Biomedical Engineering Reference
In-Depth Information
Switch
Selects network paths at high speeds
UPS
Provides uninterruptible power for network electronics, especially servers
Wireless Hub
Provides mobile, cable-free access to servers, shared resources, and the Internet
from anywhere within range of the hub
Wireless Modem Allows workstations and laptops to communicate with a wireless hub (access
point)
Servers
The centerpiece of most bioinformatics networks is a server (or more than one) that supplies files
and applications to workstations, printers, and other clients. Servers are typically high-speed
dedicated computers with several GB of RAM, multi-GB fast hard drives, and over-engineered power
supplies that can withstand power surges and other challenges. Servers vary in size and shape,
degree of redundancy, performance, expansion options, amount of noise generated in normal
operation, the type of operating system supported, management software, security features, power
supply design, amount of cache memory, and price.
Servers are no longer relegated to footlocker-sized cases, but are available in units as small as a
pizza box that can be easily stacked in racks to provide high server densities. Related to form factor
is the operating environment, in that the compact size often necessitates the use of high-volume fans
that not only move large quantities of air over the densely populated motherboards, but that
generate considerable noise as well. As such, servers may need to be mounted in a separate room or
closet, away from researchers whose work the noise may disrupt. Also related to form factor is the
provision for redundancy in the two most common server failure points—the mechanical disks and
the power supplies. Many server designs provide internal redundant disks and power supplies that
take over as soon as the main units fail.
The typical server used in a bioinformatics laboratory has between 1 and 8 GB of RAM, several
hundred GB of disk storage distributed between 2 and 8 drives, 2 power supplies, BIOS password
protection, and virus protection. Performance, as measured by throughput in Mbps average response
time in milliseconds, and thousands of requests handled per second, is a function of the processor,
operating system, amount of RAM available, cache memory, and overall design.
The most common server operating systems are Microsoft Windows 2000, Linux, Solaris, UNIX, and
Microsoft .NET. Windows 2000 commands about a third of the server market, in part because of the
familiar graphical user interface (GUI) and compatibility with relatively inexpensive server hardware.
The relatively new Microsoft .NET Server is Windows 2000-based with added Web development tools.
Linux, an increasingly popular operating system for servers and bioinformatics workstations, accounts
for only about 5 percent of the overall server operating system market. An advantage of using Linux
as a server operating system is cost savings and an abundance of license-free (albeit Spartan)
utilities. Linux is considered more stable and reliable than Windows 2000, but more difficult to use. In
comparison, Solaris commands a little over 15 percent of the server market, followed by IBM AIX and
HP's UX. These various flavors of UNIX account for over a third of the server market, especially in
high-end applications, such as massive sequence databases.
In addition to generic servers that serve content to clients on the network, there are specialized
server designs, such as cache, file, print, mail, proxy, and terminal servers. A cache server
dynamically pulls frequently accessed content from the main servers and maintains the content in
cache for later use. The purpose of a cache server is to speed content to clients and to reduce
network traffic at the server site. One of the challenges with cache servers is ensuring that the
cached files are current and synchronized with the files on the source server. Cache servers usually
double as proxy servers, which are designed to intercept and manage client requests in a way that
provides increased security by matching incoming messages with outgoing requests. A proxy server
acts as a filter that passes valid requests on to a file or Web server or, if it's configured as a cache
server, serves the content from its cache. Because the functionality of proxy, firewall, and caching
servers is so tightly integrated, they are commonly combined in a single device.
