NWA-PCUG Newsletter Article, December 2002
Processing Speed of a Computer
by Grant Wales
gwales@cox-internet.com
(click to email author)


The primary measure of a computer's computational speed is the rate at which it is clocked, in MHz or GHz. However, that factor alone is not the only index that determines how fast the computer can handle processing tasks.

This became clear to me when I made a recent change in my computer's architecture while not changing the processor chip or it's clock rate. The processor is an 450 MHz AMD 6-II, and it was used with a mother board which defaulted to the PIO-4 DMA protocol. "I upgraded by getting a mother board that would support the Ultra DMA 66 protocol, as well as a few slower protocols. At the same time, I got a Western Digital 30 MB hard drive which would support Ultra DMA protocols 33, 66, and 100.

When the upgraded computer was completed I marveled at how much faster it had become. It was dramatic enough that I judged it to be about 50 percent faster.

When examining BIOS settings, I chose "Auto" rather than "Disabled" on the line that said Primary Master UDMA in the Integrated Peripherals screen. When the computer boots, I see a black and white screen that says UDMA 66 opposite the line that says Primary Master, in addition to a few other notations on hard drive size, etc.

Not all computers will show a black and white screen as some will display a big "splash" screen instead. If you have a black and white screen that vanishes before all significant data can be reviewed, you can hit the Pause key on your keyboard. This retains the black and white display until you hit the "Pause" or "Esc" keys on your keyboard. One way to get a good idea whether a desktop computer uses a UDMA protocol of 66 or faster is to open it and look at the construction of the IDE cable that connects to the hard drive. Most of the earlier IDE cables had 40 flat foil conductors within the gray cable. IDE cables made for the UDMA 66 protocol or faster look similar, except that there are 80 round wires, and if you look closely at the connector that goes into the IDE socket of the mother board, it will have a blue color code.

Reviews of the performance of UDMA 33, 66, and 100 indicate that there is major improvement when going from UDMA 33 (or similar, like PIO-4) to UDMA 66, while there is minor improvement when going from UDMA 66 to UDMA 100.

With a functioning UDMA 66 protocol, your computer can convey burst rates of data transfer up to 66 MB/sec.

If you have a computer whose mother board does not have an IDE interface for these faster transfer protocols, you can obtain a card that will enable this function if you have a vacant PCI slot. A major supplier of this type of card is Promise Technology, Inc. A brief description of their UDMA card may be found at:

http://store.westerndigital.com/product.asp?sku=1014916, which is a page from the Western Digital online "store."

There are many other factors that have a role in determining how fast a processor will work. One of these is the "front bus" speed, which is selected on the mother board, and is within the constraints of the front bus speeds supported by the mother board. Typical front bus speeds in use today are 100 MHz and 133 MHz, although newer computers are using 200 MHz and 266 MHz bus speeds. Ratings on the RAM card speed are also a factor, and to take the most advantage of the higher front bus speed, you should select RAM cards which allow best performance.

Another key factor is the access time of the hard drive, which is generally related to the rotational speed of the drive. An access time (sometimes called "latency") below 9 msec. is good by today's standards. The rotational speeds have been getting higher, some were around 3400 RPM six to ten years ago, and currently available hard drives of 7200 RPM becoming more prevalent than the older 5400 RPM drives.

Another factor is the amount of L2 (level 2) and L1 (level 1) system cache memory available to the processor. Generally, L2 memory has resided on a separate chip from the microprocessor chip, but recent developments in faster processors have provide L2 within the chip. L1 memory resides within the processor. The system cache is a set of relatively fast buffers (memory registers) between the very fast processor and the relatively slow memory that serves it.

L1 cache is faster but smaller than L2 cache. Some of the recent chips with internal L2 cache make this memory nearly as fast as the L1 cache, thus further relieving the requirement for large storage capacity in L1 cache.

L1 memory is a parameter that is not often listed in the description of the computer in which it is sold. A typical value of L1 cache has been 64 MB. Typical recent values for L2 cache are 256 KB or 512 KB. Price differentials for processors (and for computers) of the same clock speed rating often reflect whether the cache memory is competitive.

Generally, it is only in older build-from-scratch computers that you are likely to find that cache memory is inadequate.

An important factor for those who access the net is the connect speed to your internet server, but this is not a topic addressed here.

Fortunately for many of us, we accept the assembled computer as it is and then customize it with the software and the settings we choose to make it do what we want. The innards of a computer are chosen before it is sold, and tend to have components matched to each other. Since computer configurations are always part of a rapid evolutionary process, the date of purchase of a computer will often reflect whether things like the UDMA protocol of that era was installed. When buying a computer, it is useful for us to know what goodies appear on the "sticker" and to make a judgment about it's cost and performance before we select one to buy. Some of the "sticker" items that are not tabulated among the major parameters may have a noticeable bearing on performance.

Installing additional RAM is quite easy to do on a desktop computer once it is opened, and is one of the things a hardware "newbie" can do, as long as they get the right memory card(s). RAM is the next level of system cache (can be considered level 3) that is slower than L2 but is often larger than L2.

Unless a person wants to work either with elaborate games or with big media files, we are at a point where additional processing speed above about 500 MHz will not add much to our experience, but then - we can only buy what's available. Also, there are advances in operating systems and in application programs and peripherals which have minimum system requirements that keep driving up the performance requirements for such things as processor speed and RAM.

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