diff --git a/.gitignore b/.gitignore
index b56a9aa8..ebed6c9c 100644
--- a/.gitignore
+++ b/.gitignore
@@ -1,10 +1,6 @@
-*.o
-*.o.d
-*.sw*
-semu
+build/
 
 # Linux-specific
-*.dtb
 Image
 ext4.img
 rootfs.cpio
diff --git a/.gitmodules b/.gitmodules
index eb01e2ac..e54f640f 100644
--- a/.gitmodules
+++ b/.gitmodules
@@ -1,12 +1,12 @@
-[submodule "mini-gdbstub"]
-    path = mini-gdbstub
-    url = https://github.com/RinHizakura/mini-gdbstub
-    shallow = true
-[submodule "minislirp"]
-	path = minislirp
+[submodule "3rdparty/mini-gdbstub"]
+	path = 3rdparty/mini-gdbstub
+	url = https://github.com/RinHizakura/mini-gdbstub
+	shallow = true
+[submodule "3rdparty/minislirp"]
+	path = 3rdparty/minislirp
 	url = https://github.com/edubart/minislirp
-    shallow = true
-[submodule "portaudio"]
-    path = portaudio
-    url = https://github.com/PortAudio/portaudio
-    shallow = true
+	shallow = true
+[submodule "3rdparty/portaudio"]
+	path = 3rdparty/portaudio
+	url = https://github.com/PortAudio/portaudio
+	shallow = true
diff --git a/3rdparty/mini-gdbstub b/3rdparty/mini-gdbstub
new file mode 160000
index 00000000..39020f21
--- /dev/null
+++ b/3rdparty/mini-gdbstub
@@ -0,0 +1 @@
+Subproject commit 39020f212aa2aec4c7b9d1686a78a11b64db0535
diff --git a/minislirp b/3rdparty/minislirp
similarity index 100%
rename from minislirp
rename to 3rdparty/minislirp
diff --git a/3rdparty/portaudio b/3rdparty/portaudio
new file mode 160000
index 00000000..c3f922fa
--- /dev/null
+++ b/3rdparty/portaudio
@@ -0,0 +1 @@
+Subproject commit c3f922fa19712b00961a54f21365803239ec834d
diff --git a/Makefile b/Makefile
index 96030288..4101ea2f 100644
--- a/Makefile
+++ b/Makefile
@@ -1,9 +1,14 @@
 include mk/common.mk
 include mk/check-libs.mk
 
+THIRDPARTY_DIR := 3rdparty
+INCLUDE_DIR := include
+BUILD_DIR := build
+SRC_DIR := src
+
 CC ?= gcc
 CFLAGS := -O2 -g -Wall -Wextra
-CFLAGS += -include common.h
+CFLAGS += -I$(INCLUDE_DIR) -I$(THIRDPARTY_DIR) -include $(INCLUDE_DIR)/common.h
 
 # clock frequency
 CLOCK_FREQ ?= 65000000
@@ -11,11 +16,15 @@ DT_CFLAGS := -D CLOCK_FREQ=$(CLOCK_FREQ)
 CFLAGS += $(DT_CFLAGS)
 
 OBJS_EXTRA :=
+LIBS_EXTRA :=
+
 # command line option
 OPTS :=
 
 LDFLAGS :=
 
+SHELL_HACK := $(shell mkdir -p $(BUILD_DIR))
+
 # virtio-blk
 ENABLE_VIRTIOBLK ?= 1
 $(call set-feature, VIRTIOBLK)
@@ -24,7 +33,7 @@ MKFS_EXT4 ?= mkfs.ext4
 ifeq ($(call has, VIRTIOBLK), 1)
     OBJS_EXTRA += virtio-blk.o
     DISKIMG_FILE := ext4.img
-    OPTS += -d $(DISKIMG_FILE)
+    OPTS += -d $(BUILD_DIR)/$(DISKIMG_FILE)
     MKFS_EXT4 := $(shell which $(MKFS_EXT4))
     ifndef MKFS_EXT4
 	MKFS_EXT4 := $(shell which $$(brew --prefix e2fsprogs)/sbin/mkfs.ext4)
@@ -77,8 +86,9 @@ $(call set-feature, VIRTIOSND)
 ifeq ($(call has, VIRTIOSND), 1)
     OBJS_EXTRA += virtio-snd.o
 
-    PA_LIB := portaudio/lib/.libs/libportaudio.a
-    PA_CFLAGS := -Iportaudio/include
+    PORTAUDIO_DIR := $(THIRDPARTY_DIR)/portaudio
+    PA_LIB := $(PORTAUDIO_DIR)/lib/.libs/libportaudio.a
+    PA_CFLAGS := -I$(PORTAUDIO_DIR)/include
     PA_CONFIG_PARAMS :=
     LDFLAGS += $(PA_LIB)
     CFLAGS += $(PA_CFLAGS)
@@ -105,9 +115,10 @@ ifeq ($(call has, VIRTIOSND), 1)
     # -lm separately.
     LDFLAGS += -lpthread
 
-portaudio/Makefile:
-	git submodule update --init portaudio
-$(PA_LIB): portaudio/Makefile
+$(PORTAUDIO_DIR)/Makefile:
+	git submodule update --init $(PORTAUDIO_DIR)
+
+$(PA_LIB): $(PORTAUDIO_DIR)/Makefile
 	cd $(dir $<) && git clean -fdx && git reset --hard HEAD
 	cd $(dir $<) && ./configure \
         --enable-static \
@@ -119,10 +130,10 @@ $(PA_LIB): portaudio/Makefile
         --disable-dependency-tracking \
         $(PA_CONFIG_PARAMS)
 	$(MAKE) -C $(dir $<)
-main.o: $(PA_LIB)
-virtio-snd.o: $(PA_LIB)
+$(BUILD_DIR)/main.o: $(PA_LIB)
+$(BUILD_DIR)/virtio-snd.o: $(PA_LIB)
 # suppress warning when compiling PortAudio
-virtio-snd.o: CFLAGS += -Wno-unused-parameter
+$(BUILD_DIR)/virtio-snd.o: CFLAGS += -Wno-unused-parameter
 endif
 
 # Set libm as the last dependency so that no need to set -lm seperately.
@@ -132,8 +143,9 @@ LDFLAGS += -lm
 # after git submodule.
 .DEFAULT_GOAL := all
 
-BIN = semu
-all: $(BIN) minimal.dtb
+BIN = $(BUILD_DIR)/semu
+
+all: $(BIN) $(BUILD_DIR)/minimal.dtb
 
 OBJS := \
 	riscv.o \
@@ -145,34 +157,36 @@ OBJS := \
 	aclint.o \
 	$(OBJS_EXTRA)
 
-deps := $(OBJS:%.o=.%.o.d)
+objs := $(foreach obj,$(OBJS),$(BUILD_DIR)/$(obj))
+deps := $(patsubst %.o,$(BUILD_DIR)/%.o.d,$(OBJS))
 
-GDBSTUB_LIB := mini-gdbstub/build/libgdbstub.a
-LDFLAGS += $(GDBSTUB_LIB)
-mini-gdbstub/Makefile:
+MINI_GDBSTUB_DIR := $(THIRDPARTY_DIR)/mini-gdbstub
+MINI_GDBSTUB_LIB := $(MINI_GDBSTUB_DIR)/build/libgdbstub.a
+LDFLAGS += $(MINI_GDBSTUB_LIB)
+$(THIRDPARTY_DIR)/mini-gdbstub/Makefile:
 	git submodule update --init $(dir $@)
-$(GDBSTUB_LIB): mini-gdbstub/Makefile
+$(MINI_GDBSTUB_LIB): $(MINI_GDBSTUB_DIR)/Makefile
 	$(MAKE) -C $(dir $<)
-$(OBJS): $(GDBSTUB_LIB)
+LIBS_EXTRA += $(MINI_GDBSTUB_LIB)
 
 ifeq ($(call has, VIRTIONET), 1)
-MINISLIRP_DIR := minislirp
-MINISLIRP_LIB := minislirp/src/libslirp.a
+MINISLIRP_DIR := $(THIRDPARTY_DIR)/minislirp
+MINISLIRP_LIB := $(MINISLIRP_DIR)/src/libslirp.a
 LDFLAGS += $(MINISLIRP_LIB)
 $(MINISLIRP_DIR)/src/Makefile:
 	git submodule update --init $(MINISLIRP_DIR)
 $(MINISLIRP_LIB): $(MINISLIRP_DIR)/src/Makefile
 	$(MAKE) -C $(dir $<)
-$(OBJS): $(MINISLIRP_LIB)
+LIBS_EXTRA += $(MINISLIRP_LIB)
 endif
 
-$(BIN): $(OBJS)
+$(BIN): $(objs)
 	$(VECHO) "  LD\t$@\n"
 	$(Q)$(CC) -o $@ $^ $(LDFLAGS)
 
-%.o: %.c
+$(BUILD_DIR)/%.o: $(SRC_DIR)/%.c $(LIBS_EXTRA)
 	$(VECHO) "  CC\t$@\n"
-	$(Q)$(CC) -o $@ $(CFLAGS) -c -MMD -MF .$@.d $<
+	$(Q)$(CC) -o $@ $(CFLAGS) -c -MMD -MF $@.d $<
 
 DTC ?= dtc
 
@@ -196,40 +210,42 @@ S := $E $E
 CFLAGS += -D SEMU_BOOT_TARGET_TIME=10
 
 SMP ?= 1
-.PHONY: riscv-harts.dtsi
-riscv-harts.dtsi:
+.PHONY: $(INCLUDE_DIR)/riscv-harts.dtsi
+$(INCLUDE_DIR)/riscv-harts.dtsi:
 	$(Q)python3 scripts/gen-hart-dts.py $@ $(SMP) $(CLOCK_FREQ)
 
-minimal.dtb: minimal.dts riscv-harts.dtsi
+$(BUILD_DIR)/minimal.dtb: $(SRC_DIR)/minimal.dts $(INCLUDE_DIR)/riscv-harts.dtsi
 	$(VECHO) " DTC\t$@\n"
 	$(Q)$(CC) -nostdinc -E -P -x assembler-with-cpp -undef \
+	    -I$(INCLUDE_DIR) \
 	    $(DT_CFLAGS) \
 	    $(subst ^,$S,$(filter -D^SEMU_FEATURE_%, $(subst -D$(S)SEMU_FEATURE,-D^SEMU_FEATURE,$(CFLAGS)))) $< \
 	    | $(DTC) - > $@
 
-# Rules for downloading prebuilt Linux kernel image
-include mk/external.mk
-
-ext4.img:
+$(BUILD_DIR)/$(DISKIMG_FILE):
 	$(Q)dd if=/dev/zero of=$@ bs=4k count=600
 	$(Q)$(MKFS_EXT4) -F $@
 
-check: $(BIN) minimal.dtb $(KERNEL_DATA) $(INITRD_DATA) $(DISKIMG_FILE)
+.PHONY: download-artifacts
+download-artifacts:
+	$(Q)scripts/download-artifacts.sh Image $(BUILD_DIR)
+	$(Q)scripts/download-artifacts.sh rootfs $(BUILD_DIR)
+
+check: $(BIN) $(BUILD_DIR)/minimal.dtb $(BUILD_DIR)/$(DISKIMG_FILE) download-artifacts
 	@$(call notice, Ready to launch Linux kernel. Please be patient.)
-	$(Q)./$(BIN) -k $(KERNEL_DATA) -c $(SMP) -b minimal.dtb -i $(INITRD_DATA) -n $(NETDEV) $(OPTS)
+	$(Q)$(BIN) -k $(BUILD_DIR)/Image -c $(SMP) -b $(BUILD_DIR)/minimal.dtb -i $(BUILD_DIR)/rootfs.cpio -n $(NETDEV) $(OPTS)
 
 build-image:
 	scripts/build-image.sh
 
 clean:
-	$(Q)$(RM) $(BIN) $(OBJS) $(deps)
-	$(Q)$(MAKE) -C mini-gdbstub clean
-	$(Q)$(MAKE) -C minislirp/src clean
+	$(Q)$(RM) $(BIN) $(objs) $(deps)
+	$(Q)$(MAKE) -C $(THIRDPARTY_DIR)/mini-gdbstub clean
+	$(Q)$(MAKE) -C $(THIRDPARTY_DIR)/minislirp/src clean
+	$(Q)$(MAKE) -C $(THIRDPARTY_DIR)/portaudio clean
 
 distclean: clean
-	$(Q)$(RM) riscv-harts.dtsi
-	$(Q)$(RM) minimal.dtb
-	$(Q)$(RM) Image rootfs.cpio
-	$(Q)$(RM) ext4.img
+	$(Q)$(RM) $(INCLUDE_DIR)/riscv-harts.dtsi
+	$(Q)$(RM) $(BUILD_DIR)/*
 
 -include $(deps)
diff --git a/common.h b/include/common.h
similarity index 100%
rename from common.h
rename to include/common.h
diff --git a/device.h b/include/device.h
similarity index 100%
rename from device.h
rename to include/device.h
diff --git a/feature.h b/include/feature.h
similarity index 100%
rename from feature.h
rename to include/feature.h
diff --git a/netdev.h b/include/netdev.h
similarity index 100%
rename from netdev.h
rename to include/netdev.h
diff --git a/riscv.h b/include/riscv.h
similarity index 100%
rename from riscv.h
rename to include/riscv.h
diff --git a/riscv_private.h b/include/riscv_private.h
similarity index 100%
rename from riscv_private.h
rename to include/riscv_private.h
diff --git a/utils.h b/include/utils.h
similarity index 100%
rename from utils.h
rename to include/utils.h
diff --git a/virtio.h b/include/virtio.h
similarity index 100%
rename from virtio.h
rename to include/virtio.h
diff --git a/mini-gdbstub b/mini-gdbstub
deleted file mode 160000
index 18a3746f..00000000
--- a/mini-gdbstub
+++ /dev/null
@@ -1 +0,0 @@
-Subproject commit 18a3746fda1a03d82b31bc6b8f15c47e5808cee1
diff --git a/mk/external.mk b/mk/external.mk
deleted file mode 100644
index dceeef78..00000000
--- a/mk/external.mk
+++ /dev/null
@@ -1,27 +0,0 @@
-# For each external target, the following must be defined in advance:
-#   _DATA_URL : the hyperlink which points to archive.
-#   _DATA : the file to be read by specific executable.
-#   _DATA_SHA1 : the checksum of the content in _DATA
-
-COMMON_URL = https://github.com/sysprog21/semu/raw/blob
-
-# kernel
-KERNEL_DATA_URL = $(COMMON_URL)/Image.bz2
-KERNEL_DATA = Image
-KERNEL_DATA_SHA1 = 72a8454575508d09210f067b25239cd51b929d27
-
-# initrd
-INITRD_DATA_URL = $(COMMON_URL)/rootfs.cpio.bz2
-INITRD_DATA = rootfs.cpio
-INITRD_DATA_SHA1 = 18bd639c17fc299c317f8fed1c845e7dda296748
-
-define download
-$($(T)_DATA):
-	$(VECHO) "  GET\t$$@\n"
-	$(Q)curl --progress-bar -O -L -C - "$(strip $($(T)_DATA_URL))"
-	$(Q)echo "$(strip $$($(T)_DATA_SHA1))  $$@.bz2" | $(SHA1SUM) -c -
-	$(Q)bunzip2 $$@.bz2
-endef
-
-EXTERNAL_DATA = KERNEL INITRD
-$(foreach T,$(EXTERNAL_DATA),$(eval $(download)))
diff --git a/portaudio b/portaudio
deleted file mode 160000
index e97effb2..00000000
--- a/portaudio
+++ /dev/null
@@ -1 +0,0 @@
-Subproject commit e97effb2b910e579efe8c5af40b43adf19fd8c33
diff --git a/scripts/download-artifacts.sh b/scripts/download-artifacts.sh
new file mode 100755
index 00000000..c9423e0f
--- /dev/null
+++ b/scripts/download-artifacts.sh
@@ -0,0 +1,88 @@
+#!/bin/sh
+
+BASE_URL="https://github.com/sysprog21/semu/raw/blob"
+
+IMAGE_SHA1="72a8454575508d09210f067b25239cd51b929d27"
+ROOTFS_SHA1="18bd639c17fc299c317f8fed1c845e7dda296748"
+
+DEST_DIR="./build"
+
+if [ -z "$1" ]; then
+    echo "No file name provided. Please provide a target as the first argument."
+    exit 1
+fi
+
+case "$1" in
+    "Image")
+        FULL_URL="${BASE_URL}/Image.bz2"
+        LOCAL_FILE_PATH="${DEST_DIR}/Image"
+        FILE_SHA1="${IMAGE_SHA1}"
+        ;;
+    "rootfs")
+        FULL_URL="${BASE_URL}/rootfs.cpio.bz2"
+        LOCAL_FILE_PATH="${DEST_DIR}/rootfs.cpio"
+        FILE_SHA1="${ROOTFS_SHA1}"
+        ;;
+    *)
+        echo "Invalid target: \"$1\""
+        echo "Available keywords are: Image, rootfs"
+        exit 1
+        ;;
+esac
+
+if [ ! -z "$2" ]; then
+    DEST_DIR="$2" 
+else
+    echo "No destination directory provided. Using the default one: \"$DEST_DIR\""
+fi
+
+if [ ! -d "$DEST_DIR" ]; then
+    mkdir -p "$DEST_DIR"
+fi
+
+if [ ! -f "${LOCAL_FILE_PATH}.bz2" ]; then
+    NEED_REDOWNLOAD="1"
+
+    echo "The file \"${LOCAL_FILE_PATH}.bz2\" was not found. Downloading..."
+else
+    SHA1_CHECK_RES=$(echo "${FILE_SHA1} ${LOCAL_FILE_PATH}.bz2" | sha1sum -c - >/dev/null 2>&1 || echo "failed")
+
+    if [ "$SHA1_CHECK_RES" = "failed" ]; then
+        NEED_REDOWNLOAD="1"
+
+        echo "Local file \"${LOCAL_FILE_PATH}.bz2\" already exists. Checking SHA1... Failed"
+
+        # if the existing file is larger, the extra part would be ignored by "curl -C".
+        rm "${LOCAL_FILE_PATH}.bz2"
+
+        echo "Re-downloading file..."
+    else
+        echo "Local file \"${LOCAL_FILE_PATH}.bz2\" already exists. Checking SHA1... Passed"
+        echo "File is up-to-date. Skipping download."
+    fi
+fi
+
+if [ ! -z "$NEED_REDOWNLOAD" ]; then
+    curl --progress-bar -L -C - "$FULL_URL" -o "${LOCAL_FILE_PATH}.bz2"
+
+    SHA1_CHECK_RES=$(echo "${FILE_SHA1} ${LOCAL_FILE_PATH}.bz2" | sha1sum -c - >/dev/null 2>&1 || echo "failed")
+
+    if [ "$SHA1_CHECK_RES" = "failed" ]; then
+        echo "Checking SHA1... Failed"
+        echo "Error: The SHA1 might be outdated. Please update your local copy and try again."
+        exit 1
+    else
+        echo "Checking SHA1... Passed"
+    fi
+fi
+
+echo "Extracting from \"${LOCAL_FILE_PATH}.bz2\""
+
+bunzip2 --keep "${LOCAL_FILE_PATH}.bz2" >/dev/null 2>&1
+
+if [ ! -f "$LOCAL_FILE_PATH" ]; then
+    echo "Something went wrong! The file \"$LOCAL_FILE_PATH\" was not found."
+    exit 1
+else
+    echo "Completed!"
+fi
diff --git a/aclint.c b/src/aclint.c
similarity index 100%
rename from aclint.c
rename to src/aclint.c
diff --git a/main.c b/src/main.c
similarity index 100%
rename from main.c
rename to src/main.c
diff --git a/minimal.dts b/src/minimal.dts
similarity index 100%
rename from minimal.dts
rename to src/minimal.dts
diff --git a/netdev.c b/src/netdev.c
similarity index 100%
rename from netdev.c
rename to src/netdev.c
diff --git a/plic.c b/src/plic.c
similarity index 100%
rename from plic.c
rename to src/plic.c
diff --git a/ram.c b/src/ram.c
similarity index 100%
rename from ram.c
rename to src/ram.c
diff --git a/riscv.c b/src/riscv.c
similarity index 99%
rename from riscv.c
rename to src/riscv.c
index bd92f1f0..59acc2fa 100644
--- a/riscv.c
+++ b/src/riscv.c
@@ -1,6 +1,5 @@
 #include <stdio.h>
 
-#include "common.h"
 #include "device.h"
 #include "riscv.h"
 #include "riscv_private.h"
diff --git a/slirp.c b/src/slirp.c
similarity index 100%
rename from slirp.c
rename to src/slirp.c
diff --git a/uart.c b/src/uart.c
similarity index 100%
rename from uart.c
rename to src/uart.c
diff --git a/utils.c b/src/utils.c
similarity index 100%
rename from utils.c
rename to src/utils.c
diff --git a/virtio-blk.c b/src/virtio-blk.c
similarity index 99%
rename from virtio-blk.c
rename to src/virtio-blk.c
index c64cda78..6f214d4f 100644
--- a/virtio-blk.c
+++ b/src/virtio-blk.c
@@ -9,7 +9,6 @@
 #include <sys/stat.h>
 #include <unistd.h>
 
-#include "common.h"
 #include "device.h"
 #include "riscv.h"
 #include "riscv_private.h"
diff --git a/virtio-net.c b/src/virtio-net.c
similarity index 99%
rename from virtio-net.c
rename to src/virtio-net.c
index 9fb9baaf..6f0683bf 100644
--- a/virtio-net.c
+++ b/src/virtio-net.c
@@ -11,7 +11,6 @@
 #include <sys/ioctl.h>
 #include <sys/uio.h>
 
-#include "common.h"
 #include "device.h"
 #include "riscv.h"
 #include "riscv_private.h"
diff --git a/virtio-rng.c b/src/virtio-rng.c
similarity index 99%
rename from virtio-rng.c
rename to src/virtio-rng.c
index 2876fe09..7a3aad4d 100644
--- a/virtio-rng.c
+++ b/src/virtio-rng.c
@@ -4,7 +4,6 @@
 #include <string.h>
 #include <unistd.h>
 
-#include "common.h"
 #include "device.h"
 #include "riscv.h"
 #include "riscv_private.h"
diff --git a/virtio-snd.c b/src/virtio-snd.c
similarity index 100%
rename from virtio-snd.c
rename to src/virtio-snd.c