diff --git a/src/core/emu.zig b/src/core/emu.zig
index 55d475f..0f321c2 100644
--- a/src/core/emu.zig
+++ b/src/core/emu.zig
@@ -75,7 +75,7 @@ pub fn loadFirm(allocator: Allocator, system: System, firm_path: []const u8) !vo
         const buf = try file.readToEndAlloc(allocator, try file.getEndPos());
         defer allocator.free(buf);
 
-        @memcpy(system.bus7.bios[0..buf.len], buf);
+        try system.bus7.bios.load(allocator, buf);
     }
 
     { // NDS9 BIOS
@@ -90,7 +90,7 @@ pub fn loadFirm(allocator: Allocator, system: System, firm_path: []const u8) !vo
         const buf = try file.readToEndAlloc(allocator, try file.getEndPos());
         defer allocator.free(buf);
 
-        @memcpy(system.bus9.bios[0..buf.len], buf);
+        try system.bus9.bios.load(allocator, buf);
     }
 }
 
diff --git a/src/core/nds7/Bios.zig b/src/core/nds7/Bios.zig
new file mode 100644
index 0000000..9bff1ce
--- /dev/null
+++ b/src/core/nds7/Bios.zig
@@ -0,0 +1,47 @@
+const std = @import("std");
+
+const Allocator = std.mem.Allocator;
+
+const log = std.log.scoped(.nds7_bios);
+
+const KiB = 0x400;
+const len = 16 * KiB;
+
+buf: ?*align(4) [len]u8 = null,
+
+// FIXME: Currently we dupe here, should we just take ownership?
+pub fn load(self: *@This(), allocator: Allocator, data: []u8) !void {
+    if (data.len != len) {
+        const acutal_size = @as(f32, @floatFromInt(data.len)) / KiB;
+        log.warn("BIOS was {d:.2} KiB (should be {} KiB)", .{ acutal_size, len });
+    }
+
+    const buf = try allocator.alignedAlloc(u8, 4, len);
+    @memset(buf, 0);
+    @memcpy(buf[0..data.len], data);
+
+    self.* = .{ .buf = buf[0..len] };
+}
+
+pub fn deinit(self: @This(), allocator: Allocator) void {
+    if (self.buf) |ptr| allocator.destroy(ptr);
+}
+
+// Note: Parts of 16MiB addrspace that aren't mapped to BIOS are typically undefined
+pub fn read(self: *const @This(), comptime T: type, address: u32) T {
+    const readInt = std.mem.readIntLittle;
+    const byte_count = @divExact(@typeInfo(T).Int.bits, 8);
+
+    // if (address >= len) return 0x0000_0000; // TODO: What is undefined actually?
+
+    const ptr = self.buf orelse {
+        log.err("read(T: {}, address: 0x{X:0>8}) from BIOS but none was found!", .{ T, address });
+        @panic("TODO: ability to load in NDS7 BIOS just-in-time");
+    };
+
+    return readInt(T, ptr[address & (len - 1) ..][0..byte_count]);
+}
+
+pub fn write(_: *const @This(), comptime T: type, address: u32, value: T) void {
+    log.err("write(T: {}, address: 0x{X:0>8}, value: 0x{X:}) but we're in the BIOS!", .{ T, address, value });
+}
diff --git a/src/core/nds7/Bus.zig b/src/core/nds7/Bus.zig
index 338c8be..0598322 100644
--- a/src/core/nds7/Bus.zig
+++ b/src/core/nds7/Bus.zig
@@ -5,6 +5,7 @@ const Scheduler = @import("../Scheduler.zig");
 const SharedCtx = @import("../emu.zig").SharedCtx;
 const Wram = @import("../emu.zig").Wram;
 const Vram = @import("../ppu.zig").Vram;
+const Bios = @import("Bios.zig");
 const forceAlign = @import("../emu.zig").forceAlign;
 
 const Allocator = std.mem.Allocator;
@@ -20,18 +21,13 @@ main: *[4 * MiB]u8,
 shr_wram: *Wram,
 wram: *[64 * KiB]u8,
 vram: *Vram,
-io: io.Io,
 
-bios: *[16 * KiB]u8,
+io: io.Io,
+bios: Bios,
 
 pub fn init(allocator: Allocator, scheduler: *Scheduler, ctx: SharedCtx) !@This() {
     const wram = try allocator.create([64 * KiB]u8);
     @memset(wram, 0);
-    errdefer allocator.destroy(wram);
-
-    const bios = try allocator.create([16 * KiB]u8);
-    @memset(bios, 0);
-    errdefer allocator.destroy(bios);
 
     return .{
         .main = ctx.main,
@@ -41,13 +37,13 @@ pub fn init(allocator: Allocator, scheduler: *Scheduler, ctx: SharedCtx) !@This(
         .scheduler = scheduler,
         .io = io.Io.init(ctx.io),
 
-        .bios = bios,
+        .bios = .{},
     };
 }
 
 pub fn deinit(self: *@This(), allocator: Allocator) void {
     allocator.destroy(self.wram);
-    allocator.destroy(self.bios);
+    self.bios.deinit(allocator);
 }
 
 pub fn reset(_: *@This()) void {}
@@ -73,7 +69,7 @@ fn _read(self: *@This(), comptime T: type, comptime mode: Mode, address: u32) T
     }
 
     return switch (aligned_addr) {
-        0x0000_0000...0x01FF_FFFF => readInt(T, self.bios[address & 0x3FFF ..][0..byte_count]),
+        0x0000_0000...0x01FF_FFFF => self.bios.read(T, address),
         0x0200_0000...0x02FF_FFFF => readInt(T, self.main[aligned_addr & 0x003F_FFFF ..][0..byte_count]),
         0x0300_0000...0x037F_FFFF => switch (self.io.shr.wramcnt.mode.read()) {
             0b00 => readInt(T, self.wram[aligned_addr & 0x0000_FFFF ..][0..byte_count]),
@@ -107,7 +103,7 @@ fn _write(self: *@This(), comptime T: type, comptime mode: Mode, address: u32, v
     }
 
     switch (aligned_addr) {
-        0x0000_0000...0x01FF_FFFF => log.err("tried to read from NDS7 BIOS: 0x{X:0>8}", .{aligned_addr}),
+        0x0000_0000...0x01FF_FFFF => self.bios.write(T, address, value),
         0x0200_0000...0x02FF_FFFF => writeInt(T, self.main[aligned_addr & 0x003F_FFFF ..][0..byte_count], value),
         0x0300_0000...0x037F_FFFF => switch (self.io.shr.wramcnt.mode.read()) {
             0b00 => writeInt(T, self.wram[aligned_addr & 0x0000_FFFF ..][0..byte_count], value),
diff --git a/src/core/nds9/Bios.zig b/src/core/nds9/Bios.zig
new file mode 100644
index 0000000..daf831b
--- /dev/null
+++ b/src/core/nds9/Bios.zig
@@ -0,0 +1,49 @@
+const std = @import("std");
+
+const Allocator = std.mem.Allocator;
+
+const log = std.log.scoped(.nds7_bios);
+
+const KiB = 0x400;
+
+const _len = 4 * KiB; // real size of the NDS9 BIOS
+const len = 32 * KiB; // size allocated to NDS9 BIOS
+
+buf: ?*align(4) [len]u8 = null,
+
+// FIXME: Currently we dupe here, should we just take ownership?
+pub fn load(self: *@This(), allocator: Allocator, data: []u8) !void {
+    if (data.len != _len) {
+        const acutal_size = @as(f32, @floatFromInt(data.len)) / KiB;
+        log.warn("BIOS was {d:.2} KiB (should be {} KiB)", .{ acutal_size, len });
+    }
+
+    const buf = try allocator.alignedAlloc(u8, 4, len);
+    @memcpy(buf[0..data.len], data);
+    @memset(buf[data.len..], 0);
+
+    self.* = .{ .buf = buf[0..len] };
+}
+
+pub fn deinit(self: @This(), allocator: Allocator) void {
+    if (self.buf) |ptr| allocator.destroy(ptr);
+}
+
+// Note: Parts of 16MiB addrspace that aren't mapped to BIOS are typically undefined
+pub fn read(self: *const @This(), comptime T: type, address: u32) T {
+    const readInt = std.mem.readIntLittle;
+    const byte_count = @divExact(@typeInfo(T).Int.bits, 8);
+
+    // if (address >= len) return 0x0000_0000; // TODO: What is undefined actually?
+
+    const ptr = self.buf orelse {
+        log.err("read(T: {}, address: 0x{X:0>8}) from BIOS but none was found!", .{ T, address });
+        @panic("TODO: ability to load in NDS9 BIOS just-in-time");
+    };
+
+    return readInt(T, ptr[address & (len - 1) ..][0..byte_count]);
+}
+
+pub fn write(_: *const @This(), comptime T: type, address: u32, value: T) void {
+    log.err("write(T: {}, address: 0x{X:0>8}, value: 0x{X:}) but we're in the BIOS!", .{ T, address, value });
+}
diff --git a/src/core/nds9/Bus.zig b/src/core/nds9/Bus.zig
index 459a21f..7611197 100644
--- a/src/core/nds9/Bus.zig
+++ b/src/core/nds9/Bus.zig
@@ -5,6 +5,7 @@ const Ppu = @import("../ppu.zig").Ppu;
 const Scheduler = @import("../Scheduler.zig");
 const SharedCtx = @import("../emu.zig").SharedCtx;
 const Wram = @import("../emu.zig").Wram;
+const Bios = @import("Bios.zig");
 const forceAlign = @import("../emu.zig").forceAlign;
 
 const Allocator = std.mem.Allocator;
@@ -17,21 +18,16 @@ const log = std.log.scoped(.nds9_bus);
 
 main: *[4 * MiB]u8,
 wram: *Wram,
+scheduler: *Scheduler,
+
 io: io.Io,
 ppu: Ppu,
-
-bios: *[32 * KiB]u8,
-
-scheduler: *Scheduler,
+bios: Bios,
 
 pub fn init(allocator: Allocator, scheduler: *Scheduler, ctx: SharedCtx) !@This() {
     const dots_per_cycle = 3; // ARM946E-S runs twice as fast as the ARM7TDMI
     scheduler.push(.{ .nds9 = .draw }, 256 * dots_per_cycle);
 
-    const bios = try allocator.create([32 * KiB]u8);
-    @memset(bios, 0);
-    errdefer allocator.destroy(bios);
-
     return .{
         .main = ctx.main,
         .wram = ctx.wram,
@@ -39,13 +35,13 @@ pub fn init(allocator: Allocator, scheduler: *Scheduler, ctx: SharedCtx) !@This(
         .scheduler = scheduler,
         .io = io.Io.init(ctx.io),
 
-        .bios = bios,
+        .bios = .{},
     };
 }
 
 pub fn deinit(self: *@This(), allocator: Allocator) void {
     self.ppu.deinit(allocator);
-    allocator.destroy(self.bios);
+    self.bios.deinit(allocator);
 }
 
 pub fn reset(_: *@This()) void {
@@ -77,7 +73,7 @@ fn _read(self: *@This(), comptime T: type, comptime mode: Mode, address: u32) T
         0x0300_0000...0x03FF_FFFF => self.wram.read(T, .nds9, aligned_addr),
         0x0400_0000...0x04FF_FFFF => io.read(self, T, aligned_addr),
         0x0600_0000...0x06FF_FFFF => self.ppu.vram.read(T, .nds9, aligned_addr),
-        0xFFFF_0000...0xFFFF_FFFF => readInt(T, self.bios[address & 0x0000_7FFF ..][0..byte_count]),
+        0xFFFF_0000...0xFFFF_FFFF => self.bios.read(T, address),
         else => warn("unexpected read: 0x{x:0>8} -> {}", .{ aligned_addr, T }),
     };
 }
@@ -107,7 +103,7 @@ fn _write(self: *@This(), comptime T: type, comptime mode: Mode, address: u32, v
         0x0300_0000...0x03FF_FFFF => self.wram.write(T, .nds9, aligned_addr, value),
         0x0400_0000...0x04FF_FFFF => io.write(self, T, aligned_addr, value),
         0x0600_0000...0x06FF_FFFF => self.ppu.vram.write(T, .nds9, aligned_addr, value),
-        0xFFFF_0000...0xFFFF_FFFF => log.err("tried to read from NDS9 BIOS: 0x{X:0>8}", .{aligned_addr}),
+        0xFFFF_0000...0xFFFF_FFFF => self.bios.write(T, address, value),
         else => log.warn("unexpected write: 0x{X:}{} -> 0x{X:0>8}", .{ value, T, aligned_addr }),
     }
 }