Intel Processor Socket Types (Jan 00)
In order to make life simple, Intel took to giving the sockets for their processors numbers so you could refer to them easily. This means you can go into a shop and ask for a new Intel processor to fit your motherboard, which has a socket X. It isn't as simple as this, of course, as now you have to think about whether the correct combination of voltages is available to the socket. Later Pentium processors need more than one voltage to operate and this wasn't accounted for in earlier motherboards. Beware! And read your motherboard manual carefully.
This was last revised
05-Jan-2000 but changes regularly. Some information may already be out of date.
Socket 1
This is an obscure 486 socket that you are unlikely to encounter. It contains
three rings of 17x17 pins (169 in total) and supports 486 processors up
to the DX2-66 at 5V. It's definitely not zero-insertion force and you're
unlikely to get the chip out in one piece without a special tool.
Socket 2
As Socket One, but with 19x19 pins (238 in total). This was an improvement
on Socket One to support the planned Intel Pentium overdrive chip (P24T)
- if you could get the 486 out without leaving half the pins behind.
Socket 3
Again for the 486 processor, this time with 3.3V support. The original 486
ran on 5 volts whereas later versions (the DX2-100) ran at 3.3V. All the
motherboard Socket Three could be switched to accept the DX2-66 which was
the last of the 5V 486s, but the reverse is not necessarily true. Intel
does produce an 'Pentium' overdrive that will fit this socket - the P24T.
It runs at 83MHz, but obviously can't give you the double-width bus of the
Pentium. It never came down in price and is rather hard to get hold of now.
In my experience, it is also rather hard to get working.
Socket 4
This is original Pentium 60 and 66MHz socket. These operated on a straightforward
5V and are incompatible with the P75 and greater. The only other chip you
can use with this socket is the Intel Pentium 60/66 overdrive, which uses
a clock multiplier to get things moving faster. Don't try to plug anything
else into a Socket Four, and don't waste your money on the overdrive - it
will not be as fast as a modern Pentium of the same speed because the old
motherboard will present a serious bottleneck.
Socket 5
When the low-voltage Pentium 75 appeared, Socket Five replaced Socket Four.
This supports all Pentiums up to 133MHz (occasionally only 120MHz due to
lack of jumpers on the board) and was rapidly replaced by Socket Seven,
which is a superset of socket 5.
Socket 6
Yet another 486 socket, this time for 3.3V processors only. In practice
this means the 486DX4-100 or its Pentium overdrive chip. This socket is
rare.
Socket 7
This is the current Pentium Socket, which is used for the P75 to P233 and
MMX chips and the AMD/IBM/Cyrix/IDT Pentium equivalents. It will also accept
all Socket Five processors. It differs from Socket Five in that the specification
requires a higher current be available for the 3.3V supply, in includes
a 'key' pin and has support for dual-voltage processor detection and higher
clock multiplier rates.
Unfortunately some of these processors require 3.3V or 2.9V or 2.8V to operate
(as well as 5V on some pins). The motherboard documentation should tell
you which processors are supported and which jumpers are required to support
them. A few motherboards, from late 1996 onwards, are 'auto-sensing' which
means there are no jumpers to fiddle with. This is not always made clear
in the manual, which often lists settings for non-existent jumper anyway.
Your only option if there are no jumpers is to plug and pray.
Super Socket 7
Intel tried to kill of Socket 7 and move everyone to Slot 1. The rest of
the world decided it liked socket 7 and upgraded it to run at 100MHz in
order to run faster versions of the AMD K6.
Socket 8
This special socket is for the Pentium Pro, and this is all you can fit
in to one. The advantage of a Pentium Pro is that you can easily build a
four-processor system using it. The disadvantages are cost, performance
and cost. You don't hear too much about the Pentium Pro these days, and
Intel is about to kill it. There is now an overdrive version, which boosts
the speed to up to 333MHz. It's really a Pentium II in a different package,
as far as I can tell, with the exception that the connection to the on-board
cache runs at full speed.
Socket 370
Another attempt by to kill Socket 7, and Super Socket 7 along with it. The
Socket 370 is so named because it supports 370 pins. It is, presumably,
cheaper to produce than a Slot 1 system and is designed to take a specially
packaged version of the Intel Celeron. The Celeron is a cheap version of
the Pentium II which, up until Socket 370, went into a Slot 1 motherboard.
Interestingly, the Celeron is just about as fast as the Pentium II at the
same clock speed, and Intel have had to increase the clock speed to keep
up with AMD. This means that you're better off buying a Celeron than a PII
(or even PIII). It's a bit of a farce.
Now Intel are releasing a Pentium III to fit into a socket 370 and you can
get adapters to plug a 370 processor into a Slot 1 motherboard.
Slot 1
When Intel switched from sockets to slots with the Pentium II the numbering
was restarted. Slot One was for the Pentium II, running from 233MHz to 333MHz.
A variant on Slot One boosts the motherboard bus speed from 66MHz to 100MHz
which can be used to support Pentium III processors up to 600MHz last time
I checked, with the latest 133MHz bus speeds offering 733MHz processors.
This was once assumed to be what Slot 2 was all about, but see below. Early
Slot 1 boards running with a 100MHz bus option could be identified because
the only chip-set to support this speed was the 440BX. The GX set was released
next, and now most modern chipsets support it.
Originally Slot 1 was limited to 450MHz for the main processor but that
has been thrown out of the window. I mention this in case anyone remembers
me saying this was the case in the last revision. It was the case then.
Finally, take care when upgrading from a 66MHz external bus Pentium II to
a 100MHz version - even if the motherboard is designed to run at this speed
the RAM may not be. As 100MHz DIMMs cost more, the chances are pretty good
that they won't have been fitted as standard.
Slot 2
This was the designated replacement for the Pentium Pro - the Pentium II
Xeon. The Xeon is designed with servers in mind, with eight-way multiprocessing,
error correction; thermal protection and other goodies built in. Originally
available in 400 and 450MHz variants with between 512K and 1Mb of level
two cache, they aren't cheap. I'm not sure they were even called Slot 2
in the end.
Slot A
This is AMD's bid to displace Intel in the processor stakes. Having built
better Socket Seven processors than Intel for quite some time, AMD have
now produced a better Slot to go with their next generation processor -
the K7 (released as Athlon). With a cleverly devised instruction set, 200+MHz
external and 500+MHz internal speeds and massive amounts of cache it'll
be an interesting processor if and when they produce one (they have now
and the rest is history).
Although Slot A is physically the same as Slot 1 the processors won't be
compatible, at least initially. Isn't that always the way?
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