Adders, Latches, Memory

10 atomic recall cards. Export to Anki and let spaced repetition do its slow work.

In Anki: File → Import, choose this TSV, set field separator to Tab, deck = Sand to Silicon · Ch 20, note type = Basic.

Front	Back
What are the three inputs and two outputs of a full adder?	Inputs: two operand bits and a carry-in. Outputs: sum and carry-out.
How many NAND gates does a full adder require?	Nine NAND gates.
What is a ripple-carry adder?	A chain of full adders in which the carry-out of bit i feeds the carry-in of bit i+1; the answer ripples through bit by bit.
What is the ALU?	Arithmetic Logic Unit — the collection of adders, subtractors, shifters, bitwise logic units, and comparators that does a CPU’s arithmetic in one clock cycle.
What is an SR latch built from?	Two cross-coupled NAND gates — each gate’s output feeds the other gate’s input.
How many transistors does an SR latch use in CMOS?	Eight — four transistors per NAND gate, two gates.
How frequently must DRAM be refreshed, per the JEDEC spec?	Within every 64 milliseconds.
How many architectural general-purpose registers does x86-64 have?	16 (rax, rbx, rcx, …).
How many architectural general-purpose registers does ARM64 have?	31 (x0 through x30; x31 is reserved as zero or stack pointer).
Why are registers the fastest memory in the computing universe?	They live next to the ALU, are built from cross-coupled NANDs, and are accessed in a single clock cycle — a third of a nanosecond at 3 GHz.