diff --git a/src/guest/bios/bios.c b/src/guest/bios/bios.c
index 9c38b13e..c767f9ab 100644
--- a/src/guest/bios/bios.c
+++ b/src/guest/bios/bios.c
@@ -8,7 +8,6 @@
 #include "guest/bios/syscalls.h"
 #include "guest/dreamcast.h"
 #include "guest/gdrom/gdrom.h"
-#include "guest/gdrom/iso.h"
 #include "guest/rom/flash.h"
 #include "guest/sh4/sh4.h"
 #include "render/imgui.h"
@@ -215,88 +214,51 @@ static int bios_boot(struct bios *bios) {
   const uint32_t BOOT1_ADDR = 0x8c008000;
   const uint32_t BOOT2_ADDR = 0x8c010000;
   const uint32_t SYSINFO_ADDR = 0x8c000068;
-  const int sector_fmt = GD_SECTOR_ANY;
-  const int sector_mask = GD_MASK_DATA;
-  const int sector_size = 2048;
-  uint8_t tmp[0x10000];
 
   LOG_INFO("bios_boot using hle bootstrap");
 
-  /* get the session for the main data track */
-  struct gd_spi_session data_session;
-  gdrom_get_session(gd, 2, &data_session);
-  int data_fad = data_session.fad;
-
   /* load ip.bin bootstrap */
   {
-    int r = gdrom_read_sectors(gd, data_fad, 16, sector_fmt, sector_mask, tmp,
-                               sizeof(tmp));
-    if (!r) {
+    /* bootstrap occupies the first 16 sectors of the data track */
+    struct gd_spi_session data_session;
+    gdrom_get_session(gd, 2, &data_session);
+
+    uint8_t tmp[DISC_MAX_SECTOR_SIZE * 16];
+    int read = gdrom_read_sectors(gd, data_session.fad, 16, GD_SECTOR_ANY,
+                                  GD_MASK_DATA, tmp, sizeof(tmp));
+    if (!read) {
+      LOG_WARNING("bios_boot failed to copy IP.BIN");
       return 0;
     }
-    as_memcpy_to_guest(space, BOOT1_ADDR, tmp, r);
+
+    as_memcpy_to_guest(space, BOOT1_ADDR, tmp, read);
   }
 
   /* load 1st_read.bin into ram */
   {
-    static const char *bootfile = "1ST_READ.BIN";
+    const char *bootfile = "1ST_READ.BIN";
 
-    /* read primary volume descriptor */
-    int r = gdrom_read_sectors(gd, data_fad + ISO_PVD_SECTOR, 1, sector_fmt,
-                               sector_mask, tmp, sizeof(tmp));
-    if (!r) {
-      return 0;
-    }
-
-    struct iso_pvd *pvd = (struct iso_pvd *)tmp;
-    CHECK(pvd->type == 1);
-    CHECK(memcmp(pvd->id, "CD001", 5) == 0);
-    CHECK(pvd->version == 1);
-
-    /* check root directory for the bootfile */
-    struct iso_dir *root = &pvd->root_directory_record;
-    int len = align_up(root->size.le, sector_size);
-    int fad = GDROM_PREGAP + root->extent.le;
-    int n = len / sector_size;
-    r = gdrom_read_sectors(gd, fad, n, sector_fmt, sector_mask, tmp,
-                           sizeof(tmp));
-    if (!r) {
-      return 0;
-    }
-
-    uint8_t *ptr = tmp;
-    uint8_t *end = tmp + len;
-
-    while (ptr < end) {
-      struct iso_dir *dir = (struct iso_dir *)ptr;
-      const char *filename = (const char *)(ptr + sizeof(*dir));
-
-      if (memcmp(filename, bootfile, strlen(bootfile)) == 0) {
-        break;
-      }
-
-      /* dir entries always begin on an even byte */
-      ptr = (uint8_t *)filename + dir->name_len;
-      ptr = (uint8_t *)align_up((intptr_t)ptr, (intptr_t)2);
-    }
-
-    if (ptr == end) {
-      LOG_WARNING("bios_boot failed to find '%s'", bootfile);
+    int fad;
+    int len;
+    int found = gdrom_find_file(gd, bootfile, &fad, &len);
+    if (!found) {
+      LOG_WARNING("bios_boot failed to find %s", bootfile);
       return 0;
     }
 
     /* copy the bootfile into ram */
-    struct iso_dir *dir = (struct iso_dir *)ptr;
-    fad = GDROM_PREGAP + dir->extent.le;
-    n = align_up(dir->size.le, sector_size) / sector_size;
-    r = gdrom_copy_sectors(gd, fad, sector_fmt, sector_mask, n, space,
-                           BOOT2_ADDR);
-    if (!r) {
+    uint8_t *tmp = malloc(len);
+    int read = gdrom_read_bytes(gd, fad, len, tmp, len);
+    if (read != len) {
+      LOG_WARNING("bios_boot failed to copied %s", bootfile);
+      free(tmp);
       return 0;
     }
 
-    LOG_INFO("bios_boot found '%s' at fad=%d size=%d", bootfile, fad,
-             dir->size.le);
+    as_memcpy_to_guest(space, BOOT2_ADDR, tmp, read);
+    free(tmp);
+
+    LOG_INFO("bios_boot found '%s' at fad=%d size=%d", bootfile, fad, len);
   }
 
   /* write system info */
diff --git a/src/guest/bios/syscalls.c b/src/guest/bios/syscalls.c
index a07688ea..ba8d5035 100644
--- a/src/guest/bios/syscalls.c
+++ b/src/guest/bios/syscalls.c
@@ -134,20 +134,27 @@ static void bios_gdrom_mainloop(struct bios *bios) {
   switch (bios->cmd_code) {
     case GDC_PIOREAD:
     case GDC_DMAREAD: {
-      uint32_t fad = bios->params[0];
-      uint32_t n = bios->params[1];
+      int fad = bios->params[0];
+      int num_sectors = bios->params[1];
       uint32_t dst = bios->params[2];
       uint32_t unknown = bios->params[3];
       int fmt = GD_SECTOR_ANY;
       int mask = GD_MASK_DATA;
 
-      LOG_SYSCALL("GDC_DMAREAD fad=0x%x n=0x%x dst=0x%x unknown=0x%x", fad, n,
-                  dst, unknown);
+      LOG_SYSCALL("GDC_DMAREAD fad=0x%x n=0x%x dst=0x%x unknown=0x%x", fad,
+                  num_sectors, dst, unknown);
 
       /* dma read functionality changes somehow when this in non-zero */
       CHECK_EQ(unknown, 0);
 
-      int read = gdrom_copy_sectors(gd, fad, fmt, mask, n, space, dst);
+      int read = 0;
+      uint8_t tmp[DISC_MAX_SECTOR_SIZE];
+
+      for (int i = fad; i < fad + num_sectors; i++) {
+        int n = gdrom_read_sectors(gd, i, 1, fmt, mask, tmp, sizeof(tmp));
+        as_memcpy_to_guest(space, dst + read, tmp, n);
+        read += n;
+      }
 
       bios->result[2] = read;
       /* result[3] seems to signals if data is remaining, calculated by:
diff --git a/src/guest/gdrom/disc.c b/src/guest/gdrom/disc.c
index d5055ef5..24969e91 100644
--- a/src/guest/gdrom/disc.c
+++ b/src/guest/gdrom/disc.c
@@ -3,6 +3,101 @@
 #include "core/string.h"
 #include "guest/gdrom/cdi.h"
 #include "guest/gdrom/gdi.h"
+#include "guest/gdrom/iso.h"
+
+int disc_find_file(struct disc *disc, const char *filename, int *fad,
+                   int *len) {
+  uint8_t tmp[0x10000];
+
+  /* get the session for the main data track */
+  struct session *session = disc_get_session(disc, 1);
+  struct track *data_track = disc_get_track(disc, session->first_track);
+
+  /* read primary volume descriptor */
+  int read = disc_read_sectors(disc, data_track->fad + ISO_PVD_SECTOR, 1,
+                               GD_SECTOR_ANY, GD_MASK_DATA, tmp, sizeof(tmp));
+  if (!read) {
+    return 0;
+  }
+
+  struct iso_pvd *pvd = (struct iso_pvd *)tmp;
+  CHECK(pvd->type == 1);
+  CHECK(memcmp(pvd->id, "CD001", 5) == 0);
+  CHECK(pvd->version == 1);
+
+  /* check root directory for the file
+     FIXME recurse subdirectories */
+  struct iso_dir *root = &pvd->root_directory_record;
+  int root_len = root->size.le;
+  int root_fad = GDROM_PREGAP + root->extent.le;
+  read = disc_read_bytes(disc, root_fad, root_len, tmp, sizeof(tmp));
+  if (!read) {
+    return 0;
+  }
+
+  uint8_t *ptr = tmp;
+  uint8_t *end = tmp + root_len;
+
+  while (ptr < end) {
+    struct iso_dir *dir = (struct iso_dir *)ptr;
+    const char *name = (const char *)(ptr + sizeof(*dir));
+
+    if (memcmp(name, filename, strlen(filename)) == 0) {
+      break;
+    }
+
+    /* dir entries always begin on an even byte */
+    ptr = (uint8_t *)name + dir->name_len;
+    ptr = (uint8_t *)align_up((intptr_t)ptr, (intptr_t)2);
+  }
+
+  if (ptr == end) {
+    return 0;
+  }
+
+  struct iso_dir *dir = (struct iso_dir *)ptr;
+  *fad = GDROM_PREGAP + dir->extent.le;
+  *len = dir->size.le;
+
+  return 1;
+}
+
+int disc_read_bytes(struct disc *disc, int fad, int len, void *dst,
+                    int dst_size) {
+  CHECK_LE(len, dst_size);
+
+  uint8_t tmp[DISC_MAX_SECTOR_SIZE];
+  int rem = len;
+
+  while (rem) {
+    int n = disc->read_sectors(disc, fad, 1, GD_SECTOR_ANY, GD_MASK_DATA, tmp,
+                               sizeof(tmp));
+    CHECK(n);
+
+    /* don't overrun */
+    n = MIN(n, rem);
+    memcpy(dst, tmp, n);
+
+    rem -= n;
+    dst += n;
+    fad++;
+  }
+
+  return len;
+}
+
+int disc_read_sectors(struct disc *disc, int fad, int num_sectors,
+                      int sector_fmt, int sector_mask, void *dst,
+                      int dst_size) {
+  return disc->read_sectors(disc, fad, num_sectors, sector_fmt, sector_mask,
+                            dst, dst_size);
+}
+
+void disc_get_toc(struct disc *disc, int area, struct track **first_track,
+                  struct track **last_track, int *leadin_fad,
+                  int *leadout_fad) {
+  disc->get_toc(disc, area, first_track, last_track, leadin_fad, leadout_fad);
+}
 
 struct track *disc_lookup_track(struct disc *disc, int fad) {
   int num_tracks = disc_get_num_tracks(disc);
@@ -28,19 +123,6 @@ struct track *disc_lookup_track(struct disc *disc, int fad) {
   return NULL;
 }
 
-int disc_read_sectors(struct disc *disc, int fad, int num_sectors,
-                      int sector_fmt, int sector_mask, void *dst,
-                      int dst_size) {
-  return disc->read_sectors(disc, fad, num_sectors, sector_fmt, sector_mask,
-                            dst, dst_size);
-}
-
-void disc_get_toc(struct disc *disc, int area, struct track **first_track,
-                  struct track **last_track, int *leadin_fad,
-                  int *leadout_fad) {
-  disc->get_toc(disc, area, first_track, last_track, leadin_fad, leadout_fad);
-}
-
 struct track *disc_get_track(struct disc *disc, int n) {
   return disc->get_track(disc, n);
 }
diff --git a/src/guest/gdrom/disc.h b/src/guest/gdrom/disc.h
index 4c9df28b..4d263fea 100644
--- a/src/guest/gdrom/disc.h
+++ b/src/guest/gdrom/disc.h
@@ -66,10 +66,13 @@ int disc_get_num_sessions(struct disc *disc);
 struct session *disc_get_session(struct disc *disc, int n);
 int disc_get_num_tracks(struct disc *disc);
 struct track *disc_get_track(struct disc *disc, int n);
+struct track *disc_lookup_track(struct disc *disc, int fad);
+int disc_find_file(struct disc *disc, const char *filename, int *fad, int *len);
 void disc_get_toc(struct disc *disc, int area, struct track **first_track,
                   struct track **last_track, int *leadin_fad, int *leadout_fad);
 int disc_read_sectors(struct disc *disc, int fad, int num_sectors,
                       int sector_fmt, int sector_mask, void *dst, int dst_size);
-struct track *disc_lookup_track(struct disc *disc, int fad);
+int disc_read_bytes(struct disc *disc, int fad, int len, void *dst,
+                    int dst_size);
 
 #endif
diff --git a/src/guest/gdrom/gdrom.c b/src/guest/gdrom/gdrom.c
index 5a912b79..e7a7f2f6 100644
--- a/src/guest/gdrom/gdrom.c
+++ b/src/guest/gdrom/gdrom.c
@@ -467,24 +467,14 @@ static void gdrom_event(struct gdrom *gd, enum gd_event ev, int arg) {
   cb(gd, arg);
 }
 
-int gdrom_copy_sectors(struct gdrom *gd, int fad, int fmt, int mask,
-                       int num_sectors, struct address_space *space,
-                       uint32_t dst) {
+int gdrom_read_bytes(struct gdrom *gd, int fad, int len, uint8_t *dst,
+                     int dst_size) {
   if (!gd->disc) {
-    LOG_WARNING("gdrom_copy_sectors failed, no disc");
+    LOG_WARNING("gdrom_read_sectors failed, no disc");
     return 0;
   }
 
-  int read = 0;
-  uint8_t tmp[DISC_MAX_SECTOR_SIZE];
-
-  for (int i = fad; i < fad + num_sectors; i++) {
-    int n = disc_read_sectors(gd->disc, i, 1, fmt, mask, tmp, sizeof(tmp));
-    as_memcpy_to_guest(space, dst + read, tmp, n);
-    read += n;
-  }
-
-  return read;
+  return disc_read_bytes(gd->disc, fad, len, dst, dst_size);
 }
 
 int gdrom_read_sectors(struct gdrom *gd, int fad, int num_sectors, int fmt,
@@ -496,11 +486,18 @@ int gdrom_read_sectors(struct gdrom *gd, int fad, int num_sectors, int fmt,
 
   LOG_GDROM("gdrom_read_sectors [%d, %d)", fad, fad + num_sectors);
 
-  int read =
-      disc_read_sectors(gd->disc, fad, num_sectors, fmt, mask, dst, dst_size);
-  CHECK(read);
+  return disc_read_sectors(gd->disc, fad, num_sectors, fmt, mask, dst,
+                           dst_size);
+}
 
-  return read;
+int gdrom_find_file(struct gdrom *gd, const char *filename, int *fad,
+                    int *len) {
+  if (!gd->disc) {
+    LOG_WARNING("gdrom_find_file failed, no disc");
+    return 0;
+  }
+
+  return disc_find_file(gd->disc, filename, fad, len);
 }
 
 void gdrom_get_subcode(struct gdrom *gd, int format, uint8_t *data, int size) {
diff --git a/src/guest/gdrom/gdrom.h b/src/guest/gdrom/gdrom.h
index f790bc51..80b9f293 100644
--- a/src/guest/gdrom/gdrom.h
+++ b/src/guest/gdrom/gdrom.h
@@ -4,7 +4,6 @@
 #include "guest/gdrom/disc.h"
 #include "guest/gdrom/gdrom_types.h"
 
-struct address_space;
 struct dreamcast;
 struct gdrom;
 
@@ -24,10 +23,10 @@ void gdrom_get_toc(struct gdrom *gd, int area, struct gd_spi_toc *toc);
 void gdrom_get_session(struct gdrom *gd, int session,
                        struct gd_spi_session *ses);
 void gdrom_get_subcode(struct gdrom *gd, int format, uint8_t *data, int size);
+int gdrom_find_file(struct gdrom *gd, const char *filename, int *fad, int *len);
 int gdrom_read_sectors(struct gdrom *gd, int fad, int num_sectors, int fmt,
                        int mask, uint8_t *dst, int dst_size);
-int gdrom_copy_sectors(struct gdrom *gd, int fad, int fmt, int mask,
-                       int num_sectors, struct address_space *space,
-                       uint32_t dst);
+int gdrom_read_bytes(struct gdrom *gd, int fad, int len, uint8_t *dst,
+                     int dst_size);
 
 #endif