diff --git a/bricks/cityhub/city_hub.ld b/bricks/cityhub/city_hub.ld
index 2b070fb8a..aef4b071b 100644
--- a/bricks/cityhub/city_hub.ld
+++ b/bricks/cityhub/city_hub.ld
@@ -6,7 +6,8 @@
     GNU linker script for LEGO Powered Up City Hub
 */
 
-/* Specify the memory areas */
+/* Memory areas. NB: Total storage size (FLASH_USER_0 + FLASH_USER_1)
+   MUST match PBDRV_CONFIG_BLOCK_DEVICE_FLASH_STM32_SIZE */
 MEMORY
 {
     /* Non-erasable BLE bootloader (LEGO LWP3). Device boots only if all words
@@ -15,7 +16,7 @@ MEMORY
     /* The firmware. Installed via BLE bootloader. */
     FLASH_FIRMWARE (rx)   : ORIGIN = 0x08005000, LENGTH = 220K
     /* User data written by the firmware during shutdown. */
-    FLASH_USER_0 (rx)       : ORIGIN = 0x0803C000, LENGTH = 12K
+    FLASH_USER_0 (rx)     : ORIGIN = 0x0803C000, LENGTH = 12K
     /* As above, but this part is not counted by bootloader checksum. */
     FLASH_USER_1 (rx)     : ORIGIN = 0x0803F000, LENGTH = 4K
     RAM (xrw)             : ORIGIN = 0x20000000, LENGTH = 32K
@@ -23,6 +24,9 @@ MEMORY
 
 "MAGIC_OFFSET" = 0x100;
 _stack_size = 4K;
+
+/* Start of data storage. */
 _pbdrv_block_device_storage_start = ORIGIN(FLASH_USER_0);
-_pbdrv_block_device_storage_size = LENGTH(FLASH_USER_0) + LENGTH(FLASH_USER_1);
+
+/* Portion of the data parsed for the checksum on boot. */
 _pbsys_program_load_checked_size = LENGTH(FLASH_USER_0);
diff --git a/bricks/movehub/move_hub.ld b/bricks/movehub/move_hub.ld
index ad3c73505..50f533d13 100644
--- a/bricks/movehub/move_hub.ld
+++ b/bricks/movehub/move_hub.ld
@@ -6,7 +6,8 @@
     GNU linker script for LEGO BOOST Move Hub
 */
 
-/* Specify the memory areas */
+/* Memory areas. NB: Total storage size (FLASH_USER_0 + FLASH_USER_1)
+   MUST match PBDRV_CONFIG_BLOCK_DEVICE_FLASH_STM32_SIZE */
 MEMORY
 {
     /* Non-erasable BLE bootloader (LEGO LWP3). Device boots only if all words
@@ -15,7 +16,7 @@ MEMORY
     /* The firmware. Installed via BLE bootloader. */
     FLASH_FIRMWARE (rx)   : ORIGIN = 0x08005000, LENGTH = 104K
     /* User data written by the firmware during shutdown. */
-    FLASH_USER_0 (rx)       : ORIGIN = 0x0801F000, LENGTH = 2K
+    FLASH_USER_0 (rx)     : ORIGIN = 0x0801F000, LENGTH = 2K
     /* As above, but this part is not counted by bootloader checksum. */
     FLASH_USER_1 (rx)     : ORIGIN = 0x0801F800, LENGTH = 2K
     RAM (xrw)             : ORIGIN = 0x20000000, LENGTH = 16K
@@ -23,6 +24,9 @@ MEMORY
 
 "MAGIC_OFFSET" = 0x100;
 _stack_size = 3K;
+
+/* Start of data storage. */
 _pbdrv_block_device_storage_start = ORIGIN(FLASH_USER_0);
-_pbdrv_block_device_storage_size = LENGTH(FLASH_USER_0) + LENGTH(FLASH_USER_1);
+
+/* Portion of the data parsed for the checksum on boot. */
 _pbsys_program_load_checked_size = LENGTH(FLASH_USER_0);
diff --git a/bricks/technichub/technic_hub.ld b/bricks/technichub/technic_hub.ld
index 54ede546e..99ac77543 100644
--- a/bricks/technichub/technic_hub.ld
+++ b/bricks/technichub/technic_hub.ld
@@ -6,7 +6,8 @@
     GNU linker script for LEGO Technic Hub
 */
 
-/* Specify the memory areas */
+/* Memory areas. NB: Total storage size (FLASH_USER_0 + FLASH_USER_1)
+   MUST match PBDRV_CONFIG_BLOCK_DEVICE_FLASH_STM32_SIZE */
 MEMORY
 {
     /* Non-erasable BLE bootloader (LEGO LWP3). Device boots only if all words
@@ -23,6 +24,9 @@ MEMORY
 
 "MAGIC_OFFSET" = 0x200;
 _stack_size = 8K;
+
+/* Start of data storage. */
 _pbdrv_block_device_storage_start = ORIGIN(FLASH_USER_0);
-_pbdrv_block_device_storage_size = LENGTH(FLASH_USER_0) + LENGTH(FLASH_USER_1);
+
+/* Portion of the data parsed for the checksum on boot. */
 _pbsys_program_load_checked_size = LENGTH(FLASH_USER_0);
diff --git a/lib/pbio/drv/block_device/block_device_flash_stm32.c b/lib/pbio/drv/block_device/block_device_flash_stm32.c
index 4f4d3612a..5425c0caf 100644
--- a/lib/pbio/drv/block_device/block_device_flash_stm32.c
+++ b/lib/pbio/drv/block_device/block_device_flash_stm32.c
@@ -21,12 +21,6 @@
 
 #include STM32_HAL_H
 
-uint32_t pbdrv_block_device_get_size(void) {
-    // Defined in linker script.
-    extern uint32_t _pbdrv_block_device_storage_size;
-    return (uint32_t)(&_pbdrv_block_device_storage_size);
-}
-
 void pbdrv_block_device_init(void) {
 }
 
@@ -37,7 +31,7 @@ PT_THREAD(pbdrv_block_device_read(struct pt *pt, uint32_t offset, uint8_t *buffe
     PT_BEGIN(pt);
 
     // Exit on invalid size.
-    if (size == 0 || offset + size > pbdrv_block_device_get_size()) {
+    if (size == 0 || offset + size > PBDRV_CONFIG_BLOCK_DEVICE_FLASH_STM32_SIZE) {
         *err = PBIO_ERROR_INVALID_ARG;
         PT_EXIT(pt);
     }
@@ -59,7 +53,7 @@ static pbio_error_t block_device_erase_and_write(uint8_t *buffer, uint32_t size)
     static const uint32_t base_address = (uint32_t)(&_pbdrv_block_device_storage_start[0]);
 
     // Exit if size is 0, too big, or not a multiple of double-word size.
-    if (size == 0 || size > pbdrv_block_device_get_size() || size % sizeof(uint64_t)) {
+    if (size == 0 || size > PBDRV_CONFIG_BLOCK_DEVICE_FLASH_STM32_SIZE || size % sizeof(uint64_t)) {
         return PBIO_ERROR_INVALID_ARG;
     }
 
@@ -75,11 +69,11 @@ static pbio_error_t block_device_erase_and_write(uint8_t *buffer, uint32_t size)
         .PageAddress = base_address,
         #elif defined(STM32L4)
         .Banks = FLASH_BANK_1, // Hard coded for STM32L431RC.
-        .Page = (FLASH_SIZE - (pbdrv_block_device_get_size())) / FLASH_PAGE_SIZE,
+        .Page = (FLASH_SIZE - (PBDRV_CONFIG_BLOCK_DEVICE_FLASH_STM32_SIZE)) / FLASH_PAGE_SIZE,
         #else
         #error "Unsupported target."
         #endif
-        .NbPages = pbdrv_block_device_get_size() / FLASH_PAGE_SIZE,
+        .NbPages = PBDRV_CONFIG_BLOCK_DEVICE_FLASH_STM32_SIZE / FLASH_PAGE_SIZE,
         .TypeErase = FLASH_TYPEERASE_PAGES
     };
 
diff --git a/lib/pbio/drv/block_device/block_device_w25qxx_stm32.c b/lib/pbio/drv/block_device/block_device_w25qxx_stm32.c
index 79c521b01..0dede3b4c 100644
--- a/lib/pbio/drv/block_device/block_device_w25qxx_stm32.c
+++ b/lib/pbio/drv/block_device/block_device_w25qxx_stm32.c
@@ -360,7 +360,7 @@ PT_THREAD(pbdrv_block_device_read(struct pt *pt, uint32_t offset, uint8_t *buffe
     PT_BEGIN(pt);
 
     // Exit on invalid size.
-    if (size == 0 || offset + size > pbdrv_block_device_get_size()) {
+    if (size == 0 || offset + size > PBDRV_CONFIG_BLOCK_DEVICE_W25QXX_STM32_SIZE) {
         *err = PBIO_ERROR_INVALID_ARG;
         PT_EXIT(pt);
     }
@@ -377,7 +377,7 @@ PT_THREAD(pbdrv_block_device_read(struct pt *pt, uint32_t offset, uint8_t *buffe
         size_now = pbio_math_min(size - size_done, FLASH_SIZE_READ);
 
         // Set address for this read request and send it.
-        set_address_be(&cmd_request_read.buffer[1], bdev.pdata->start_address + offset + size_done);
+        set_address_be(&cmd_request_read.buffer[1], PBDRV_CONFIG_BLOCK_DEVICE_W25QXX_STM32_START_ADDRESS + offset + size_done);
         PT_SPAWN(pt, &child, spi_command_thread(&child, &cmd_request_read, err));
         if (*err != PBIO_SUCCESS) {
             goto out;
@@ -467,7 +467,7 @@ PT_THREAD(pbdrv_block_device_store(struct pt *pt, uint8_t *buffer, uint32_t size
     PT_BEGIN(pt);
 
     // Exit on invalid size.
-    if (size == 0 || size > pbdrv_block_device_get_size()) {
+    if (size == 0 || size > PBDRV_CONFIG_BLOCK_DEVICE_W25QXX_STM32_SIZE) {
         *err = PBIO_ERROR_INVALID_ARG;
         PT_EXIT(pt);
     }
@@ -483,7 +483,7 @@ PT_THREAD(pbdrv_block_device_store(struct pt *pt, uint8_t *buffer, uint32_t size
     for (offset = 0; offset < size; offset += FLASH_SIZE_ERASE) {
         // Writing size 0 means erase.
         PT_SPAWN(pt, &child, flash_erase_or_write(&child,
-            bdev.pdata->start_address + offset, NULL, 0, err));
+            PBDRV_CONFIG_BLOCK_DEVICE_W25QXX_STM32_START_ADDRESS + offset, NULL, 0, err));
         if (*err != PBIO_SUCCESS) {
             goto out;
         }
@@ -493,7 +493,7 @@ PT_THREAD(pbdrv_block_device_store(struct pt *pt, uint8_t *buffer, uint32_t size
     for (size_done = 0; size_done < size; size_done += size_now) {
         size_now = pbio_math_min(size - size_done, FLASH_SIZE_WRITE);
         PT_SPAWN(pt, &child, flash_erase_or_write(&child,
-            bdev.pdata->start_address + size_done, buffer + size_done, size_now, err));
+            PBDRV_CONFIG_BLOCK_DEVICE_W25QXX_STM32_START_ADDRESS + size_done, buffer + size_done, size_now, err));
         if (*err != PBIO_SUCCESS) {
             goto out;
         }
@@ -505,10 +505,6 @@ PT_THREAD(pbdrv_block_device_store(struct pt *pt, uint8_t *buffer, uint32_t size
     PT_END(pt);
 }
 
-uint32_t pbdrv_block_device_get_size(void) {
-    return bdev.pdata->end_address - bdev.pdata->start_address;
-}
-
 PROCESS(pbdrv_block_device_w25qxx_stm32_init_process, "w25qxx");
 
 void pbdrv_block_device_init(void) {
diff --git a/lib/pbio/drv/block_device/block_device_w25qxx_stm32.h b/lib/pbio/drv/block_device/block_device_w25qxx_stm32.h
index 705803347..232cb39ea 100644
--- a/lib/pbio/drv/block_device/block_device_w25qxx_stm32.h
+++ b/lib/pbio/drv/block_device/block_device_w25qxx_stm32.h
@@ -40,15 +40,6 @@ typedef struct {
     IRQn_Type irq;
     /** The /CS pin. */
     const pbdrv_gpio_t pin_ncs;
-    /**
-     * Platform-specific starting address on the chip from where we can safely
-     * write data. All reads and writes to the block device are relative to
-     * this chip address. This can be used to protect the first region of flash
-     * if it is used to store things like bootloader information.
-     */
-    uint32_t start_address;
-    /** Ending address (exclusive) complementary to the start_address. */
-    uint32_t end_address;
 } pbdrv_block_device_w25qxx_stm32_platform_data_t;
 
 /**
diff --git a/lib/pbio/include/pbdrv/block_device.h b/lib/pbio/include/pbdrv/block_device.h
index 36ff130d3..4554dfba0 100644
--- a/lib/pbio/include/pbdrv/block_device.h
+++ b/lib/pbio/include/pbdrv/block_device.h
@@ -18,13 +18,6 @@
 
 #if PBDRV_CONFIG_BLOCK_DEVICE
 
-/**
- * Gets the size of the block device.
- *
- * @return              The maximum size that can be read or written.
- */
-uint32_t pbdrv_block_device_get_size(void);
-
 /**
  * Read data from a storage device.
  *
@@ -71,9 +64,6 @@ PT_THREAD(pbdrv_block_device_store(struct pt *pt, uint8_t *buffer, uint32_t size
 
 #else
 
-static inline uint32_t pbdrv_block_device_get_size(void) {
-    return 0;
-}
 static inline PT_THREAD(pbdrv_block_device_read(struct pt *pt, uint32_t offset, uint8_t *buffer, uint32_t size, pbio_error_t *err)) {
     PT_BEGIN(pt);
     *err = PBIO_ERROR_NOT_SUPPORTED;
diff --git a/lib/pbio/platform/city_hub/pbdrvconfig.h b/lib/pbio/platform/city_hub/pbdrvconfig.h
index 01d6a64de..150bcc3ab 100644
--- a/lib/pbio/platform/city_hub/pbdrvconfig.h
+++ b/lib/pbio/platform/city_hub/pbdrvconfig.h
@@ -24,6 +24,7 @@
 
 #define PBDRV_CONFIG_BLOCK_DEVICE                   (1)
 #define PBDRV_CONFIG_BLOCK_DEVICE_FLASH_STM32       (1)
+#define PBDRV_CONFIG_BLOCK_DEVICE_FLASH_STM32_SIZE  (16 * 1024) // Must match FLASH_USER_0 + FLASH_USER_1 in linker script
 
 #define PBDRV_CONFIG_BLUETOOTH                      (1)
 #define PBDRV_CONFIG_BLUETOOTH_STM32_CC2640         (1)
diff --git a/lib/pbio/platform/city_hub/pbsysconfig.h b/lib/pbio/platform/city_hub/pbsysconfig.h
index bc954ab7c..2587e9095 100644
--- a/lib/pbio/platform/city_hub/pbsysconfig.h
+++ b/lib/pbio/platform/city_hub/pbsysconfig.h
@@ -1,12 +1,15 @@
 // SPDX-License-Identifier: MIT
 // Copyright (c) 2020-2022 The Pybricks Authors
 
+#include "pbdrvconfig.h"
+
 #define PBSYS_CONFIG_BATTERY_CHARGER                (0)
 #define PBSYS_CONFIG_BLUETOOTH                      (1)
 #define PBSYS_CONFIG_HUB_LIGHT_MATRIX               (0)
 #define PBSYS_CONFIG_MAIN                           (1)
 #define PBSYS_CONFIG_PROGRAM_LOAD                   (1)
-#define PBSYS_CONFIG_PROGRAM_LOAD_PROGRAM_DATA_SIZE (20 * 1024)
 #define PBSYS_CONFIG_PROGRAM_LOAD_OVERLAPS_BOOTLOADER_CHECKSUM (1)
+#define PBSYS_CONFIG_PROGRAM_LOAD_RAM_SIZE          (20 * 1024)
+#define PBSYS_CONFIG_PROGRAM_LOAD_ROM_SIZE          (PBDRV_CONFIG_BLOCK_DEVICE_FLASH_STM32_SIZE)
 #define PBSYS_CONFIG_STATUS_LIGHT                   (1)
 #define PBSYS_CONFIG_STATUS_LIGHT_BATTERY           (0)
diff --git a/lib/pbio/platform/debug/pbsysconfig.h b/lib/pbio/platform/debug/pbsysconfig.h
index 1f908cc44..b0acee237 100644
--- a/lib/pbio/platform/debug/pbsysconfig.h
+++ b/lib/pbio/platform/debug/pbsysconfig.h
@@ -6,7 +6,8 @@
 #define PBSYS_CONFIG_HUB_LIGHT_MATRIX               (0)
 #define PBSYS_CONFIG_MAIN                           (1)
 #define PBSYS_CONFIG_PROGRAM_LOAD                   (1)
-#define PBSYS_CONFIG_PROGRAM_LOAD_PROGRAM_DATA_SIZE (64 * 1024)
+#define PBSYS_CONFIG_PROGRAM_LOAD_RAM_SIZE          (64 * 1024)
+#define PBSYS_CONFIG_PROGRAM_LOAD_ROM_SIZE          (0)
 #define PBSYS_CONFIG_PROGRAM_LOAD_OVERLAPS_BOOTLOADER_CHECKSUM (0)
 #define PBSYS_CONFIG_STATUS_LIGHT                   (1)
 #define PBSYS_CONFIG_STATUS_LIGHT_BATTERY           (0)
diff --git a/lib/pbio/platform/essential_hub/pbdrvconfig.h b/lib/pbio/platform/essential_hub/pbdrvconfig.h
index 7532e2bcd..7cd63e184 100644
--- a/lib/pbio/platform/essential_hub/pbdrvconfig.h
+++ b/lib/pbio/platform/essential_hub/pbdrvconfig.h
@@ -35,6 +35,12 @@
 #define PBDRV_CONFIG_BLOCK_DEVICE                   (1)
 #define PBDRV_CONFIG_BLOCK_DEVICE_W25QXX_STM32      (1)
 #define PBDRV_CONFIG_BLOCK_DEVICE_W25QXX_STM32_W25Q32 (1)
+// Carve out 256K from the reserved 1M area at the start of the flash.
+// This avoids touching the file system, the area read by the LEGO
+// bootloader and the area used by upstream MicroPython. Currently, this
+// just needs to be big enough to back up the user program on shutdown.
+#define PBDRV_CONFIG_BLOCK_DEVICE_W25QXX_STM32_START_ADDRESS (512 * 1024)
+#define PBDRV_CONFIG_BLOCK_DEVICE_W25QXX_STM32_SIZE (256 * 1024)
 
 #define PBDRV_CONFIG_BUTTON                         (1)
 #define PBDRV_CONFIG_BUTTON_GPIO                    (1)
diff --git a/lib/pbio/platform/essential_hub/pbsysconfig.h b/lib/pbio/platform/essential_hub/pbsysconfig.h
index 41c5985db..c7711d15a 100644
--- a/lib/pbio/platform/essential_hub/pbsysconfig.h
+++ b/lib/pbio/platform/essential_hub/pbsysconfig.h
@@ -6,7 +6,8 @@
 #define PBSYS_CONFIG_HUB_LIGHT_MATRIX               (0)
 #define PBSYS_CONFIG_MAIN                           (1)
 #define PBSYS_CONFIG_PROGRAM_LOAD                   (1)
-#define PBSYS_CONFIG_PROGRAM_LOAD_PROGRAM_DATA_SIZE (256 * 1024)
+#define PBSYS_CONFIG_PROGRAM_LOAD_RAM_SIZE          (258 * 1024)
+#define PBSYS_CONFIG_PROGRAM_LOAD_ROM_SIZE          (PBDRV_CONFIG_BLOCK_DEVICE_W25QXX_STM32_SIZE)
 #define PBSYS_CONFIG_PROGRAM_LOAD_OVERLAPS_BOOTLOADER_CHECKSUM (0)
 #define PBSYS_CONFIG_STATUS_LIGHT                   (1)
 #define PBSYS_CONFIG_STATUS_LIGHT_BATTERY           (1)
diff --git a/lib/pbio/platform/essential_hub/platform.c b/lib/pbio/platform/essential_hub/platform.c
index 147839285..117da2f25 100644
--- a/lib/pbio/platform/essential_hub/platform.c
+++ b/lib/pbio/platform/essential_hub/platform.c
@@ -630,12 +630,6 @@ const pbdrv_block_device_w25qxx_stm32_platform_data_t pbdrv_block_device_w25qxx_
         .bank = GPIOB,
         .pin = 12,
     },
-    // Carve out 256K from the reserved 1M area at the start of the flash.
-    // This avoids touching the file system, the area read by the LEGO
-    // bootloader and the area used by upstream MicroPython. Currently, this
-    // just needs to be big enough to back up the user program on shutdown.
-    .start_address = 512 * 1024,
-    .end_address = 768 * 1024,
 };
 
 // USB
diff --git a/lib/pbio/platform/move_hub/pbdrvconfig.h b/lib/pbio/platform/move_hub/pbdrvconfig.h
index c9b3084ec..d3d8a1a05 100644
--- a/lib/pbio/platform/move_hub/pbdrvconfig.h
+++ b/lib/pbio/platform/move_hub/pbdrvconfig.h
@@ -20,6 +20,7 @@
 
 #define PBDRV_CONFIG_BLOCK_DEVICE                   (1)
 #define PBDRV_CONFIG_BLOCK_DEVICE_FLASH_STM32       (1)
+#define PBDRV_CONFIG_BLOCK_DEVICE_FLASH_STM32_SIZE  (4 * 1024) // Must match FLASH_USER_0 + FLASH_USER_1 in linker script
 
 #define PBDRV_CONFIG_BLUETOOTH                      (1)
 #define PBDRV_CONFIG_BLUETOOTH_STM32_BLUENRG        (1)
diff --git a/lib/pbio/platform/move_hub/pbsysconfig.h b/lib/pbio/platform/move_hub/pbsysconfig.h
index 59fa95046..0bc07f69c 100644
--- a/lib/pbio/platform/move_hub/pbsysconfig.h
+++ b/lib/pbio/platform/move_hub/pbsysconfig.h
@@ -1,12 +1,15 @@
 // SPDX-License-Identifier: MIT
 // Copyright (c) 2020-2022 The Pybricks Authors
 
+#include "pbdrvconfig.h"
+
 #define PBSYS_CONFIG_BATTERY_CHARGER                (0)
 #define PBSYS_CONFIG_BLUETOOTH                      (1)
 #define PBSYS_CONFIG_HUB_LIGHT_MATRIX               (0)
 #define PBSYS_CONFIG_MAIN                           (1)
 #define PBSYS_CONFIG_PROGRAM_LOAD                   (1)
-#define PBSYS_CONFIG_PROGRAM_LOAD_PROGRAM_DATA_SIZE (7 * 1024)
 #define PBSYS_CONFIG_PROGRAM_LOAD_OVERLAPS_BOOTLOADER_CHECKSUM (1)
+#define PBSYS_CONFIG_PROGRAM_LOAD_RAM_SIZE          (7 * 1024)
+#define PBSYS_CONFIG_PROGRAM_LOAD_ROM_SIZE          (PBDRV_CONFIG_BLOCK_DEVICE_FLASH_STM32_SIZE)
 #define PBSYS_CONFIG_STATUS_LIGHT                   (1)
 #define PBSYS_CONFIG_STATUS_LIGHT_BATTERY           (0)
diff --git a/lib/pbio/platform/prime_hub/pbdrvconfig.h b/lib/pbio/platform/prime_hub/pbdrvconfig.h
index 917f08ba9..487dfc798 100644
--- a/lib/pbio/platform/prime_hub/pbdrvconfig.h
+++ b/lib/pbio/platform/prime_hub/pbdrvconfig.h
@@ -35,6 +35,12 @@
 #define PBDRV_CONFIG_BLOCK_DEVICE                   (1)
 #define PBDRV_CONFIG_BLOCK_DEVICE_W25QXX_STM32      (1)
 #define PBDRV_CONFIG_BLOCK_DEVICE_W25QXX_STM32_W25Q256 (1)
+// Carve out 256K from the reserved 1M area at the start of the flash.
+// This avoids touching the file system, the area read by the LEGO
+// bootloader and the area used by upstream MicroPython. Currently, this
+// just needs to be big enough to back up the user program on shutdown.
+#define PBDRV_CONFIG_BLOCK_DEVICE_W25QXX_STM32_START_ADDRESS (512 * 1024)
+#define PBDRV_CONFIG_BLOCK_DEVICE_W25QXX_STM32_SIZE (256 * 1024)
 
 #define PBDRV_CONFIG_BUTTON                         (1)
 #define PBDRV_CONFIG_BUTTON_RESISTOR_LADDER         (1)
diff --git a/lib/pbio/platform/prime_hub/pbsysconfig.h b/lib/pbio/platform/prime_hub/pbsysconfig.h
index 7dc8ab8b8..c29611886 100644
--- a/lib/pbio/platform/prime_hub/pbsysconfig.h
+++ b/lib/pbio/platform/prime_hub/pbsysconfig.h
@@ -6,7 +6,8 @@
 #define PBSYS_CONFIG_HUB_LIGHT_MATRIX               (1)
 #define PBSYS_CONFIG_MAIN                           (1)
 #define PBSYS_CONFIG_PROGRAM_LOAD                   (1)
-#define PBSYS_CONFIG_PROGRAM_LOAD_PROGRAM_DATA_SIZE (256 * 1024)
+#define PBSYS_CONFIG_PROGRAM_LOAD_RAM_SIZE          (258 * 1024)
+#define PBSYS_CONFIG_PROGRAM_LOAD_ROM_SIZE          (PBDRV_CONFIG_BLOCK_DEVICE_W25QXX_STM32_SIZE)
 #define PBSYS_CONFIG_PROGRAM_LOAD_OVERLAPS_BOOTLOADER_CHECKSUM (0)
 #define PBSYS_CONFIG_STATUS_LIGHT                   (1)
 #define PBSYS_CONFIG_STATUS_LIGHT_BATTERY           (1)
diff --git a/lib/pbio/platform/prime_hub/platform.c b/lib/pbio/platform/prime_hub/platform.c
index dac3f915c..03927e8a3 100644
--- a/lib/pbio/platform/prime_hub/platform.c
+++ b/lib/pbio/platform/prime_hub/platform.c
@@ -923,12 +923,6 @@ const pbdrv_block_device_w25qxx_stm32_platform_data_t pbdrv_block_device_w25qxx_
         .bank = GPIOB,
         .pin = 12,
     },
-    // Carve out 256K from the reserved 1M area at the start of the flash.
-    // This avoids touching the file system, the area read by the LEGO
-    // bootloader and the area used by upstream MicroPython. Currently, this
-    // just needs to be big enough to back up the user program on shutdown.
-    .start_address = 512 * 1024,
-    .end_address = 768 * 1024,
 };
 
 // USB
diff --git a/lib/pbio/platform/technic_hub/pbdrvconfig.h b/lib/pbio/platform/technic_hub/pbdrvconfig.h
index 766d394ea..0c514c407 100644
--- a/lib/pbio/platform/technic_hub/pbdrvconfig.h
+++ b/lib/pbio/platform/technic_hub/pbdrvconfig.h
@@ -25,6 +25,7 @@
 
 #define PBDRV_CONFIG_BLOCK_DEVICE                   (1)
 #define PBDRV_CONFIG_BLOCK_DEVICE_FLASH_STM32       (1)
+#define PBDRV_CONFIG_BLOCK_DEVICE_FLASH_STM32_SIZE  (16 * 1024) // Must match FLASH_USER_0 + FLASH_USER_1 in linker script
 
 #define PBDRV_CONFIG_BLUETOOTH                      (1)
 #define PBDRV_CONFIG_BLUETOOTH_STM32_CC2640         (1)
diff --git a/lib/pbio/platform/technic_hub/pbsysconfig.h b/lib/pbio/platform/technic_hub/pbsysconfig.h
index dfda9f900..7d4e95737 100644
--- a/lib/pbio/platform/technic_hub/pbsysconfig.h
+++ b/lib/pbio/platform/technic_hub/pbsysconfig.h
@@ -1,12 +1,15 @@
 // SPDX-License-Identifier: MIT
 // Copyright (c) 2020-2022 The Pybricks Authors
 
+#include "pbdrvconfig.h"
+
 #define PBSYS_CONFIG_BATTERY_CHARGER                (0)
 #define PBSYS_CONFIG_BLUETOOTH                      (1)
 #define PBSYS_CONFIG_HUB_LIGHT_MATRIX               (0)
 #define PBSYS_CONFIG_MAIN                           (1)
 #define PBSYS_CONFIG_PROGRAM_LOAD                   (1)
-#define PBSYS_CONFIG_PROGRAM_LOAD_PROGRAM_DATA_SIZE (32 * 1024)
 #define PBSYS_CONFIG_PROGRAM_LOAD_OVERLAPS_BOOTLOADER_CHECKSUM (1)
+#define PBSYS_CONFIG_PROGRAM_LOAD_RAM_SIZE          (32 * 1024)
+#define PBSYS_CONFIG_PROGRAM_LOAD_ROM_SIZE          (PBDRV_CONFIG_BLOCK_DEVICE_FLASH_STM32_SIZE)
 #define PBSYS_CONFIG_STATUS_LIGHT                   (1)
 #define PBSYS_CONFIG_STATUS_LIGHT_BATTERY           (0)
diff --git a/lib/pbio/sys/program_load.c b/lib/pbio/sys/program_load.c
index 811afdb99..5ff945861 100644
--- a/lib/pbio/sys/program_load.c
+++ b/lib/pbio/sys/program_load.c
@@ -19,6 +19,11 @@
 
 #include "core.h"
 
+// Sanity check that application RAM is enough to load ROM and still do something useful
+#if PBSYS_CONFIG_PROGRAM_LOAD_RAM_SIZE < PBSYS_CONFIG_PROGRAM_LOAD_ROM_SIZE + 2048
+#error "Application RAM must be at least ROM size + 2K."
+#endif
+
 /**
  * Map of loaded data. All data types are little-endian.
  */
@@ -44,7 +49,7 @@ typedef struct {
     /**
      * Data of the application program (code + heap).
      */
-    uint8_t program_data[PBSYS_CONFIG_PROGRAM_LOAD_PROGRAM_DATA_SIZE] __attribute__((aligned(sizeof(void *))));
+    uint8_t program_data[PBSYS_CONFIG_PROGRAM_LOAD_RAM_SIZE] __attribute__((aligned(sizeof(void *))));
 } data_map_t;
 
 // The data map sits at the start of user RAM.
@@ -90,7 +95,7 @@ static void pbsys_program_load_update_checksum(void) {
 
 // Gets the (constant) maximum program size.
 static inline uint32_t pbsys_program_load_get_max_program_size() {
-    return pbdrv_block_device_get_size() - MAP_HEADER_SIZE;
+    return PBSYS_CONFIG_PROGRAM_LOAD_ROM_SIZE - MAP_HEADER_SIZE;
 }
 
 /**