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Ken Shirriff

The original Pentium was power-hungry, so Intel soon released an updated version that could turn off the clock to parts that weren't being used, saving power. The original (P5 architecture, part number 80501) on the left has a noticeably larger die and package than the update (P54C, 80502). The original was built with Intel'ss 800 nm BiCMOS process, while the update was 600 nm.

Two Pentium packages. Each package is a purple ceramic square with a silicon die in the middle and a grid of numerous gold-plated pins surrounding the die. This package is called a Pin Grid Array (PGA).
16 comments
Ken Shirriff

Here's a closeup of the die showing the Pentium Processor name and the Intel copyright. The M-in-a-circle is a Mask Work symbol, like a copyright but for IC masks. I convinced the Unicode Consortium to add the symbol to Unicode, but I don't think any fonts support it yet: 🆭
Edit: seems like the symbol works for lots of people.
3/N

A closeup of the die showing tiny text with bond wires on either side.
[DATA EXPUNGED]
Ken Shirriff

@thomasmey As Wikipedia says, the presence of the copyright symbol "continues to affect remedies available to a copyright holder whose work is infringed."

Ken Shirriff

The Pentium die has a lot of initials from the designers, in various shapes and sizes. These photos show a subset of the initials. Intel removed the initials from the next revision (80502).
4/5

A closeup of the die showing dozens of initials between two bond wires.
Initials of various sizes next to some circuitry. The initials are arranged vertically. Some are either a pair of initials or four letters, it's unclear. E.g. ZBGK. There is a three-letter initial: YBM
Initials formed by vias. The vias between two metal layers are arranged to make letters as a grid of dots.
Small and large initials arranged vertically and horizontally.
Ken Shirriff

I made this diagram to show the different functional blocks on the Pentium P5 die.
5/5

The Pentium die with functional blocks labeled. The code cache and data cache are large blocks on the left. The integer datapath (the superscalar integer execution unit) is a vertical rectangle in the middle. The floating point unit is a vertical rectangle next to it. Instruction fetch and instruction decode are at the top, with branch prediction logic nearby along with the microcode ROM.
Tommy Thorn

@kenshirriff The Bus Interface Logic block seems shockingly large, half the area of either cache. What's going on?

Ken Shirriff

@tommythorn In comparison, on the 8086, the Bus Interface Unit is roughly half the chip. The Bus Interface is doing a lot: performing prefetches, handling memory and I/O bus cycles, handling interrupts, bus hold, bus locking, cache operations, and so forth.

Ryan Finnie

@kenshirriff TIL Zaphod Beeblebrox was a chip designer. Explains why he went on to put his initials onto his own brain.

sofia ☮️🏴

@kenshirriff i see it, it's pixelated so i'm pretty sure its from GNU Unifont.

Danny Boling ☮️

@kenshirriff

Ken, do you recall what the dimensions are of this label? I suspect the vertical lines are an indication of something but I don't know of what.

Ken Shirriff

@IAmDannyBoling The vertical lines are columns of 5 tiny dots, vias from the power and ground rails to the metal layer below.

Danny Boling ☮️

@kenshirriff

Right. But what are the dimensions of the label itself? I'd love to know just how tiny that label must be.

Ken Shirriff

@IAmDannyBoling The label is pretty big by IC standards: the rectangle holding the text is 1.1 by 0.2 mm.

Danny Boling ☮️

@kenshirriff

That's even smaller than I thought it would be. Thank you so much for your entertaining and very inform posts, Ken.

XtoF

@kenshirriff I think I remember that the oroginal Pentium was still a 5V chip. If correct, that would explain a good deal of its power consumption.

Ken Shirriff

@xtof Yes, the Pentium using 5V was a lot of the power consumption problem.

slash

@kenshirriff I can't help but compare this to ENIAC, and ESDAC, where the clock was how all the parts worked together to produce the result. The idea of turning it off to some parts of the machine is a crazy leap of invention.

(Of course, in ENIAC, if you didn't need parts of the machine, you just jumpered around them. I think they still consumed mass quantities of power, though.)

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