103a-ai PC Lab

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Ellen's Open-it Up! Lab

The main parts inside a computer, and how they work

The Processor is the fundamental part of a computer that makes it… well, a computer. The Processor (also called a CPU, short for central processing unit, or a microprocessor, or “the Chip”) is essentially a glorified two-bit adder. That means that by combining thousands of simple silicone transistors into a single chip, and organizing them with Boolean Gates, we can create a simple calculator-like “brain” which is capable of nearly any function. Using the Boolean logic functions AND, OR, and NOT, and the binary code of electrical impulses traveling through the transistors, the Processor can accomplish almost limitless tasks - as long as you can write programs in a language that the CPU understands and as long as you have memory. The Processor has its own memory cache and is also connected to larger memory storage – both permanent and temporary – which we’ll talk about more below. The speed at which a CPU processes information determines how many GHz (or gigahertz) it is. For example, if your computer says it has a 3 GHz processor (which is the current standard for new computers) then that means your CPU is processing 3 billion instructions per second. Per second! It would take well beyond your lifetime to be able to process 3 billion separate instructions. CPU’s used to process in MHz (or megahertz) which were millions of instructions per second. Processors can be any of several brands including Intel Pentium Processors (which are what we were dealing with in our Open It Up! Lab), K6’s, Sparc’s, or Power PC’s.

Computer Memory is stored in several ways. First, there’s the small memory cache in the CPU itself which the Processor uses to work on current tasks. Second, there are the SIMM memory cards, or memory sticks, which attach to the motherboard (more explanation later) and also the CPU, allowing the Processor to have access to substantial short-term, temporary, easily-accessible memory while it operates, also making it possible for the Processor to pre-fetch. Pre-fetching is when the CPU goes to long-term memory in order to retrieve data it needs for a specific task and then it estimates what other relevant data it might need to complete related tasks in the very near future and retrieves that data as well. Third is the long-term, permanent storage of the hard disk, or hard drive, which I’ll explain below. The data stored in these memory systems is organized in bits, bytes, Megabytes, and Gigabytes. A bit (short for binary input) is a single unit of information – essentially either the 1 or the 0 (the on or the off, the true or the false). 8 bits is a byte and allows for up to 256 (or 2 to the 8th power) possible bits of data. Megabytes are a million bits and Gigabytes are a billion. That’s an awful lot of available memory storage – and therefore an enormous amount of memory to house the operating system (which organizes and instructs all the essential functions of the computer and serves as the platform for absorbing and interpreting any and all software programs) and also to run programs with. Think of how much memory must be used in finding the solution to a simple mathematical equation. Now imagine how much you might need to run a word processing program. By using the language of binary, condensing information into bits, bytes, etcetera, and by advancing silicon transistor technology, computers can now do enormous amounts of processing while fitting into smaller and smaller packages. Memory storage that used to fill a room now fills a few memory cards or “chips.”

The CDROM/DVDROM Drive or Optical Drive is the hardware in a computer that allows it to read information off of a CD or DVD and use it (or at least display/play it). The surface of every CD or DVD is covered with billions of microscopic pits – each pit represents a bit - and by the presence or absence of a pit, a pattern is created which the optical laser in a CD/DVD reader uses to read how many bits there are and in what order, which the computer interprets as data (through the miracle of programming!). The surface is literally pitted so that the laser gets bumped along to the next track without just endlessly following around the same track forever. Because of the microscopic pits, even a minor scratch can derail the laser and completely compromise the ability of the computer to read and/or interpret the data.

The Hard Disk or Hard Drive is the permanent or long-term memory storage for the computer. Every Hard Disk is literally a highly smooth and polished disk suspended in a casing with a read-write head just above it. The highly reflective surface of the disk is completely smooth (unlike a CD or DVD with their billions of pits) and magnetized with the same kind of material used for cassette tapes. Because magnets naturally have two poles, it is very easy to transmit binary data magnetically. And since data is added or removed magnetically, this also creates the danger of easy accidental erasure by having your computer’s hard disk too close to a strong magnet. The read-write head speeds across the radius of the disk while the disk spins at high speed. As fast as the disk spins, the read-write head can move so fast that it appears to be flicking back and forth between two locations, rather than covering the entire surface of each track on the hard disk. As the disk spins, the read-write head reads the entire length of each “track” on the hard disk, each track being loaded with stored bits of memory, and doesn’t skip to the next track until it has been all the way around the disk on its first track. The speed at which the hard disk operates is incredible. It is common for a hard disk to send data to the CPU at 5 to 40 megabytes per second and for it to only take 10 to 20 milliseconds for the Processor to receive data it requests from the hard-disk.

The Power Supply provides the electrical energy the computer needs to function. While a computer, being relatively highly efficient, needs only 5 to 12 volts of electricity to operate, 110 volts are the common load for U.S. electrical sources. Typical electrical wiring also delivers electricity in AC or alternating currents which are infinitely easier to send over long distances; but computers require steady DC or direct currents to function, so the power supply also serves as an adaptor which regulates the flow of electricity and converts AC into DC.

Cables are the physical connectors between the different parts of a computer which are flexible and mobile and therefore not wedded to the motherboard, unlike the metal wiring which connects the circuits and chips on the motherboard’s surface. The cables function like bit-highways, transmitting data between various components of the computer. Cables are sized based on how many bits they transport.

The Motherboard is the hardware that makes computers possible. It serves as the physical platform on which all the essential components depend for inter-communication. The motherboard is basically millions of transistors and wiring with ports, buses, and sockets to attach to all the other essential components. The kind of Processor in your computer is determined by which socket the motherboard has built into it to receive the CPU. The amount of RAM memory (the temporary memory found on the SIMM cards) is determined by what type of bus (or interface) and how many slots of this bus are built into the motherboard. Optional features are determined by what kind of daughter boards or memory cards fit into the PCI bus on your motherboard – this determines things like extra temporary memory, audio cards, graphics cards, and any manner of other special features you expect from a computer. The motherboard is basically the communication highway of the computer, and by sending electrical impulses (and therefore data or bits) along the millions of tiny wires built into the motherboard, this hardware permits the functioning of the entire computer system.

The system time and basic settings for the computer are regulated by the real time clock which is powered by a small battery. This battery keeps constant time for the whole computer and allows it to stay consistent and functional. A crystal (quartz) attached to the battery maintains a constantly consistent time, just like a metronome, because when quartz is stimulated by electricity it resonates with a naturally consistent pulse. This rhythm, powered by the battery, is what allows the real time clock to maintain its internal sense of time for the whole computer.


  • Personal notes from lectures and labs presented in CSC103: How Computers Work. Instructor: Dominic Thiebaut.

Lab report

Ellen & Adriana Take Apart a Computer

Monday, September 22, 2008

We took apart a 2000 Dell PC but are not sure which model number it was. Here're photos of what it looked like before we tore into it:

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Here's the insides before we messed with it all:

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Here's a section of the side of the computer casing which still has the riser card (or daughter board) screwed in with an audio card attached to the PCI interface on the riser card. It was pretty cool to learn such geeky terms as "PCI Bus" and the distinctions between a graphics card and an audio card and other additional options.

103-ai audiocard.jpg

Here I am with front and rear views of our power supply:

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And this is Adriana holding our CPU! It took us awhile to remember/realize that the CPU was hidden under its own little cooling fan - before that we kept thinking one of the smaller chips on the surface of the motherboard might be our CPU.

103a-ai CPU.jpg

Speaking of which... our beloved motherboard! (back and front)

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It actually took us some time to get down that far; here are more pics of the insides of our computer as we got closer to total disassembly. In the first one you can see the green plastic covers which protected the fan and casing for the CPU. The second photo shows the side of the computer case with the daughter board and audio card still attached to the mother board. In the third, we've emptied the whole shell except for the motherboard and you can see the CPU's personal fan still screwed into the side of the computer case.

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This is Adriana giggling with our optical drive (or the CD/DVD drive):

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Here's me being delighted with memory sticks:

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And speaking of memory, here's our hard-disk! I really wanted to tear it apart but one of the screws was wedged too tightly and our screwdriver couldn't keep a firm grip. Ah well, some day.

103a-ai hardisk.jpg

Adriana got creative with computer parts (specifically the CPU, memory sticks, and an extra cable):

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Here's the audio card finally being separated from the riser card (daughter board) and two photos showing the CPU still settled on its motherboard throne and then the seat of the CPU after we've lifted the little lever and taken the CPU away.

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The tiny button battery!

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And here's everything getting piled back inside with reckless abandon:

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It was super satisfying to finally see all the parts inside these machines I've used almost daily for 12 years. They're really much more simple than I had imagined - even if the actual lay-out of the chips and boards and the overall design is quite complex.