Byte Memory · Lesson 7 of 30 · about 10 minutes
Memory: The Computer’s Notebook
Store and actually retrieve a byte after overwriting R0.
01 / Explain
Understand the idea
The memory grid has 256 byte cells, addressed 0 through 255. STORE 10 writes R0 into address 10. LOAD [10] reads the stored byte back; plain LOAD 10 loads the literal number ten.
Registers and memory are different places. Clearing R0 does not clear memory. The lab marks memory reads and writes separately, including writes of zero; a zero cell can still have been used.
02 / Try
Watch it happen
Square brackets perform a real memory read. Watch cells 0 and 1.
LOAD 42
STORE 0
LOAD 99
STORE 1
LOAD 0
LOAD [0]
PRINT
LOAD [1]
PRINT
HALTUse Step to follow one instruction at a time. You can change the example and replay it.
03 / Challenge
Make it work
Read a byte-valued input (0–255), save it at memory address 10, clear R0, then retrieve it from memory and print it.
The checker runs your current editor program in a fresh machine for each of 3 test cases. It supplies inputs and seeded memory itself; the lab’s current output and memory do not decide your result.
INPUT
STORE 10
LOAD 0
# Read address 10 back.
HALTNeed a hint?
Use LOAD [10], with brackets.
Reveal a worked solution
Read the program, predict each instruction’s effect, then step through it in the lab.
INPUT
STORE 10
LOAD 0
LOAD [10]
PRINT
HALTEmoji CPU lab
Emoji program
Type LOAD, ADD, or another opcode then Space to insert emoji. Ctrl/⌘ + Enter runs or pauses; Escape pauses; Ctrl/⌘ + ] indents. Tab moves focus. Labels use a colon. Jumps use zero-based instruction addresses.
Instruction map and breakpoints (0)
Breakpoints stop before an instruction. Run resumes past the stopped breakpoint once; Step executes it directly. Editing source clears old breakpoints and machine state.
CPU registers
- R0
- 0
- R1
- 0
- R2
- 0
- R3
- 0
- R4
- 0
- R5
- 0
- R6
- 0
- R7
- 0
Stacks and loop frames
SP = 255 − data depth − call depth. The stack is separate from memory.
Data stack (bottom → top)
Empty
Call return addresses (bottom → top)
Empty
Loop frames
Empty
Output and input
Run a PRINT instruction to see output.
Queued input: Empty
Memory · 256 bytes · 0 nonzero
Each cell shows address:value. R = read this step; W = written this step. Select a cell to inspect or initialize it before execution. Use arrow keys to move, Home/End for the row, and Ctrl/⌘ + Home/End for the whole memory.
Execution trace · 0 entries
Recent entries below. Inspect any zero-based index to see complete detached before/after state.
Check your challenge
You can run this check any time. Every case must pass to record completion.
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