The hard drive's role is often overlooked in the world of video editing; it's seen more as a means of storage than an integral part of the encoding and capture process. In fact the casual user will look at disk capacity rather than performance when upgrading or buying a new PC. So now you're armed with the fact that disk performance counts in the tasks of video editing, it's time to look a little closer at the technology available.
How fast can you go - hard disk speeds
A major contributing factor to disk performance in the speed at which the disk spins. Essentially, the faster the disk spins, the quicker data can be read and written. The speed of the disk is measured in Revolutions per Minute (RPM) with standard IDE (also known as ATA) drives (more on that later!) generally coming in two speeds: 5400RPM and 7200RPM. Obviously, the latter speed is quicker and therefore performance is enhanced. Why is the speed of the disk so important? Put simply, capturing digital video involved the transfer of huge amounts of data. In order to capture the video in real time, your PC has to both process and store this data. The CPU deals with the processing, but the hard drive physically stores the data. So if the disk is too slow, you may end up with what's know as "dropped frames" - the vast amounts of data that's being generated can't all be written to the hard drive, so you end up with small "chunks" of your video not being saved. These dropped frames make you video look "jumpy". A slow hard disk combined with a slow CPU and/or insufficient RAM will inevitably lead to dropped frames in digital capture. A recent query at www.videoforums.co.uk where a forum member was pulling out her hair over dropped frames was solved by capturing to an internal hard drive rather than the external drive she was using. External drives are perfect for storage, but lousy at video capture - most external drives are 5400RPM. If you want to store video on a slower disk, capture to a fast one, then transfer at it's leisure once captured. (The data no longer has to be transferred in real time).
Lets go even faster - data transfer speeds
So we know the spin speed is important, but what about the rate at which the data is transferred? With disk performances increasing, the actual data transfer rate needs to keep pace with these improvements. Once again, not all disks are created equal, with IDE drives coming in three flavours: Ultra ATA/33, Ultra ATA/66 and Ultra ATA/100. The numbers at the end signify the speed of data transfer, e.g. 100MB/sec, although this is a theoritical limit and actual rates are normally less, especially in the case of ATA/100. One word of warning though - your motherboard must support the higher end transfer rates in order to fully utilise the speed increases,
and a A 40-pin 80-conductor IDE cable must be used on Ultra ATA/66 and Ultra ATA/100 drives or transfer rates will be limited to the rate of Ultra ATA/33. You can still use ATA/100 drives on boards that aren't supported: backward compatibility simply means that the speed will be limited. Infact, you'll probably find that ATA/100 has become the de-facto standard.
The data buffer
Its not just the speed of the disk we need to look at. Another important factor is the size of the memory buffer. As mentioned above, capturing digital video in real time involves processing huge amounts of data - so the hard disk needs to keep pace with the amount of raw data flowing during capture. During video editing, you'll be accessing data continuously. If you're working on the same piece of video, you'll be accessing the same data time and time again. This is where the disk cache comes into play; the most recently accessed data is stored in a buffer so that data can be read more quickly. Your PC will check to see if the data is stored in the buffer and provide it from the high speed RAM rather than the disk - and at a far quicker speed.
The next step - SCSI and Serial ATA drives
Serial ATA or SATA drives take disk performance to the next level. Parallel disk technology (PATA) is reaching its limit and. SATA drives allow the continued development of performance whilst maintaining stability. Other benefits include reduced power consumption and better airflow within your PC (those wide IDE cable cables are replaced with neat cabling allowing improved thermal dynamics). Most new motherboards come with SATA connections as standard, so new PCs will start to be shipped with SATA drives. Disk performance of these disks beats even the most expensive IDE drive, with data transfer rates of 150MB/s being achieved on first generation drives.
Overall, there's alot to look out for when buying a new hard disk drive. It's wise not to overlook the importance of buying a high performance drive for a video editing PC. In fact bigger, faster and more stable drives are being released all the time thanks to SATA technology. So check out performance tests on sites such as www.tomshardware.com and invest your money wisely!
What's more, disk maintenance is an important factor. Make sure your drives are regularly defragmented! Its no use having a super fast disk if the files are fragmented all over the hard drive!
