There are two different types of resources in modern computer systems; physical resources and logical resources. Physical resources typically include processors, memory, and peripheral devices. Logical resources are operating system abstractions that are given temporary control over physical resources.
Physical resources vary fairly dramatically from computer to computer. For example, a typical PC system might have 640K of memory, one 20Mbyte Winchester disk, one floppy disk drive, a single keyboard, and a single video display. A typical mainframe system has several parallel processors, hundreds of disks, tens of millions of bytes of memory, hundreds of terminals, tapes, and other special purpose peripherals, and is connected to a global network with thousands of other similar computers.
Logical resources are essentially identical on all Unix(tm) systems, and are generally divided into processes and files. One of the major advantages of Unix(tm) over other systems from a programming, administration, and usage standpoint, is that the wide variety of physical resources can be controlled through these two simple abstractions. The net effect is that Unix(tm) administration is not fundamentally different for a PC than for a mainframe. It's only a matter of scale.
We sometimes use the term ``space'' to talk about files, and the term ``time'' to talk about processes because these are the basic abstract types of resources available in a computer, and they are the fundamental performance related phenomena that we are concerned about in dealing with computers from an optimization standpoint. Time can generally be traded for space in using computers, and this is the major performance related tradeoff that we have to control in order to efficiently use the resources of a Unix(tm) system.