A computer is a device that processes data under the control of stored instructions to produce information. Computers can be analog or digital, and classified as supercomputers, mainframes, minis, micros, desktops, laptops, or palmtops. The two main types of supercomputers are the Tianhe-2 in China and Titan in the United States. Computers have various components like a CPU, memory, and input/output devices. Memory can be volatile RAM or non-volatile ROM, and is measured in bits, bytes, kilobytes, megabytes, and larger units. Storage devices have varying capacities depending on their type.

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Computer
A computer is a device or set of
device, which work under the
control of a stored problem (which
can be changed), automatically
accepting and processing data to
produce information.

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Classification ofComputerComputer
Analog
Digital
Super
Mainframe
Mini
Micro
Desktop
Laptop
Notebook
Palmtop
Hybrid

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Analog Computer

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Super Computer
Name Tianhe-2
Location Guangzhou, China
Operating Kylin Linux
Memory 1,375 TB
Storage 12.5 PB
Speed 33.86 PFLOPS
Cost 390 million USD
Purpose Research and Education
Name Titan
Location Oak Ridge N. Laboratory
Operating Cary Linux
Memory 693.5 TB
Storage 40 PB
Speed 17.59 PFLOPS
Cost 97 million USD
Purpose Scientific Research

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Mainframe Computer

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MiniComputer

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Desktop, Laptop, and Palmtop Computer

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Units of Computer
Input System Output
Keyboard
CPU/Processor
MonitorArithmetic
Logic Unit
Control
Unit
Mouse Motherboard Printer
Joystick Ram PlotterPrinter
Scanner HardDiskDrive Microfilm
Disk(CD,Floppy) PowerSupply Disk(CD,Floppy)
CardReader AGP Card/VGACard Speaker/SoundBox
Digital Camera LANCard
Microphone SoundCard
Modem

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Types of Computer Memory
Volatile
RAM
DRAM (DDR, SDRAM)  SRAM
In development
T-RAM  Z-RAM  TTRAM
Historical
Williams-Kilburn tube (1946-
47)  Delay line memory
(1947)  Selection tube (1953)
 Dekatron
Non-volatile
ROM
Mask ROM  PROM  EPROM  EEPROM
NVRAM
Flash Memory
Early stage NVRAM
nvSRAM  FeRAM  MRAM  PRAM
Mechanical
Magnetic tape  Hard Drive  Optical Drive
In development
CBRAM  SONOS  RRAM  Racetrack memory 
NRAM  Millipede memory  FJG
Historical
Paper data storage (1725)  Drum memory (1932) 
Megnatic-core memory (1949)  Plated wire
memory (1957)  Thin-film memory (1962) 
Twistor memory (~1968)  Bubble memory (~1970)

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Classification ofComputer Memory
Memory
Primary/
Volatile
RAM
SRAM DRAM
Secondary/
Non-volatile
ROM
Mask ROM PROM EPROM
EEPROM
Mechanical
Magnetictape Hard drive
Opticaldrive

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Units of MemoryMeasurements
1 Bit = Binary Digit
8 Bits = 1 Byte
1024 Bytes = 1 KB (Kilo Byte)
1024 KB = 1 MB (Mega Byte)
1024 MG = 1 GB (Giga Byte)
1024 GB = 1 PB (Peta Byte)
1024 PB = 1 TB (Tera Byte)
1024 TB = 1 EB (Exa Byte)
1024 EB = 1 ZB (Zetta Byte)
1024 ZB = 1 YB (Yotta Byte)
1024 YB = 1 (Bronto Byte)
1024 Brontobyte = 1 (Geop Byte)

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StorageDevices Capacity of
MicroComputer
RAM HDD
Pen/Flash
Drive
Floppy Disk CD
DVD
Single Layer Dual Layer
128 MB 40 GB 2 GB 1.44 MB 700 MB Normal
256 MB 80 GB 4 GB 4.7 GB 8.5 GB
512 MB 320 GB 8 GB Blu-Ray
2 GB 500 GB 16 GB 25 GB 50 GB
4 GB 1 TB 32 GB
8 GB 2 TB 60 GB
16 GB 128 GB