Download - Anatomy of a Computer RAM, ROM, CPU, etc. Chapter 4 in Computing Essentials (O’Leary and O’Leary)
A chip off the old block
Millions of transistors are connected into what is called an integrated circuit or chip
Chips are made from silicon (a semiconductor, a material halfway between a conductor and an insulator)
“Silicon valley” is a nickname for the region south of San Francisco that contains an unusually high concentration of computer companies.
CPU
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 III is a microprocessor
Extending the brain analogy
Similar to dividing the brain into Brain stem Forebrain
We divide the CPU into Control Unit Arithmetic Logic Unit (ALU)
How good is your computer?
Computing means moving bits around, so an important question is how many bits can be handled at one time
Word size: how many bits are handled at a time (8, 16, 32, 64) by memory or the processor
Bus size: how many bits can move around at once analogy: two-lane, four-lane or eight-lane highway
Bus speed: how fast they move
How fast is it?
Each of the computer’s manipulations (instructions) begins with 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) There are gigahertz machines now
Middle number written on LaSalle’s computers
Speed II
Sometimes one instruction can be started before the previous one was complete
Like have a batter on deckSo another measure of speed is useful instructions per second, given in MIPS
(millions of instructions per second) (considered by some to be a misleading
measure of speed)
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
If you can’t stand the heat
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 whirring away on old computers
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 Newer computers have a port in
the front for convenience
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
SCSI port
Small computer system interfacepronounced “scuzzy”allows more than one device to be
connected to a single portdaisy 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
A connector in every port
Ports have connectors, as do cablesconnectors come in two varieties
male: have pins sticking out female: have holes to receive pins
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 so long as the appropriate software is installed
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
Some types of cards
video or graphics card: enhances computer’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
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
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 (“stored program concept”)
Reading and Writing
The basic actions involving memory are WRITING: putting information into
memory READING: getting information from
memoryThe rest of the time memory just
holds onto information
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
RAM
Random Access MemoryThe memory the user uses The programs one loads and the
data one enters are here Lost when the computer is turned off “volatile” memoryWhy is it called random?
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
Some Types of RAM
Dynamic RAM (DRAM): dynamic means changing, which for memory is not necessarily a good thing, so dynamic memory must be continually refreshed Synchronous DRAM: when the memory and a
clock work together to send blocks of data more efficiently
Static RAM (SRAM): doesn’t need constant refreshing, is faster but more expensive than dynamic
Cache
pronounced “cash”The computer puts information it
anticipates (guesses) you will use soon in a place which is accessed more quickly
A correct guess is called “a cache hit”, an incorrect guess “a cache miss”
Caching improves speed
Some kinds of cache
Memory cache: put information from DRAM into SRAM (high-speed memory) L1 on the chip with the microprocessor L2 on a different chip
Disk cache: put information from storage (floppy or hard drive) into memory
Browser cache: put information from internet into hard drive
Buffer
where data coming in (from input devices) or going out (to output devices) is stored until the transaction is complete
Printer buffer: when you send something to print, it may not print right away, but instead sit in the printer buffer awhile There is usually an icon on the task bar
indicating that you have something in the printer buffer