See also my section on SuperComputers.


CPU (Central Processing Unit). A CPU is the core of a computer, i.e. the processor, the ALU (Arithmetic Logic Unit), and the internal memory. It is composed of the main silicon chips of the computer which do the actual processing, as opposed to merely supporting functions like RAM or controlling peripherals. The processor itself is often referred to as the CPU.

  1. The CPU takes data from the RAM and input devices. The CPU takes two kinds of data:
    1. Instructions. The jobs (commands, data processing orders). EG: A Print command.
    2. User Data. The content (input data) that the instructions work on. EG: An image.
  2. The CPU then process the data.
  3. The CPU then outputs the data to the RAM. The RAM communicates with the and I/O (input/output) devices.

The system bus (FSB, Front Side Bus) is the data throughput between the CPU and the RAM.

Applications usually know how to give instructions to a family or sub-family of CPUs (EG: x86 CPUs). The outer layer of a CPU can then translate (decode) the application instruction into internal instructions that that particular member of that family can understand (EG: 80286 CPU).

This layering enables some degree of backwards compatibility and encapsulation. However each generation of a family added new instructions (amongst other changes) so that some applications required the new generation to work. EG: +26 instructions with the 80386, +6 with the 80486, and +8 with the Pentium.

There are different groups of internal instructions, which is outside of the family "grouping". Here they are in chronological order.

From the 80386DX and on, all CPUs have FPUs (Floating Point Unit processors) built in to help deal with non-whole numbers.

The clock speed (clock frequency) of a CPU refers to the number of clock ticks per second, hence this is usually measured in MHz. The clock ticks is tied to a crystal on the CPU and basically the CPU does something with each clock tick. The clock speed is one of the most common measure for the power of a CPU.

The internal clock speed (inside the CPU) could run higher than the external clock speed because of electromagnetic noise on the system bus or limitations on the RAM MHz. Clock factoring (clock doubling) is when the internal MHz is greater than the external MHz. Variations on the clock factor was the primary reason for the x486 variations.

Because of clock factoring, caches have been used to buffer data or store it temporarily since the 4th generation.

The register (data width) refers to how many bits the CPU can handle simultaneously.

Since the 5th generation some CPUs have enabled more pipelines (parallel processing) within the CPU so more instructions can be executed per clock tick.


Here are the CPUs that are compatible with the UNIX, DOS, and Windows OSes.

(usu. by Intel)
Year Transistors Basic Stats Notes
0th 4004 1971 --    
1st 8086 1978 29,000 0.5 MIPS
5-10 MHz.
8087 FPU.
16 b register.
16 b bus.
8088 1979   0.5 MIPS
5-8 MHz.
The IBM PC and PC/XT.
2nd 80286 1984 134,000 1.5 MIPS
8-12 MHz.
The AT.
80287 FPU.
Virtual memory.
16 MB address space.
3rd 80386       80387 FPU.
32 b register.
80386DX 1985 275,000 10 MIPS
16-33 MHz.
FPU built in.
Multi tasking.
4 GB address space.
80386SX 1988   2.5 MIPS
16 b bus
16-33 MHz
80386SL 1990   5 MIPS
32 b bus
20-25 MHz
32 b bus.
Better power management.
4th 80486DX 1989   30 MIPS
25-50 MHz
8 KB L1.
80486SX 1991   20 MIPS
16-33 MHz
Like DX but without the coprocessor.
80486DX2 1992   50 MIPS
50-66 MHz
8 KB L1.
80486DX4 1994 1,200,000 70 MIPS
75-100 MHz
16 KB L1.
5th Pentium  (80586) 1993 3,100,000 125 MIPS
60-200 MHz
64 b bus.
6x86 by Cyrix 1996      
K5 by AMD 1996      
WinChip C6 by IDT 1997 3,500,000    
5th + Pentium MMX 1997 4,500,000 166-200 MHz 32 KB L1.
6x86MX by IBM/Cyrix 1997 6,000,000    
WinChip2 3D by IDT 1998 6,000,000    
6th Pentium Pro (80686) 1995 5,500,000 150-200 MHz 16 KB L1 and 256 KB L2.
Socket 8.
K6 by AMD 1997 8,800,000   64 KB L1.
Pentium II 1997 7,500,000 233-333 MHz 32 KB L1.
Slot 1.
K6-2 by AMD 1998 9,300,000   64 KB L1.
6th + Mobile Pentium II   7,400,000    
Mobile Celeron 1998/06 18,900,000   32 KB L1 + 128 KB L2.
Xeon 1998   400+ MHz Slot 2 form factor for data transfer between the CPU and L2.
Pentium III 1999 19,300,000 450+ MHz 32 KB L1.
K6-3 by AMD       64 KB L1 + 256 KB L2.
Pentium III CuMine 1999 28,000,000   32 KB L1 + 256 KB L2.
7th K7 Athlon by AMD 1999 22,000,000   128 KB L1.
K7 Athlon Thunderbird by AMD 2000 37,000,000   128 KB L1 + 256 KB L2.
Pentium 4 "Meced" 2001 42,000,000   VLIW.
8th Opteron "SledgeHammer" by AMD       64 b register.
Itanium "Madison" 2003-05     Hyper-Threading.
Itanium 2 "Deefield" 2003-09     Lower voltage and size.

Here are CPUs compatible with the Macintosh OS, with the later ones also UNIX OS capable.

CPU Year Notes
6800 1984  
68020 1986  
68030 1987  
68040 & 68LC040 1992  
68060 1993  
Power PC 601 1994 RISC
Power PC 603 & 603e 1995  
Power PC 604 & 604e 1996  
Power PC G3 740 & 750 1997  
Power PC G4 1999 iMacs, Xserve.
64 b register.


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