Pentium





The Pentium, is an x86 architecture microprocessor by Intel which first
shipped on March 22, 1993. It is the successor to the 486 line. The Pentium
was originally to be named 80586 or i586, but the name was changed to
Pentium because numbers could not be trademarked.

Major changes from the 486:

   * Superscalar architecture - The Pentium has two datapaths that allow it
     to complete more than one instruction per clock cycle. One pipe (called
     "U") can handle any instruction, while the other (called "V") can
     handle the simplest, most common instructions.
   * 64-bit data path - This doubles the amount of information pulled from
     the memory on each fetch.
   * MMX instructions (later models only) - Special 64-bit functions
     designed for use in multimedia applications.

Pentium architecture chips offered just under twice the performance of a 486
processor per clock cycle. The fastest Intel 486 parts were about the same
speed as a first-generation Pentium; a few late-model AMD 486 parts were
roughly equal to the Pentium-75.

The earliest Pentiums had a clock speed of 66 MHz, with a 60 MHz version
also being produced. Later on 75, 90, 120, 133, 150, 166, 200, and 233 MHz
versions gradually became available. Pentium Overdrive processors were
released at speeds of 63 and 83MHz as an upgrade option for older 486-class
computers.

The original Pentium microprocessor had the internal code name P5, and was a
pipelined in-order superscalar microprocessor. This was followed by the
P54C, a compaction which was dual-processor ready. Subsequently, the P55C
was released as the Pentium with MMX Technology (usually just called Pentium
MMX); it was based on the P5 core, but had significant changes for MMX and
improved instruction decoding.

In early 5 volt 60 MHz and 66 MHz Pentiums, a problem in the floating point
unit code when doing division was discovered in 1994 and is known as the
Pentium FDIV bug. These early examples of Pentium processors were also known
for their fragility and relatively high levels of heat-production.

Intel has retained the Pentium brand name for later generations of processor
architectures, which are internally quite different from the Pentium itself:

   * Pentium Pro
   * Pentium II
   * Pentium III
   * Pentium 4
   * Pentium M

It can be seen from this that brand name is only loosely related to the
nature of a CPU's microarchitecture. The Pentium brand is now used for
desktop parts, the Celeron brand is used for "value" parts (typically lower
performance and lower price), and the Xeon brand is used for
high-performance parts suitable for servers and power-users. The same basic
microarchitecture may be used for all brands, but implementations may differ
in clock speeds, cache sizes, and package and sockets. Moreover, the same
name is used for chips with unrelated microarchitectures.