Make sure global variables are zerod before exiting bios post.
diff --git a/src/post.c b/src/post.c
index 851dbae..216ed06 100644
--- a/src/post.c
+++ b/src/post.c
@@ -536,6 +536,10 @@
     // XXX - original bios calls ata_detect before rom scan.
     rom_scan(0xc8000, 0xe0000);
 
+    // reset the memory (some boot loaders such as syslinux suppose
+    // that the memory is set to zero)
+    memset((void*)0x40000, 0, 0x40000); // XXX - shouldn't use globals
+
     callrom(SEG_BIOS, OFFSET_begin_boot);
 }