Anatomy of a Computer

1. Anatomy of a Computer RAM, ROM, CPU, etc. [This material can be found in Chapt. 3 of Discovering Computers 2000 (Shelly, Cashman and Vermaat).]

2. A chip off the old block • Millions of transistors are connected into what is called an integrated circuit or chip • The most important chip in a computer is the microprocessor • The microprocessor houses the Central Processing Unit (CPU), the “brain” of the computer • Ex. The Pentium II is a microprocessor

3. How many? • Word size and bus width • Computing means moving bits around, so an important question is how many bits can be handled at one time • analogy: two-lane, four-lane or eight-lane highway

4. How fast? • Each of the computer’s manipulations (instructions) begins a “tick” of the clock • So the faster the clock ticks, the faster the computer • Clock speed: a measure of how fast the computer is, given in MHz (megahertz - millions of cycles per second) • Middle number written on LaSalle’s computers

5. How fast? (Cont.) • Sometimes one instruction can be started before the previous one was complete • Like have a batter on deck • So another measure of speed is useful • Instructions per second, another measure of speed, is measured in MIPS (millions of instructions per second)

6. The mother of all circuit boards • chips and other things are connected together on what is called a circuit board • the mother board, a.k.a. the system board, holds the main components of the computer • CPU • clock • connectors • expansion slots, ETC.

7. The fan and the sink • The chips, especially the microprocessor can get hot • heat sink: the strangely shaped metal or ceramic structure sitting on the processor that serves to draw away the heat • there’s also a little fan near the processor; that’s often what you hear on old computers

8. A link to the outside world • The process of putting information into or getting information out of a computer is called interfacing or input/output (IO) • ports are sockets, typically in the back of a computer, where one plugs in the cable connecting the computer to the IO devices

9. Two types • serial • data sent one bit at a time • for modems and some printers • cable can be very long • ex. MIDI, USB • parallel • data sent eight bits at a time • limit on length of cable • ex. SCSI

10. SCSI port • Small computer system interface • pronounced “scuzzy” • allows more than one device to be connected to a single port • daisy chain: getting the output for a second output device from the first (rather than directly from the computer), the output for a third can come from the second and so on

11. A connector in every port • Ports have connectors, as do cables • connectors come in two varieties • male: have pins sticking out • female: have holes to receive pins

12. Analog to Digital • Any measurement that can be converted to an electronic signal (voltage or current) can be directly fed into a computer • the original data is often continuous (analog) and must be converted into digital form • This signal can be fed in through a port (typically the RS-232 port) so long as the appropriate software is installed

13. In the cards • Expansion Slot: A socket designed to hold the circuit board for the device, such as a sound or video card, that adds capability to the computer system • Adapter cards: additional circuitry and chips that extend your PC’s capabilities allowing you to customize it

14. Some types of cards • video or graphics card: enhancescomputer’s ability to convert output into video and send it to the monitor • Sound card: improves your computer’s sound capabilities, be it input (microphone) or output (speakers) • internal modem: allows computer to connect to networks via phone lines and such

15. Plug and play • refers to computer’s capability to figure out what to do when new expansion cards and devices are added • this way the user does not have to know how to “configure” the system

16. Memories • Saving information we have entered (e.g. onto floppies) is referred to as “storage;” it is long term and slow by computer standards (storage  memory) • Before we save the data, it is in the computer’s memory, i.e. in memory chips, which hold the information temporarily • Memory also holds the instructions a computer needs to operate

17. ROM • Read Only Memory • This memory is loaded up by the manufacturer (some is programmable) • contains low-level instructions for the computer • Not lost when the computer is turned off • “nonvolatile” memory • “stored program concept”

18. RAM • Random Access Memory • The memory the user uses • The programs one loads and the data one enters are here • Lost when the computer is turned off • “volatile” memory • random?

19. Random Vs. Sequential • A cassette tape is sequential access; you have to go through song one and two to get to song three • A CD is random access; you can jump directly to song three

20. Some Types of RAM • Dynamic RAM (D-RAM): dynamic means changing, which for memory is not necessarily a good thing, so dynamic memory must be continually refreshed • Synchronous DRAM — when the memory update and clock are better coordinated (“in synch”) • Static RAM (SRAM) doesn’t need constant refreshing, is faster but more expensive than dynamic

21. Cache • pronounced “cash” • it’s an area of high-speed memory (often SRAM) • Instead of looking through the slower RAM, data is looked for here first, a speedy intermediary • You often encounter the term while surfing the web; data from a web site can be stored in a cache

22. Buffer and Clipboard • Buffer: where data coming in (from input devices) or going out (to output devices) is stored until the transaction is complete • Clipboard: Memory location where data is placed during an application such as word processing (cutting or copying puts data on the clipboard); it is also used to transfer data from one application to another (e.g. from Excel to Word)