# Is there a one-to-one relationship between bits and transistors?

I am a beginning student of computer science trying to understand hardware architecture.

I am wondering if 1 bit is always equal to 1 transistor. If not, what is the relationship between bits and transistors? How are bits implemented at the hardware (transistor) level?

As far as I understand, data is stored as a sequence of bits, and components like RAM consist of transistors, so it seems like each of those bits would be stored in a transistor.

• No. Apples and Oranges. You can't compare bits to transistors. A single transistor can't store anything. Recommended material: youtube.com/… Mar 13, 2022 at 16:06
• Related: Wikipedia: DRAM Most importantly, though: It does not matter. Except for very special environments, you should never have to worry about these details, as they are abstracted away by the architecture and operaring system. Mar 13, 2022 at 16:17
• A standard light switch is 1 bit of information - it's "on" or "off", 1 or 0. But this comparison is no more meaningful than asking whether a transistor - which may be "on" or "off" -- is 1 bit. You could, if so inclined, design a circuit where the on/off state of a single transistor conveyed 1 bit of data - we tend to call those "I/O lines". For memory, there are better choices, for example various flip-flops.
– passer-by
Mar 13, 2022 at 22:10

### No, not exactly, and not even close except for a special case or 2

A bit is an abstract unit of information.

A transistor is a physical thing, a current (BJT) or voltage-controlled (FET) switch, more or less. Modern digital logic uses FETs (CMOS), so voltage-controlled.

In DRAM, a transistor and a capacitor can temporarily store a bit (when used as part of a DRAM array with other transistors for addressing and so on).

Or a single transistor plus a resistor can (in RTL logic) implement a NOT gate which flips 1 bit. (A CMOS NOT gate takes 2 transistors.)

In general no, it's not sensible to say that a transistor is a bit. If you're talking about how many transistors are needed to implement a cache or register file with a given capacity, then it becomes relevant that an SRAM cell usually consists of 6 or more transistors. (https://en.wikipedia.org/wiki/Static_random-access_memory#Design). Using more than 6 can help it work more stably at low voltages, saving power. (Modern CPUs have such tiny transistors that they're more limited by power density than number of transistors. See http://www.lighterra.com/papers/modernmicroprocessors/ - it's a very good overview of CPU-architecture stuff, but at a higher level than individual transistors.)

When not part of a whole array of memory, a bit might be stored by a flip-flop / latch made of multiple transistors to implement clock, set/reset, and input, depending on what type of flip-flop.

That wikipedia link shows some flip-flop designs. A bit is the state of voltages on those transistors, not the transistors themselves. Or you can say that the flip-flop has a storage capacity of 1 bit.