Counting Transistors: Why 1.16B and 995M Are Both Correctby Anand Lal Shimpi on September 15, 2011 12:16 PM EST
Yesterday we published Ivy Bridge's transistor count as 1.48 billion. It turns out that was wrong as Intel's Mooly Eden accidentally read the B in billion as an 8 while on stage. The real number is 1.4 billion. When we published that story we compared it to Intel's Sandy Bridge, which at launch was said to be 995 million transistors. However at IDF Intel had been using another number: 1.16 billion transistors. It turns out both are right, but why is there a difference?
When designing a microprocessor you end up with a schematic of all of the circuits and transistors in the design. With the design schematic done layout is next on the list. However sometimes in the process of moving from the schematic to layout phase, transistor count baloons. The reason is simple. There are some circuits which may be represented by a single transistor at the schematic phase, but for more efficient layout use four transistors in tandem. For Sandy Bridge the 995M number is for the number of transistors in the schematic, while 1.16 billion is how many transistors are put down at the fab. Both are correct, but the 1.16B number is directly comparable to Ivy Bridge's 1.4B transistors.
That puts Ivy Bridge's transistor count at 20.7% higher than Sandy Bridge, which is more in line with what to expect from a tick.