Why's My Computer Slow?

 

Mary has been an experienced Windows user for quite some time. She does all her work on the computer. The performance of her computer is not spectacular, but in Mary's mind, it is bearable. Lately, she finds it hard to get work done on time because her computer is becoming very slow. She knows that her PC is connected to the network, so she assumes that the network is slowing her PC down. So she calls up the Computing Services Centre (CSC) to ask for guidance. The CSC is more than willing to help, but before giving any technical advice, the CSC would like Mary to be aware of the things that can cause a drop in computer performance. The CSC tries to explain to her in the following sequence starting from the PC level:

• Is your PC configured correctly?

  In order to perform well in a Windows environment, a 486 PC with at least 8 MB RAM and free hard disk space of no less than 5 MB is required. Performance can increase with faster CPUs and more memory. This often involves replacing system motherboards, or even replacing an entire workstation. If your hard disk is an old slow type (40 & 100 MB), replace it with one that has a higher capacity immediately. With the right hardware, one will also need to configure the DOS to make the PC run faster. Parameters that need to be set in config.sys include the buffer size (File=60, Buffer=20), loading of smart drive (smartdrv.sys) and EMS (expanded memory). The latter may require fine tuning in order to function best. Since Mary works in the Windows environment most of the time, a minimum of 5 MB extra hard disk space is required for permanent file swapping if possible. The more disk space is set as virtual memory, the better the PC will perform. Another factor one should also consider is the data bus (typically 8 bits, 16 bits, or 32 bits). Wider data bus paths accommodate greater transfer bandwidth. When the operating system, device drivers, and bus devices utilize the full bus bandwidth, performance improves dramatically.

• Do you have a high performance Network Interface Card (NIC)?

  Basically, you need a network interface card installed in your PC before you can access services on the network. There is no hard and fast rule as to what type of Network Interface Card will perform best. If you have an 8-bit card or an old version one installed, your PC bounds to be slow. Fortunately, it will be replaced with a faster 16-bit NIC by the CSC soon. The higher the bus width (16 bits or 32 bits), the greater the speed at which data passes to and from the network. However, this alone cannot guarantee fast computer performance because complicated software configurations and inefficient program code writing can result in poor computer performance even though you have a reasonably fast NIC card.

• Could it be your departmental server?

  Like your own PC, the machine that is dedicated as the server for the entire department is also governed by its hardware and software configurations. The server has to be powerful and efficient enough to perform tasks such as providing software packages and shared disk space for individual PCs, coordinate printing jobs, data backup, maintenance etc. If this is the bottleneck, performance limitations can be improved or eliminated through future well-planned departmental server upgrades by the CSC. Nevertheless, even the fastest server will become slow if there is a considerable number of concurrent users accessing the server.

• How is your PC connected to the Ethernet Local Area Network (LAN)?

  The next thing to check is where your PC is located. In general, each department has its own LAN on the campus network CTNET. Ideally the departmental server and all the PCs within the department should be connected to the same local network. However, in reality, offices of the same department are often scattered on campus. For this very reason, some PCs may be situated miles away from their server on a different LAN. To load software from the departmental server will then require passing through the busy FDDI backbone, thus slowing down the overall performance.

  

• Is your Ethernet LAN overloaded?

  Few years back, a rule of thumb was to put no more than 100 PCs on one Ethernet segment. The goal was to keep the average bandwidth utilization under 20%. At that time, both the PCs and their network cards were slow, and there were only a few bandwidth-intensive applications. Nowadays, depending on the needs, the maximum number of PCs per segment may be 50, 20, 10, or even 1 (dedicated Ethernet). There is no consistent pattern on how a PC would use the network, so it is difficult to measure its needs for bandwidth. Preferably each PC could have its dedicated Ethernet, but this is too costly and not an efficient way to use network bandwidth. The solution is to use a switching device which would allow one to dynamically assign any number of PCs to an Ethernet segment. Usually such a device would switch between the Ethernet segments and a faster backbone which is FDDI or ATM. In view of this, the CSC will set up pilot networks with switching hubs, structured UTP wiring and a FDDI backbone switch soon. Results gathered will provide a blueprint for our future campus network.

• Which Network protocol are you using?

  Network protocol efficiency would affect network performance. LAN based protocols (nonroutable) such as Netbeui, LAST, etc. generally have better performance than the routable protocols such as DECNET, TCP/IP, IPX, etc. You can now have the choice to choose your desired protocol on the CTNET menu. However, the more protocols loaded into your PC, the slower the network performance.

• Did someone in your department tap an unauthorized device on the network?

  If the answer is yes and the CSC was not informed of such a case, problems will bound to occur. A number of such incidents have already been found in the past. Unauthorized attachments could be a workstation, a PC or networking equipment such as hubs, bridges and routers. Departmental LAN users may then experience poor network performance, as these unauthorized devices may not be configured correctly. The attachment of these unknown devices may even violate network specifications governing the number of allowed network stations and the length of Ethernet LANs. You should notify CSC promptly once you are aware of such occurrences.

• Could it be the central hosts?

  You may find it slow accessing university-wide services such as the library, the university yellow pages and bulletin board on the central host machines. The reason may be due to the fact that the central hosts are too busy and that their capacity is insufficient to accommodate a large number of users concurrently. The latter situation will be improved through time as the CSC will continue to monitor the central hosts and perform upgrades when neccessary.

• Are you using Internet?

  If you are using Internet and the time it takes to open a Web page is long, then the problem lies with the internet links. Three factors may affect the speed. Firstly, it could be the server at the other end that is slow. Secondly, it could be the local network connections in Hong Kong, for example, if you are accessing the HKU's library. Thirdly, the link to the outside world may not be powerful enough. With regard to the third factor, soon we shall see marked improvements when the Internet link between HARNET (Hong Kong Academic and Research NETwork) and the U.S is upgraded from its current speed of 128Kbps to T-1 speed(1.544 Mbps).

Conclusion

Terms:

bandwidth	The amount of data that can be sent through a given communications circuit per second.
LAN	A data communications network which is geographically limited (typically to a 1 km radius) allowing easy interconnection of terminals, microprocessors and computers within adjacent buildings. Ethernet and FDDI are examples of standard LANs.
protocol	A set of formal rules describing how to transmit data, especially across a network.
Web	It refers to the "World Wide Web". It is a distributed information retrieval system in which all information, from any source on the Internet can be accessed in a consistent and simple way.
T-1	A facility used to transmit a DS-1 formatted digital signal at 1.544 Megabits per second.

Computing Services Centre City University of Hong Kong ccnetcom@cityu.edu.hk