JUMPDEST validation prevents landing inside a PUSH immediate sequence. Without it, an attacker could encode a PUSH32 containing 0x5B (JUMPDEST) in its data bytes, then jump to that embedded byte — executing unintended code. The validator scans the bytecode linearly, skipping PUSH immediates, and marks only true JUMPDEST opcodes as valid targets.

Cold SLOAD costs 2100 gas, warm costs 100 gas. This was introduced in EIP-2929 (Berlin upgrade). The rationale is that the first access to a storage slot requires disk I/O, while subsequent accesses hit an in-memory cache. The 21x cost difference reflects the performance gap between disk and memory.

CALLER ($I_s$) is the address that directly invoked the current execution context — it changes with each nested CALL. ORIGIN ($I_o$) is the externally-owned account (EOA) that initiated the transaction — it never changes regardless of call depth. Using ORIGIN for authorization is a security anti-pattern because a malicious contract could trick a user into signing a transaction that calls through it, making ORIGIN appear as the user's address.

The total memory cost up to words 32-byte words is: $C_{mem}=3\cdot \text{words}+\lfloor {\text{words}}^2/512\rfloor$. The gas actually charged on each expansion is the delta: $C_{mem}(\text{new})-C_{mem}(\text{old})$. The linear term (3 gas/word) makes small allocations cheap. The quadratic term makes large allocations progressively expensive — 320 KB (10,000 words) costs ~225,312 gas total, making it impractical to allocate unbounded memory. This prevents DoS attacks where contracts allocate gigabytes on every node.

The EVM was designed as a minimal, low-level execution target — closer to assembly than to a high-level language. Structured control flow (if/else, for, while) is handled by the compiler (Solidity → bytecode). The EVM provides just the primitive jumps, which are simpler to implement correctly in consensus-critical code and easier to gas-meter. This design also makes the bytecode verifiable — you can statically analyze JUMPDEST positions without executing the code.