diff --git a/javascripts/cpu/arm.js b/javascripts/cpu/arm.js
new file mode 100644
index 0000000..ef88a42
--- /dev/null
+++ b/javascripts/cpu/arm.js
@@ -0,0 +1,272 @@
+import { FLAGS, LinearMemory, RegisterFile, setAddFlags, setLogicalFlags, setSubFlags, u64 } from "./memory.js";
+
+const read32 = (memory, pc) => memory.u32(pc);
+
+export class ArmCpu {
+  #memory;
+  #regs = new RegisterFile();
+  #syscall;
+  #halted = false;
+  #steps = 0;
+
+  constructor({ memory = new LinearMemory(), onSyscall } = {}) {
+    this.#memory = memory;
+    this.#syscall = onSyscall ?? (() => 0n);
+    this.reset();
+  }
+
+  get memory() {
+    return this.#memory;
+  }
+
+  get halted() {
+    return this.#halted;
+  }
+
+  get steps() {
+    return this.#steps;
+  }
+
+  registers() {
+    return this.#regs.snapshot();
+  }
+
+  reset({ pc = 0n, sp = BigInt(this.#memory.size - 16) } = {}) {
+    this.#regs = new RegisterFile();
+    this.#regs.rip = u64(pc);
+    this.#regs.set(31, 0n); // XZR/SP handled specially
+    this.#regs.set(16, u64(sp)); // use X16 as SP stand-in for toys; also keep x31 via rsp slot
+    this.#regs.set(4, u64(sp));
+    this.#halted = false;
+    this.#steps = 0;
+  }
+
+  load(bytes, address = 0n) {
+    this.#memory.load(bytes, address);
+    this.#regs.rip = u64(address);
+  }
+
+  #x(index) {
+    return index === 31 ? 0n : this.#regs.get(index);
+  }
+
+  #setX(index, value) {
+    if (index !== 31) this.#regs.set(index, u64(value));
+  }
+
+  #sp() {
+    return this.#regs.get(4);
+  }
+
+  #setSp(value) {
+    this.#regs.set(4, u64(value));
+  }
+
+  #nzcv(result, kind, left = 0n, right = 0n) {
+    if (kind === "add") setAddFlags(this.#regs, left, right, result);
+    else if (kind === "sub") setSubFlags(this.#regs, left, right, result);
+    else setLogicalFlags(this.#regs, result);
+  }
+
+  #cond(code) {
+    const z = (this.#regs.rflags & FLAGS.ZF) !== 0n;
+    const n = (this.#regs.rflags & FLAGS.SF) !== 0n;
+    const c = (this.#regs.rflags & FLAGS.CF) !== 0n;
+    const v = (this.#regs.rflags & FLAGS.OF) !== 0n;
+    switch (code) {
+      case 0x0:
+        return z; // EQ
+      case 0x1:
+        return !z; // NE
+      case 0x2:
+        return c; // CS/HS
+      case 0x3:
+        return !c; // CC/LO
+      case 0x4:
+        return n; // MI
+      case 0x5:
+        return !n; // PL
+      case 0x6:
+        return v; // VS
+      case 0x7:
+        return !v; // VC
+      case 0x8:
+        return c && !z; // HI
+      case 0x9:
+        return !c || z; // LS
+      case 0xa:
+        return n === v; // GE
+      case 0xb:
+        return n !== v; // LT
+      case 0xc:
+        return !z && n === v; // GT
+      case 0xd:
+        return z || n !== v; // LE
+      case 0xe:
+        return true; // AL
+      default:
+        return false;
+    }
+  }
+
+  step() {
+    if (this.#halted) return false;
+    const pc = this.#regs.rip;
+    const word = read32(this.#memory, pc) >>> 0;
+    this.#regs.rip = u64(pc + 4n);
+
+    // NOP: d503201f
+    if (word === 0xd503201f) {
+      this.#steps += 1;
+      return true;
+    }
+
+    // RET (X30)
+    if (word === 0xd65f03c0) {
+      this.#regs.rip = this.#x(30);
+      this.#steps += 1;
+      return true;
+    }
+
+    // SVC #imm: d4000001 | (imm16 << 5)
+    if ((word & 0xffe0001f) >>> 0 === 0xd4000001) {
+      const result = this.#syscall({
+        nr: this.#x(8),
+        args: [this.#x(0), this.#x(1), this.#x(2), this.#x(3), this.#x(4), this.#x(5)],
+        cpu: this,
+      });
+      if (result === null || result === undefined) this.#halted = true;
+      else this.#setX(0, result);
+      this.#steps += 1;
+      return !this.#halted;
+    }
+
+    // MOVZ Xd, #imm16, LSL #shift
+    if ((word & 0xff800000) >>> 0 === 0xd2800000) {
+      const rd = word & 31;
+      const imm16 = (word >> 5) & 0xffff;
+      const hw = (word >> 21) & 3;
+      this.#setX(rd, BigInt(imm16) << BigInt(hw * 16));
+      this.#steps += 1;
+      return true;
+    }
+
+    // MOVK Xd, #imm16, LSL #shift
+    if ((word & 0xff800000) >>> 0 === 0xf2800000) {
+      const rd = word & 31;
+      const imm16 = (word >> 5) & 0xffff;
+      const hw = (word >> 21) & 3;
+      const shift = BigInt(hw * 16);
+      const mask = 0xffffn << shift;
+      this.#setX(rd, (this.#x(rd) & ~mask) | (BigInt(imm16) << shift));
+      this.#steps += 1;
+      return true;
+    }
+
+    // ADD/SUB Xd, Xn, #imm12
+    if ((word & 0x7f000000) === 0x11000000 || (word & 0x7f000000) === 0x51000000) {
+      const rd = word & 31;
+      const rn = (word >> 5) & 31;
+      const imm = BigInt((word >> 10) & 0xfff);
+      const shift = (word >> 22) & 3;
+      const value = imm << BigInt(shift === 1 ? 12 : 0);
+      const left = rn === 31 ? this.#sp() : this.#x(rn);
+      const isSub = (word & 0x40000000) !== 0;
+      const result = isSub ? u64(left - value) : u64(left + value);
+      if ((word & 0x20000000) !== 0) this.#nzcv(result, isSub ? "sub" : "add", left, value);
+      if (rd === 31) this.#setSp(result);
+      else this.#setX(rd, result);
+      this.#steps += 1;
+      return true;
+    }
+
+    // ADD/SUB Xd, Xn, Xm
+    if ((word & 0x7fe0fc00) === 0x0b000000 || (word & 0x7fe0fc00) === 0x4b000000) {
+      const rd = word & 31;
+      const rn = (word >> 5) & 31;
+      const rm = (word >> 16) & 31;
+      const left = this.#x(rn);
+      const right = this.#x(rm);
+      const isSub = (word & 0x40000000) !== 0;
+      const result = isSub ? u64(left - right) : u64(left + right);
+      if ((word & 0x20000000) !== 0) this.#nzcv(result, isSub ? "sub" : "add", left, right);
+      this.#setX(rd, result);
+      this.#steps += 1;
+      return true;
+    }
+
+    // AND/ORR/EOR Xd, Xn, Xm
+    if (
+      (word & 0x7fe0fc00) === 0x0a000000 ||
+      (word & 0x7fe0fc00) === 0x2a000000 ||
+      (word & 0x7fe0fc00) === 0x4a000000
+    ) {
+      const rd = word & 31;
+      const rn = (word >> 5) & 31;
+      const rm = (word >> 16) & 31;
+      const left = this.#x(rn);
+      const right = this.#x(rm);
+      let result;
+      if ((word & 0x7fe0fc00) === 0x0a000000) result = left & right;
+      else if ((word & 0x7fe0fc00) === 0x2a000000) result = left | right;
+      else result = left ^ right;
+      this.#nzcv(result, "logic");
+      this.#setX(rd, result);
+      this.#steps += 1;
+      return true;
+    }
+
+    // LDR/STR Xt, [Xn, #imm12*8]
+    if ((word & 0xffc00000) >>> 0 === 0xf9400000 || (word & 0xffc00000) >>> 0 === 0xf9000000) {
+      const rt = word & 31;
+      const rn = (word >> 5) & 31;
+      const imm = BigInt((word >> 10) & 0xfff) << 3n;
+      const base = rn === 31 ? this.#sp() : this.#x(rn);
+      const address = u64(base + imm);
+      if ((word & 0xffc00000) >>> 0 === 0xf9400000) this.#setX(rt, this.#memory.u64(address));
+      else this.#memory.u64(address, this.#x(rt));
+      this.#steps += 1;
+      return true;
+    }
+
+    // B imm26
+    if ((word & 0xfc000000) >>> 0 === 0x14000000) {
+      let imm = word & 0x03ffffff;
+      if (imm & 0x02000000) imm |= ~0x03ffffff;
+      this.#regs.rip = u64(pc + BigInt(imm) * 4n);
+      this.#steps += 1;
+      return true;
+    }
+
+    // B.cond
+    if ((word & 0xff000010) >>> 0 === 0x54000000) {
+      let imm = (word >> 5) & 0x7ffff;
+      if (imm & 0x40000) imm |= ~0x7ffff;
+      if (this.#cond(word & 0xf)) this.#regs.rip = u64(pc + BigInt(imm) * 4n);
+      this.#steps += 1;
+      return true;
+    }
+
+    // BL imm26
+    if ((word & 0xfc000000) >>> 0 === 0x94000000) {
+      let imm = word & 0x03ffffff;
+      if (imm & 0x02000000) imm |= ~0x03ffffff;
+      this.#setX(30, this.#regs.rip);
+      this.#regs.rip = u64(pc + BigInt(imm) * 4n);
+      this.#steps += 1;
+      return true;
+    }
+
+    throw new Error(`unsupported aarch64 word ${word.toString(16)} at ${pc}`);
+  }
+
+  run({ maxSteps = 100_000 } = {}) {
+    while (!this.#halted && this.#steps < maxSteps) {
+      if (!this.step()) break;
+    }
+    if (!this.#halted && this.#steps >= maxSteps) throw new Error("CPU step limit exceeded");
+    return this.registers();
+  }
+}
+
+export const createArm = (options) => new ArmCpu(options);
diff --git a/javascripts/cpu/x86.js b/javascripts/cpu/x86.js
index 70c3b6a..7091d07 100644
--- a/javascripts/cpu/x86.js
+++ b/javascripts/cpu/x86.js
@@ -1,4 +1,4 @@
-import { FLAGS, LinearMemory, RegisterFile, i64, setAddFlags, setLogicalFlags, setSubFlags, u64 } from "./memory.js";
+import { FLAGS, LinearMemory, RegisterFile, setAddFlags, setLogicalFlags, setSubFlags, u64 } from "./memory.js";
 
 const REG = Object.freeze({
   rax: 0,
diff --git a/javascripts/index.js b/javascripts/index.js
index ad4f143..ae47126 100644
--- a/javascripts/index.js
+++ b/javascripts/index.js
@@ -1,5 +1,6 @@
 export { createShell, MemoryFS, profiles } from "./shell.js";
 export { BlockDevice, BlockFS, createBlockFS } from "./block.js";
 export { createX86, LinearMemory, X86Cpu } from "./cpu/x86.js";
+export { createArm, ArmCpu } from "./cpu/arm.js";
 export { createManuals } from "./man.js";
 export { mountShell } from "./ui.js";
diff --git a/package.json b/package.json
index 19ac7d0..93176a6 100644
--- a/package.json
+++ b/package.json
@@ -12,6 +12,7 @@
   },
   "files": [
     "javascripts/block.js",
+    "javascripts/cpu/arm.js",
     "javascripts/cpu/memory.js",
     "javascripts/cpu/x86.js",
     "javascripts/commands.js",
diff --git a/tools/scripts/test.js b/tools/scripts/test.js
index 5bb1cef..3526031 100644
--- a/tools/scripts/test.js
+++ b/tools/scripts/test.js
@@ -16,6 +16,7 @@ import { join, relative } from "node:path";
 import { runInNewContext } from "node:vm";
 import { createManuals, readLimited } from "../../javascripts/man.js";
 import { BlockDevice, BlockFS } from "../../javascripts/block.js";
+import { createArm } from "../../javascripts/cpu/arm.js";
 import { createX86 } from "../../javascripts/cpu/x86.js";
 import { MemoryFS, createShell, profiles } from "../../javascripts/shell.js";
 import { createWasm } from "../../javascripts/wasm.js";
@@ -444,3 +445,23 @@ console.log("shell.js core: ok");
   assert.equal(cpu.halted, true);
   console.log("shell.js x86: ok");
 }
+
+{
+  // movz x0, #42; movz x8, #1; add x8, x8, #4; svc #0
+  const program = Uint8Array.from([
+    0x40, 0x05, 0x80, 0xd2, 0x28, 0x00, 0x80, 0xd2, 0x08, 0x11, 0x00, 0x91, 0x01, 0x00, 0x00, 0xd4,
+  ]);
+  let saw = null;
+  const cpu = createArm({
+    onSyscall: ({ nr, args }) => {
+      saw = { nr, args: [...args] };
+      return null;
+    },
+  });
+  cpu.load(program);
+  cpu.run();
+  assert.equal(saw?.nr, 5n);
+  assert.equal(saw?.args[0], 42n);
+  assert.equal(cpu.halted, true);
+  console.log("shell.js arm: ok");
+}