first attempt. partial copy and stuff.

code/modules/modular_computers/file_system/computer_file.dm

@@ -0,0 +1,39 @@
+var/global/file_uid = 0
+
+/datum/computer_file/
+	var/filename = "NewFile" 								// Placeholder. No spacebars
+	var/filetype = "XXX" 									// File full names are [filename].[filetype] so like NewFile.XXX in this case
+	var/size = 1											// File size in GQ. Integers only!
+	var/obj/item/weapon/computer_hardware/hard_drive/holder	// Holder that contains this file.
+	var/unsendable = 0										// Whether the file may be sent to someone via NTNet transfer or other means.
+	var/undeletable = 0										// Whether the file may be deleted. Setting to 1 prevents deletion/renaming/etc.
+	var/uid													// UID of this file
+
+/datum/computer_file/New()
+	..()
+	uid = file_uid
+	file_uid++
+
+/datum/computer_file/Destroy()
+	if(!holder)
+		return ..()
+
+	holder.remove_file(src)
+	// holder.holder is the computer that has drive installed. If we are Destroy()ing program that's currently running kill it.
+	if(holder.holder2 && holder.holder2.active_program == src)
+		holder.holder2.kill_program(1)
+	holder = null
+	..()
+
+// Returns independent copy of this file.
+/datum/computer_file/proc/clone(var/rename = 0)
+	var/datum/computer_file/temp = new type
+	temp.unsendable = unsendable
+	temp.undeletable = undeletable
+	temp.size = size
+	if(rename)
+		temp.filename = filename + "(Copy)"
+	else
+		temp.filename = filename
+	temp.filetype = filetype
+	return temp