diff --git a/hw/core/machine.c b/hw/core/machine.c
index fbd91be..2951ed7 100644
--- a/hw/core/machine.c
+++ b/hw/core/machine.c
@@ -403,11 +403,20 @@ bool machine_usb(MachineState *machine)
     return machine->usb;
 }
 
+static void machine_class_init(ObjectClass *oc, void *data)
+{
+    MachineClass *mc = MACHINE_CLASS(oc);
+
+    /* Default 128 MB as guest ram size */
+    mc->default_ram_size = 128 * M_BYTE;
+}
+
 static const TypeInfo machine_info = {
     .name = TYPE_MACHINE,
     .parent = TYPE_OBJECT,
     .abstract = true,
     .class_size = sizeof(MachineClass),
+    .class_init    = machine_class_init,
     .instance_size = sizeof(MachineState),
     .instance_init = machine_initfn,
     .instance_finalize = machine_finalize,
diff --git a/include/hw/boards.h b/include/hw/boards.h
index 3ddc449..b2b4698 100644
--- a/include/hw/boards.h
+++ b/include/hw/boards.h
@@ -108,6 +108,7 @@ struct MachineClass {
     const char *default_display;
     GlobalProperty *compat_props;
     const char *hw_version;
+    ram_addr_t default_ram_size;
 
     HotplugHandler *(*get_hotplug_handler)(MachineState *machine,
                                            DeviceState *dev);
diff --git a/include/qemu-common.h b/include/qemu-common.h
index 644b46d..0347974 100644
--- a/include/qemu-common.h
+++ b/include/qemu-common.h
@@ -186,6 +186,12 @@ int64_t strtosz(const char *nptr, char **end);
 int64_t strtosz_suffix(const char *nptr, char **end, const char default_suffix);
 int64_t strtosz_suffix_unit(const char *nptr, char **end,
                             const char default_suffix, int64_t unit);
+#define K_BYTE     (1ULL << 10)
+#define M_BYTE     (1ULL << 20)
+#define G_BYTE     (1ULL << 30)
+#define T_BYTE     (1ULL << 40)
+#define P_BYTE     (1ULL << 50)
+#define E_BYTE     (1ULL << 60)
 
 /* used to print char* safely */
 #define STR_OR_NULL(str) ((str) ? (str) : "null")
diff --git a/vl.c b/vl.c
index 801d487..86e81c5 100644
--- a/vl.c
+++ b/vl.c
@@ -120,8 +120,6 @@ int main(int argc, char **argv)
 #include "qom/object_interfaces.h"
 #include "qapi-event.h"
 
-#define DEFAULT_RAM_SIZE 128
-
 #define MAX_VIRTIO_CONSOLES 1
 #define MAX_SCLP_CONSOLES 1
 
@@ -1306,7 +1304,11 @@ void hmp_usb_del(Monitor *mon, const QDict *qdict)
 
 MachineState *current_machine;
 
-static void machine_class_init(ObjectClass *oc, void *data)
+/*
+ * Transitional class registration/init used for converting from
+ * legacy QEMUMachine to MachineClass.
+ */
+static void qemu_machine_class_init(ObjectClass *oc, void *data)
 {
     MachineClass *mc = MACHINE_CLASS(oc);
     QEMUMachine *qm = data;
@@ -1344,7 +1346,7 @@ int qemu_register_machine(QEMUMachine *m)
     TypeInfo ti = {
         .name       = name,
         .parent     = TYPE_MACHINE,
-        .class_init = machine_class_init,
+        .class_init = qemu_machine_class_init,
         .class_data = (void *)m,
     };
 
@@ -2641,13 +2643,13 @@ out:
     return 0;
 }
 
-static void set_memory_options(uint64_t *ram_slots, ram_addr_t *maxram_size)
+static void set_memory_options(uint64_t *ram_slots, ram_addr_t *maxram_size,
+                               MachineClass *mc)
 {
     uint64_t sz;
     const char *mem_str;
     const char *maxmem_str, *slots_str;
-    const ram_addr_t default_ram_size = (ram_addr_t)DEFAULT_RAM_SIZE *
-                                        1024 * 1024;
+    const ram_addr_t default_ram_size = mc->default_ram_size;
     QemuOpts *opts = qemu_find_opts_singleton("memory");
 
     sz = 0;
@@ -3763,7 +3765,13 @@ int main(int argc, char **argv, char **envp)
         machine_class = machine_parse(optarg);
     }
 
-    set_memory_options(&ram_slots, &maxram_size);
+    if (machine_class == NULL) {
+        fprintf(stderr, "No machine specified, and there is no default.\n"
+                "Use -machine help to list supported machines!\n");
+        exit(1);
+    }
+
+    set_memory_options(&ram_slots, &maxram_size, machine_class);
 
     loc_set_none();
 
@@ -3792,12 +3800,6 @@ int main(int argc, char **argv, char **envp)
     }
 #endif
 
-    if (machine_class == NULL) {
-        fprintf(stderr, "No machine specified, and there is no default.\n"
-                "Use -machine help to list supported machines!\n");
-        exit(1);
-    }
-
     current_machine = MACHINE(object_new(object_class_get_name(
                           OBJECT_CLASS(machine_class))));
     if (machine_help_func(qemu_get_machine_opts(), current_machine)) {
