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In the usual processor-architecture sense, a load reads a value from memory into a processor register; a store writes a value from a register to memory. They are opposite directions of data transfer. The exact meaning depends on the context: in JVM bytecode, for example, load and store move values between local variables and the operand stack.
How load and store work in a processor
Memory holds data at addresses; registers are small storage locations inside the processor that instructions can use directly. A load takes data from an addressed memory location and places it in a register. A store takes data held in a register and writes it to an addressed memory location.
In MIT OpenCourseWare’s Beta load-store architecture example, LD reads the value at an effective address and puts it in a register, while ST writes register data to that address. In that architecture, these are the only instructions that access memory values. The Beta example calculates the effective address from a register value plus a sign-extended 16-bit constant encoded in the instruction; other architectures may calculate addresses differently. MIT OpenCourseWare: Computation Structures.
Load vs. store at a glance
| Operation | Data moves | Typical purpose |
|---|---|---|
| Load | Memory address → register | Make a value in memory available to processor instructions |
| Store | Register → memory address | Save a register value to memory |
The arrows describe the conventional processor-level meaning. They do not mean that every programming environment uses the words for the same source and destination.
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How the terms differ by context
LLVM intermediate representation
In LLVM IR, a load reads from the memory address supplied by a pointer operand. A store writes a specified value to the address supplied by its destination pointer. LLVM also defines variants such as atomic and volatile operations; those rules are specific to LLVM IR rather than universal definitions for CPU instructions. LLVM Language Reference: load instruction and store instruction.
Java Virtual Machine bytecode
In JVM bytecode, load and store refer to movement within an execution frame, not necessarily a direct read from or write to main memory. A load instruction transfers a value from a local variable to the operand stack; a store instruction transfers a value from the operand stack to a local variable. The JVM specification lists typed families such as iload, lload, fload, dload, and aload, along with corresponding store instructions. Java Virtual Machine Specification, Chapter 6.
Is a load the same as moving an immediate value?
No. In the usual processor terminology, a load reads data from an address in memory. An immediate-move instruction uses a value encoded directly in the instruction rather than fetching that value from a separate memory address. The exact instruction names and available forms vary by architecture. The JVM also distinguishes constant-loading instructions from its local-variable load instructions, so check the instruction set or virtual-machine specification relevant to the code you are reading.
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How to identify what an instruction loads or stores
- Check the context. Determine whether the code is a CPU instruction, LLVM IR, or virtual-machine bytecode.
- Find the source and destination. A processor load typically has a memory address as its source and a register as its destination; a processor store has a register as its source and a memory address as its destination.
- Read the instruction’s addressing rules. The address may be calculated from registers, constants, or other architecture-specific operands.
- Do not infer a memory access from the word alone. In JVM bytecode, load and store refer to local-variable and operand-stack transfers.
