Note: This article is old, dating back to May 2009, and severely outdated. Whatever the information included in my post below, it’s probably advisable not to care today. As a simple fact of the matter, tell yourself that if your computer does not yet support 64 bit, it’s time to get a new one.

From 32 bit to 64 bit

You’ve heard the drill, any system with 4GiB+ of RAM requires a 64 bit operating system. Why? Because the total addressing space of the memory (the number of locations on the physical memory of your computer) in 32 bit memory architectures is limited to a total of 4 GiB.

This can be calculated with the following formula: 2³², which equals 4,294,967,296 bytes, or 4 GiB.

Conversely, 64 bit has the following formula: 2⁶⁴, which equals a rather stunning 18,446,744,073,709,551,616 bytes, which translates into 16 EiB or 17,179,869,184 GiB.

So, it’ll take a while before we run out of addressing space in 64 bit memory architectures.

Anyway, you’ve probably recently heard about that thing called PAE, or Physical Address Extension. Most likely, you’ve heard it as a trick to make Windows XP recognize that extra ram, or your 32 bit Vista perhaps.

Is it true? Does it really work? The short answer is yes. It does work. However, we need to dive in the specifics a little bit to know why in the world Microsoft and other hardware/software companies decided to hide this Intel invention.

PAE Explained

When inventing the x86 architecture, and incidentally the x86-64 architecture (also known by its maker Advanced Micro Devices as AMD64), Intel also created something called Physical Address Extension (PAE) as a feature of the x86 architecture to make up for future memory limitations of the 32 bit architecture.

The trick is not a trick, it is a real hardware feature that consists of augmenting the number of memory address lines on the CPU from 32 bit to 36 bit, bumping the total possible amount of memory from 4 GiB to 64 GiB.

However, the processor remains a 32 bit processor, as well as its supporting motherboard and memory chips, preventing simultaneous use of more than 4 GiB. In other words, it remains possible to exploit the total 64 GiB of memory but no single virtual ram instance (ie. Photoshop) or physical memory unit can use more than 4 GiB of memory at the same time.

This translates into the impossibility of mounting anything else than 4 GiB sticks of RAM in your system, and probably even a total of 4 GiB because of the 32 bit architecture of your motherboard, which most likely only supports a total of 4 GiB of RAM, regardless of the CPU.

Now, since the total simultaneous limit is 4 GiB, you may be wondering how the operating system is capable of expanding this to 64 GiB. Effectively, since the x86 architecture is old and very common, it’s been long since operating systems including Windows and Unix variants like Mac OS X and Linux support the PAE extension, and with a few registry hacks, it’s possible to enable this “hidden” feature of Windows and other operating systems (in which case it’s something else than registry).

In Windows, this is called Address Windowing Extensions (AWE), where it involves mapping/spanning, or “Windowing”, an operating system across to more than a single virtual instance of 4 GiB of memory (or an application).

Why nobody told you

If you’re just a tad geeky in computers, you probably understood right away why software and hardware makers are pushing you towards 64 bit right away instead of temporarily using PAE.

And there, I’ve just said it, it’s a temporary solution. In a few years, systems will already be exceeding 64 GiB of memory, and applications (virtual memory instances) will need much more than blocks of 4 GiB of memory, a limitation of PAE.

Since 64 bit is a much more future-ready effort, instead of having to do two switches in a short period of time, Intel and Microsoft, among other companies, decided to literally hide this capability and make 64 bit the only apparent way to get more than 4 GiB of addressing space.

Should you use PAE

For the moment, if you’ve been using anything else than Windows, for instance, a Mac, the 64 bit issue should not have been an issue for you because prior earlier Apple processors like the PowerPC G5 (before the Intel x86-64 switch) were already 64 bit architectures.

Unlike Microsoft Windows and Linux, Apple’s tight integration of hardware and software allowed a much harder transition, from the IBM PowerPC to the Intel x86-64 microprocessor architecture, to be done in a very smooth way.

However, Microsoft’s much larger user base doesn’t allow this freedom and Windows XP remains a largely 32 bit operating system, seeing very limited support of its 64 bit counterpart, released in 2003, the same year Apple released its own first 64 bit system, the Power Mac G5.

To smooth in the transition, Microsoft also made Windows Vista and its more recent Windows 7 into two editions, 32 bit and 64 bit, although in this case, support is much more widespread, especially caused by the wider availability of 64 bit processors from Intel.

Along with Windows Vista came the mainstreaming of 4 GiB of system RAM and its related problems.

If you were hesitating to swith over Windows Vista 64 bit and found PAE to be a good solution to solve your RAM problem while keeping Windows XP, I would reconsider.

With the imminent launch of Windows 7 and Windows XP’s extended support period ending in 2014, PAE is but a very temporary solution.

How to

But hey, it can be useful where 64 bit is not possible because of a 32 bit processor, so why not. Here goes, this option is compatible with any Intel Pentium Pro, Pentium II, III, 4, Core, Core 2, Core i7 and + processor, along with every recent AMD processors and Athlon series.

Windows XP

1. Open an explorer window
2. Tools > Folder Options > View Tab
3. Check the radio box written “Show hidden files and folders”
4. Click OK to accept changes and close the dialog box
5. Go to your local drive where Windows is installed, most likely C:
6. Locate the file called BOOT.INI
7. Right-click on the file and click Properties
8. In the Properties dialog box, make sure the Read-only attribute is unchecked (checking it will prevent you from modifying the file)
9. Click OK to accept changes and close the dialog box
10. Open the BOOT.INI (default opens with Notepad)
11. It should look something like this:

[boot loader] timeout=30 default=multi(0)disk(0)rdisk(0)partition(1)\WINNT [operating systems] multi(0)disk(0)rdisk(0)partition(1)\WINNT=”Microsoft Windows XP Professional” /noexecute=optin /fastdetect

12. Append at the end of last line the following: /PAE
13. It should now look like this:

[boot loader] timeout=30 default=multi(0)disk(0)rdisk(0)partition(1)\WINNT [operating systems] multi(0)disk(0)rdisk(0)partition(1)\WINNT=”Microsoft Windows XP Professional” /noexecute=optin /fastdetect /PAE

14. If it does, save the file, exit Notepad and restart Windows

Congratulations, your Windows XP system now runs with PAE enabled.

Windows Vista / Windows 7

1. Click on the Start Orb
2. Search for CMD
3. Right-click CMD or Command Promt in the search results and click Run as administrator
4. In the command line, enter:
bcdedit /set pae ForceEnable
5. Close the command line

Congratulations, your Windows Vista/7 32 bit system now runs with PAE enabled.

To install PAE on a specific boot if you’re using a dual/multi-boot system, refer to the MSDN BCDEdit /set command documentation for instructions on how to set the ID of the boot.

Note: Official Microsoft documentation does not as of this writing specify explicit support for PAE in Windows 7.

Note: Applications not specifically built to use the AWE api from Microsoft will not be able to use more than 4 GiB of RAM even though PAE is enabled, this includes about every non server-specific application possible, so no, Photoshop and company won’t support more than 4 GiB of RAM each.

Note: Even though PAE technically enables 64 GiB of RAM, Windows XP, along with Windows Vista 32 bit, is limited to a total of 4 GiB. Detailed information can be found in this MSDN article on memory limits of Windows. Windows Vista 32 bit and Windows 7 32 bit also support PAE, as mentioned in other Microsoft articles spread amongst MSDN and other resources. However, Microsoft documentation isn’t clear on whether it is the physical RAM limit or the physical total addressable memory limit that is 4 GiB so results of enabling PAE may vary. With luck, they meant the total physical RAM limit, and not the total physical addressable memory limit, since this one is already 4 GiB with the 32 bit architecture, which would make PAE useless.

Note: Although the x86-64 (64 bit) architecture does support PAE, Windows’s AWE does not support it.

Note: Even though Intel’s specifications limit PAE to an extended total of 36 bit of addressable memory, it is technically possible to example this amount without changing the hardware. For example, Windows Server 2003 SP1 Datacenter Edition uses a special 37 bit PAE capable of supporting 128 GiB of RAM.

Mac and Linux

PowerMac processors are 64 bit since the G5, and any Intel Mac is 64 bit too, so you don’t have to worry about PAE at all, just the OS’s own RAM limitations (up to 16 TiB of RAM in OS X Snow Leopard 10.6). In Linux, any distro on the 2.6 version and up of the kernel has PAE included native and most often enabled by default, so it’s another thing you don’t have to worry about.

The world of computing uses many metrics to measure data. Probably the most significant is the amount of bits contained in a given file. However, no one has ever truly agreed on the way we write these measures, and efforts to standardize this are only ever recent.

Nevertheless, many governments and companies have started moving ahead with the adoption of more standard practices, even though companies like Microsoft have not yet adapted.

Why Should You Know This?

But the real question is: why should you, as a user, know this? Why should you care about kb, kB and KiB at all? It turns out that the moment you use a computer, it concerns you. Better yet, with today’s caps on Internet bandwidth, understanding the difference between the various measures is of crucial importance to understanding your telecom bill. There’s more to it than simple measures, but it’s at least part of the puzzle.

First off, the bit and the byte

In computers, data; documents, pictures, videos and music, all consist of binary information somewhere in the memory of your computer. Binary information is represented by 1s and 0s.

These 1s and 0s are understood by your computer via electricity. In its most basic state, 0 represents off, and 1 represents on. Various techniques are used to represent such data in different medias. For example, compact discs present a series of microscopic holes on a circular plate, where a hole may represent 1, no hole may represent 0.

One such 1 or 0 is always measured as a bit. Fun trivia, a standard CD has 5.6 billion possible holes, or in other words a capacity of 5.6 billion bits.

But a bit alone doesn’t mean much. All it can do is tell the computer whether it represents 1 or 0, not very exciting, which is where the word comes in. The word represents the natural unit of data understood by a processor. It’s a group of bits that represents the most basic data set a processor can understand. For example, in typical systems, the letter A is represented by the 8-bit word 01000001. It’s called 8-bit because it has a length of 8 bits. Therefore, if you throw 16 bits at the processor, it will divide them in 2 distinct data sets and try to understand these.

But a processor cannot understand individual bits. It is bound by its word size, meaning that if you throw 7 bits at a processor designed to handle 8-bit words, it won’t understand.

Because of this limitation, bits alone are not a good way to represent data when programming a computer. To solve this, we need to use the byte, a unit meant to represent a set of bits.

Historically, because the byte was not defined as a fixed size, it was analogous to a word. However, in modern systems, byte is universally 8 bits, stemming from the once popular 8-bit word size. But modern processors use varying word sizes, so the use of words to quantify data is ill-advised.

In this way, word is a unit relegated to the specifics of memory management in processor architectures, while byte is strictly used as a general unit of data representing 8 bits.

To sum it all, what’s important to know is that on an 8-bit word length computer, data can only be represented in multiples of 8 bits. Therefore, bits are seldom-used in the representation of data, in favor of the byte, except perhaps in the measuring of Internet connections speed, usually in bits per second.

Handling Larger Numbers

Once computer innovation started to ramp up, the quantity of data we work with continually expanded. Before engineers knew it, they had to deal with thousands of bytes, instigating the need for a way to sum up data into smaller numbers. Unlike money, which exists since way longer than bits and bytes, it was easy to perceive how we would eventually reach much more than billions of bytes of data. To sum up things better, engineers decided to borrow on the SI system, otherwise known as the “Le Système International d’Unités”, or International System of Units, a French invention to sum up large numbers in the metric system. If you live elsewhere than in the United States, you’re probably already familiar with this notation appearing in nearly everything.

In the SI system, a lower case k represents a thousand, a capital M represents a million, a capital G represents a billion, etc. Each measure has its full written form too, which consists of a prefix to add to any measure. For data, in order to represent a thousand bytes, you can say a kilobyte, a megabyte for a million, and so on.

The importance of case sensitivity: The SI system makes great use of lower and capital case for its acronym. For example, while a million is represented by an upper case M or mega, a milli, or 1/1000th, is represented by a lowercase m. When combined with the measures for distances, the very similar Mm and mm represent vastly different things, namely a megameter and a millimeter, the later being one billion times smaller.

In the case of a bit, the SI system does well. Since the SI system is always used at the power of 10, it is possible to use it perfectly standardly with the bit. 1000 bits is equal to 1 kilobit (kb).

However, when it comes to bytes, the story was a bit different. Because of the computer’s binary nature, memory addresses (where the data is physically located on a memory chip) are written in binary sequences. As such, the number of addressable memory locations are counted with a power of 2. For example, an 8 bit address space has a total addressable memory of 256 bytes. However, newer 16 bit memory architectures at the time could now jump-start the 256 bytes limit produce a much more potent 65,536 bytes of addressing space. Applying the SI system at the power of 10 on this produced a somewhat awkward number, 65.536 kilobytes (kB). To remedy the situation, engineers took the SI system and made it at the power of 2 to match memory addressable space, so that a kilobyte would equal 1024 bytes while a kilobit still equaled 1000 bits, bringing confusion still reigning into the world of computing today and a nice round 64 kilobytes of memory for the 16 bit architecture.

Controversy

Invented in America where the metric system has not yet been adopted as of 2009, the secluded world of computing did not wake anyone up with their awkward borrow on the SI system until 1995, when the IUPAC and the NIST proposed to a newer unambiguous system to the IEC, only to be accepted in 1999, giving birth the kibibyte and the mebibyte, a play on the word kilobinary and megabinary, later followed by the other higher multiples in 2000.

However, by that time, it was already 40 years since the computer industry had been using the SI multiples at power of 2. 10 years after the standardization of the IEC format, adoption has been nearly innexistant, with the only systems using the measure being rare very recent Linux distributions. Even the latest Windows and Mac OS X still use the SI prefixes for bytes.

But using the SI prefixes for bytes isn’t necessarily wrong, since the IEC standard allows it. Only, you have to use them at the power of 10, so one kilobyte equals 1000 bytes, and one kibibyte equals 1024 bytes. It goes without saying that this is a highly contested and controversial standard. It does bring clarity and non ambiguousness, but it also brings confusion for legacy systems.

For example, MP3 player users are used to see their storage capacity in GB when it should be in GiB. Adding the i will obviously bring in a lot of questionning in stores where a brand might not use the same notation. Most store clerks would probably been unable to even explain the difference. This is why marketing forces at Apple and Microsoft, along with almost every hardware manufacturer, decided to keep the original measurement.

Additionally, there’s very little explanation to why this system should be implemented at all. Afterall, in traditionnal computing, a kilobyte never meant anything else than 1024 bytes, so there’s very little proof at how the IEC’s newer system may improve the situation. Memory manufacturers won’t start making memory systems in multiples of 10 and so many think that the confusing would just be transfered over to the kibibyte, which would often been mistook for a thousand bytes.

Adoption

However, when it comes to the educated world, standards make a long way. Most of today’s technical documentation and teaching material has adopted IEC’s standard, refering to kilobytes as multiples of 10, and kibibytes as multiples of 2. This means that computer classes in school will start teaching it that way, and that eventually, operating system makers and memory companies will have to adapt, regardless of controversy.

Conclusion

While your computer probably still uses the wrong notation, assuming you’re reading this article as of 2009, future systems will probably adopt the IEC standard, so let’s review the whole thing. I’ve also included the bit version of the IEC, known as the kibibit (Kib) and its brothers, in this review, along with an in-depth explanation of capitalization rules in red.

Note on k/K: Although the SI system makes an absolute use of a lower case k for a thousand because the upper case K is for a degree kelvin, remember that the computer use of the SI system has never been standardized into the SI’s base or derived units and many sources suggest that a capital K can also be used for a thousand.

A KB or a Kb cannot be mistaken for a kelvinbyte or kelvinbit because it doesn’t make sense. Also, since the binary system doesn’t make use of subdivisions and thus does not possess the lower case d, c, m and other prefixes, only the k being lower case would make for an inconsistent notation.

For these reasons, the IEC chose to have the kibibyte with a capital K and many often use a capital K for a kilobyte and a kylobit. Note that the use of a lower case k (ie. kiB) for a kibibyte is not accepted.

As the writer of this article though, I am a very purist person when it comes to standards. Since the kilobyte and the kilobit are both borrowing on the SI standard, I think they should use a lower case k, regardless of application. However this hasn’t been standardized, and you can use whichever you think is better. The review here under uses a lower case k.

1 bit      (b)   = 1 bit          (b)
1 byte     (B)   = 8 bit          (b)

1 kilobyte (kB)  = 1000 bytes     (B)
1 megabyte (MB)  = 1000 kilobytes (kB)
1 gigabyte (GB)  = 1000 megabytes (MB)
1 terabyte (TB)  = 1000 gigabytes (GB)

1 kibibyte (KiB) = 1024 bytes     (B)
1 mebibyte (MiB) = 1024 kibibytes (KiB)
1 gibibyte (GiB) = 1024 mebibytes (MiB)
1 tebibyte (TiB) = 1024 gibibytes (GiB)

Higher prefixes can be seen here for the SI system, and here for the IEC system.

Kibibits, mebibits and else also exist, effectively meaning bit multiples at the power of 2, exactly like kibibytes, mebibytes and company. However, the IEC pretty much created this standard just for the sake of it, as it isn’t really useful. Maybe in the future 1024 bit architectures will be called 1 kibibit architectures, but most architectures are far from 1024 bit in any cases.

Also, another notation exists for bits instead of b. Literaly using the full word bit instead, however invariable. The SI prefix is the traditional k, M, G, etc. and the IEC prefix is Ki, Mi, Gi, etc. So this goes like this: Kibit, Mibit, Gibit. The IEC seems to particularily encourage this notation to further distinguish between a byte and a bit traditionnally only being difference by a lower and an upper case.

Some time, brilliant stuff happens on the Internet. What would you do without Charlie Bit my Finger on YouTube… Well, no, really smart stuff, like Wikipedia or Google.

In my opinion, there is now a third product on the Internet that I classify “as smart” as Google or Wikipedia, Wolfram Alpha. Not a very markety name, but hey, every geek knows Wolfram. Go there now, http://www.wolframalpha.com/ and input some mathematics, or anything. Take a look at the examples especially, cause at first you might think you’re just too stupid to use it.

Well, I’m thinking this might just make math homework a lot easier.