--- /dev/null
+#ifndef HEADER_LOADER_H
+#define HEADER_LOADER_H
+
+/* Constants fixed by the PC BIOS. */
+#define LOADER_BASE 0x7c00 /* Physical address of loader's base. */
+#define LOADER_SIZE 0x200 /* Loader size in bytes (one disk sector). */
+
+/* Physical address of kernel base. */
+#define LOADER_KERN_BASE 0x100000 /* 1 MB. */
+
+/* The loader maps 4 MB of the start of physical memory to this
+ virtual base address. Later, the kernel adds the rest of
+ physical memory to the mapping.
+ This must be aligned on a 4 MB boundary. */
+#define LOADER_PHYS_BASE 0xb0000000 /* 3 GB. */
+
+/* Offsets within the loader. */
+#define LOADER_BIOS_SIG (LOADER_SIZE - 2) /* aa55 BIOS signature. */
+#define LOADER_CMD_LINE (LOADER_BIOS_SIG - 0x80) /* Kernel command line. */
+#define LOADER_RAM_PAGES (LOADER_CMD_LINE - 4) /* # of pages of RAM. */
+
+#endif /* loader.h */