diff --git a/tools/io.hpp b/tools/io.hpp
new file mode 100644
index 0000000..b8da0ef
--- /dev/null
+++ b/tools/io.hpp
@@ -0,0 +1,63 @@
+#pragma once
+
+#include "internal/sys.hpp"
+
+#include <cstdint>
+#include <string>
+
+namespace host_tool
+{
+
+class HostIoInterface
+{
+  public:
+    virtual ~HostIoInterface() = default;
+
+    /**
+     * Attempt to write bytes from source to offset into the host memory device.
+     *
+     * @param[in] offset - offset into the host memory device.
+     * @param[in] length - the number of bytes to copy from source.
+     * @param[in] source - the souce of the bytes to copy to the memory device.
+     * @return true on success, false on failure (such as unable to initialize
+     * device).
+     */
+    virtual bool write(const std::size_t offset, const std::size_t length,
+                       const void* const source) = 0;
+};
+
+class DevMemDevice : public HostIoInterface
+{
+  public:
+    explicit DevMemDevice(const internal::Sys* sys = &internal::sys_impl) :
+        sys(sys)
+    {
+    }
+
+    /* On destruction, close /dev/mem if it was open. */
+    ~DevMemDevice()
+    {
+        if (opened)
+        {
+            sys->close(devMemFd);
+        }
+    }
+
+    /* Don't allow copying or assignment, only moving. */
+    DevMemDevice(const DevMemDevice&) = delete;
+    DevMemDevice& operator=(const DevMemDevice&) = delete;
+    DevMemDevice(DevMemDevice&&) = default;
+    DevMemDevice& operator=(DevMemDevice&&) = default;
+
+    bool write(const std::size_t offset, const std::size_t length,
+               const void* const source) override;
+
+  private:
+    static const std::string devMemPath;
+    bool opened = false;
+    int devMemFd = -1;
+    void* devMemMapped = nullptr;
+    const internal::Sys* sys;
+};
+
+} // namespace host_tool