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.

  • 2
    \$\begingroup\$ No. Apples and Oranges. You can't compare bits to transistors. A single transistor can't store anything. Recommended material: youtube.com/… \$\endgroup\$
    – tkausl
    Mar 13, 2022 at 16:06
  • 1
    \$\begingroup\$ 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. \$\endgroup\$
    – DevSolar
    Mar 13, 2022 at 16:17
  • \$\begingroup\$ 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. \$\endgroup\$
    – passer-by
    Mar 13, 2022 at 22:10

1 Answer 1


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.


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