Number 318 - November 2009

Computer Performance Considerations
by Gary Bentley, SW International Personal Computer Club (TX),
When I evaluate what might be done to maximize the performance of a computer system, whether that be a system already in use or one I might be specifying for order (i.e., specifying the hardware with a particular level of performance in mind for the intended application) I look at several key factors.    The most critical factor is how much system RAM is available (if you are ordering a new system then you can also order faster RAM and be cognizant of addressing issues). I will state flatly that, all factors being equal, the more RAM available, the faster your computer system will operate. In the same vein, if you want to make full use of that system RAM, get an external graphics card with its own RAM so you don't force your system to share RAM with the video display. If you are specifying a new computer, get the fastest FSB (front side bus) speed you can afford with the microprocessor and then match the RAM bus speed to take advantage of that high bus speed. Don't let a computer maker fool you with a low system price while handing off old slow RAM to you when the motherboard and processor would support faster bus speed RAM. New systems will always use DDR RAM, so that should not be a consideration (and older systems will not be able to use it).    Don't be confused by discussions of virtual memory and page files. If you have a large amount of RAM (1 GB or more with Windows XP-3 or 4 GB with Vista, the OS memory hog of all time), your system will rarely need to page out process memory onto the hard drive paging file. You can check that in Task Manager (hit CTRL SHIFT ESC or CTRL ALT DEL or right click the Task Bar and select Task Manager) by looking at the Performance tab and the Physical Memory Total in conjunction with the Commit Charge. The Physical Memory Total is the amount of RAM you have in your system. The Commit Charge is the total memory allocated to programs and the operating system. If the Commit Charge (Total or Peak) doesn't exceed the amount of RAM, then the hard drive pagefile is rarely if ever being used and your system should be running at full RAM speed without hard drive performance issues (except when loading the OS and starting an application, etc.).    You can also use Performance Monitor (Start, Administrative Tools, Performance) and look at the Memory, Pages Output/Sec parameter. Even if the amount of committed memory exceeds available RAM, if the actual Pages Output/ Sec is low or zero most of the time (quoting Microsoft) there is no significant performance problem related to available RAM. I doubt there would be any reason for the typical home user to require a 64 bit computer in order to utilize sufficient RAM.    The second most critical factor is the performance of the hard drive, i.e., the amount of utilization of your hard drive (present or anticipated for the application), the speed at which the drive platters rotate, and the speed of the interface to your hard drive. You never want to reach 50% of capacity of your hard drive. The more data you have on a hard drive the farther the disk drive read/write head has to move inward on the spinning platter to get to the data (on the average). This increases the seek time, the time required for the read/write head to position itself over the desired concentric data track on the spinning disk platter. So, use a hard drive with sufficient storage that you do not exceed 40% or so of the storage capacity (high performance server hard drives often are destroked or short stroked, i.e., limited to 40% or less so as to keep the data on the outer edge of the platters where it can be quickly reached).	Once the read/write head reaches a track then the rotational speed of the platter comes into play, introducing latency, the time required for the desired sector of the track to rotate into position beneath the head. How do you reduce latency? Get a hard drive that spins as fast as you can afford. Most desktop hard drives now spin at 7200 RPM (don't let them slip you a 5400 RPM drive on your desktop or your laptop!). If your drive has a slower RPM, you can increase performance by purchasing a 7200 RPM drive. Note that high performance server drives spin at 10,000 and 15,000 RPM, but those drives are expensive.    If you are evaluating a replacement drive (or specifying the hard drive in a new system), look at the access time parameter for the drive. This will generally be around 11 milliseconds for 7200 RPM desktop PC ATA/SATA drives. The access time will include seek time and rotational latency. As for the type of interface, ATA drives (which peaked at around 133 MB/sec interface performance, setting aside internal data rate of around 60 MB/s and PCI bus rate considerations) are no longer offered, so you will see SATA (serial ATA) drives in a new computer. I wouldn't bother attempting to replace an ATA drive in an old PC with a SATA drive. You would need a SATA controller card as well as SATA drive and you might as well just purchase a new computer.    The current SATA interface rate is 3 Gbps (the initial SATA interface was 1.5 Gbps), i.e., 3 gigabits per second. That translates to approximately 300 MB/sec. However, the actual rate that the read head can read the data off the spinning platter of the drive is closer to 100 MB/sec (the internal data rate). You therefore can benefit by having a drive with a large cache memory, where a large amount of data has been read internally by the hard drive before the interface is accessed, at which time the interface can burst perform at the full interface speed of 3 Gbps/300 MB/sec. I note that even the expensive server grade SCSI and SAS drives have about that same external interface transfer rate, i.e., 300 - 320 MB/sec, so their increased performance is coming directly from the high rotational speeds (10 - 15 K) and fast seeks, giving access times of 3 - 5 ms vs. 11 ms or so for desktop SATA drives. Defragmenting your drive regularly will help keep the drive operating at peak efficiency.    A less critical factor is the speed of the microprocessor itself (FSB considerations aside as they relate to RAM access speed). A faster microprocessor or a dual or quad core processor will allow applications, their processes and threads to execute faster (to actually run the microprocessor instructions of which a program is composed) once the instructions and data reach the microprocessor.    So, if you have processing intensive applications like video or music (studio) production and editing (or scientific number crunching), faster and more core processors will speed things up considerably, but only if you have plenty of RAM and a high performance hard drive.    This article has been obtained from APCUG with the author's permission for publication by APCUG member groups; all other uses require the permission of the author (see e-mail address above).
Number 318 - November 2009