One of the most important parts of a computer is the Central Processing
Unit (CPU). In a spider web of electronic highways from and to other parts of
the computer the CPU carries out all kinds of instructions. The real CPU is
a very small piece of silicon referred to as the core which is embedded in a
larger casing we call the CPU. Very thin wires attached to the core connect
to larger pins on the packaging. And finally, the pins on the packaging interface
with the motherboard through a Socket.
first CPU's, like the 8080, 8085, 8086 and 8088 had a packaging called DIP,
Dual In Line Package. The Socket for this type of packaging is called DIL, Dual
In Line. Compared to todays Sockets the DIL looks very basic. To insert the
CPU it had to be placed on the Socket and then pressed into it. Much like, for
example a graphics card in an AGP slot. There were only 40 pins, but quite some
force was already needed to press the CPU into the socket.
When the 80286 came, the packaging was changed to the Pin Grid Array,
PGA. This packaging type was also used for the 80386. The CPU still had to be
placed on the socket and then pressed into it. With the 132 pins of the 386
this was a though and potentially dangerous job, 132 pins gave quite some resistance
before slipping into the socket. Bending pins was not unusual even breaking
pins off was possible!
1989 Intel introduced the 486, this CPU had even more pins than a 386 and it
was clear the socket had to change. There had to be a way to install a CPU safely
into a socket, no more bent or broken pins! The result of the search was the
ZIF socket, Zero Insertion Force Socket. This Socket has three parts, the first
part is soldered on the motherboard and has the connectors for the pins of the
CPU. The second part moves over the first part, it will hold the CPU in its
place and is connected to the third part, a lever. Place the CPU in the socket,
then push the lever down. The second part will push the pins firmly against
the contacts of the first part et voila! Almost without force the CPU can connect
with the motherboard.
From the 486 on, all sockets had a name and what better way than to
start with the number 1. The first Socket for the 486 was the SOCKET 1.
After the 486 came the Pentium. The first version which ran at speeds
of 60 and 66MHz used the Socket 4. The ZIF construction was of course used,
how else could a 273 pin CPU be installed?
||Pentium 60 en 66MHz
||Pentium 75 t/m 200MHz
||Pentium, AMD K6/K6-2/K6-3, Cyrix M1/M2
in the CPU business go fast and when Intel worked on their next generation CPU,
a new socket was designed. The Pentium Pro was introduced in 1995 and used the
Socket 8. This CPU was big, bigger than any CPU Intel had designed until then.
The Pentium Pro had the core and secondary cache integrated into one package.
||Pentium Pro 150 - 200MHz
After the Pentium came the Pentium II, the CPU that would be the king
of performance. In order to have the best performance of all CPU at that time
large amounts of cache was needed. Intel had planned to include the secondary
cache into the CPU core, but production techniques at the time were not advanced
enough to do this reliably and cost effective. Another solution had to be found
and Intel came up with this idea : Put the CPU package on a small PCB together
with some cache chips and use the PCB to interface with the motherboard! Slot
1 was born, best described as a ridge with a total of 242 contact points where
the Pentium II package had to be pushed into. No Zero insertion force with a
Slot interface!. The Server market was not forgotten by Intel and the Xeon,
a server CPU, used Slot 2.
||PII, PIII en Celeron
||PII Xeon en P III Xeon
Production techniques developed further and by the time Intel was ready
to introduce their next generation Pentium III it was possible to include the
secondary cache onto the core.
The Slot 1-2 solution was not necessary anymore and the Socket was reinstated.
||PIII, Celeron, Cyrix III
But what about AMD? They have their own line of CPU´s, what sort
of sockets did they use? AMD used the Socket 7 for a long time, the K6, K6-2
and K6-3 all used it. But with the CPU after the K6 family, the K7 also known
as the Athlon (Classic), AMD introduced their own Slot interface. AMD ran into
the same problems as Intel with the secondary cache and used the same solution,
put the CPU and the secondary cach on a PCB. The Athlon used Slot A which was
a reversed Slot 1 with 242 contact points.
After some time AMD´s production facilities were able to include
the secondary cache onto the core and AMD switched back to the Socket. After
all it is cheaper to manufacture a CPU than a CPU and some cache on a PCB. AMD
used Socket A with 453 pins for their socket Athlons.
||Athlon, Athlon XP, Athlon MP and Duron
Next generation CPU´s from AMD and Intel like the Opteron and
Itanium will use new sockets with more pins for increased speed and performance.
It looks like the socket will be used for some time to come but developments
won´t stop and who knows, maybe we will see a return of the Slot!
||AMD Athlon 64
||Intel Itanium 2