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Computer

The word computer can be defined in many ways and can also take many different meanings; a somewhat common definition may be this: computer is a machine that automatically performs mathematical computations. We can also see it as a machine for processing information or, very generally, as any tool that helps computation, in which case one's fingers or even a mathematical formula itself can be considered a computer. Here we are of course mostly concerned with electronic digital computers.

We can divide computers based on many attributes, e.g.:

Computers are theoretically studied by computer science. The kind of computer we normally talk about consists of two main parts:

The power of computers is limited, Alan Turing mathematically proved that there exist problems that can never be completely solved by any algorithm, i.e. there are problems a computer (including our brain) will never be able to solve (even if solution exists). This is related to the fact that the power of mathematics itself is limited in a similar way (see Godel's theorems). Turing also invented the theoretical model of a computer called the Turing machine. Besides the mentioned theoretical limitation, many solvable problems may take too long to compute, at least with computers we currently know (see computational complexity and P vs NP).

Typical Computer

Computers we normally talk about in daily conversations are electronic digital mostly personal computers such as desktops and laptops, possibly also cell phones, tablets etc.

Such a computer consists of some kind of case (chassis), internal hardware plus peripheral devices that serve for input and output -- these are for example a keyboard and mouse (input devices), a monitor (output device) or harddisk (input/output device). The internals of the computer normally include:

  • motherboard: The main electronic circuit of the computer into which other components are plugged and which creates the network and interfaces that interconnect them (a chipset). It contains slots for expansion cards as well as connectors for external devices, e.g. USB. In a small memory on the board there is the most basic software (firmaware), such as BIOS, to e.g. enable installation of other software. The board also carries the clock generator for synchronization of all hardware, heat sensors etc.
  • CPU (central processing unit): Core of the computer, the chip plugged into motherboard that performs general calculations and which runs programs, i.e. software.
  • RAM/working memory: Lower capacity volatile (temporary, erased when powered off) working memory of the computer, plugged into motherboard. It is used as a "pen and paper" by the CPU when performing calculations.
  • disk: Non-volatile (persisting when powered off) large capacity memory for storing files and other data, connected to the motherboard via some kind of bus. Different types of disks exist, most commonly hard disks and SSDs.
  • expansion cards (GPU, sound card, network card, ...): Additional hardware cards plugged into motherboard for either enabling or accelerating specific functionality (e.g. GPU for graphics etc.).
  • PSU (power supply unit): Converts the input electrical power from the plug to the electrical power needed by the computer.
  • other things like fans for cooling, batteries in laptops etc.

Notable Computers

Here is a list of notable computers that have existed.

name year specs (max, approx) comment
Antikythera mechanism -125 ~30 gears, largest with 223 teth 1st known comp., by Greeks (mech., analog)
Z3 1941 176B RAM, CPU 10Hz 22bit 2600 relays 1st fully programmable electronic digital computer
ENIAC 1945 ~85B RAM, ~5KHz CPU, 18000 vaccum tubes 1st general purpose computer
PDP 11 1970 4M RAM, CPU 1.25Mhz 16bit legendary mini
Apple II 1977 64K RAM, 1MHz CPU 8bit popular TV-attached home computer by Apple
Atari 800 1979 8K RAM, CPU 1.7MHz 8bit popular TV-attached home computer by Atari
VIC 20 1980 32K RAM, 1MHz CPU 8bit, 20K ROM successful TV-connected home computer by Commodore
IBM PC 1981 256K RAM, CPU 4.7MHz 16bit, BASIC, DOS 1st personal computer as we know it now, modular
Commodore 64 1982 64K RAM, 20K ROM, CPU 1MHz 8bit very popular TV-connected home computer
ZX Spectrum 1982 128K RAM, CPU 3.5MHz 8bit successful UK TV-connected home comp. by Sinclair
NES/Famicom 1983 2K RAM, 2K VRAM, CPU 1.7MHz 8bit, PPU TV-connected Nintendo game console
Amiga 1985 256K RAM, 256K ROM, CPU 7MHz 16bit, AmigaOS personal compuer by Commodore, ahead of its time
SNES 1990 128K RAM, 64K VRAM, CPU 21MHz 16bit game console, NES successor
Deep Blue 1995 30 128MHz CPUs, ~11 GFLOPS 1st computer to defeat world chess champion
GameBoy Color 1998 32K RAM, 16K VRAM, CPU 2MHz 8bit, 160x144 handheld gaming console from Ninetendo
GameBoy Advance 2001 ~256K RAM, 96K VRAM, CPU 16MHz 32bit ARM, 240x160 handheld gaming console from Ninetendo
ThinkPad X200 2008 8G RAM, CPU 2.6GHz, Wifi legendary laptop, great constr., freedom friendly
ThinkPad T400 2008 8G RAM, CPU 2.8GHz, Wifi legendary laptop, great constr., freedom friendly
Raspberry Pi 3 2016 1G RAM, CPU 1.4GHz ARM, Wifi very popular tiny inexpensive SBC
Arduboy 2016 2.5K RAM, CPU 16MHz ARM 8bit, 1b display tiny Arduino open console
Pokitto 2017 36K RAM, 256K ROM, CPU 72MHz ARM indie educational open console
Raspberry Pi 4 2019 8G RAM, CPU 1.5GHz ARM, Wifi tiny inexpensive SBC, usable as desktop
PD computer planner LRS computer
Deep Thought fictional computer from Hitchhiker's Guide ...

TODO: mnt reform 2, ti-89, PS, XBox, quantum?