diff --git a/src/drivers/bus/isa.c b/src/drivers/bus/isa.c
new file mode 100644
index 00000000..2ca1cfd2
--- /dev/null
+++ b/src/drivers/bus/isa.c
@@ -0,0 +1,123 @@
+#include "etherboot.h"
+#include "isa.h"
+
+/*
+ * isa.c implements a "classical" port-scanning method of ISA device
+ * detection.  The driver must provide a list of probe addresses
+ * (probe_addrs), together with a function (probe_addr) that can be
+ * used to test for the physical presence of a device at any given
+ * address.
+ *
+ * Note that this should probably be considered the "last resort" for
+ * device probing.  If the card supports ISAPnP or EISA, use that
+ * instead.  Some cards (e.g. the 3c509) implement a proprietary
+ * ISAPnP-like mechanism.
+ *
+ * The ISA probe address list can be overridden by config.c; if 
+ */
+
+/*
+ * Ensure that there is sufficient space in the shared dev_bus
+ * structure for a struct isa_device.
+ *
+ */
+DEV_BUS( struct isa_device, isa_dev );
+static char isa_magic[0]; /* guaranteed unique symbol */
+
+/*
+ * Find an ISA device matching the specified driver
+ *
+ */
+int find_isa_device ( struct isa_device *isa, struct isa_driver *driver ) {
+	unsigned int i;
+	uint16_t ioaddr;
+
+	/* Initialise struct isa if it's the first time it's been used. */
+	if ( isa->magic != isa_magic ) {
+		memset ( isa, 0, sizeof ( *isa ) );
+		isa->magic = isa_magic;
+	}
+
+	/* Iterate through any ISA probe addresses specified by
+	 * config.c, starting where we left off.
+	 */
+	for ( i = isa->probe_idx ; i < isa_extra_probe_addr_count ; i++ ) {
+		/* If we've already used this device, skip it */
+		if ( isa->already_tried ) {
+			isa->already_tried = 0;
+			continue;
+		}
+
+		/* Set I/O address */
+		ioaddr = isa_extra_probe_addrs[i].addr;
+
+		/* An I/O address of 0 in extra_probe_addrs list means
+		 * stop probing (i.e. don't continue to the
+		 * driver-provided list)
+		 */
+		if ( ! ioaddr )
+			goto notfound;
+
+		/* Use probe_addr method to see if there's a device
+		 * present at this address.
+		 */
+		if ( driver->probe_addr ( ioaddr ) ) {
+			isa->probe_idx = i;
+			goto found;
+		}
+	}
+
+	/* Iterate through all ISA probe addresses provided by the
+	 * driver, starting where we left off.
+	 */
+	for ( i = isa->probe_idx - isa_extra_probe_addr_count ;
+	      i < driver->addr_count ; i++ ) {
+
+		/* If we've already used this device, skip it */
+		if ( isa->already_tried ) {
+			isa->already_tried = 0;
+			continue;
+		}
+
+		/* Set I/O address */
+		ioaddr = driver->probe_addrs[i].addr;
+
+		/* Use probe_addr method to see if there's a device
+		 * present at this address.
+		 */
+		if ( driver->probe_addr ( ioaddr ) ) {
+			isa->probe_idx = i + isa_extra_probe_addr_count;
+			goto found;
+		}
+	}
+
+ notfound:
+	/* No device found */
+	isa->probe_idx = 0;
+	return 0;
+
+ found:
+	DBG ( "Found %s ISA device at address %hx\n", driver->name, ioaddr );
+	isa->ioaddr = ioaddr;
+	isa->already_tried = 1;
+	return 1;
+}
+
+/*
+ * Find the next ISA device that can be used to boot using the
+ * specified driver.
+ *
+ */
+int find_isa_boot_device ( struct dev *dev, struct isa_driver *driver ) {
+	struct isa_device *isa = ( struct isa_device * )dev->bus;
+
+	if ( ! find_isa_device ( isa, driver ) )
+		return 0;
+
+	dev->name = driver->name;
+	dev->devid.bus_type = ISA_BUS_TYPE;
+	dev->devid.vendor_id = driver->mfg_id;
+	dev->devid.device_id = driver->prod_id;
+
+	return 1;
+}
diff --git a/src/include/isa.h b/src/include/isa.h
index fe5c557b..7ac97ea0 100644
--- a/src/include/isa.h
+++ b/src/include/isa.h
@@ -2,27 +2,78 @@
 #define ISA_H
 
 #include "isa_ids.h"
+#include "dev.h"
 
-struct dev;
-
-struct isa_driver
-{
-	int type;
-	const char *name;
-	int (*probe)(struct dev *, unsigned short *);
-	unsigned short *ioaddrs;
+/*
+ * A physical ISA device
+ *
+ */
+struct isa_device {
+	char *magic; /* must be first */
+	unsigned int probe_idx;
+	uint16_t ioaddr;
+	int already_tried;
 };
 
-#ifndef __HYPERSTONE__
-#define __isa_driver	__attribute__ ((used,__section__(".drivers.isa")))
-#else 
-#define __isa_driver	__attribute__ ((used,__section__(".drivisa")))
-#endif
+/*
+ * An individual ISA device, identified by probe address
+ *
+ */
+struct isa_probe_addr {
+	uint16_t addr;
+} __attribute__ (( packed ));
 
-extern const struct isa_driver isa_drivers[];
-extern const struct isa_driver isa_drivers_end[];
+/*
+ * An ISA driver, with a probe address list and a probe_addr method.
+ * probe_addr() should return 1 if a card is physically present,
+ * leaving the other operations (read MAC address etc.) down to the
+ * main probe() routine.
+ *
+ */
+struct isa_driver {
+	const char *name;
+	struct isa_probe_addr *probe_addrs;
+	unsigned int addr_count;
+	int ( * probe_addr ) ( uint16_t addr );
+	uint16_t mfg_id;
+	uint16_t prod_id;
+};
 
-#define ISA_ROM(IMAGE, DESCRIPTION)
+/*
+ * Define an ISA driver
+ *
+ */
+#define ISA_DRIVER( _name, _probe_addrs, _probe_addr, _mfg_id, _prod_id ) { \
+	.name = _name,							    \
+	.probe_addrs = _probe_addrs,					    \
+	.addr_count = sizeof ( _probe_addrs ) / sizeof ( probe_addrs[0] ),  \
+	.probe_addr = _probe_addr,					    \
+	.mfg_id = _mfg_id,						    \
+	.prod_id = _prod_id,						    \
+}
+
+/*
+ * ISA_ROM is parsed by parserom.pl to generate Makefile rules and
+ * files for rom-o-matic.
+ *
+ */
+#define ISA_ROM( IMAGE, DESCRIPTION )
+
+/*
+ * Functions in isa.c
+ *
+ */
+extern int find_isa_device ( struct isa_device *eisa,
+			     struct isa_driver *driver );
+extern int find_isa_boot_device ( struct dev *dev,
+				  struct isa_driver *driver );
+
+/*
+ * config.c defines isa_extra_probe_addrs and isa_extra_probe_addr_count.
+ *
+ */
+extern struct isa_probe_addr isa_extra_probe_addrs[];
+extern unsigned int isa_extra_probe_addr_count;
 
 #endif /* ISA_H */