How to Buy a Hard Disk

Mac's hard disk is one of its least celebrated but most important components. Without it, not only would you have nowhere to store the documents you create, but the operating system that makes a Mac unique would have nowhere to load from.

How To Buy A Hard Disk
Your Mac's hard disk is one of its least celebrated but most important components. Without it, not only would you have nowhere to store the documents you create, but the operating system that makes a Mac unique would have nowhere to load from. The only time most of us think about hard disks is when we begin to run out of space, but whether you're replacing an internal drive or looking to buy an external hard disk, there's a lot to consider. In this guide, we'll explain the different physical formats for today's hard disks, making sure you know the difference between SATA and ATA connections, and which of these you need. We'll also demonstrate various configuration options for tower-based systems, provide some general advice for working with data, and make sure you're aware of some Macs' limitations in dealing with hard disks. Along the way, we'll be looking at how to fit hard disks, examine some of the alternatives and discuss when to use the various formatting options offered by Mac OS X.

Remember that a hard disk is used for more than just storing files: it holds your operating system and acts as a temporary dump for files that your Mac creates as it's working. Virtual memory technologies swap out data from your RAM to the hard disk when you're trying to run lots of applications at once, and also provide better performance.

Choosing the best hard disk for your Mac is about much more than just walking into a shop and picking up the highest-capacity option from the shelf. You need to understand what you'll be using it for, where it will be used, and if there's a better alternative to your initial plan. That's what we're here to help you with. The flow chart on these pages should give you a better idea of the type of disk you should buy, and our advice over the page will ensure you have all the knowledge you need to make the right choice.

INTERNAL/EXTERNAL

The most obvious choice to make when buying a new hard disk is whether to fit one inside your Mac - possibly as a replacement for, or in addition to your existing hard disk - or buy an external drive that can be added to your setup just by plugging it into your Mac's USB or FireWire connection.

Internal drives are usually cheaper than their external counterparts, simply because external drives charge you for the case and controller technologies, as well as for the basic hard disk inside.

If you want an easily portable disk, you should opt for one based not on the relatively chunky 3.5in mechanisms found in desktop and large-capacity external hard disks, but the smaller 2.5in hard disks. These are not only smaller and lighter, but since they use less power than their bulkier cousins, they can usually draw power from the USB or FireWire buses. This also means you don't have to lug a power supply and cables around with you.

There are portable disks based on even smaller, 1.8in platters, but these are relatively poor value in terms of price per gigabyte when compared with other formats, and they're not substantially smaller.

All external disks basically wrap a casing around an off-the-shelf hard disk, and it's usually very easy to open external cases and swap drives around - although it may void any warranty you have. If you're swapping out one internal drive for another just because you need more capacity, you should consider buying an external case for the old internal one, extending its life and giving you extra flexibility. Cases are available for 2.5in and 3.5in mechanisms. Make sure you pick one with the correct internal connection - ATA or SATA - for the drive you'll be fitting.

EXTERNAL CONNECTIONS

With the exception of a few high-end solutions using eSATA or SCSI for ultra-fast data transfer, most external hard disks have USB 2 and/or FireWire 400 connections. Many of the more professional models for both 2.5in and 3.5in disks can also feature the faster FireWire 800 connection.

In theory, USB 2, with a theoretical maximum throughput of 480Mbit/sec, should be slightly faster than FireWire 400, at up to 400Mbit/sec. However, in reality, the same drive connected over USB 2 performs significantly less well than when it's connected over FireWire 400.

FireWire 800 ports are much less common: in the Mac range, they're only found in Power Mac G5s and high-end PowerBooks and MacBook Pros, and in an even smaller percentage of the PC desktop and notebook market. Again, although the theoretical transfer rate is greater than the previous generation - 800Mbit/sec versus 400Mbit/sec - you don't get double the data-transfer speed. The controllers and physical mechanisms of the hard disks in today's models don't sustain transfer speeds great enough to take full advantage of this faster connection interface.

Older Macs are likely only to include USB 1.1 and FireWire 400, so if you're buying a hard disk in order to transfer data between them and PCs (which tend only to feature USB 2 ports), it makes sense to buy a disk that features both USB 2 and FireWire 400 connections. This means you can connect the drive to your Mac using FireWire to transfer data and then use the faster USB 2 connection when hooked up to a PC.

Limiting yourself to USB only would mean it would take ages for files to copy over the older USB 1.1 connection on your old Mac, and a FireWire-only drive is less compatible with the world of PCs.

INTERNAL CONNECTIONS

Most modern hard disks use one of two connection types to link into your Mac internally. ATA (Advanced Technology Attachment) is still the more common type of connection, but it's being replaced with the simpler, faster SATA (Serial ATA) technology.

With the older ATA connection, the theoretical maximum data throughput is 133MB/sec, compared with 150MB/sec with the first-generation SATA connection, and 300MB/sec with SATA II. However, speed isn't the only differentiator. (Besides, even today's drives struggle to produce a sustained transfer rate of over 80MB/sec, so these faster theoretical throughputs are, at the moment, only future proofing for the interface). SATA drives have their own dedicated connection and bandwidth, dropping the need to designate one drive as master and another as slave on a single bus. SATA drives can also be hot-swapped.

Except for vintage Macs, pre-G5 towers used ATA drives, as did all laptops prior to the introduction of the MacBook Pro. You can check which interfaces your Mac has by launching System Profiler.

Tower-based Macs can accept a SATA controller card into a free PCI slot to give you access to internal SATA disks, or you could consider adding a card that gives access to external SATA (eSATA) disks, of which the majority currently available are external Raid solutions. eSATA cards are even available for the MacBook Pro's ExpressCard slot (see www.vydeo.com for more information).

CAPACITY

Broadly, you should try to buy the biggest drive you can possibly afford. At worst, you should have around 10% of your hard disk free for the Mac to use as a scratch disk as it performs routine memory management and other tasks. Keep an eye on resellers such as www.ebuyer.com and bigpockets.co.uk for end-of-line and other deals on high-capacity hard disks, and check price comparison sites such as www.pricerunner.co.uk, www.kelkoo.co.uk and froogle.google.co.uk to find the best price.

Most Macs that use the ATA connection limit can't address the full capacity of disks larger than 128GB, so it's not worth adding a 250GB internal disk, say, to a Sawtooth Power Mac G4. If you need high-capacity storage, you'll either need to add another bus (either SATA or based on a newer ATA controller), usually via PCI, or add an external disk.

OTHER CHARACTERISTICS

As well as the amount that a given hard disk will hold, there are other characteristics that should influence your buying decision. The first is spindle speed - that is, the number of times per second that the physical platters revolve. This largely governs both how quickly data can be transferred to and from the disk, and how quickly the drive can position the relevant spot on the disk under the read/write heads to find the information you want.

The second is the buffer, a small area of flash RAM that holds frequently and recently accessed data to speed up data retrieval. Generally speaking, bigger buffers are better. Reliability is of paramount importance, but since manufacturers have started to abandon the traditional mean-time-betweenfailure (MTBF) yard stick, claiming it's not an accurate practical measurement of reliability, our best advice is to pick a drive with a generous warranty and maintain a consistent backup regime.

CONFIGURATION

If you're just replacing an internal drive, or adding a second drive either internally or externally, it's a simple enough process. If you need to copy data from your existing internal disk onto a replacement unit, the easiest thing to do is to buy an external case, fit the replacement drive in it and use OS X 10.4's Restore tab in Disk Utility (earlier versions don't create bootable backups) or Carbon Copy Cloner from www.bombich.com to duplicate the data from the old internal to the new internal currently fitted in an external case. Once the transfer has completed, you can swap the drives around and your old internal drive will now be a handy external.

This goes for laptop drives as well as those from desktop machines. However, while working with desktop hard disks is easy, we'd recommend not tinkering with laptops unless you're very sure of yourself.

You could also consider adding a Raid (redundant array of independent disks) system to your tower Mac. This can be done quickly and cheaply simply by adding a second internal disk and using Disk Utility to Raid the volumes together to provide speed or security benefits. A much more robust solution, though, is either to fit a dedicated hardware Raid controller card or buy an external Raid box that will manage the process of controlling the flow of data for you, and simply pass the data requested to the Mac over an eSATA or more familiar USB or FireWire connection.

When you format your drive, it's best to pick the Mac's native system, Mac OS Extended (often called HFS+) Journaled. Indeed, if we're talking about your boot drive, it can't use the main alternative format types, Unix and MS-DOS. Although, if you're formatting an external drive to shuttle data between different computer, it would be wise to format it using the MS-DOS option. Macs can read and write to this no problem - as can PCs - but Windows can't natively read HFS or HFS+ drives.

ALTERNATIVES

If all you need is a little capacity to shuttle documents around, consider a USB memory stick: they're cheap, require no extra cables or power supplies, and they're very small. Crucial's Gizmo drives impressed us with their speed and value for money (see www.crucial.com/uk for more information). Digital camera memory cards and Microdrives can also be pressed into service for small amounts of data, with the addition of a memory card reader. Alternatively, you could use web-based file transfer services to move files between Internetconnected Macs. Subscribers to Apple's .Mac service could use their iDisk, and everyone can use sites such as www.mailbigfile.com. An iPod can act as an external disk - check the relevant option in iTunes' preferences.

Author: Christopher Phin
How to buy a hard disk



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