Disk detail

Should you upgrade your PC with a SATA hard disk (as tested on page 39) or buy one of the other types on the market? Who knows? You soon will..

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By  Published  December 1, 2006

When it comes to your PC’s internal storage, the type of hard disk you have sat inside the case will determine two things: the number of gigabytes on offer and their performance, in terms of the access, read and write speeds you can expect. Format-wise, at the consumer level there are three types of disk to choose from, and these are differentiated by their interface connections (i.e. what type of cable and connection they use to connect to your computer’s main- or motherboard). So let’s start with the most basic type on offer and move upwards from there... First came IDE The IDE - Integrated Drive Electronics - interface has been the de-facto standard on PC motherboards for roughly 15 years now. Generally you can expect to find two IDE ports per mainboard, which can in turn be used to connect two IDE drives each. These ports look like thin, wide rectangles - and are generally positioned near a motherboard’s memory slots. Meanwhile the IDE cable that connects these to their respective drives is the flat, wide ribbon cable (also known as IDE cabling) you’ll no doubt already know. As mentioned, each IDE port can actually support two hard disk drives - a ‘master’ and a ‘slave’ (the performance of the latter being determined by the master, because this master acts as a controller). Therefore, if you have two IDE drives, a good piece of advice is that you set the newest model as the master. The maximum data transfer speed applicable to IDE connections is 133Mbytes/sec. If you’re using two drives on the same IDE port (or channel) this bandwidth will be split; the drive that starts to work on a job first is generally given data transfer preference, which means it will perform at its maximum potential. If the other drive then begins working it will use the remaining bandwidth. IDE interfaces transfers several bits of data at once (in ‘parallel’ mode) whilst our next connection standard, Serial ATA (Advanced Technology Attachment) just sends one data bit at a time. While transferring data in parallel might sound faster, corruption problems often arise from trying to transfer data quickly in parallel along a cable (the difficulty being to keep the groups of data bits equal), which is why the newer SATA method actually works out faster. (New IDE drives are these days known as Parallel ATA - or PATA models, the difference being that older IDE drive capacities are limited to a maximum of 8.4Gbytes, whereas PATA version drives are unlimited capacity-wise.) In terms of data transfer speeds, the first incarnation of SATA (which has been around for three years now) tops out at 150Mbytes/sec, whilst the newer SATA2 (which hit late last year), can manage up to 300Mbytes/sec. Which brings us nicely onto ‘scuzzy’ - SCSI - or Small Computer System Interface. This ‘parallel’ technology works similarly to IDE (PATA), in that data is transferred in bit groups. However, where it gets complicated is that there are currently numerous different variants of SCSI - which range in terms of their data speeds from 5Mbytes/sec (SCSI) up to 320Mbytes/sec (Ultra320 SCSI). SCSI has been around for almost as long as IDE, which is why there are such low data speed versions around, however SCSI controllers (in the form of PCI cards that sit on the motherboard) currently appear on the market at speeds of 80Mbytes/sec and above. Put simply, the particular SCSI controller you buy and install in your PC will determine the transfer speeds you’ll get running between this controller and any SCSI hard drives you’re using. So why would any user buy a SCSI controller that offers a lower data speed that SATA and/or IDE can manage, such as 80Mbytes/sec? Well it’s all about the drives. SCSI hard disks now generally run at a rotational speed of 10,000rpm (compared to 7200rpm in the past), which makes for faster data seek and transfer times. (At the very top-end you can now even get 15,000rpm screamers from firms such as Maxtor and Seagate.) Another advantage of SCSI drives is that SCSI cables run longer than both SATA and IDE cables, so you have more positioning flexibility when it comes to locating your hard disks inside a workstation or server chassis, plus SCSI utilises less CPU brainpower than IDE and SATA (meaning using your drive won’t in turn slow your system down much).The most basic SCSI controller you can buy supports up to four devices, whilst at the top end you can link up to 16 disks to a single controller. Now that’s some serious storage potential. Matt Wade

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