A bit is the smallest piece of information a computer deals with: it’s literally a single digit, either a zero or a one. Every computer’s processor works on a particular system based on handling a fixed number of bits at any one instant. Since around the early 1990s, most PCs were built to run on 32-bit processors, but in the past five years 64-bit systems have become more common.
Note that this isn’t the same thing as memory, which is measured in multiples of bytes (a byte is made up of eight bits). Memory is how much information a computer can literally remember without having to refer to a disk
or other storage device (and therefore deal with more quickly). The processor’s bit rating is how much information is handled at any precise moment.
Because the processor is such an integral part of a computer, its operating system has to be specifically written to fit a particular bit rating. Microsoft produced both 32-bit and 64-bit editions of XP and Vista and, to some people’s surprise, will do so for Windows 7 (the successor to Vista).
A 32-bit system has two inherent limitations caused by the underlying arithmetic. Firstly, it can only cope with a maximum of 4GB of memory. Secondly, it’s very difficult to get a 32-bit system to cope with a single application taking up more than 2GB of memory.
While this limit has always existed, it’s not really become an issue until recent years. That’s partly because 4GB has only recently become a relatively affordable amount of memory for a desktop computer system, partly because Vista uses so much memory that running multiple programs can easily hit the 4GB limit, and partly because recent video games have been the first to break the 2GB barrier.
With 64-bit systems, this simply isn’t a problem. Mathematically speaking, a 64-bit processor could cope with more than 17 billion GB of memory. In practice, though, it seems inconceivable anyone could ever make memory chips with that much capacity that physically fit inside a desktop computer.
The other main benefit is that a 64-bit processor can process some data twice as quickly. The speed increase will vary from task to task though; rarely will a computer run ‘twice as fast’ overall.
The majority of new computers now come with 64-bit processors, and the proportion is rising at a quickening rate. The 64-bit editions of Windows can cope with software designed for 32-bit systems through a ‘compatibility mode’, though this can have patchy results. Also, drivers (the software that links a hardware device to Windows) can be a particular problem.
64-bit systems will inevitably become more common for two reasons: software will become more memory-intensive, pushing the limits of 32-bit systems; and falling prices will eventually make 4GB of memory or more ‘the norm’ rather than a luxury.
However, Microsoft’s decision to produce a 32-bit edition of Windows 7 suggests they expect 32-bit systems to still be in common use well into the next decade.