web browsing? Word Processing?Spreadsheet? Make CD’s?Edit photos or movies? ???

Shopping for a Computer 2. Determine the types of hardware needed for the software. Make a list of hardware specifications. , Web browsing, and other Internet related software requires a modem or other hardware to connect to the Internet.

Shopping for a Computer Word processing, spreadsheet, and presentation graphics don’t require a super-fast processor or much memory. Want to print your document? You will need a printer.

Shopping for a Computer Large databases, lots of music files, photos, or videos require a large amount of hard drive space and a lot of memory. Want to make your own music CDs? You need a writable CD drive.

Shopping for a Computer If you use statistical or mathematical, photo editing, or video editing software, you’ll need a fast processor and a lot of memory. Want to watch movies on your computer? You’ll need a DVD drive and a fast processor.

Shopping for a Computer 3. Set a price range. Typical PC’s sell from $ 500 to $ 2000 Some software will come with the system, but you may need to purchase additional software to meet your needs. The cheapest computer is usually not the best choice.

Shopping for a Computer 4. Learn about manufacturers, their reputations, service and support provided, etc. Instructor’s Top 5: Hewlett-Packard (Compaq) Dell Gateway IBM Sony

Shopping for a Computer 5. Compare available systems Sunday paper ads Store flyers TV ads Manufacturer’s web sites Watch the fine print. “after rebates”, “monitor sold separately”, “when you sign up for MSN”, are common.

This Week’s Ad Celeron Processor: 2.4 GHz (gigahertz) Memory: 256 MB (megabytes) Hard drive: 80 GB (gigabytes) Other drives: DVD and CD-RW Monitor: 17” color Printer: color inkjet Manufacturer: Medion $ ($ after rebates)

End of Chapter Questions 1. The electrical circuitry that executes program instructions is the ______. a. register b. operator c. central processing unit d. bus line

End of Chapter Questions 2. The entire computer system is coordinated by ___. a. the ALU b. the control unit c. registers d. arithmetic operators

End of Chapter Questions 5. The primary storage unit is also known as _____. a. a register b. Mass storage c. Secondary storage d. memory

End of Chapter Questions 8. Computer operations are synchronized by _____. a. the CPU clock b. The binary system c. megabytes d. E-time

End of Chapter Questions 12. A letter, digit, or special character is represented by a ______. a. bit b. byte c. kilobyte d. megabyte

End of Chapter Questions 14. _____ cache is built into the CPU chip. a. L1 b. L2 c. external d. disk

End of Chapter Questions 16. The main circuit board in a personal computer is called the _____. a. fatherboard b. motherboard c. ram/bus board d. ASCII board