The Power Mac Storage FAQ

Those of you who frequent the Power Mac forum have probably noticed the never ending questions regarding storage upgrading and limitations in the various Power Mac models. So, I felt it necessary to write up a storage FAQ for everybody to refer to.

I am, however, not the hardware expert on the forums and I do occasionally make mistakes and oversights. So if you have a correction or additional information to contribute to the FAQ, send me a private message or make a post below, as I will be leaving this thread open to posts for that very reason.

Over time, I do intend to expand the FAQ as it becomes necessary, so check back from time to time.

So, on with the FAQs;

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Q: I am looking to upgrade the internal storage of my Power Mac. How large of a drive can I use?

A: This is easily the number one question pertaining to storage upgrading here at MacNN. And with good reason, as there is no definitive way for the average user to know the limitations of their machine. As with most things, Apple does not include this bit of useful information in the manual.

There is essentially a wall that exists when it comes to storage capacity, we'll call it the '128GB Barrier'. The 128GB Barrier is prevalent on pretty much every Macintosh with IDE until 2002. If your machine has this limitation, the largest you will ever see any IDE/ATA drive appear as is 128GBs, regardless of actual capacity. Contrary to what is frequently believed, partitioning does not provide a way around this as the limitation is on the bus itself, not the size of the partition.

If you own one of the following Power Macintosh models, you will have to deal with the 128GB limitation when upgrade time comes around;

Power Macintosh G3 - Beige
Power Macintosh G3 - B&W
Power Macintosh G4 - PCI/Yikes!
Power Macintosh G4 - Sawtooth
Power Macintosh G4 - Gigabit Ethernet
Power Macintosh G4 - Cube
Power Macintosh G4 - Digital Audio
Power Macintosh G4 - QuickSilver '2001' (733MHz, 867MHz, Dual 800MHz)

In 2002, Apple adapted a newer IDE controller with the QuickSilver '2002' model that made use of 48-bit addressing, thus alleviating the 128GB barrier and allowing the use of IDE drives in excess of 250GBs+. If you own one of the following Power Macintosh models, you're free to roam the storage prairie with no restraints;

Power Macintosh G4 - QuickSilver '2002' (800MHz, 933MHz, Dual 1GHz)
Power Macintosh G4 - MDD '2002' (Dual 867MHz, Dual 1GHz, Dual 1.25GHz)
Power Macintosh G4 - MDD '2003' (Single 1GHz, Dual 1.25GHz, Dual 1.42GHz)

One common misconception is that ATA-100 or ATA-133 are necessary for large drive support. This is untrue. It just so happens that ATA-100/133 became prevalent at the same time as 48-bit LBA. Thus, pretty much all ATA-100/133 controllers have large drive support, but they are not one and the same.

The QuickSilver '2002' model featured an ATA-66 controller in conjunction with 48-bit addressing, and thus is capable of using large drives. The same goes for the secondary ATA-66 controller in MDD machines, which is also capable of supporting large drives.

Q: I have a machine that cannot see drives larger than 128GBs, what can I do to use large drives?

A: The easiest solution is to pick up an ATA-100/133 or Serial-ATA PCI card. All ATA cards currently on the market feature 48-bit LBA, and thus have large drive support. Currently, these cards can be had for between $60-$80.

For many people, ATA cards are the better solution as they are compatible with older ATA drives. However, the industry is in the progress of migrating to Serial-ATA, which is a faster hot-swappable version of ATA. After a year or two on the market, the prices of Serial-ATA drives and cards are in line with ATA/IDE drives and cards. So if you're looking to assemble a new storage setup and aren't worried about preserving the use of your older ATA/IDE drive, Serial-ATA is the better choice if only because it is more future proof.

Question 1. My machine has the 128/137 GB limit, but like most of us, I'm cheap. Less money is good, and I don't want to blow good money on another PCI card or a FireWire enclosure. My PCI slots might even be filled already. Is there another way to use bigger drives?

Answer 1. Yes
Intech has released a software product that will allow G3s and older G4s to use the full size on large drives. It is $25, or $15 when purchased with a drive from OWC.

This is mostly a fix for use with OSX 10.2 or higher, and it has some limitations. You cannot boot from a partition above the 128 GB point, and their kext file must be present in any OSX install that must see the high partition. In other words, recovery CDs that do not have the Intech extension will not see the stuff above 128 GB.

Since the machine may not always see stuff above the 128 GB mark, the drive should be partitioned so that no partition crosses the 128 GB mark.

For OS9 to see above the 128 GB line, you need to buy their full SpeedTools product, and format the drive with that product. On the plus side, OS9 can boot from a partition above the 128 GB mark.

For more precise details on the limitations, read their product page and check out the product's ReadMe file.

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Question 2. The large drive limitation is sometimes listed as 128 GB, sometimes as 137 GB. What gives? Oh, and when I format a new drive, it comes up smaller than the advertised size. Who is ripping me off?

Answer 2. Uh, it's one of those math things. And the HD manufacturers use different math from the rest of us.

Computer memory capacities are measured in a kind of binary math. 2^10 = 1,024 which is close to 1,000 - a natural decimal size. It is conventional with computers to measure RAM, Video RAM, HD capacity, USB flash drives, buffer sizes, cache sizes, and just about everything else in binary-based math. Using multiples of 1,024.

1 KB = 1,024 bytes
1 MB = 1,024 KB
1 GB = 1,024 MB
1 TB = 1,024 GB

TB = TeraByte, your hard drives will soon be this large. Your system RAM will take a bit longer to get into this range. Sometime around the year 2020 maybe, at current rates. RAM sizes seem to double about every 2 years.

The 128 GB limit is the addressing limit of the earlier ATA spec. Space on a hard drive is divided into "blocks" which are 512 bytes in size. The earlier ATA spec used 28-bit addresses to specify which block you want to address on a hard drive. 2^28 blocks times 512 bytes per block = 128 GB.

The later ATA spec uses LBA-48 (Long Block Addressing - 48 bits) to specify the block address. So the new limit is 2^48 blocks times 512 bytes per block = 128 PetaBytes. That's 131,072 TeraBytes. It will take at least a few years to hit this new limit.

Now about the different numbers for drive size. Someone in the hard drive business noticed that decimal math is more common in the retail world. And it gives smaller numbers.

Conventional binary memory measurements, again:
1 KB = 1,024 bytes
1 MB = 1,024 KB or (1,024 x 1,024) or 1,048,576 bytes
1 GB = 1,024 MB or (1,024 x 1,024 x 1,024) or 1,073,741,824 bytes
1 TB = 1,024 GB or (1,024 x 1,024 x 1,024 x 1,024) or 1,099,511,627,776 bytes

Suppose they offer you a 100 GB drive, but measure it with the decimal size? Here is how the sizes compare:
100 GB decimal = 100,000,000,000 bytes
100 GB binary = 107,374,182,400 bytes

So with nothing more than different math, they can offer you a smaller 100 GB drive. Costs less to make, and the numbers can be defended as honest. After all, pure decimal math is used just about everywhere outside of computers. Even with computers, you don't usually order 1,024 computers for your office building. You order 1,000 computers for your 1,000 secretaries. Actually, most of us here don't order that many computers at all. Pity, it would be cool to get your computers delivered by a truck with a fork lift.

You buy your new 100 GB drive from them, with some fine print on the side of the box. Install the drive. Once your computer recognizes the drive, it reports the size in the more conventional binary sizes used by computers. Congratulations, you just bought a 93 GB drive. Uh, wait ... you paid for a 100 GB drive. Where's the rest of it?

Read the fine print that came with your new drive. The fine print will say that the manufacturer measures 1 GB as one billion bytes exactly. Now divide 100 billion bytes by (1,073,741,824 bytes per binary GB) and you get the binary size of approx 93 GB.

So that is how they do it, and this is true of all hard drive manufacturers. Oh, and the 128 GB / 137 GB limit? It is the same size, measured both ways.

128 GB binary = 137,438,953,472 bytes.

137 GB in HD factory GigaBytes. Do you remember why you liked math?