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Virtual
exhibition |
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Move the mouse over the picture to find out more. The physical version of this exhibition can be found in the Faculty Tower building, basement level, next to the elevators.
This unit is about 5 years old, and working fine. The more recent ones are about half this size, and provide about twice as much power. The cables entering the cabinet carry the electricity not only to the mainboard on bottom shelf, but also for the hard and floppy drives. The led display on the top shelf gets its full supply via the motherboard.
This display is a home-made appliance, made by Elod Csirmaz. The bigger black dots (2) next to the leds are transistors, the small ones (3) are resistors. The total cost of the parts of this display was around 1 dollar. The wires (4) connect the display to the parallel port of the add-on composite card on the bottom shelf of the same cabinet; the running computer program has instructions to determine the status of the leds in the matrix. By arranging the leds differently, or having more leds you can produce your own living show. This small gadget is a peripheral of the computer. Similar devices can be used, when attached to a PC, for switching lamps on and off, closing and opening doors, or starting the microwave in the morning. This is an output device, as in this case the information flows from the machine outwards.
This hard drive used to hold 1 gigabyte of information. This means one thousand Megabytes, or one thousand times one million bytes, i.e. 1,000,000,000 bytes. This information is about as much as can be found in 2,500 books altogether. To hold that much data, all four sides of the two metal disks are used; the W/R heads can swing into around 1000 different positions. In each position, as the disks turn under the heads, the full information on all of these four surfaces is read, or written. Then the heads move the next position to read the next chunk of data. The part of the surface which is swept by the heads in a single turn of the disks is called cylinder. When the drive is in idle position, as is in the picture, the head is in the innermost cylinder, or in the parking position. When it starts, the disks start to spin, and the heads are moved to the outermost cylinder, the home position. There is some information about the hard drive itself: how the data is arranged, what are the encoding methods, etc. Thus the drive first wants to read all of these data; if it cannot do that then the whole drive is unusable. For the rest this is not so critical: if there are erroneous positions on the disks, the drive itself can rearrange the data so that that place will never be used later. In each half an hour, the drive is switched on. You can hear the click when the power supply starts pouring energy into it. It waits about two or three seconds, then the disks start to spin. They make about 10,000 rounds per second. When the disks are at full speed, the drive moves the R/W heads into their home position, reads the data stored there, and then it is ready to accept commands from the computer. When switching off, first it moves the heads into the parking lot, then stops the disks.
At the upper right-hand corner is the electronics (1); that chip is a complete computer by itself. This chip talks to the main board via the keyboard cable. The mainboard instructs the keyboard as to which led should be on and which led off; and the keyboard sends the status of its keys. The main ingredient of this keyboard is the green foil seen on the left-hand side (2). The black dots (3) are two interweaving conductors each, which are not connected. Above each dot there is a key; the key rests on a rubber bell (4). When the key is pushed, the rubber bell collapses, and the black coal dot at the lower side is pushed against the conductors. The conductors are thus connected; this is recognized by the small computer and recorded as a "key hit". Similarly, when the key is released, the rubber bell pops up, and then the conductors are disconnected; this signifies as "key release".
Hard drives are for storing big amount of data. As they are very sensitive devices, they are covered and their innermost secrets are not revealed.
1. This red metal disk is from a 20 Mbyte hard drive. Those drives worked on the same principle as their more recent siblings. Drives with 40 Mbyte capacity had two of that kind of disks installed. 2. These are the metal disks on larger capacity drives (120 Mbyte on the left and 720 Mbyte on the right). 3. This long arm keeps the write/read heads, one for each surface (two for one disk, four for two disks). They are not much bigger than the period at the end of this sentence. They write and read information to and from the disks. The long arm positions the heads into almost a thousand different positions very accurately. 4. This is the cover of the right disk drive. The small white filter absorbs even those microscopic dust particles which get into the case. 5. The electronic part connects on one hand to the mechanical device and the computer. It is responsible to position the head, rotating the disks, understanding the messy information coming from the reading heads, and delivering the appropriate signals to the writing heads. It has also a built-in error-correcting algorithm, which can recover a 32 bit data even if one of the bits is wrong.
3.5 inch high density floppy drive
In the long upper slot marked by (1) is the write/read head. The head moves forward and backward as the drive reads the information from the floppy. The small metal cylinder at the right-hand corner (2) is the stepping engine; its task is to move the head into one of the 80 possible positions, called cylinders. Every half an hour, the computer switches on the drive. First the disk starts spinning, then the head moves backward to the farthest position (i.e. when it is reading from the outermost part of the floppy), then it makes several steps toward the center. Usually this device is covered by a metal sheet (removed here). The cover's purpose is twofold: first, it keeps (part of) the dirt off the heads; and second, it shields the device electromagnetically, thus it can work more reliable.
The 1.2 floppy drive was a big technical advancement, the biggest problem to be solved was to produce finer electromagnetical dust. This dust is similar to the one used for video tapes, the difference is the density of writing. The higher density, that is the higher capacity, required a more uniform and finer dust. The 1.2 floppy drive was the standard attachment to the IBM AT (Advanced Technology) personal computers. The write/read head (1) is at the far end, next to it is the electronics (2). The rotating engine is just under the device. In each half an hour a "floppy demo" is played, when both floppy drives are switched on. First the inserted floppies start spinning, then the head moves backward to the farthest position (i.e. when it is reading from the outermost part of the floppy). Then the head makes several steps toward the center.
The easiest way to make one is to have a long strip of paper, and using Scotch tape, stick together the short ends just after making a half turn. You can see this strip on the right. The strip has many interesting features. It has only one side: you cannot paint one side blue, and the other one red. Also, it has a single edge: if you trace the edge with your finger, then you will visit every point there. The edge is like a simple circle. Making the edge from a wire, it can be opened to a full circle.
The 3-dimensional mouse in the middle is a home-made appliance which makes it possible to navigate not only on a flat surface (that is, a mouse pad), but also in space, moving the pointer up and down. It was built on a traditional 2-dimensional mouse.
A. One of the novel architecture design features in IBM machines is the extension slots. The longer ones are for 16 bite AT extension cards, the shorter ones for 8 bit XT cards. The motherboard lacks a lot of features, such as connection to a floppy and hard drive, to network, to a mouse, or even to video. These features were provided by add-in cards. B. The motherboard needs memory, too. This one has holder for two type of memory chips. The white holder is for more recent ones (as item 3 is in the working motherboard). The black slots are for older types of these chips. When all memory is installed, the machine had 4 Mbytes, an huge amount that time. C. This empty slot is for the coprocessor. The main processor, which is just right to this empty slot and is of type 286, uses only integer numbers for all computation. Calculations using high precision numbers, such as 1.23, were emulated, i.e. made similar to the methods taught in elementary schools. The coprocessor is a chip which can do those calculations much faster. D. The Read Only Memory (ROM) contains a program communicating to the keyboard; this is where its name comes from: keyboard controller. E. This pair of ROM is the BIOS - Basic Input/Output Service. Its content is preserved even when the machine is switched off. Here are stored those instructions which are executed when the machine is switched on, and also those which provide a very basic functionality. F. This is the power intake, these prongs should be connected to the power supply. On the right you can see the cable to the keyboard, too.
1. This is the power intake. The wires are coming from the power supply. Slightly to the left of the wires is a red cylinder, this is a standby battery. It helps to save configuration information and the date when switching off the machine. 2. These are the so-called BIOS chips. This acronym stands for Basic Input/Output Service. The chips are Read Only Memories (ROMs), and contain a large program. The chips preserve their contents, they do not require any power supply. 3. This is the memory. The white holder has eight slots, and the memory chips can be inserted into these. In this configuration there are four chips, each chip contains 1Mbyte (i.e. 1,000,000 bytes) memory. There are other varieties of chips, 128 kbyte, 256 kbyte (out of which 4 gives 1 Mbyte), 1, and 4 Mbyte memory chips. If all slots are filled with 4Mbyte chips, the total memory would be 32 Mbytes. Presently the machine has a total of 4 Mbyte memory. This memory is also called Random Access Memory (RAM), because its contents can be reached in any order (and not only sequentially as for tapes). These memory cells consist of millions of tiny capacitors. To sustain their status they need power. Thus the content of this memory is lost whenever the machine is switched off. 4. This big chip is the processor itself. Presently it is an Intel 486. The processor executes all the instructions which are stored in the memory. When the machine is switched on, the memory is empty; thus at boot-time, those instructions are executed that are placed at a predetermined place of the BIOS chips. The program checks the attached units, searches for a floppy or hard drive, reads instructions from there, and finally jumps to the read instructions. Intel processors are in the 86 family. The very first one produced in the seventies was called 8086, which was also an advanced edition of an earlier 8080. This was followed by 8186, then by the 286 chip. The 386 had a more advanced architecture; and the 586 was renamed pentium as a reference to the digit 5. 5. Next to the keyboard socket you can see an external battery, this backs up the battery on the motherboard. 6. One of the important novel design features of the IBM Personal Computers was the so-called modularity. It means that slots are provided along with connections to the motherboard's vital wires, which can hold different add-on cards produced by different manufacturers. Here we can see two such cards here. This one is a video card; it produces video signals for the monitor. At boot time the motherboard checks the presence of a video card, and if it can find none, stops. 7. Another add-on card is this composite-card. As its name suggests, it performs a variety of duties; originally these were fulfilled by several cards. At the right-hand side you can see the parallel port connector which connects to the led matrix display. Above this parallel port is the serial port connector which can be attached to a mouse, or to a modem. The card also has two wide wire strips; one goes to the floppy drives, and the other goes to a 8. working hard drive; this time with the metal cover on. It is enclosed in a metal frame; this hard drive contains the demo program. 9. These leds are usually on the front panel of the computer case. The yellow one shows that the main board gets power supply, and the red one indicates hard disk activity: reading or writing data to the hard drive (8).
This early portable machine is a 386 NoteBook, made by Siemens-Nixdorf. The keyboard has been removed, below it you can see the batteries (the yellow cylinders on the left), next to it the hard drive (black box), and a high density floppy drive, with its cover on. Below the LCD panel screen you can see some of the memory chips and the processor itself. The item is a courtesy of professor Nenad Miscevic.
The shelf shows two kinds of network cards. Items 1, 2, and 3 are ethernet, and item 4 is an IBM token ring card. Being older and practically extinct, the token ring card works as follows. Several dozen machines with such cards could be connected into a large loop, using a coaxial cable. The cards, like kids playing, form a ring. There is a token, which is passed from one card to the next one along the ring. When a card wants to transmit, waits until it gets the token, and then sends the message to some other card on the ring. This arrangement prevents two cards speaking at the same time. Unfortunately when there are over twenty machines on the ring, it takes quite a lot until the token arrives to a particular place. The other possibility is to let all cards talk immediately when there is no traffic on the wire. In this case, however, special care should be taken to handle collision, i.e. when two cards start to transmit simultaneously, or almost at the same time. If both of them restart transmitting in a similar way, the collision would occur again and again. Thus in this case the card waits for a random amount of time. This is in nutshell the idea behind the ethernet technology invented by Robert Metcalfe in 1972 at the Xerox Palo Alto Research Center (PARC). This work was an outgrowth of his dissertation at Harvard on "Packet Networks". Interestingly, the dissertation was initially rejected by the University for not being analytical enough. It later won acceptance when he added some more equations to it. Ethernet got its name as a way of describing an essential feature of the system: the physical medium (i.e. a cable) carries bits to all stations, much the same way that the old luminiferous ether was once thought to propagate electromagnetic waves through space.
The larger floppy has paper cover, and quite frequently it was folded, punched, made the disk (and the information on it) useless. The small one is in a hard plastic envelope, which provides better protection. The white paper is a cleansing appliance, which constantly cleans the disk surface as the plastic disc rotates. |
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![[exhibition display]](images/exhibition_szekreny.jpg)
This
is a traditional power supply; the switch is on the left hand side;
facing you is the fan which cools down the unit. The unit converts
the electric voltage coming from the wall outlets (220 volts in
Europe, 110 in USA) to the 5 and 12 volts used inside computers.
This
small display consists of 15 Light Emitting Diodes (leds) arranged
conveniently in a three by five matrix (1). Each
led can be switched on or off independently of the others, thus
a sizeable amount of patterns can appear. Some of them resemble
letters, you can try to figure out what messages are presented.
Hard
Drives are for storing big amount of information. As they are very
sensitive devices, they are covered and their innermost secrets
are not revealed. The two round metal disks at the top are covered
by very fine magnetizable dust (similar material what is used for
video and sound tapes). The writing/reading heads at the tip of
the long handle rewrite and read the magnetic status of the incredibly
small parts of the disks. The distance between the heads and the
surface of the disks is smaller than one tenth of the diameter of
a hair. If a dust particle from the air gets between them, it would
damage the disk beyond any hope of data recovery. This is (one of
the) reason why hard drives are sealed, and tampering with the seal
voids all warranty. 
Your
keyboard when taken apart. There are several different type of keyboards;
this one on this display is only one of the several possible architectures.
They
are called hard because the rotating disc is made of hard metal,
and not of soft plastic as is the case in 
One
of your most well-known device: the 3.5 inch High Density Floppy
Drive, aka small floppy (as opposed to the older 
A
fossil from ancient times: the 1.2 floppy drive. It got its name
from its largest capacity, which is 1.2 Mbytes. (Compare it with
the 
This
shelf is a little tour into an interesting mathematical subject,
namely topology. What you see here is several varieties of the famous
Moebius strip, named after the famous 19th century mathematician
The
two models - the eggs - show what this strip becomes when the edge
is straightened out. A three dimensional computer generated picture
can be seen by 
This
286-motherboard is the base of a typical IBM AT (short for Advanced
Technology) personal computer (better known as
PC). You can compare this with a 
The
heart of all computers is the motherboard. Let us make a short tour
around it. 
Network
cards are add-on cards which fit into the extension slots of the
The
large, 5 and 1/4 inch size floppy (A), and the
smaller, more recent 3 and 1/2 inch floppy (B),
as taken out from its cover. The information is written to the (dark)
plastic disk. The disk is inside an envelope which supposedly protects
it.