``` MOVE "e:" IN "CPMstuff" ``` Attempting to mount a drive that's already assigned will produce the error **Already exists, 0:1**. In order to do that, you'll first need to unmount the drive with **MOVE ... OUT**. The syntax is even simpler: **MOVE** *drive* **OUT** So to unmount the disk image from **b:** we just need to give: ``` MOVE "b:" OUT ``` You cannot unmount the **c:** drive and attempting to do so will report an **In use, 0:1** error. You can however temporarily eject it (for example to write to it or just change it to a different version of *NextZXOS*, or even a game). Doing that without powering down or just arbitrarily, can damage your card beyond repair so you must be VERY careful. Since the potential for damage is great, *NextZXOS* has a special command to address that specific need called **REMOUNT**. Remount is given without any parameters and upon invocation it will prompt you to: ``` Remove/insert SD and press Y ``` Once you see the message you can eject your SD card, and when you reinsert it, press **Y**. *NextZXOS* will perform the same mounting procedure it performs on boot (for all drives) and your SD card contents will be safe! ### Virtual filesystem management – .mkdata and .mkswap As we've already demonstrated, *NextZXOS* can read unprotected *+3DOS* and *IDEDOS* *virtual disks*, but how are these made? There are two ways to do it: We can either create them externally using special imaging software or right on *NextZXOS*, with the use of a specialised *dot command* called **.mkdata**. Its syntax is as follows: **.mkdata** *filespec* [*size*] where *filespec* must follow the requirements set forth in the *Filenames section* for legal filenames omitting the drive and *size* is an optional number from **1** to **16** (in Megabytes). Leaving *size* blank, will select the default size of 16 Megabytes. You can use ANY filename, however only filenames with a **.p3d** *type*, named as described in the *automounting section* earlier in this chapter and located inside **c:/nextzxos/** will be *automounted*. Here are some examples: To make an 8 Megabyte *automountable* (as **a:**) *virtual disk*: ``` .mkdata /nextzxos/drv-a.p3d 8 ``` To make a 16 Megabyte *virtual disk* that can be manually mounted in **c:/images/**: ``` .mkdata /images/disk.p3d ``` In order to make a *virtual disk* in a different *drive* you need to first change to it. For example: ``` CD "d:" .mkdata /images/disk.p3d ``` will make a 16 Megabyte *virtual disk image file* named **disk.p3d** in **d:/images/**. *NextZXOS* also supports *virtual memory* in the form of *virtual swap partitions*. These are similar to the *virtual disk images* with the difference that they cannot be mounted as drives. You can make *virtual swap partition images* with the **.mkswap** *dot command* which follows the same syntax as **.mkdata**. **.mkswap** *filespec* [*size*] To make an 8 Megabyte virtual swap partition image named swp-0.p3s you will need to give: